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Cyanobacteria

Cyanobacteria, also called Cyanobacteriota or Cyanophyta, are a phylum of autotrophic gram-negative bacteria that can obtain biological energy via oxygenic photosynthesis. The name "cyanobacteria" refers to their bluish green (cyan) color,  which forms the basis of cyanobacteria's informal common name, blue-green algae,   although as prokaryotes they are not scientifically classified as algae.

Cyanobacteria are probably the most numerous taxon to have ever existed on Earth and the first organisms known to have produced oxygen, having appeared in the middle Archean eon and apparently originated in a freshwater or terrestrial environment. Their photopigments can absorb the red- and blue-spectrum frequencies of sunlight (thus reflecting a greenish color) to split water molecules into hydrogen ions and oxygen. The hydrogen ions are used to react with carbon dioxide to produce complex organic compounds such as carbohydrates (a process known as carbon fixation), and the oxygen is released as a byproduct. By continuously producing and releasing oxygen over billions of years, cyanobacteria are thought to have converted the early Earth's anoxic, weakly reducing prebiotic atmosphere into an oxidizing one with free gaseous oxygen (which would have been immediately removed by various surface reductants previously), resulting in the Great Oxidation Event and the "rusting of the Earth" during the early Proterozoic, dramatically changing the composition of life forms on Earth. The subsequent adaptation of early single-celled organisms to survive in oxygenous environments likely had led to endosymbiosis between anaerobes and aerobes, and hence the evolution of eukaryotes during the Paleoproterozoic.

Cyanobacteria use photosynthetic pigments such as various forms of chlorophyll, carotenoids, phycobilins to convert the photonic energy in sunlight to chemical energy. Unlike heterotrophic prokaryotes, cyanobacteria have internal membranes. These are flattened sacs called thylakoids where photosynthesis is performed. Photoautotrophic eukaryotes such as red algae, green algae and plants perform photosynthesis in chlorophyllic organelles that are thought to have their ancestry in cyanobacteria, acquired long ago via endosymbiosis. These endosymbiont cyanobacteria in eukaryotes then evolved and differentiated into specialized organelles such as chloroplasts, chromoplasts, etioplasts, and leucoplasts, collectively known as plastids.

Sericytochromatia, the proposed name of the paraphyletic and most basal group, is the ancestor of both the non-photosynthetic group Melainabacteria and the photosynthetic cyanobacteria, also called Oxyphotobacteria.

The cyanobacteria Synechocystis and Cyanothece are important model organisms with potential applications in biotechnology for bioethanol production, food colorings, as a source of human and animal food, dietary supplements and raw materials. Cyanobacteria produce a range of toxins known as cyanotoxins that can cause harmful health effects in humans and animals.

Overview

Cyanobacteria are a very large and diverse phylum of photosynthetic prokaryotes. They are defined by their unique combination of pigments and their ability to perform oxygenic photosynthesis. They often live in colonial aggregates that can take on a multitude of forms. Of particular interest are the filamentous species, which often dominate the upper layers of microbial mats found in extreme environments such as hot springs, hypersaline water, deserts and the polar regions, but are also widely distributed in more mundane environments as well. They are evolutionarily optimized for environmental conditions of low oxygen. Some species are nitrogen-fixing and live in a wide variety of moist soils and water, either freely or in a symbiotic relationship with plants or lichen-forming fungi (as in the lichen genus Peltigera).

Cyanobacteria are globally widespread photosynthetic prokaryotes and are major contributors to global biogeochemical cycles. They are the only oxygenic photosynthetic prokaryotes, and prosper in diverse and extreme habitats. They are among the oldest organisms on Earth with fossil records dating back at least 2.1 billion years. Since then, cyanobacteria have been essential players in the Earth's ecosystems. Planktonic cyanobacteria are a fundamental component of marine food webs and are major contributors to global carbon and nitrogen fluxes. Some cyanobacteria form harmful algal blooms causing the disruption of aquatic ecosystem services and intoxication of wildlife and humans by the production of powerful toxins (cyanotoxins) such as microcystins, saxitoxin, and cylindrospermopsin. Nowadays, cyanobacterial blooms pose a serious threat to aquatic environments and public health, and are increasing in frequency and magnitude globally.

Cyanobacteria are ubiquitous in marine environments and play important roles as primary producers. They are part of the marine phytoplankton, which currently contributes almost half of the Earth's total primary production. About 25% of the global marine primary production is contributed by cyanobacteria.

Within the cyanobacteria, only a few lineages colonized the open ocean: Crocosphaera and relatives, cyanobacterium UCYN-A, Trichodesmium, as well as Prochlorococcus and Synechococcus. From these lineages, nitrogen-fixing cyanobacteria are particularly important because they exert a control on primary productivity and the export of organic carbon to the deep ocean, by converting nitrogen gas into ammonium, which is later used to make amino acids and proteins. Marine picocyanobacteria (Prochlorococcus and Synechococcus) numerically dominate most phytoplankton assemblages in modern oceans, contributing importantly to primary productivity. While some planktonic cyanobacteria are unicellular and free living cells (e.g., Crocosphaera, Prochlorococcus, Synechococcus); others have established symbiotic relationships with haptophyte algae, such as coccolithophores. Amongst the filamentous forms, Trichodesmium are free-living and form aggregates. However, filamentous heterocyst-forming cyanobacteria (e.g., Richelia, Calothrix) are found in association with diatoms such as Hemiaulus, Rhizosolenia and Chaetoceros.

Marine cyanobacteria include the smallest known photosynthetic organisms. The smallest of all, Prochlorococcus, is just 0.5 to 0.8 micrometres across. In terms of numbers of individuals, Prochlorococcus is possibly the most plentiful genus on Earth: a single millilitre of surface seawater can contain 100,000 cells of this genus or more. Worldwide there are estimated to be several octillion (1027, a billion billion billion) individuals. Prochlorococcus is ubiquitous between latitudes 40°N and 40°S, and dominates in the oligotrophic (nutrient-poor) regions of the oceans. The bacterium accounts for about 20% of the oxygen in the Earth's atmosphere.

Morphology
Cyanobacteria are variable in morphology, ranging from unicellular and filamentous to colonial forms. Filamentous forms exhibit functional cell differentiation such as heterocysts (for nitrogen fixation), akinetes (resting stage cells), and hormogonia (reproductive, motile filaments). These, together with the intercellular connections they possess, are considered the first signs of multicellularity.

Many cyanobacteria form motile filaments of cells, called hormogonia, that travel away from the main biomass to bud and form new colonies elsewhere. The cells in a hormogonium are often thinner than in the vegetative state, and the cells on either end of the motile chain may be tapered. To break away from the parent colony, a hormogonium often must tear apart a weaker cell in a filament, called a necridium.

Some filamentous species can differentiate into several different cell types:
 * Vegetative cells – the normal, photosynthetic cells that are formed under favorable growing conditions
 * Akinetes – climate-resistant spores that may form when environmental conditions become harsh
 * Thick-walled heterocysts – which contain the enzyme nitrogenase vital for nitrogen fixation in an anaerobic environment due to its sensitivity to oxygen.

Each individual cell (each single cyanobacterium) typically has a thick, gelatinous cell wall. They lack flagella, but hormogonia of some species can move about by gliding along surfaces. Many of the multicellular filamentous forms of Oscillatoria are capable of a waving motion; the filament oscillates back and forth. In water columns, some cyanobacteria float by forming gas vesicles, as in archaea. These vesicles are not organelles as such. They are not bounded by lipid membranes, but by a protein sheath.

Nitrogen fixation

Some cyanobacteria can fix atmospheric nitrogen in anaerobic conditions by means of specialized cells called heterocysts. Heterocysts may also form under the appropriate environmental conditions (anoxic) when fixed nitrogen is scarce. Heterocyst-forming species are specialized for nitrogen fixation and are able to fix nitrogen gas into ammonia (NH3), nitrites (NO2-) or nitrates (NO3-), which can be absorbed by plants and converted to protein and nucleic acids (atmospheric nitrogen is not bioavailable to plants, except for those having endosymbiotic nitrogen-fixing bacteria, especially the family Fabaceae, among others).

Free-living cyanobacteria are present in the water of rice paddies, and cyanobacteria can be found growing as epiphytes on the surfaces of the green alga, Chara, where they may fix nitrogen. Cyanobacteria such as Anabaena (a symbiont of the aquatic fern Azolla) can provide rice plantations with biofertilizer.

Carbon fixation
Cyanobacteria use the energy of sunlight to drive photosynthesis, a process where the energy of light is used to synthesize organic compounds from carbon dioxide. Because they are aquatic organisms, they typically employ several strategies which are collectively known as a " concentrating mechanism" to aid in the acquisition of inorganic carbon ( or bicarbonate). Among the more specific strategies is the widespread prevalence of the bacterial microcompartments known as carboxysomes, which co-operate with active transporters of CO2 and bicarbonate, in order to accumulate bicarbonate into the cytoplasm of the cell. Carboxysomes are icosahedral structures composed of hexameric shell proteins that assemble into cage-like structures that can be several hundreds of nanometres in diameter. It is believed that these structures tether the -fixing enzyme, RuBisCO, to the interior of the shell, as well as the enzyme carbonic anhydrase, using metabolic channeling to enhance the local concentrations and thus increase the efficiency of the RuBisCO enzyme.

Electron transport
In contrast to purple bacteria and other bacteria performing anoxygenic photosynthesis, thylakoid membranes of cyanobacteria are not continuous with the plasma membrane but are separate compartments. The photosynthetic machinery is embedded in the thylakoid membranes, with phycobilisomes acting as light-harvesting antennae attached to the membrane, giving the green pigmentation observed (with wavelengths from 450 nm to 660 nm) in most cyanobacteria.

While most of the high-energy electrons derived from water are used by the cyanobacterial cells for their own needs, a fraction of these electrons may be donated to the external environment via electrogenic activity.

Respiration
Respiration in cyanobacteria can occur in the thylakoid membrane alongside photosynthesis, with their photosynthetic electron transport sharing the same compartment as the components of respiratory electron transport. While the goal of photosynthesis is to store energy by building carbohydrates from CO2, respiration is the reverse of this, with carbohydrates turned back into CO2 accompanying energy release.

Cyanobacteria appear to separate these two processes with their plasma membrane containing only components of the respiratory chain, while the thylakoid membrane hosts an interlinked respiratory and photosynthetic electron transport chain. Cyanobacteria use electrons from succinate dehydrogenase rather than from NADPH for respiration.

Cyanobacteria only respire during the night (or in the dark) because the facilities used for electron transport are used in reverse for photosynthesis while in the light.

Electron transport chain
Many cyanobacteria are able to reduce nitrogen and carbon dioxide under aerobic conditions, a fact that may be responsible for their evolutionary and ecological success. The water-oxidizing photosynthesis is accomplished by coupling the activity of photosystem (PS) II and I (Z-scheme). In contrast to green sulfur bacteria which only use one photosystem, the use of water as an electron donor is energetically demanding, requiring two photosystems.

Attached to the thylakoid membrane, phycobilisomes act as light-harvesting antennae for the photosystems. The phycobilisome components (phycobiliproteins) are responsible for the blue-green pigmentation of most cyanobacteria. The variations on this theme are due mainly to carotenoids and phycoerythrins that give the cells their red-brownish coloration. In some cyanobacteria, the color of light influences the composition of the phycobilisomes. In green light, the cells accumulate more phycoerythrin, which absorbs green light, whereas in red light they produce more phycocyanin which absorbs red. Thus, these bacteria can change from brick-red to bright blue-green depending on whether they are exposed to green light or to red light. This process of "complementary chromatic adaptation" is a way for the cells to maximize the use of available light for photosynthesis.

A few genera lack phycobilisomes and have chlorophyll b instead (Prochloron, Prochlorococcus, Prochlorothrix). These were originally grouped together as the prochlorophytes or chloroxybacteria, but appear to have developed in several different lines of cyanobacteria. For this reason, they are now considered as part of the cyanobacterial group.

Metabolism
In general, photosynthesis in cyanobacteria uses water as an electron donor and produces oxygen as a byproduct, though some may also use hydrogen sulfide a process which occurs among other photosynthetic bacteria such as the purple sulfur bacteria.

Carbon dioxide is reduced to form carbohydrates via the Calvin cycle. The large amounts of oxygen in the atmosphere are considered to have been first created by the activities of ancient cyanobacteria. They are often found as symbionts with a number of other groups of organisms such as fungi (lichens), corals, pteridophytes (Azolla), angiosperms (Gunnera), etc. The carbon metabolism of cyanobacteria include the incomplete Krebs cycle, the pentose phosphate pathway, and glycolysis.

There are some groups capable of heterotrophic growth, while others are parasitic, causing diseases in invertebrates or algae (e.g., the black band disease).

Ecology

Cyanobacteria can be found in almost every terrestrial and aquatic habitat – oceans, fresh water, damp soil, temporarily moistened rocks in deserts, bare rock and soil, and even Antarctic rocks. They can occur as planktonic cells or form phototrophic biofilms. They are found inside stones and shells (in endolithic ecosystems). A few are endosymbionts in lichens, plants, various protists, or sponges and provide energy for the host. Some live in the fur of sloths, providing a form of camouflage.

Aquatic cyanobacteria are known for their extensive and highly visible blooms that can form in both freshwater and marine environments. The blooms can have the appearance of blue-green paint or scum. These blooms can be toxic, and frequently lead to the closure of recreational waters when spotted. Marine bacteriophages are significant parasites of unicellular marine cyanobacteria.

Cyanobacterial growth is favoured in ponds and lakes where waters are calm and have little turbulent mixing. Their lifecycles are disrupted when the water naturally or artificially mixes from churning currents caused by the flowing water of streams or the churning water of fountains. For this reason blooms of cyanobacteria seldom occur in rivers unless the water is flowing slowly. Growth is also favoured at higher temperatures which enable Microcystis species to outcompete diatoms and green algae, and potentially allow development of toxins.

Based on environmental trends, models and observations suggest cyanobacteria will likely increase their dominance in aquatic environments. This can lead to serious consequences, particularly the contamination of sources of drinking water. Researchers including Linda Lawton at Robert Gordon University, have developed techniques to study these. Cyanobacteria can interfere with water treatment in various ways, primarily by plugging filters (often large beds of sand and similar media) and by producing cyanotoxins, which have the potential to cause serious illness if consumed. Consequences may also lie within fisheries and waste management practices. Anthropogenic eutrophication, rising temperatures, vertical stratification and increased atmospheric carbon dioxide are contributors to cyanobacteria increasing dominance of aquatic ecosystems.

Cyanobacteria have been found to play an important role in terrestrial habitats and organism communities. It has been widely reported that cyanobacteria soil crusts help to stabilize soil to prevent erosion and retain water. An example of a cyanobacterial species that does so is Microcoleus vaginatus. M. vaginatus stabilizes soil using a polysaccharide sheath that binds to sand particles and absorbs water. M. vaginatus also makes a significant contribution to the cohesion of biological soil crust.

Some of these organisms contribute significantly to global ecology and the oxygen cycle. The tiny marine cyanobacterium Prochlorococcus was discovered in 1986 and accounts for more than half of the photosynthesis of the open ocean. Circadian rhythms were once thought to only exist in eukaryotic cells but many cyanobacteria display a bacterial circadian rhythm.

"Cyanobacteria are arguably the most successful group of microorganisms on earth. They are the most genetically diverse; they occupy a broad range of habitats across all latitudes, widespread in freshwater, marine, and terrestrial ecosystems, and they are found in the most extreme niches such as hot springs, salt works, and hypersaline bays. Photoautotrophic, oxygen-producing cyanobacteria created the conditions in the planet's early atmosphere that directed the evolution of aerobic metabolism and eukaryotic photosynthesis. Cyanobacteria fulfill vital ecological functions in the world's oceans, being important contributors to global carbon and nitrogen budgets." – Stewart and Falconer

Cyanobionts

Some cyanobacteria, the so-called cyanobionts (cyanobacterial symbionts), have a symbiotic relationship with other organisms, both unicellular and multicellular. As illustrated on the right, there are many examples of cyanobacteria interacting symbiotically with land plants. Cyanobacteria can enter the plant through the stomata and colonize the intercellular space, forming loops and intracellular coils. Anabaena spp. colonize the roots of wheat and cotton plants. Calothrix sp. has also been found on the root system of wheat. Monocots, such as wheat and rice, have been colonised by Nostoc spp.,  In 1991, Ganther and others isolated diverse heterocystous nitrogen-fixing cyanobacteria, including Nostoc, Anabaena and Cylindrospermum, from plant root and soil. Assessment of wheat seedling roots revealed two types of association patterns: loose colonization of root hair by Anabaena and tight colonization of the root surface within a restricted zone by Nostoc.

The relationships between cyanobionts (cyanobacterial symbionts) and protistan hosts are particularly noteworthy, as some nitrogen-fixing cyanobacteria (diazotrophs) play an important role in primary production, especially in nitrogen-limited oligotrophic oceans. Cyanobacteria, mostly pico-sized Synechococcus and Prochlorococcus, are ubiquitously distributed and are the most abundant photosynthetic organisms on Earth, accounting for a quarter of all carbon fixed in marine ecosystems. In contrast to free-living marine cyanobacteria, some cyanobionts are known to be responsible for nitrogen fixation rather than carbon fixation in the host. However, the physiological functions of most cyanobionts remain unknown. Cyanobionts have been found in numerous protist groups, including dinoflagellates, tintinnids, radiolarians, amoebae, diatoms, and haptophytes. Among these cyanobionts, little is known regarding the nature (e.g., genetic diversity, host or cyanobiont specificity, and cyanobiont seasonality) of the symbiosis involved, particularly in relation to dinoflagellate host.

Collective behaviour

Some cyanobacteria – even single-celled ones – show striking collective behaviours and form colonies (or blooms) that can float on water and have important ecological roles. For instance, billions of years ago, communities of marine Paleoproterozoic cyanobacteria could have helped create the biosphere as we know it by burying carbon compounds and allowing the initial build-up of oxygen in the atmosphere. On the other hand, toxic cyanobacterial blooms are an increasing issue for society, as their toxins can be harmful to animals. Extreme blooms can also deplete water of oxygen and reduce the penetration of sunlight and visibility, thereby compromising the feeding and mating behaviour of light-reliant species.

As shown in the diagram on the right, bacteria can stay in suspension as individual cells, adhere collectively to surfaces to form biofilms, passively sediment, or flocculate to form suspended aggregates. Cyanobacteria are able to produce sulphated polysaccharides (yellow haze surrounding clumps of cells) that enable them to form floating aggregates. In 2021, Maeda et al. discovered that oxygen produced by cyanobacteria becomes trapped in the network of polysaccharides and cells, enabling the microorganisms to form buoyant blooms. It is thought that specific protein fibres known as pili (represented as lines radiating from the cells) may act as an additional way to link cells to each other or onto surfaces. Some cyanobacteria also use sophisticated intracellular gas vesicles as floatation aids.

The diagram on the left above shows a proposed model of microbial distribution, spatial organization, carbon and O2 cycling in clumps and adjacent areas. (a) Clumps contain denser cyanobacterial filaments and heterotrophic microbes. The initial differences in density depend on cyanobacterial motility and can be established over short timescales. Darker blue color outside of the clump indicates higher oxygen concentrations in areas adjacent to clumps. Oxic media increase the reversal frequencies of any filaments that begin to leave the clumps, thereby reducing the net migration away from the clump. This enables the persistence of the initial clumps over short timescales; (b) Spatial coupling between photosynthesis and respiration in clumps. Oxygen produced by cyanobacteria diffuses into the overlying medium or is used for aerobic respiration. Dissolved inorganic carbon (DIC) diffuses into the clump from the overlying medium and is also produced within the clump by respiration. In oxic solutions, high O2 concentrations reduce the efficiency of CO2 fixation and result in the excretion of glycolate. Under these conditions, clumping can be beneficial to cyanobacteria if it stimulates the retention of carbon and the assimilation of inorganic carbon by cyanobacteria within clumps. This effect appears to promote the accumulation of particulate organic carbon (cells, sheaths and heterotrophic organisms) in clumps.

It has been unclear why and how cyanobacteria form communities. Aggregation must divert resources away from the core business of making more cyanobacteria, as it generally involves the production of copious quantities of extracellular material. In addition, cells in the centre of dense aggregates can also suffer from both shading and shortage of nutrients. So, what advantage does this communal life bring for cyanobacteria?

New insights into how cyanobacteria form blooms have come from a 2021 study on the cyanobacterium Synechocystis. These use a set of genes that regulate the production and export of sulphated polysaccharides, chains of sugar molecules modified with sulphate groups that can often be found in marine algae and animal tissue. Many bacteria generate extracellular polysaccharides, but sulphated ones have only been seen in cyanobacteria. In Synechocystis these sulphated polysaccharide help the cyanobacterium form buoyant aggregates by trapping oxygen bubbles in the slimy web of cells and polysaccharides.

Previous studies on Synechocystis have shown type IV pili, which decorate the surface of cyanobacteria, also play a role in forming blooms. These retractable and adhesive protein fibres are important for motility, adhesion to substrates and DNA uptake. The formation of blooms may require both type IV pili and Synechan – for example, the pili may help to export the polysaccharide outside the cell. Indeed, the activity of these protein fibres may be connected to the production of extracellular polysaccharides in filamentous cyanobacteria. A more obvious answer would be that pili help to build the aggregates by binding the cells with each other or with the extracellular polysaccharide. As with other kinds of bacteria, certain components of the pili may allow cyanobacteria from the same species to recognise each other and make initial contacts, which are then stabilised by building a mass of extracellular polysaccharide.

The bubble flotation mechanism identified by Maeda et al. joins a range of known strategies that enable cyanobacteria to control their buoyancy, such as using gas vesicles or accumulating carbohydrate ballasts. Type IV pili on their own could also control the position of marine cyanobacteria in the water column by regulating viscous drag. Extracellular polysaccharide appears to be a multipurpose asset for cyanobacteria, from floatation device to food storage, defence mechanism and mobility aid.

Cellular death
One of the most critical processes determining cyanobacterial eco-physiology is cellular death. Evidence supports the existence of controlled cellular demise in cyanobacteria, and various forms of cell death have been described as a response to biotic and abiotic stresses. However, cell death research in cyanobacteria is a relatively young field and understanding of the underlying mechanisms and molecular machinery underpinning this fundamental process remains largely elusive. However, reports on cell death of marine and freshwater cyanobacteria indicate this process has major implications for the ecology of microbial communities/   Different forms of cell demise have been observed in cyanobacteria under several stressful conditions,  and cell death has been suggested to play a key role in developmental processes, such as akinete and heterocyst differentiation, as well as strategy for population survival.

Cyanophages
Cyanophages are viruses that infect cyanobacteria. Cyanophages can be found in both freshwater and marine environments. Marine and freshwater cyanophages have icosahedral heads, which contain double-stranded DNA, attached to a tail by connector proteins. The size of the head and tail vary among species of cyanophages. Cyanophages, like other bacteriophages, rely on Brownian motion to collide with bacteria, and then use receptor binding proteins to recognize cell surface proteins, which leads to adherence. Viruses with contractile tails then rely on receptors found on their tails to recognize highly conserved proteins on the surface of the host cell.

Cyanophages infect a wide range of cyanobacteria and are key regulators of the cyanobacterial populations in aquatic environments, and may aid in the prevention of cyanobacterial blooms in freshwater and marine ecosystems. These blooms can pose a danger to humans and other animals, particularly in eutrophic freshwater lakes. Infection by these viruses is highly prevalent in cells belonging to Synechococcus spp. in marine environments, where up to 5% of cells belonging to marine cyanobacterial cells have been reported to contain mature phage particles.

The first cyanophage, LPP-1, was discovered in 1963. Cyanophages are classified within the bacteriophage families Myoviridae (e.g. AS-1, N-1), Podoviridae (e.g. LPP-1) and Siphoviridae (e.g. S-1).

Movement

It has long been known that filamentous cyanobacteria perform surface motions, and that these movements result from type IV pili. Additionally, Synechococcus, a marine cyanobacteria, is known to swim at a speed of 25 μm/s by a mechanism different to that of bacterial flagella. Formation of waves on the cyanobacteria surface is thought to push surrounding water backwards. Cells are known to be motile by a gliding method and a novel uncharacterized, non-phototactic swimming method that does not involve flagellar motion.

Many species of cyanobacteria are capable of gliding. Gliding is a form of cell movement that differs from crawling or swimming in that it does not rely on any obvious external organ or change in cell shape and it occurs only in the presence of a substrate. Gliding in filamentous cyanobacteria appears to be powered by a "slime jet" mechanism, in which the cells extrude a gel that expands quickly as it hydrates providing a propulsion force, although some unicellular cyanobacteria use type IV pili for gliding.

Cyanobacteria have strict light requirements. Too little light can result in insufficient energy production, and in some species may cause the cells to resort to heterotrophic respiration. Too much light can inhibit the cells, decrease photosynthesis efficiency and cause damage by bleaching. UV radiation is especially deadly for cyanobacteria, with normal solar levels being significantly detrimental for these microorganisms in some cases.

Filamentous cyanobacteria that live in microbial mats often migrate vertically and horizontally within the mat in order to find an optimal niche that balances their light requirements for photosynthesis against their sensitivity to photodamage. For example, the filamentous cyanobacteria Oscillatoria sp. and Spirulina subsalsa found in the hypersaline benthic mats of Guerrero Negro, Mexico migrate downwards into the lower layers during the day in order to escape the intense sunlight and then rise to the surface at dusk. In contrast, the population of Microcoleus chthonoplastes found in hypersaline mats in Camargue, France migrate to the upper layer of the mat during the day and are spread homogeneously through the mat at night. An in vitro experiment using Phormidium uncinatum also demonstrated this species' tendency to migrate in order to avoid damaging radiation. These migrations are usually the result of some sort of photomovement, although other forms of taxis can also play a role.

Photomovement – the modulation of cell movement as a function of the incident light – is employed by the cyanobacteria as a means to find optimal light conditions in their environment. There are three types of photomovement: photokinesis, phototaxis and photophobic responses.

Photokinetic microorganisms modulate their gliding speed according to the incident light intensity. For example, the speed with which Phormidium autumnale glides increases linearly with the incident light intensity.

Phototactic microorganisms move according to the direction of the light within the environment, such that positively phototactic species will tend to move roughly parallel to the light and towards the light source. Species such as Phormidium uncinatum cannot steer directly towards the light, but rely on random collisions to orient themselves in the right direction, after which they tend to move more towards the light source. Others, such as Anabaena variabilis, can steer by bending the trichome.

Finally, photophobic microorganisms respond to spatial and temporal light gradients. A step-up photophobic reaction occurs when an organism enters a brighter area field from a darker one and then reverses direction, thus avoiding the bright light. The opposite reaction, called a step-down reaction, occurs when an organism enters a dark area from a bright area and then reverses direction, thus remaining in the light.

Earth history
Stromatolites are layered biochemical accretionary structures formed in shallow water by the trapping, binding, and cementation of sedimentary grains by biofilms (microbial mats) of microorganisms, especially cyanobacteria.

During the Precambrian, stromatolite communities of microorganisms grew in most marine and non-marine environments in the photic zone. After the Cambrian explosion of marine animals, grazing on the stromatolite mats by herbivores greatly reduced the occurrence of the stromatolites in marine environments. Since then, they are found mostly in hypersaline conditions where grazing invertebrates cannot live (e.g. Shark Bay, Western Australia). Stromatolites provide ancient records of life on Earth by fossil remains which date from 3.5 Ga ago. The oldest undisputed evidence of cyanobacteria is dated to be 2.1 Ga ago, but there is some evidence for them as far back as 2.7 Ga ago. Cyanobacteria might have also emerged 3.5 Ga ago. Oxygen concentrations in the atmosphere remained around or below 0.001% of today's level until 2.4 Ga ago (the Great Oxygenation Event). The rise in oxygen may have caused a fall in the concentration of atmospheric methane, and triggered the Huronian glaciation from around 2.4 to 2.1 Ga ago. In this way, cyanobacteria may have killed off most of the other bacteria of the time.

Oncolites are sedimentary structures composed of oncoids, which are layered structures formed by cyanobacterial growth. Oncolites are similar to stromatolites, but instead of forming columns, they form approximately spherical structures that were not attached to the underlying substrate as they formed. The oncoids often form around a central nucleus, such as a shell fragment, and a calcium carbonate structure is deposited by encrusting microbes. Oncolites are indicators of warm waters in the photic zone, but are also known in contemporary freshwater environments. These structures rarely exceed 10 cm in diameter.

One former classification scheme of cyanobacterial fossils divided them into the porostromata and the spongiostromata. These are now recognized as form taxa and considered taxonomically obsolete; however, some authors have advocated for the terms remaining informally to describe form and structure of bacterial fossils.

Origin of photosynthesis
Oxygenic photosynthesis only evolved once (in prokaryotic cyanobacteria), and all photosynthetic eukaryotes (including all plants and algae) have acquired this ability from endosymbiosis with cyanobacteria or their endosymbiont hosts. In other words, all the oxygen that makes the atmosphere breathable for aerobic organisms originally comes from cyanobacteria or their plastid descendants.

Cyanobacteria remained the principal primary producers throughout the latter half of the Archean eon and most of the Proterozoic eon, in part because the redox structure of the oceans favored photoautotrophs capable of nitrogen fixation. However, their population is argued to have varied considerably across this eon. Archaeplastids such as green and red algae eventually surpassed cyanobacteria as major primary producers on continental shelves near the end of the Neoproterozoic, but only with the Mesozoic (251–65 Ma) radiations of secondary photoautotrophs such as dinoflagellates, coccolithophorids and diatoms did primary production in marine shelf waters take modern form. Cyanobacteria remain critical to marine ecosystems as primary producers in oceanic gyres, as agents of biological nitrogen fixation, and, in modified form, as the plastids of marine algae.

Origin of chloroplasts
Primary chloroplasts are cell organelles found in some eukaryotic lineages, where they are specialized in performing photosynthesis. They are considered to have evolved from endosymbiotic cyanobacteria. After some years of debate, it is now generally accepted that the three major groups of primary endosymbiotic eukaryotes (i.e. green plants, red algae and glaucophytes) form one large monophyletic group called Archaeplastida, which evolved after one unique endosymbiotic event.

The morphological similarity between chloroplasts and cyanobacteria was first reported by German botanist Andreas Franz Wilhelm Schimper in the 19th century Chloroplasts are only found in plants and algae, thus paving the way for Russian biologist Konstantin Mereschkowski to suggest in 1905 the symbiogenic origin of the plastid. Lynn Margulis brought this hypothesis back to attention more than 60 years later but the idea did not become fully accepted until supplementary data started to accumulate. The cyanobacterial origin of plastids is now supported by various pieces of phylogenetic, genomic, biochemical  and structural evidence. The description of another independent and more recent primary endosymbiosis event between a cyanobacterium and a separate eukaryote lineage (the rhizarian Paulinella chromatophora) also gives credibility to the endosymbiotic origin of the plastids.

In addition to this primary endosymbiosis, many eukaryotic lineages have been subject to secondary or even tertiary endosymbiotic events, that is the "Matryoshka-like" engulfment by a eukaryote of another plastid-bearing eukaryote.

Chloroplasts have many similarities with cyanobacteria, including a circular chromosome, prokaryotic-type ribosomes, and similar proteins in the photosynthetic reaction center. The endosymbiotic theory suggests that photosynthetic bacteria were acquired (by endocytosis) by early eukaryotic cells to form the first plant cells. Therefore, chloroplasts may be photosynthetic bacteria that adapted to life inside plant cells. Like mitochondria, chloroplasts still possess their own DNA, separate from the nuclear DNA of their plant host cells and the genes in this chloroplast DNA resemble those in cyanobacteria. DNA in chloroplasts codes for redox proteins such as photosynthetic reaction centers. The CoRR hypothesis proposes this co-location is required for redox regulation.

Marine origins

Cyanobacteria have fundamentally transformed the geochemistry of the planet. Multiple lines of geochemical evidence support the occurrence of intervals of profound global environmental change at the beginning and end of the Proterozoic (2,500–542 Mya). While it is widely accepted that the presence of molecular oxygen in the early fossil record was the result of cyanobacteria activity, little is known about how cyanobacteria evolution (e.g., habitat preference) may have contributed to changes in biogeochemical cycles through Earth history. Geochemical evidence has indicated that there was a first step-increase in the oxygenation of the Earth's surface, which is known as the Great Oxidation Event (GOE), in the early Paleoproterozoic (2,500–1,600 Mya). A second but much steeper increase in oxygen levels, known as the Neoproterozoic Oxygenation Event (NOE), occurred at around 800 to 500 Mya. Recent chromium isotope data point to low levels of atmospheric oxygen in the Earth's surface during the mid-Proterozoic, which is consistent with the late evolution of marine planktonic cyanobacteria during the Cryogenian; both types of evidence help explain the late emergence and diversification of animals.

Understanding the evolution of planktonic cyanobacteria is important because their origin fundamentally transformed the nitrogen and carbon cycles towards the end of the Pre-Cambrian. It remains unclear, however, what evolutionary events led to the emergence of open-ocean planktonic forms within cyanobacteria and how these events relate to geochemical evidence during the Pre-Cambrian. So far, it seems that ocean geochemistry (e.g., euxinic conditions during the early- to mid-Proterozoic) and nutrient availability likely contributed to the apparent delay in diversification and widespread colonization of open ocean environments by planktonic cyanobacteria during the Neoproterozoic.

Genetics
Cyanobacteria are capable of natural genetic transformation. Natural genetic transformation is the genetic alteration of a cell resulting from the direct uptake and incorporation of exogenous DNA from its surroundings. For bacterial transformation to take place, the recipient bacteria must be in a state of competence, which may occur in nature as a response to conditions such as starvation, high cell density or exposure to DNA damaging agents. In chromosomal transformation, homologous transforming DNA can be integrated into the recipient genome by homologous recombination, and this process appears to be an adaptation for repairing DNA damage.

DNA repair
Cyanobacteria are challenged by environmental stresses and internally generated reactive oxygen species that cause DNA damage. Cyanobacteria possess numerous E. coli-like DNA repair genes. Several DNA repair genes are highly conserved in cyanobacteria, even in small genomes, suggesting that core DNA repair processes such as recombinational repair, nucleotide excision repair and methyl-directed DNA mismatch repair are common among cyanobacteria.

Taxonomy
Historically, bacteria were first classified as plants constituting the class Schizomycetes, which along with the Schizophyceae (blue-green algae/Cyanobacteria) formed the phylum Schizophyta, then in the phylum Monera in the kingdom Protista by Haeckel in 1866, comprising Protogens, Protamaeba, Vampyrella, Protomonae, and Vibrio, but not Nostoc and other cyanobacteria, which were classified with algae, later reclassified as the Prokaryotes by Chatton.

The cyanobacteria were traditionally classified by morphology into five sections, referred to by the numerals I–V. The first three – Chroococcales, Pleurocapsales, and Oscillatoriales – are not supported by phylogenetic studies. The latter two – Nostocales and Stigonematales – are monophyletic as a unit, and make up the heterocystous cyanobacteria.

The members of Chroococales are unicellular and usually aggregate in colonies. The classic taxonomic criterion has been the cell morphology and the plane of cell division. In Pleurocapsales, the cells have the ability to form internal spores (baeocytes). The rest of the sections include filamentous species. In Oscillatoriales, the cells are uniseriately arranged and do not form specialized cells (akinetes and heterocysts). In Nostocales and Stigonematales, the cells have the ability to develop heterocysts in certain conditions. Stigonematales, unlike Nostocales, include species with truly branched trichomes.

Most taxa included in the phylum or division Cyanobacteria have not yet been validly published under The International Code of Nomenclature of Prokaryotes (ICNP) except: The remainder are validly published under the International Code of Nomenclature for algae, fungi, and plants.
 * The classes Chroobacteria, Hormogoneae, and Gloeobacteria
 * The orders Chroococcales, Gloeobacterales, Nostocales, Oscillatoriales, Pleurocapsales, and Stigonematales
 * The families Prochloraceae and Prochlorotrichaceae
 * The genera Halospirulina, Planktothricoides, Prochlorococcus, Prochloron, and Prochlorothrix

Formerly, some bacteria, like Beggiatoa, were thought to be colorless Cyanobacteria.

The currently accepted taxonomy is based on the List of Prokaryotic names with Standing in Nomenclature (LPSN) and National Center for Biotechnology Information (NCBI). Class "Cyanobacteriia"
 * Subclass "Gloeobacteria" Cavalier-Smith 2002
 * Gloeobacterales Cavalier-Smith 2002
 * Subclass "Phycobacteria" Cavalier-Smith 2002
 * Acaryochloridales Miyashita et al. 2003 ex Strunecký & Mareš 2022 [incl. Thermosynechococcales]
 * Aegeococcales Strunecký & Mareš 2022
 * "Elainellales"
 * "Eurycoccales"
 * Geitlerinematales Strunecký & Mareš 2022
 * Gloeoemargaritales Moreira et al. 2016
 * "Leptolyngbyales" Strunecký & Mareš 2022
 * Nodosilineales Strunecký & Mareš 2022
 * Oculatellales Strunecký & Mareš 2022
 * "Phormidesmiales"
 * Prochlorococcaceae Komárek & Strunecky 2020 {"PCC-6307"}
 * Pseudanabaenales Hoffmann, Komárek & Kastovsky 2005
 * "Pseudophormidiales"
 * Thermostichales Komárek & Strunecký 2020
 * Synechococcophycidae Hoffmann, Komárek & Kastovsky 2005
 * "Limnotrichales"
 * Prochlorotrichales Strunecký & Mareš 2022 (PCC-9006)
 * Synechococcales Hoffmann, Komárek & Kastovsky 2005
 * Nostocophycidae Hoffmann, Komárek & Kastovsky 2005
 * Cyanobacteriales Rippka & Cohen-Bazire 1983 (Chamaesiphonales, Chroococcales, Chroococcidiopsidales, Nostocales, Oscillatoriales, Pleurocapsales, Spirulinales, Stigonematales)

Biotechnology
The unicellular cyanobacterium Synechocystis sp. PCC6803 was the third prokaryote and first photosynthetic organism whose genome was completely sequenced. It continues to be an important model organism. Cyanothece ATCC 51142 is an important diazotrophic model organism. The smallest genomes have been found in Prochlorococcus spp. (1.7 Mb) and the largest in Nostoc punctiforme (9 Mb). Those of Calothrix spp. are estimated at 12–15 Mb, as large as yeast.

Recent research has suggested the potential application of cyanobacteria to the generation of renewable energy by directly converting sunlight into electricity. Internal photosynthetic pathways can be coupled to chemical mediators that transfer electrons to external electrodes. In the shorter term, efforts are underway to commercialize algae-based fuels such as diesel, gasoline, and jet fuel. Cyanobacteria have been also engineered to produce ethanol and experiments have shown that when one or two CBB genes are being over expressed, the yield can be even higher.

Cyanobacteria may possess the ability to produce substances that could one day serve as anti-inflammatory agents and combat bacterial infections in humans. Cyanobacteria's photosynthetic output of sugar and oxygen has been demonstrated to have therapeutic value in rats with heart attacks. While cyanobacteria can naturally produce various secondary metabolites, they can serve as advantageous hosts for plant-derived metabolites production owing to biotechnological advances in systems biology and synthetic biology.

Spirulina's extracted blue color is used as a natural food coloring.

Researchers from several space agencies argue that cyanobacteria could be used for producing goods for human consumption in future crewed outposts on Mars, by transforming materials available on this planet.

Human nutrition
Some cyanobacteria are sold as food, notably Arthrospira platensis (Spirulina) and others (Aphanizomenon flos-aquae).

Some microalgae contain substances of high biological value, such as polyunsaturated fatty acids, amino acids, proteins, pigments, antioxidants, vitamins, and minerals. Edible blue-green algae reduce the production of pro-inflammatory cytokines by inhibiting NF-κB pathway in macrophages and splenocytes. Sulfate polysaccharides exhibit immunomodulatory, antitumor, antithrombotic, anticoagulant, anti-mutagenic, anti-inflammatory, antimicrobial, and even antiviral activity against HIV, herpes, and hepatitis.

Health risks
Some cyanobacteria can produce neurotoxins, cytotoxins, endotoxins, and hepatotoxins (e.g., the microcystin-producing bacteria genus microcystis), which are collectively known as cyanotoxins.

Specific toxins include anatoxin-a, guanitoxin, aplysiatoxin, cyanopeptolin, cylindrospermopsin, domoic acid, nodularin R (from Nodularia), neosaxitoxin, and saxitoxin. Cyanobacteria reproduce explosively under certain conditions. This results in algal blooms which can become harmful to other species and pose a danger to humans and animals if the cyanobacteria involved produce toxins. Several cases of human poisoning have been documented, but a lack of knowledge prevents an accurate assessment of the risks, and research by Linda Lawton, FRSE at Robert Gordon University, Aberdeen and collaborators has 30 years of examining the phenomenon and methods of improving water safety.

Recent studies suggest that significant exposure to high levels of cyanobacteria producing toxins such as BMAA can cause amyotrophic lateral sclerosis (ALS). People living within half a mile of cyanobacterially contaminated lakes have had a 2.3 times greater risk of developing ALS than the rest of the population; people around New Hampshire's Lake Mascoma had an up to 25 times greater risk of ALS than the expected incidence. BMAA from desert crusts found throughout Qatar might have contributed to higher rates of ALS in Gulf War veterans.

Chemical control
Several chemicals can eliminate cyanobacterial blooms from smaller water-based systems such as swimming pools. They include calcium hypochlorite, copper sulphate, Cupricide (chelated copper), and simazine. The calcium hypochlorite amount needed varies depending on the cyanobacteria bloom, and treatment is needed periodically. According to the Department of Agriculture Australia, a rate of 12 g of 70% material in 1000 L of water is often effective to treat a bloom. Copper sulfate is also used commonly, but no longer recommended by the Australian Department of Agriculture, as it kills livestock, crustaceans, and fish. Cupricide is a chelated copper product that eliminates blooms with lower toxicity risks than copper sulfate. Dosage recommendations vary from 190 mL to 4.8 L per 1000 m2. Ferric alum treatments at the rate of 50 mg/L will reduce algae blooms. Simazine, which is also a herbicide, will continue to kill blooms for several days after an application. Simazine is marketed at different strengths (25, 50, and 90%), the recommended amount needed for one cubic meter of water per product is 25% product 8 mL; 50% product 4 mL; or 90% product 2.2 mL.

Climate change
Climate change is likely to increase the frequency, intensity and duration of cyanobacterial blooms in many eutrophic lakes, reservoirs and estuaries. Bloom-forming cyanobacteria produce a variety of neurotoxins, hepatotoxins and dermatoxins, which can be fatal to birds and mammals (including waterfowl, cattle and dogs) and threaten the use of waters for recreation, drinking water production, agricultural irrigation and fisheries. Toxic cyanobacteria have caused major water quality problems, for example in Lake Taihu (China), Lake Erie (USA), Lake Okeechobee (USA), Lake Victoria (Africa) and the Baltic Sea.

Climate change favours cyanobacterial blooms both directly and indirectly. Many bloom-forming cyanobacteria can grow at relatively high temperatures. Increased thermal stratification of lakes and reservoirs enables buoyant cyanobacteria to float upwards and form dense surface blooms, which gives them better access to light and hence a selective advantage over nonbuoyant phytoplankton organisms. Protracted droughts during summer increase water residence times in reservoirs, rivers and estuaries, and these stagnant warm waters can provide ideal conditions for cyanobacterial bloom development.

The capacity of the harmful cyanobacterial genus Microcystis to adapt to elevated CO2 levels was demonstrated in both laboratory and field experiments. Microcystis spp. take up CO2 and and accumulate inorganic carbon in carboxysomes, and strain competitiveness was found to depend on the concentration of inorganic carbon. As a result, climate change and increased CO2 levels are expected to affect the strain composition of cyanobacterial blooms.

title: Cyanobacteria


text:
Ghost (1990 film)

Ghost is a 1990 American supernatural romantic thriller drama film directed by Jerry Zucker from a screenplay by Bruce Joel Rubin, and starring Patrick Swayze, Demi Moore, Whoopi Goldberg, Tony Goldwyn, Vincent Schiavelli, and Rick Aviles. It focuses on Sam Wheat (Swayze), a murdered banker, whose ghost sets out to save his girlfriend, Molly Jensen (Moore), from the person who killed him – through the help of the psychic Oda Mae Brown (Goldberg).

Ghost was theatrically released on July 13, 1990, to commercial success, grossing $505 million against a budget of $22–23 million and emerging as the highest-grossing film of 1990 and at the time of its release, was the third-highest-grossing film of all time. Its success extended to the home video market, and was the most rented film of 1991 in the United States. The film received generally positive reviews from critics, with particular praise going towards the score and performances of the cast. Ghost earned five nominations at the 63rd Academy Awards: Best Picture, Best Original Score, Best Film Editing, and winning Best Supporting Actress for Goldberg and Best Original Screenplay for Rubin.

Plot
Banker Sam Wheat and his artist girlfriend Molly Jensen move into a Manhattan loft with the help of Sam's friend and co-worker Carl Bruner. One night, the couple are attacked on the street by a mugger, and though Sam appears to chase him away, he returns to a devastated Molly cradling his bloodied corpse and realizes he is dead. A bright beam of light shines down on Sam but he walks towards Molly and the light disappears.

As a ghost, a despondent Sam remains by Molly's side but is unable to interact with the physical world and other ghosts he encounters are unhelpful. Sometime later, the mugger breaks into and searches their apartment. Molly returns unexpectedly and Sam scares her cat, which can see him, causing it to attack the mugger, who flees. While pursuing the mugger, Sam is attacked by a violent ghost on the subway train who can touch physical objects. Sam follows the mugger back to his apartment, learning his name, Willie Lopez, and that Sam was deliberately targeted.

Sam later encounters Oda Mae Brown, who operates as a charlatan psychic, but he realizes she can actually hear him and demands she help him warn Molly. Though reluctant to help, Oda Mae agrees after Sam keeps her awake with his singing. Despite her intimate knowledge of Sam's and Molly's relationship, Oda Mae struggles to convince Molly the afterlife is real until Sam has Oda Mae say "ditto", his response whenever Molly said she loved him. Molly tells the police and Carl about Willie, but the police dismiss the story and reveal Oda Mae's extensive history of fraud, leaving Molly disheartened.

Meanwhile, Sam follows Carl and learns that he hired Willie to rob Sam of his book of bank passwords. Carl needs the passwords to launder $4   million in drug money through an account held by the fictional "Rita Miller" for his criminal employers. He breaks into Molly's apartment, takes the book, and later attempts to seduce her until the enraged Sam inadvertently knocks over a picture frame. Sam returns to the subway and convinces the violent ghost to teach him to focus his emotions and reliably interact with the physical world.

Sam visits Oda Mae, who is now popular with ghosts hoping to reach their living loved ones, and convinces her to pose as Rita Miller to withdraw the drug money, which she reluctantly donates to charity; Molly witnesses the transaction while visiting the bank. As Carl panics over the missing money and death threats from its owners, Sam uses his abilities to torment him. Carl visits Molly to discuss the haunting and she unwittingly reveals Oda Mae withdrew the money. While Molly is upstairs, Sam attacks Carl until he threatens to murder Molly if the money is not returned that night. Carl and Willie travel to confront Oda Mae but Sam warns her to hide and terrorizes Willie until he flees into a road and is struck and killed by a car. Shadowy figures appear and drag Willie's screaming ghost into the ground.

Oda Mae and Sam return to Molly's apartment, where he levitates a penny to convince her he is truly present. After Molly calls the police to report Carl, Oda Mae allows Sam to possess her so he can dance with Molly. However, the possession leaves him weakened and unable to help when Carl breaks into the apartment. Carl takes Molly hostage and demands the money but Sam recovers in time to attack him. In a panic, Carl ineffectually swings a metal hook and tries to escape through a window, but the hook swings back and shatters the window pane, causing a large shard of glass to impale and kill him. Sam watches as the shadowy figures drag Carl away.

As Sam checks on Molly and Oda Mae, the beam of light returns, allowing them both to see and hear him. Sam thanks Oda Mae and shares a kiss with Molly, telling her he loves her. She responds, "ditto", before Sam walks into the light.

Background and filming
Ghost was the first film Jerry Zucker directed on his own, as well as his first dramatic film. He had previously been part of the Zucker, Abrahams and Zucker directing team, known for their parody films. Zucker stated that his decision to direct Ghost was not made to distance himself from comedies or to mark a new chapter in his career, but he was merely "just looking for a good film to direct." When screenwriter Bruce Joel Rubin learned that Zucker was to direct the film and wanted to make changes to his script, he was apprehensive, as he wanted Miloš Forman or Stanley Kubrick to direct and feared Zucker would turn his script into a comedy. However, Rubin changed his mind and warmed up after dining with Zucker and being impressed by how "deeply philosophical" he was.

Harrison Ford, Michael J. Fox, Paul Hogan, Tom Hanks, Kevin Bacon, Kevin Kline, Alec Baldwin and Tom Cruise were considered for the role of Sam Wheat. Bruce Willis turned the role of Sam Wheat down as he did not understand the script and later called himself a "knucklehead" for declining. Similarly, Fox thought the film wouldn't work, and, in hindsight, regretted turning the role down. Michelle Pfeiffer, Molly Ringwald, Meg Ryan, Julia Roberts and Nicole Kidman were considered for the role of Molly Jensen. Tina Turner, Patti LaBelle, and Oprah Winfrey were either considered or auditioned for the role of Oda Mae Brown. Zucker initially was not interested in casting Whoopi Goldberg as Oda Mae, and Swayze advocated for her to be cast.

Zucker credited arguments from radio host Dennis Prager with deciding to "lighten" Rubin's original script with a moral message.

Rubin noted that he "wanted to tell a ghost story from the ghost's perspective": "One day, I was watching a production of Hamlet, which begins with the ghost of Hamlet's father saying, ‘Revenge my death,’" he recalled. "I thought, ‘Wow, let's transpose that into the 20th century; it'd be an interesting story.’ And the idea hit me."

Filming for Ghost began shooting in July 1989. Many of the interior scenes were shot at Paramount in Los Angeles. The interior of Sam and Molly's loft is a reproduction of the home and studio of artist Michele Oka Doner, built from plans she provided because she declined to allow filming in her loft. It was reconstructed in an unused loft nearby in her Soho neighborhood and featured many of the same details as the actual loft, such as radiators around columns, open stairs and a house-shaped enclosure for the refrigerator. Filming of the apartment took place at 102 Prince Street, lower Manhattan. The exterior scenes were shot in New York City, particularly in Bedford–Stuyvesant, Soho, and Wall Street, for about five weeks. The film features about 100 special effects shots. Demi Moore's famous 'boy cut' in the movie was designed by Manhattan hair stylist John Sahag.

The final scene used digital video effects. Originally it was meant to show Patrick Swayze kissing Demi Moore before walking up a mylar platform toward a bluescreen with grips in the shot. VFX supervisor Richard Edlund didn't think the audience would buy it, and used Quantel’s “Harry” video-compositing system to combine the workprint with Swayze with elements that had been shot on an Oxberry animation stand and things like an endoscope of Christmas tinsel.

Music
The music for Ghost was written by veteran French composer Maurice Jarre, whose work was nominated for the 1990 Academy Award for Best Original Score (won by John Barry for Dances with Wolves). The soundtrack also featured the 1955 song "Unchained Melody", composed by Alex North with lyrics by Hy Zaret. In Ghost, the song appears both in instrumental and vocal form, the latter being the version recorded by Bobby Hatfield of The Righteous Brothers in 1965.

The soundtrack album was issued worldwide on Milan Records, but licensed to Varèse Sarabande in North America. It was reissued with two extra tracks in 1995, and later as part of Milan's Silver Screen Edition series with the extra tracks and an interview with Maurice Jarre.

Releases and sales
The film became an unexpected box-office success,   grossing $505.7 million on a budget of between $22–23 million. It was the highest-grossing film of 1990. Box Office Mojo estimates that the film sold over 51.46 million tickets in the US. It spent eight consecutive weeks at number one at the UK box office and became the highest-grossing film of all time in the UK surpassing E.T. the Extra-Terrestrial with a gross of £23.3 million. That record would last for three years before getting surpassed by Jurassic Park in 1993. It also spent six consecutive weeks atop the Australian box office. It was also the highest-grossing film in Indonesia at the time with a gross of $3.6 million and the highest-grossing foreign film in the Philippines.

The film was released on video and LaserDisc in the United States on March 21, 1991, and sold a record 646,000 videos for rental, breaking the record set by Die Hard 2, and a record 66,040 LaserDiscs. It was the top video rental of 1991 in the United States, and generated a gross of $40 million for Paramount. The video went on sale in the fall and generated sales of $25 million.

Critical response
Ghost has an approval rating of based on  professional reviews on the review aggregator website Rotten Tomatoes, with an average rating of. Its critical consensus reads, "Ghost offers viewers a poignant romance while blending elements of comedy, horror, and mystery, all adding up to one of the more enduringly watchable hits of its era." Metacritic (which uses a weighted average) assigned Ghost a score of 52 out of 100 based on 17 critics, indicating "mixed or average reviews". Audiences polled by CinemaScore gave the film an average grade of "A" on an A+ to F scale.

Roger Ebert gave Ghost two-and-a-half out of four stars in his review for the Chicago Sun-Times, regarding the film as "no worse an offender than most ghost movies, I suppose. It assumes that even after death we devote most of our attention to unfinished business here on Earth, and that danger to a loved one is more important to a ghost than the infinity it now inhabits." He was also critical of the film's "obligatory action climax", the "ridiculous visitation from the demons of hell", the "slow study" of the Molly character, and the "single best scene" in which Sam overtakes Oda Mae's body to caress Molly: "In strict logic, this should involve us seeing Goldberg kissing Moore, but of course the movie compromises and shows us Swayze holding her - too bad, because the logical version would actually have been more spiritual and moving."

David Ansen of Newsweek, despite finding the ending too sentimental, praised the film as "a zippy pastiche that somehow manages to seem fresh even though it's built entirely out of borrowed parts." Variety magazine called the film "an odd creation – at times nearly smothering in arty somberness, at others veering into good, wacky fun." Goldberg received considerable praise for her performance. In a review for The New York Times, Janet Maslin comments "Ms. Goldberg plays the character's amazement, irritation and great gift for back talk to the hilt. This is one of those rare occasions on which the uncategorizable Ms. Goldberg has found a film role that really suits her, and she makes the most of it." Even some writers who gave negative reviews of Ghost extended praise to Goldberg's work in the film.

Accolades
In 2002, the film ranked #96 on AFI's 100 Years... 100 Passions.

Legacy

The pottery wheel scene became widely known, and has been cited as "one of the most iconic moments of '90s cinema." It has also frequently been parodied, such as in The Naked Gun 2½: The Smell of Fear (of which Jerry Zucker served as an executive producer; it was directed by his brother David Zucker), the short British animated film Wallace and Gromit: A Matter of Loaf and Death and US TV series Two and a Half Men.

The film inspired a musical stage version, Ghost: The Musical. The show had its world premiere in Manchester, UK, in March 2011 before transferring to London from June 2011 and having its premiere on July 19, 2011. On November 13, 2010, Paramount and Shochiku released a Japanese remake of Ghost, titled Ghost: In Your Arms Again (ゴースト もういちど抱きしめたい). The remake stars Nanako Matsushima, South Korean actor Song Seung-heon, and veteran actress Kirin Kiki. In this film, the ghost is a woman, played by Matsushima.

On January 17, 2023, it was revealed by Vanity Fair that Channing Tatum and his company, Free Association, acquired the rights to the film from Paramount. Tatum announced plans to produce, and star in, a remake of the film, with himself cast in Swayze's role.

The 2023 BET+ original film The Reading pays tribute with an Easter egg, naming a minor character Oda M. Brown, though not fully named Oda  'Mae' Brown. The film is not officially associated with Ghost. However, the movie's plot deals with the supernatural psychic readings of the deceased. Brown's daughter Sky, performs spiritual readings for Emma Leeden (Mo'Nique) in a similar exorcism style Oda Mae Brown did with her clients possessing the souls of the departed. The film is written and directed by Courtney Glaude and is executive produced by Lee Daniels.

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/

title: Ghost (1990 film)


text:
Fletcher, Ohio

Fletcher is a village in Miami County, Ohio, United States. The population was 451 at the 2020 census. It is part of the Dayton Metropolitan Statistical Area.

History
Fletcher was platted in 1830. The village was named after Samuel Fletcher, a local storekeeper. The post office that had been in operation at Fletcher since 1831 closed in 2010.

Geography
According to the United States Census Bureau, the village has a total area of 0.31 sqmi, all land. Fletcher is drained by East Branch Lost Creek and West Branch Lost Creek.

The village is crossed by U.S. Route 36 and State Route 589.

2010 census
As of the census of 2010, there were 473 people, 175 households, and 133 families living in the village. The population density was 1525.8 PD/sqmi. There were 197 housing units at an average density of 635.5 /sqmi. The racial makeup of the village was 97.0% White, 0.2% Native American, 0.6% from other races, and 2.1% from two or more races. Hispanic or Latino of any race were 0.8% of the population.

There were 175 households, of which 40.6% had children under the age of 18 living with them, 56.6% were married couples living together, 11.4% had a female householder with no husband present, 8.0% had a male householder with no wife present, and 24.0% were non-families. 20.0% of all households were made up of individuals, and 8.6% had someone living alone who was 65 years of age or older. The average household size was 2.70 and the average family size was 3.06.

The median age in the village was 36 years. 27.7% of residents were under the age of 18; 8.1% were between the ages of 18 and 24; 26.4% were from 25 to 44; 24.9% were from 45 to 64; and 12.9% were 65 years of age or older. The gender makeup of the village was 51.6% male and 48.4% female.

2000 census
As of the census of 2000, there were 510 people, 189 households, and 144 families living in the village. The population density was 1,651.8 PD/sqmi. There were 207 housing units at an average density of 670.5 /sqmi. The racial makeup of the village was 98.04% White, 0.59% African American, 0.78% Native American, and 0.59% from two or more races. Hispanic or Latino of any race were 0.59% of the population.

There were 189 households, out of which 37.6% had children under the age of 18 living with them, 61.4% were married couples living together, 10.6% had a female householder with no husband present, and 23.3% were non-families. 20.1% of all households were made up of individuals, and 9.5% had someone living alone who was 65 years of age or older. The average household size was 2.70 and the average family size was 3.09.

In the village, the population was spread out, with 29.0% under the age of 18, 10.2% from 18 to 24, 29.4% from 25 to 44, 17.3% from 45 to 64, and 14.1% who were 65 years of age or older. The median age was 32 years. For every 100 females there were 103.2 males. For every 100 females age 18 and over, there were 104.5 males.

The median income for a household in the village was $41,583, and the median income for a family was $45,179. Males had a median income of $31,458 versus $26,125 for females. The per capita income for the village was $19,538. About 6.8% of families and 9.4% of the population were below the poverty line, including 8.8% of those under age 18 and 12.5% of those age 65 or over.

Economy
A Systemax factory located just east of Fletcher closed December 31, 2012.

Agriculture remains an integral part of life in Fletcher as the grain elevator, once owned by the Shepard Grain Company, is now owned by Urbana-based Champaign Landmark Inc..

An AT&T microwave radio relay tower (now abandoned) once provided several jobs for area residents. It remains standing (with the ear-shaped antennas now removed) a mile east of the village along U.S. Route 36. Ohio Bell operated the facility prior to the divestiture of the AT&T-owned Bell System in the 1980s. AT&T continued to operate the tower until the advent of fiber-optic cables and satellites which led to the replacement for the underground coaxial cable network and the use of the 318-foot steel structure now sitting vacant within the eastern Miami County farm fields.

Notable people

 * Thomas Charles Munger, judge

title: Fletcher, Ohio


text:
Laura, Ohio

Laura is a village in Miami County, Ohio, United States. The population was 398 at the 2020 census. It is part of the Dayton Metropolitan Statistical Area.

History
Laura was laid out around 1840. A post office called Laura has been in operation since 1850. The village was named after Laura, the first postmaster's daughter. Laura was incorporated as a village in 1892.

Geography
According to the United States Census Bureau, the village has a total area of 0.27 sqmi, all land.

2010 census
As of the census of 2010, there were 474 people, 174 households, and 120 families living in the village. The population density was 1755.6 PD/sqmi. There were 185 housing units at an average density of 685.2 /sqmi. The racial makeup of the village was 96.6% White, 1.7% African American, 0.4% Native American, 0.2% Asian, 0.6% from other races, and 0.4% from two or more races. Hispanic or Latino of any race were 1.5% of the population.

There were 174 households, of which 30.5% had children under the age of 18 living with them, 54.6% were married couples living together, 8.6% had a female householder with no husband present, 5.7% had a male householder with no wife present, and 31.0% were non-families. 19.0% of all households were made up of individuals, and 8% had someone living alone who was 65 years of age or older. The average household size was 2.72 and the average family size was 3.19.

The median age in the village was 38 years. 23.4% of residents were under the age of 18; 10.8% were between the ages of 18 and 24; 24% were from 25 to 44; 28.9% were from 45 to 64; and 12.9% were 65 years of age or older. The gender makeup of the village was 49.8% male and 50.2% female.

2000 census
As of the census of 2000, there were 487 people, 175 households, and 131 families living in the village. The population density was 1,714.6 PD/sqmi. There were 182 housing units at an average density of 640.8 /sqmi. The racial makeup of the village was 97.54% White, 0.21% Native American, 0.21% Asian, 0.41% from other races, and 1.64% from two or more races. Hispanic or Latino of any race were 2.26% of the population.

There were 175 households, out of which 41.1% had children under the age of 18 living with them, 60.0% were married couples living together, 8.6% had a female householder with no husband present, and 25.1% were non-families. 17.1% of all households were made up of individuals, and 6.9% had someone living alone who was 65 years of age or older. The average household size was 2.78 and the average family size was 3.18.

In the village, the population was spread out, with 29.2% under the age of 18, 7.8% from 18 to 24, 29.8% from 25 to 44, 24.2% from 45 to 64, and 9.0% who were 65 years of age or older. The median age was 35 years. For every 100 females there were 110.8 males. For every 100 females age 18 and over, there were 101.8 males.

The median income for a household in the village was $45,833, and the median income for a family was $46,250. Males had a median income of $33,542 versus $23,906 for females. The per capita income for the village was $17,912. About 2.7% of families and 2.8% of the population were below the poverty line, including 3.0% of those under age 18 and none of those age 65 or over.

title: Laura, Ohio


text:
Ludlow Falls, Ohio

Ludlow Falls is a village in Miami County, Ohio, United States. The population was 175 at the 2020 census. It is part of the Dayton Metropolitan Statistical Area. Ludlow Falls is named after surveyor Israel Ludlow.

Geography
According to the United States Census Bureau, the village has a total area of 0.18 sqmi, all land.

Ludlow Falls is a part of the Milton-Union School district located in the neighboring West Milton.

Ludlow Creek, a tributary of the Stillwater River, flows through Ludlow Falls. The village's name is derived from the waterfall of the stream located in the village.

There was a railroad line through Ludlow Falls that was built in 1881 from Springfield, Ohio to Indianapolis, Indiana. It was later owned by the New York Central Railroad. There was very little on-line traffic and the line was lightly used by the 1970s. The line was not included in the 1976 makeup of Conrail and the last train ran on March 31, 1976. The tracks were pulled up shortly thereafter.

2010 census
As of the census of 2010, there were 208 people, 81 households, and 55 families living in the village. The population density was 1155.6 PD/sqmi. There were 86 housing units at an average density of 477.8 /sqmi. The racial makeup of the village was 100.0% White. Hispanic or Latino of any race were 0.5% of the population.

There were 81 households, of which 34.6% had children under the age of 18 living with them, 40.7% were married couples living together, 17.3% had a female householder with no husband present, 9.9% had a male householder with no wife present, and 32.1% were non-families. 24.7% of all households were made up of individuals, and 3.7% had someone living alone who was 65 years of age or older. The average household size was 2.57 and the average family size was 3.04.

The median age in the village was 34 years. 28.8% of residents were under the age of 18; 7.8% were between the ages of 18 and 24; 22.7% were from 25 to 44; 33.6% were from 45 to 64; and 7.2% were 65 years of age or older. The gender makeup of the village was 52.4% male and 47.6% female.

2000 census
As of the census of 2000, there were 210 people, 81 households, and 60 families living in the village. The population density was 1,144.4 PD/sqmi. There were 88 housing units at an average density of 479.6 /sqmi. The racial makeup of the village was 98.10% White, and 1.90% from two or more races. Hispanic or Latino of any race were 0.48% of the population.

There were 81 households, out of which 37.0% had children under the age of 18 living with them, 49.4% were married couples living together, 14.8% had a female householder with no husband present, and 25.9% were non-families. 22.2% of all households were made up of individuals, and 6.2% had someone living alone who was 65 years of age or older. The average household size was 2.59 and the average family size was 2.97.

In the village, the population was spread out, with 29.0% under the age of 18, 7.6% from 18 to 24, 33.8% from 25 to 44, 21.9% from 45 to 64, and 7.6% who were 65 years of age or older. The median age was 35 years. For every 100 females there were 114.3 males. For every 100 females age 18 and over, there were 109.9 males.

The median income for a household in the village was $39,375, and the median income for a family was $43,500. Males had a median income of $32,250 versus $21,071 for females. The per capita income for the village was $16,383. About 6.9% of families and 6.9% of the population were below the poverty line, including 9.6% of those under the age of eighteen and none of those 65 or over.

title: Ludlow Falls, Ohio


text:
Piqua, Ohio

Piqua is a city in Miami County, Ohio, United States, along the Great Miami River. The population was 20,354 at the 2020 census. Located 27 mi north of Dayton, it is part of the Dayton metropolitan area.

Etymology
The word 'Piqua' is believed to be derived from a Shawnee language phrase: Othath-He-Waugh-Pe-Qua, translated as "He has risen from the ashes," related to a legend of the people. It became associated with the Pekowi, one of the five divisions of the Shawnee people, who were eventually known as the Piqua.

Early settlements
In 1749, Fort Pickawillany was constructed by the British to protect their trading post at a Miami village of the same name. It was located at the confluence of Loramie Creek and the Great Miami River.

In 1752 Charles de Langlade, an Odawa war chief of partial French Canadian descent, attacked the fort. He led more than 240 Odawa and Ojibwe warriors allied with French forces against the British and the Miami village in the Battle of Pickawillany. The Miami chief and a British trader were killed in the conflict.

After the battle, the British and Miami abandoned this site. The Miami rebuilt Pickawillany, and Piqua later developed near their village. The British soon took over the area after defeating the French in the French and Indian War.

Until 1780, Piqua had been the capital town of the Shawnee located on the Mad River about 23 miles southeast of the modern town (near Springfield). That year, an expedition by Gen. George Rogers Clark culminated in the Battle of Piqua, after which the town and surrounding fields were burned. The Shawnee relocated north and west to the Great Miami River. Piqua was settled as two separate Shawnee villages late in 1780, known as Upper Piqua and Lower Piqua.

In 1790, General Harmar found the site on the Great Miami River abandoned and in ruins, as did General Wayne in 1794.

As Gen. Anthony Wayne's Legion was returning to Greenville via Loramie's trading post and Piqua at the termination of their Indian Country campaign in fall 1794, Wayne wrote a letter to Henry Knox dated October 17, 1794, in which he recommended that forts be built at those two locations as waystations along the Miami River. A detachment of Wayne's forces from Greenville built or repaired a small fort and supply depot named Fort Piqua in Upper Piqua on the same site as the (later) farm of Col. John Johnston in winter 1794–95. Capt. J.N. Visher was made commander of the garrison. The fort was garrisoned through 1794 and 1795, and abandoned after the signing of the Treaty of Greenville in 1795.

By 1795, most of Ohio's Shawnee had moved to Missouri and those that remained migrated north to the Auglaize - the southwestern Indian towns were no more. Piqua itself was well below the Greenville Treaty line and would remain abandoned until white settlers arrived.

Modern settlement and incorporation
The first European settlers arrived in 1798, after the signing of the Treaty of Greenville ending the Northwest Indian War and opening much of Ohio to settlement. In 1807 the village, consisting of seven houses, was surveyed by Armstrong Brandon, a soldier under Gen. Anthony Wayne, and named Washington. It was about a mile southwest of the old Indian villages of Piqua.

By 1816 the Shawnee village of Piqua had been long abandoned; the state legislature, acting on citizen petition, changed the name of Washington village to Piqua. Piqua was incorporated as a town by the Ohio General Assembly in 1823.

During the war of 1812, Piqua was a waystation for men and supplies moving north. In 1819, a land office was established in Piqua which facilitated its growth.

Piqua developed along with construction of the Miami and Erie Canal between 1825 and 1845.

Rossville
Rossville, Ohio was the first free-black enclave in the region. Virginia planter John Randolph of Roanoke, who served as a U.S. representative and senator, arranged for the emancipation of his nearly 400 slaves in his will of 1833. He also provided money for his executor to relocate the freedmen to the free state of Ohio, and to buy land and supplies to help them establish a settlement. The will was challenged but in 1846, his 383 slaves gained their freedom. Most of these freedmen settled in Rumley, Ohio. Some eventually founded Rossville and an associated cemetery, known as the African Jackson Cemetery. These are located on the northeast side of the Great Miami River; they may be accessed by nearby North County Road 25-A. The community has since been incorporated into Piqua.

1913 flood
Piqua was one of the cities that suffered severe flooding during the Great Dayton Flood of 1913. Piqua is nestled in a sweeping "S" bend of the Great Miami River and experienced regular flooding before the Great Flood of 1913.

On March 22, 1913, a moderate storm moved down the St. Lawrence River basin into the Ohio River basin, with enough rain to moisten the soil upriver from the Miami River and its tributaries. The soil in that upper region is predominantly clayey glacial till, transitioning to mostly Loamy glacial till. Starting on March 23, 1913, rain began to fall for five days. The heaviest rainfall occurred on March 25 with anywhere from 2” in the southeast corner of Ohio to 5” in the area between Piqua and Troy. All together, the total amount of precipitation for this five day period was recorded from 5” in the southeast of Ohio to 11” in the swatch between Piqua and Troy.

The flood waters came with such speed and force as to move homes off their foundations, depositing untold amounts of mud in others and claiming forty-nine lives in Piqua and neighboring Rossville alone. In places, streets were damaged or washed out to varying degrees of severity. Public utilities (gas, sewer and water) were hampered to provide services, due to mud clogging up the pipes. The estimated property damage/loss in Piqua reached $1,000,000 ($26.2M in present-day dollars), excluding public utilities and farm losses. The Ohio and Erie Canal, which for 81 years had served as an important connection point from Ohio to the East Coast, was permanently closed to commercial traffic because of extensive flood damage.

Atomic City
Piqua was home to the first municipally operated nuclear power plant, the Piqua Nuclear Generating Station. The facility was built and operated between 1963 and 1966 as a demonstration project by the United States Atomic Energy Commission. The Atomic Energy Commission bought out the contract with the City of Piqua in order to terminate the operations early, citing higher-priority needs for manpower and funding, lack of programmatic interest, and technical problems.

Geography
According to the United States Census Bureau, the city has a total area of 11.89 sqmi, of which 11.62 sqmi is land and 0.27 sqmi is water.

The Great Miami River runs through Piqua. The area at the south end of town on the east side of the river is known as Shawnee.

2010 census
As of the census of 2010, there were 20,522 people, 8,318 households, and 5,425 families residing in the city. The population density was 1766.1 PD/sqmi. There were 9,311 housing units at an average density of 801.3 /sqmi. The racial makeup of the city was 92.4% White, 3.3% African American, 0.2% Native American, 0.7% Asian, 0.4% from other races, and 2.9% from two or more races. Hispanic or Latino of any race were 1.4% of the population.

There were 8,318 households, of which 32.6% had children under the age of 18 living with them, 44.9% were married couples living together, 14.2% had a female householder with no husband present, 6.1% had a male householder with no wife present, and 34.8% were non-families. 28.7% of all households were made up of individuals, and 12.2% had someone living alone who was 65 years of age or older. The average household size was 2.44 and the average family size was 2.96.

The median age in the city was 38.1 years. 24.8% of residents were under the age of 18; 8.7% were between the ages of 18 and 24; 25.6% were from 25 to 44; 26.2% were from 45 to 64; and 14.7% were 65 years of age or older. The gender makeup of the city was 48.0% male and 52.0% female.

2000 census
As of the census of 2000, there were 20,738 people, 8,263 households, and 5,585 families residing in the city. The population density was 1,939.2 PD/sqmi. There were 8,886 housing units at an average density of 830.9 /sqmi. The racial makeup of the city was 94.21% White, 3.38% African American, 0.33% Native American, 0.44% Asian, 0.27% from other races, and 1.37% from two or more races. Hispanic or Latino of any race were 0.74% of the population.

There were 8,263 households, out of which 32.7% had children under the age of 18 living with them, 50.4% were married couples living together, 12.9% had a female householder with no husband present, and 32.4% were non-families. 27.3% of all households were made up of individuals, and 11.4% had someone living alone who was 65 years of age or older. The average household size was 2.47 and the average family size was 2.99.

In the city the population was spread out, with 26.5% under the age of 18, 9.0% from 18 to 24, 28.9% from 25 to 44, 21.3% from 45 to 64, and 14.3% who were 65 years of age or older. The median age was 35 years. For every 100 females, there were 91.4 males. For every 100 females age 18 and over, there were 85.7 males.

The median income for a household in the city was $35,681, and the median income for a family was $41,804. Males had a median income of $31,808 versus $22,241 for females. The per capita income for the city was $18,719. About 9.6% of families and 12.2% of the population were below the poverty line, including 18.0% of those under age 18 and 7.9% of those age 65 or over.

Economy
The city of Piqua is the home of Hartzell Propeller, a producer of small aircraft propellers. Evenflo (formerly Questor Juvenile Furniture) is the leading manufacturer of infant and toddler car seats, and has become one of Piqua's leading employers and industries.

In the late 1890s, Southwest Ohio was the heart of the US flaxseed growing area. There were some 13 linseed oil mills in Piqua, where the flaxseed was "crushed" to extract the vegetable oil, named linseed oil. The flax fiber was used to make both cloth and paper. The oil had a variety of industrial uses. Linoleum is a manufactured flooring product for which linseed oil is the binder. One of the vegetable oil mills in Piqua burned down in the 1890s, a common fate for wooden buildings soaked with vegetable oil. Its owner, American Linseed Oil Company, dispatched Alfred Willard French, their Chief Engineer, from Brooklyn, New York, to organize and supervise the rebuilding of the oil mill.

During the rebuilding of the mill, French included a machine he had invented and patented in 1898, a "cake trimmer", and purchased the most modern equipment then available. He met the leading citizens of Piqua. They were impressed with French, who had graduated from the Massachusetts Institute of Technology in three years, and had entrepreneurial spirit. They decided to invest in a new company he wanted to start. The French Oil Mill Machinery Company was founded May 25, 1900, with French as president, to make "improved oil mill machinery". By 1905 the company was exporting its patented and rugged vegetable oil mill extraction machinery all around the world. Today, the company has customers in over 80 countries, still serving the vegetable oil extraction market (to press such seeds as soybeans, cottonseed, rapeseed, canola, and many others). In addition, the company is a world leader in synthetic rubber dewatering and drying machinery, and in hydraulic molding presses for rubber, thermoplastic and composite materials.

During the late 19th century and much of the 20th century, Piqua was a major center of underwear production. A yearly Outdoor Underwear Festival was held downtown from 1988 until shortly after the demise and demolition of the factory owned by Medalist-Allen A, a direct descendant of the Atlas Underwear Company. Originally the festival had a serious historical focus. In later years it attracted adventurous types from surrounding towns, and Piqua residents discouraged their children from attending. Heritage Green Park now occupies the former Medalist factory site.

The Meteor Motor Car Company had a brief run as an independent record label and phonograph manufacturer in the 1920s. Acquired by Wayne Corporation of Richmond, Indiana, which manufactured school buses, it operated as the Miller-Meteor division. Miller-Meteor produced ambulances and hearses before closing down in 1979.

The Piqua Coca-Cola Bottling Company, owned by the Lange family, was located on the downtown square at the northeast corner of Main and High streets. It produced its signature product along with Sprite, Tab and Fresca in glass bottles for the Upper Miami Valley; metal canned products were shipped in from a plant in Speedway, Indiana. In the mid-1970s, the plant was bought by the Dayton Coca-Cola Bottling Company. The increased demand for Coke products in two-liter plastic bottles and cans made the aging local plant obsolete; it was closed down and razed by the end of the decade. A newer bottling plant was constructed in Huber Heights. A statue of pilot Don Gentile was erected at the site of the defunct plant.

The Val Decker Packing Company, which operated until 1981, was a local producer of hams, hot dogs, and other meats and lard under the tagline "Piquality." The large red steel cans, which contained the lard product, are now sought-after as collectors' items. The building which housed the meat packing plant was renovated in 1987 for office use by the Piqua Board of Education and several small businesses.

Piqua's industrial past produced a prosperity reflected in residential areas near downtown, which contain numerous large mansions and homes. Most notable is the Leo Flesh Mansion, built in the Chateauesque style. It looms over many of the surrounding buildings in the neighborhood. A "sister" house in Dayton, Ohio, was designed by the same architect.

Piqua's shopping mall, Miami Valley Centre Mall, opened in 1988 and was renovated in the mid-1990s. Miami Valley Crossing (formerly Piqua East Mall, opened in 1970) was redesigned and updated in the late 1990s as a plaza with several anchor stores.

Top employers
According to Piqua's 2018 Comprehensive Annual Financial Report, the top employers in the city are:

Arts and culture
Fort Piqua Plaza began as the "Orr-Statler Block" building at the corner of Main and High Streets was erected in 1891 and long dominated downtown. For many years its core tenant was a hotel of more than 100 rooms, first known as the "Plaza," later as the "Favorite," and finally as the "Fort Piqua." The hotel closed in the 1980s.

The building's street-level commercial spaces were occupied by a variety of businesses over the years, including a barbershop, grocer, bank, the local telephone company business office, Western Union, a combination bus station and taxi office with a very popular soda fountain and lunch counter, and others. Just prior to the start of the Prohibition era, the hotel's bar was moved to the basement level. It is rumored to have closed only its outside entrance during those years, operating as a speakeasy.

The building suffered disrepair and neglect for a period, and renewal plans seemed unable to secure funding. In a public-private redevelopment, the building was fully renovated during a two-year project. Since 2008, its major tenant has been the city's public library. In addition, the building is the location of The Scottish Thistle, a full-scale restaurant and bar, complete with a patio for live entertainment. The building is now known as Fort Piqua Plaza.

Beginning in 1886, there were 14 companies in Piqua set up that sold underwear. There were underwear manufacturers in the city until 1993.

The Underwear Festival, in which participants wore underwear publicly and which had entertainment events, was established in 1988. Each instance was for two days. In 1990 the Associated Press stated: "Organizers cautioned that the parade is a family affair." A lack of volunteers led to the disestablishment of the festival in 1998.

Education
The Piqua City School District operates two elementary schools, one intermediate school, one middle school, a junior high school, and Piqua High School. Piqua is also home to the Upper Valley Career Center. Piqua is also home to several private schools, including Piqua Catholic School, the Piqua Seventh Day Adventist School, and the Nicholas School.

Piqua is home to Edison State Community College, established as Ohio's first general and technical college in 1973.

Media
The Piqua Daily Call was published daily from 1884 to 2019 before being consolidated with the Troy Daily News to form Miami Valley Today, which is published Tuesday through Friday in Troy.

Piqua is home to the radio stations WPTW 1570 AM and 98.1 FM, as well as WPLC 95.1 low-power FM as a repeater of Three Angels Broadcasting Network.

Transportation
Piqua has two Main Streets, one being north and southbound along Miami County Road 25-A (the former U.S. Route 25, also known as the Dixie Highway); the other running east through Shawnee. U.S. 36 also runs through much of the city, cutting the town almost directly in half. Main and Ash streets (U.S. 36) converge in Piqua's downtown. Also running through downtown is the east–west Conrail corridor; originally built as the Pennsylvania Railroad two-track throughway, this track was abandoned in 1985 during restructuring of the railroad industry. A section of it was renovated as a bike trail in the summer of 2001, and it is now known as Linear Park. The remaining rail line serving Piqua is the north and southbound Baltimore and Ohio line, now operated by CSX Transportation (CSXT).

Notable people

 * Kenneth W. Benner - brigadier general, USMC and veteran of World War II
 * Brock Bolen - football player
 * Craig Clemons - football player
 * John W. Daniels - co-founder and former CEO of Archer-Daniels-Midland (ADM)
 * Matt Finkes - New York Jets defensive end
 * Dominic Salvatore Gentile - World War II ace
 * Terri Hemmert - Chicago disc jockey at WXRT-FM
 * Charles Blue Jacket - 19th-Century Shawnee chief in Kansas, and Methodist minister
 * James Kaiser - electrical engineer who developed the Kaiser window for digital signal processing
 * Girard Edward Kalbfleisch - U.S. federal judge
 * Kristin King - player on the bronze medal-winning women's U.S. Hockey team at the 2006 Winter Olympics
 * Ollie Klee - baseball player
 * Bill Lear - inventor and businessman, founder of Lear Jet and inventor of the 8-track cartridge
 * William McCulloch - lawyer, member of U.S. House of Representatives, and an author of the Civil Rights Act of 1964
 * John F. McKinney - U.S. Representative from Ohio
 * Rich McKinney - baseball player
 * Mills Brothers - jazz musicians, inducted into the Vocal Group Hall of Fame in 1998
 * John G. Mitchell - general in the Union Army
 * J. T. Patterson - geneticist
 * Dav Pilkey - writer and illustrator of the Captain Underpants books for children
 * Quinn Pitcock - football player
 * William H. Pitsenbarger - Air Force pararescueman posthumously awarded the Medal of Honor
 * Louis Joseph Reicher - first Bishop of Austin, Texas (1948-1971)
 * Harry Reser - banjo player and bandleader of the Clicquot Club Eskimos
 * Stephen Clegg Rowan - vice admiral, U.S. Navy
 * Brandon Saine - football player
 * Helen Schelle - founding partner of Fisher-Price, toy manufacturer
 * Lawrence Yates Sherman - U.S. Senator and Lieutenant Governor of Illinois
 * Tanya Thornton Shewell - member of the Maryland House of Delegates
 * Hiram Y. Smith - lawyer and U.S. Representative from Iowa
 * Mike Smith - baseball player
 * Jack Snow - fantasy and horror author
 * Muffin Spencer-Devlin - professional golfer
 * Joseph J. Spengler - economist, statistician, and historian of economic thought
 * Aileen Cole Stewart (1893-1997), African American United States Army Nurse Corps nurse during World War I.
 * Lester J. Whitlock, U.S. Army major general
 * Joseph Widney - doctor, educator, historian, and religious leader
 * Robert M. Widney - founding father of the University of Southern California
 * James P. Wisecup - vice admiral, U.S. Navy
 * Patrick Zircher - artist, Marvel and DC comics

In popular culture

 * Dav Pilkey's Captain Underpants children's book series is set in Piqua. It was chosen because of its defunct annual "Underwear Festival".

title: Piqua, Ohio