Gita Nematbakhsh Abkenar

Mathilde Rieu
email: rieu@emse.fr

Philippe Breuil

Jean-Paul Viricelle

Development of a selective ammonia YSZ-based sensor and modeling of its response

Keywords: Mixed-potential gas sensor, Ammonia, Sensing electrode, V2O5, Response modeling. Highlights

In the present study, Au-V2O5 sensing material was tested as a sensing electrode for developing mixed-potential ammonia gas sensors. The results of gas sensing measurements indicated selective responses to NH3 while this selectivity was highly dependent on the temperature. Different V2O5 contents were tested in the sensing electrode. The results showed that by increasing V2O5 content from 15 wt.% to 50 wt.%, selective ammonia sensors could be achieved at 550 °C. The selectivity of Au-50%V2O5 sensor was also confirmed in gas mixtures of CO, NH3, NO, and NO2 gases. Modeling of the sensor responses in the ammonia concentration range 2-40 ppm at four oxygen concentrations was performed based on mixedpotential theory. Nernst and Butler-Volmer equations with an electron transfer assumption were used for data modeling.

Introduction

Selective catalyst reduction (SCR) system using ammonia gas as a reductant is one of the most reliable ways to reduce NOx emissions from diesel engine vehicles and trucks. To optimize the conversion rates of NOx and to prevent inducing excessive NH3 to the air, an ammonia sensor is required to control the SCR system [START_REF] Dai | Mixed potential NH3 sensor based on Mg-doped lanthanum silicate oxyapatite[END_REF]. There are wide ranges of studies in the literature to find a robust, sensitive, low cost and selective ammonia sensor working at high temperatures.

One of the most promising solid-state ammonia sensors suitable for harsh environments is mixed-potential type sensors with yttria-stabilized zirconia (YSZ) electrolyte [START_REF] Miura | A review of mixed-potential type zirconia-based gas sensors[END_REF][START_REF] Lee | Mixed potential NH3 sensor with LaCoO3 reference electrode[END_REF][START_REF] Schönauer-Kamin | Half-Cell Potential Analysis of an Ammonia Sensor with the Electrochemical Cell Au | YSZ | Au, V2O5-WO3-TiO2[END_REF]. The main advantages of these mixed-potential type gas sensors that distinguish them from other types of sensors, are higher stability and reproducibility, wide flexibility for targeting gas species by changing the composition of the electrodes operating under open circuit or biased mode, and the ability to detect changes in gas content on timescales of milliseconds [START_REF] Tsui | A Three Electrode Mixed Potential Sensor for Gas Detection and Discrimination[END_REF]. Indeed, these sensors have special features such as high-temperature operation, excellent sensing performance, and high chemical and mechanical stability [START_REF] Pasierb | Solid-state potentiometric gas sensors-current status and future trends[END_REF]. They have also been studied extensively due to their fast response, high sensitivity, and long-term stable results [START_REF] Lee | Mixed potential NH3 sensor with LaCoO3 reference electrode[END_REF][START_REF] Schönauer-Kamin | Half-Cell Potential Analysis of an Ammonia Sensor with the Electrochemical Cell Au | YSZ | Au, V2O5-WO3-TiO2[END_REF]. So far, numerous studies have been performed to find a sensitive and selective ammonia sensor at high temperatures. Different approaches have been suggested to achieve an effective ammonia sensor by modifying electrolyte [START_REF] Plashnitsa | Zirconia-based electrochemical gas sensors using nano-structured sensing materials aiming at detection of automotive exhausts[END_REF][START_REF] Meng | Mixed-potential type NH3 sensor based on TiO2 sensing electrode with a phase transformation effect[END_REF], reference electrode [START_REF] Lee | Mixed potential NH3 sensor with LaCoO3 reference electrode[END_REF][START_REF] Wang | Ammonia gas sensors[END_REF] or sensing electrode [START_REF] Wang | Ammonia gas sensors[END_REF][START_REF] Wang | Fabrication of well-ordered porous array mounted with gold nanoparticles and enhanced sensing properties for mixed potential-type zirconia-based NH3 sensor[END_REF][START_REF] Liu | Highly selective and stable mixed-potential type gas sensor based on stabilized zirconia and Cd2V2O7 sensing electrode for NH3 detection[END_REF][START_REF] Wang | Effect of V2O5-content on electrode catalytic layer morphology and mixed potential ammonia sensor performance[END_REF][START_REF] Schönauer | Investigation of the electrode effects in mixed potential type ammonia exhaust gas sensors[END_REF][START_REF] Plashnitsa | Spontaneous gradual accumulation of hexagonally-aligned nano-silica on gold nanoparticles embedded in stabilized zirconia: a pathway from catalytic to NH3-sensing performance[END_REF][START_REF] Satsuma | Effects of Calcination Temperature and Acid-Base Properties on Mixed Potential Ammonia Sensors Modified by Metal Oxides[END_REF][START_REF] Liu | Mixedpotential type NH3 sensor based on stabilized zirconia and Ni3V2O8 sensing electrode[END_REF].

Indeed, in these sensors, choosing a suitable material as a sensing electrode is very important for developing sensitive and selective sensors. A high electro-catalytic activity, as well as catalytic selectivity, are imperative for the sensing element of these sensors, especially in planar configuration. Among them, vanadium based sensing electrodes looks very promising. For example, Wang et al. in 2006 [9] published a patent (from Delphi Inc.) in which they reported the results of nineteen different sensors with various vanadium based electrode materials. After testing different materials, they found BiVO4 as the most appropriate material for a selective ammonia sensor. Liu et al. in 2015 [16] developed a sensor using stabilized zirconia (YSZ) and sensing electrode (SE) of Ni3V2O8 oxide. They showed that Ni3V2O8 calcined at 1000 °C exhibited the largest sensitivity in an NH3 concentration range of 50-500 ppm at 650 °C. Wang et al. in 2016 [START_REF] Wang | Effect of V2O5-content on electrode catalytic layer morphology and mixed potential ammonia sensor performance[END_REF] used V2O5-WO3-TiO2 (VWT) material to get an ammonia selective electrode. The sensing electrode was consisted of Pt covered with a porous VWT catalyst layer.

In addition, vanadium dioxide (V2O5) is also well-known as sensitive material to ammonia even at ppb levels [START_REF] Wang | Effect of V2O5-content on electrode catalytic layer morphology and mixed potential ammonia sensor performance[END_REF][START_REF] Modafferi | Electrospun V2O5 composite fibers: Synthesis, characterization and ammonia sensing properties[END_REF].

Taking into account our past results with Pt/YSZ/Au configuration for NOx sensors [START_REF] Morata | Development and characterisation of a screen-printed mixed potential gas sensor[END_REF][START_REF] Gao | Improvement of the NOx selectivity for a planar YSZ sensor[END_REF][START_REF] Romanytsia | Application of advanced morphology Au-X (X=YSZ, ZrO2) composites as sensing electrode for solid state mixed-potential exhaust NOx sensor[END_REF] and literature results dealing with NH3 sensors, especially based on V2O5 material, the objective of the present study is to developed sensitive and selective NH3 sensors, using Au-V2O5 material as sensing electrode. For this, three mass percentages of V2O5 to Au (15, 30, and 50 wt.%) are used. The results of these sensors to different interfering gases such as CO, NO2, NO, H2, and hydrocarbons are studied. In addition, sensor responses to different O2 and NH3 concentrations are investigated. Finally, mixed potential theory based on Butler-Volmer equation is used to model the obtained results.

Experimental

The fabrication of sensors was performed by a screen-printing method using R-23 Meteor 23 semi-automatic screen-printer. Commercially available Pt (ESL 5545) and Au (ESL 8880-H) inks were used while YSZ (TZ-8YS) and V2O5 (Sigma-Aldrich) homemade inks were elaborated using commercial powders. For preparing homemade inks, a binder (ESL V400A) and an organic solvent (ESL 404) were added to commercial powders. For Au-V2O5 sensing electrodes, a mixture of Au commercial ink and V2O5 home-made ink was prepared with 15, 30 and 50 wt.% of V2O5.

The sensors were developed in planar configuration on alumina substrates as supports. A YSZ electrolyte layer was first deposited on the substrate following by 2 hours sintering at 1380 °C.

The reference (RE: Pt) and sensing electrodes (SE: Au or Au-V2O5) were then printed on the YSZ layer. The sintering temperatures for Pt reference electrode and Au-V2O5 sensing electrode were 850 °C and 600 °C during 1 hour respectively. In order to provide the high working temperature of sensors, a heating element in the form of a platinum resistor was printed on the opposite side of the alumina substrate, facing the YSZ electrolyte. Fig. 1 shows the sensing and heating sides of a final sensor with different elements. Although Pt electrode is not in a reference chamber as the sensor is in planar configuration, we keep the name "reference electrode (RE)" as it has been shown that Pt behaves like a reference in such single chamber, in regards of other oxide based electrodes designed as sensing electrodes (SE) [START_REF] Miura | Highly selective CO sensor using stabilized zirconia and a couple of oxide electrodes[END_REF].

To identify the sensors with different sensing elements, the mass percentage of V2O5 is indicated in their name. Sensors with 15 wt.% V2O5 are named as Au-15%V2O5, with the same labeling for 30 wt.% V2O5 (Au-30%V2O5), and 50 wt.% V2O5 (Au-50%V2O5). A test bench was used to study the responses of two sensors working simultaneously in separate cells, thus allowing to check the signal reproducibility. A schematic of the experimental test bench is shown in Fig. 2. The various studied gases were conditioned in separated cylinders and their flow rates were monitored by mass flow regulators. The total flow rate was fixed at 60 l/h, corresponding to 30 l/h per cell. An humidifier allowed to generate and control water vapor in the gas flow. Gases first arrived in a mixing chamber before being sent to the two cells, which each contained one sensor. An FTIR gas analyzer (Gasmet DX 4015) was used to analyze the gas leaving sensor cells.

Sensors responses to different gases such as CO, NH3, NO2, NO, H2 and CxHy were studied.

The hydrocarbon gas (CxHy) used in this study was composed of 56 mol.% propene (C3H6), 28 mol.% n-butane (n-C4H10) and 16 mol.% methane (CH4). The base gas was composed of 2, 5, 12 or 16.4 mol.% O2 balanced with N2 with 1.5 vol.% absolute humidity. The sensor signal (∆𝑉 𝑅𝐸 0 ) is the potential difference between the reference electrode and the sensing electrode

(∆𝑉 𝑅𝐸 0 = VRE -VSE).
Then, the response to a target gas is defined as the difference of the sensor signal in presence of this gas minus the sensor signal under base gas with the same oxygen content (response = ∆𝑉 𝑅𝐸,𝑔𝑎𝑠 0 -∆𝑉 𝑅𝐸,𝑏𝑎𝑠𝑒𝑔𝑎𝑠 0 ). By comparing quantitatively responses of both types of sensors (Table 1), it can be observed that responses related to Au electrode decrease considerably by increasing temperature from 450°C (absolute value in the range 14-87 mV) up to 600°C (absolute value lower than 3 mV).

Regarding Au-15%V2O5 device, responses to CO, NO2 and NO also decrease in a similar way when the temperature is increased. However, NH3 response is quite less affected: its response decreases from 91mV (450°C) down to 66mV at 600°C, which remains significant in regards of the one of other gases. Hence, a selective ammonia sensor is obtained when increasing the temperature as the cross-sensitivity to other interfering gases, such as CO, NO2 and NO, is strongly reduced at 600°C, as seen in figure 3. show that the gas responses for all sensors decrease by increasing the temperature (as observed before for Au-15%V2O5). Sensors respond significantly to all gases at 450 °C and 500 °C. By increasing the temperature up to 550 °C, the selectivity of 30%V2O5 and 50%V2O5 sensors for NH3 detection is largely increased, while 15%V2O5 sensors still show responses to CO, NO2 and NO at this temperature. Finally, all sensors show selective responses toward ammonia at 600 °C.

Table 1 Comparison of Au and

One of the main challenges of these sensors is long-term stability. Since the melting point of V2O5 is 680 °C [START_REF] Levi | Stability Criteria of Fullerene-like Nanoparticles: Comparing V2O5 to Layered Metal Dichalcogenides and Dihalides[END_REF] (650 °C in some studies [START_REF] Gupta | Effect of Post Annealing on the Structural Properties of Vanadium Oxide Thin Film Deposited by RF Sputtering[END_REF]), there is a high possibility that an operating temperature of 600°C for a long period could cause damage of Au-V2O5 sensing electrode.

Indeed, test conducted at 600°C during 48 hours have confirmed a strong degradation of the sensing electrode, contrary to observations made after similar experiments at 550°C showing neither electrode degradation, nor sensor signal alteration. Therefore, a temperature of 550°C is a good compromise between long-term stability and NH3 selectivity.

At 550°C, since 50%V2O5 based sensors show a slightly improved selectivity compared to 30%V2O5 ones, especially regarding CO interference, Au-50%V2O5 sensor was selected for the rest of this study.

Morphology of Au-50%V2O5 electrode on YSZ electrolyte

The morphology of the selected Au-50%V2O5 sensing electrode was characterized by Scanning Electron Microscopy (SEM, ZEISS SUP RA-55 VP). Cross-section micrograph is shown in

Interference of H2 and CxHy gases

In prior tests, four gases CO, NH3, NO2, and NO were tested to study the selectivity of the sensors. However, the sensor may be affected by other interfering gases. Hydrocarbons (HC) are among the most important species that may cause interference for NH3 sensors in car exhaust. Apart from hydrocarbons, almost all diesel-type vehicles emit marginal amounts of hydrogen (around 0.1 mg/km). In some studies, hydrogen is reported as an interfering gas to the results of ammonia sensors [START_REF] Meng | Mixed-potential type NH3 sensor based on TiO2 sensing electrode with a phase transformation effect[END_REF]. Therefore, cross-sensitivity with these gases is also an important issue. To ensure the selectivity, Au-50%V2O5 sensors were tested with 100 ppm hydrocarbon (56 mol.% C3H6, 28 mol.% n-C4H10, 16 mol.% CH4) and 20 ppm of H2 at 550 °C.

The base gas in this experiment was also composed of 12 mol.% O2 balanced with N2 and 1.5 vol.% absolute humidity.

Au-50%V2O5 sensors responses in gas mixtures

Moreover, in previous tests, the sensing performances were studied with individual gases.

However, in a real environment of gas exhaust, the pollutant gases exist altogether, which might disturb the responses of sensors to each gas. For this reason, sensors responses in gas mixtures were studied. To understand if the sensors responses were coherent with the gas existing in the mixture, a gas analyzer instrument (Gasmet DX 4015 FTIR analyzer) was used to monitor the gas composition at the exit of sensors cells. The sensor responses in different gas mixtures (set points of 10 ppm NH3, 30 ppm NO2 and 50 ppm CO and NO) are shown in Fig. 7 (with 12 mol.% O2 balanced with N2 and 1.5 vol.% absolute humidity as base gas). Fig.

7 also shows results of gas analyses and gas concentration set point. In binary gas mixtures, when injecting NH3 in the presence of NO2, it can be seen through gas analyzer that there is no more NH3 gas at the exit. Furthermore, NO2 concentration is slightly decreased (around 20 ppm) compared to the single gas measurement (around 30 ppm). In fact, this phenomenon is also observed when there is no sensor in the cell. This means that a reaction in gas phase occurs between NH3 and NO2, and NH3 is completely consumed by NO2

(according to reaction (1)) in our experimental conditions. Hence, the absence of sensor response to NH3 when mixed with NO2 is simply explained by the fact there is no more NH3 in the gas phase, and it is also coherent with lower NO2 concentration at the cell exit. Looking at the sensor response in other binary gas mixtures, CO and NO gases do not affect significantly sensor response to NH3.

2NO 2 + O 2 + 4NH 3 → 3N 2 + 6H 2 O (1)
Considering the gas analyzer results in three-gas mixtures, the main results are similar to those observed in two gas mixtures. The sensor response to NH3 is coherent with gas analyzer results.

If NH3 is consumed by NO2, the sensor logically does not show significant responses. It is also noticed that CO presence may limit NO2/NH3 reaction. Therefore, NH3 is detected in NO2/NH3 gas mixtures only in the presence of CO. As a conclusion, the results show that the sensor responds to NH3 whenever it is present in the gas phase, and sensor responses to other gases are negligible.

Sensitivity to NH3 with varying oxygen concentrations

All previous tests were performed with a fixed oxygen content at 12 mol.%. In real conditions, Fig. 9 shows the variations of NH3 signals as a function of log(CNH3). It is seen that the signal changes linearly with the logarithm of NH3 concentrations in the examined range. This is in agreement with reported results on planar potentiometric sensor [START_REF] Schönauer-Kamin | Half-Cell Potential Analysis of an Ammonia Sensor with the Electrochemical Cell Au | YSZ | Au, V2O5-WO3-TiO2[END_REF][START_REF] Schönauer | Selective mixed potential ammonia exhaust gas sensor[END_REF] and mixed potential theory [START_REF] Fergus | Sensing mechanism of non-equilibrium solid-electrolyte-based chemical sensors[END_REF][START_REF]Solid state gas sensing[END_REF]. The slopes of the obtained lines indicate the sensitivity of the sensor to ammonia (defined with log(CNH3)), which are respectively 75.9, 69.2, 62.4, and 58.6

its
mV/decades for 2%, 5%, 12%, and 16.4% O2 concentrations. Therefore, NH3 sensitivity of the sensor decreases by increasing O2 concentration. These values are in the same range as NH3 potentiometric sensor reported in the literature [START_REF] Schönauer-Kamin | Half-Cell Potential Analysis of an Ammonia Sensor with the Electrochemical Cell Au | YSZ | Au, V2O5-WO3-TiO2[END_REF][START_REF] Schönauer | Selective mixed potential ammonia exhaust gas sensor[END_REF].

Modeling of NH3 responses under different O2 concentrations

Based on the previous experimental results (Fig. 8), and on the semi-logarithmic behavior of NH3 responses plotted in Fig. 9, a model is proposed to quantify sensor responses. For this modeling, sensor responses in the base gas (considering only electrochemical oxygen reaction) and with NH3 injections (mixed potential theory) are considered separately.

Baseline modeling (CNH3 = 0)

For the baseline of the sensor (when CNH3 = 0), an equilibrium condition is assumed for the unique electrochemical reaction of the oxygen (reaction 2, no mixed potential), so Nernst equation is used for calculating the potential of each electrode and finally the electromotive force, which corresponds to the sensor signal ∆𝑉 𝑅𝐸 0 given by equation 3. In this relation, CO2(RE) and CO2(SE) should rigorously be the activity of adsorbed oxygen species at respectively the reference electrode (Pt) and sensing electrode (Au-V2O5) [START_REF] Park | Absolute potential analysis of the mixed potential occurring at the oxide/YSZ electrode at high temperature in NOx-containing air[END_REF]. We made the hypothesis that the activity is equal to the concentrations of the considered species in the gas phase and more specifically the concentration in the gas phase at the three boundary points (electrode/YSZ/O2 interface) of each electrode. Since platinum is a highly active catalyst for oxygen reduction (reaction 2), it is assumed that the oxygen concentration CO2(RE) is equal to the oxygen concentration fixed in the gas phase. On the contrary, for the sensing Au-V2O5 electrode, due to the lower catalytic activity compared to platinum, the oxygen concentration at SE/YSZ/O2 interface will be lower, resulting in varying sensor signals versus oxygen concentration in the base gas ∆𝑉 𝑅𝐸 0 (𝐶 𝑁𝐻3 = 0).

1/2O 2 + 2e -→ O 2- (2)
∆𝑉 𝑅𝐸 0 (𝐶 𝑁𝐻3 = 0) = 𝐸 𝑂 2 (𝑅𝐸) -𝐸 𝑂 2 (𝑆𝐸) = - 𝑅𝑇 4𝐹 𝑙𝑛 𝐶 𝑂2 (𝑆𝐸) 𝐶 𝑂2 (𝑅𝐸) (3)
Through Eq. 3 and experimental measurements of ∆𝑉 𝑅𝐸 0 (𝐶 𝑁𝐻3 = 0), 𝐶 𝑂2 (𝑆𝐸) can be calculated and values are summarized in Table 2.

NH3 responses modeling

At the electrodes of a typical mixed-potential ammonia sensor [START_REF] Schönauer-Kamin | Half-Cell Potential Analysis of an Ammonia Sensor with the Electrochemical Cell Au | YSZ | Au, V2O5-WO3-TiO2[END_REF][START_REF] Moos | Ceramic multilayer gas sensors-An overview[END_REF], the reduction reaction of oxygen (reaction 2) competes with the oxidation reaction of ammonia (reaction 4).

2/3NH 3 + O 2-→ 1/3N 2 + 2e -+ H 2 O (4)
A mixed potential is established in steady-state condition when the rates of oxidation and reduction reactions are equal.

According to the mixed-potential theory, the reaction rate-limiting kinetics follow the Butler-Volmer equation, and at high over-potentials, the electric current densities (for electrochemical reactions 2 and 4) can be described by Tafel behavior with Eqs. 5 and 6 [START_REF] Wang | Fabrication of well-ordered porous array mounted with gold nanoparticles and enhanced sensing properties for mixed potential-type zirconia-based NH3 sensor[END_REF][START_REF] Liu | Mixedpotential type NH3 sensor based on stabilized zirconia and Ni3V2O8 sensing electrode[END_REF][START_REF] Garzon | Solid-state mixed potential gas sensors: theory, experiments and challenges[END_REF][START_REF] Ritter | On the influence of the NOx equilibrium reaction on mixed potential sensor signals: A comparison between FE modelling and experimental data[END_REF].

𝑖 𝑁𝐻 3 = 𝑖 𝑁𝐻 3 0 𝑒𝑥𝑝 [ 2𝛼 1 𝐹(𝐸 -𝐸 𝑁𝐻 3 0 ′ ) 𝑅𝑇 ] (5)
𝑖 𝑂 2 = 𝑖 𝑂 2 0 𝑒𝑥𝑝 [ -2𝛼 2 𝐹(𝐸 -𝐸 𝑂 2 0 ′ ) 𝑅𝑇 ] (6)
where E is the potential produced by either NH3 oxidation or O2 reduction reactions, 𝑖 𝑁𝐻 3 0 and 𝑖 𝑂 2 0 are the exchange current densities of NH3 and O2, 𝐸 𝑁𝐻 3 0 ′ and 𝐸 𝑂 2 0 ′ are the standard potentials for NH3 and O2 reactions, 𝛼 1 and 𝛼 2 are the transfer coefficients of NH3 and O2, T is the temperature, F is the Faraday constant, and R is the gas ideal constant.

Supposing that the exchange current densities follow Freundlich isotherm, 𝑖 𝑁𝐻 3 0 and 𝑖 𝑂 2 0 can be expressed by Eqs. 7 and 8 [START_REF] Wang | Fabrication of well-ordered porous array mounted with gold nanoparticles and enhanced sensing properties for mixed potential-type zirconia-based NH3 sensor[END_REF][START_REF] Liu | Mixedpotential type NH3 sensor based on stabilized zirconia and Ni3V2O8 sensing electrode[END_REF][START_REF] Garzon | Solid-state mixed potential gas sensors: theory, experiments and challenges[END_REF].

𝑖 𝑁𝐻 3 0 = 𝐵 1 𝐶 𝑁𝐻3 𝑛 (7)
𝑖 𝑂 2 0 = -𝐵 2 𝐶 𝑂2 𝑚 (8)
Where B1, B2, m, and n are Freundlich constants, 𝐶 𝑁𝐻3 and 𝐶 𝑂2 are concentrations of ammonia and oxygen respectively. When reactions 2 and 4 reach a dynamic balance (𝑖 𝑁𝐻 3 + 𝑖 𝑂 2 = 0), the mixed potential is established (Eq. 9).

𝐸 𝑚𝑖𝑥 = 𝐸 0 + 𝑚𝐴 " 𝑙𝑛𝐶 𝑂2 -𝑛𝐴 " 𝑙𝑛𝐶 𝑁𝐻3

Where

𝐸 0 = 𝑅𝑇 2(𝛼 1 + 𝛼 2 )𝐹 𝑙𝑛 𝐵 2 𝐵 1 + 𝛼 1 𝐸 𝑁𝐻 3 0 ′ + 𝛼 2 𝐸 𝑂 2 0 ′ 𝛼 1 + 𝛼 2 (10)
𝐴 " = 𝑅𝑇 2(𝛼 1 + 𝛼 2 )𝐹 [START_REF] Liu | Highly selective and stable mixed-potential type gas sensor based on stabilized zirconia and Cd2V2O7 sensing electrode for NH3 detection[END_REF] As said before, assuming that the platinum electrode behaves like a "real" reference electrode, its mixed potential is close to 0 (𝐸 𝑚𝑖𝑥 (RE)~0) [START_REF] Miura | Highly selective CO sensor using stabilized zirconia and a couple of oxide electrodes[END_REF]. Consequently, according to Eq. 12, the signal of the sensor is equal to the negative of the mixed potential of the sensing electrode.

∆𝑉 𝑅𝐸 0 (𝐶 𝑁𝐻3 ≠ 0) = 𝐸 𝑚𝑖𝑥 (𝑅𝐸) -𝐸 𝑚𝑖𝑥 (𝑆𝐸)~ -𝐸 𝑚𝑖𝑥 (𝑆𝐸) (12)
To calculate the mixed potential of the sensing electrode using Eqs. 9 to 11, estimated values of 𝑬 𝑵𝑯 𝟑 𝟎 ′ , 𝑬 𝑶 𝟐 𝟎 ′ , B1, B2, m, and n parameters are derived from the literature [START_REF] Halim | Semi-Aerobic Landfill Leachate Treatment Using Carbon-Minerals Composite Adsorbent[END_REF][START_REF] Zhang | An ammonia electrolytic cell with NiCu/C as anode catalyst for hydrogen production[END_REF][33]. These values are listed in Table 3.

Integration of baseline and NH3 responses modeling

Finally, the results of data modeling for the baseline (𝐶 𝑁𝐻3 =0), according to Nernst equation (equation 3) and for different concentrations of ammonia (𝐶 𝑁𝐻3 ≠0), according to mixed potential theory (equations 5 to 12), are plotted in Fig. 10 along with the experimental data.

There is a good agreement between the model estimated from the previous calculations (orange curve) and experimental results (blue curve). Consequently, this validates the proposed model to describe ammonia response of the used single chamber sensor.

Conclusion

For developing a selective mixed-potential ammonia sensor, a vanadium oxide-based material (Au-V2O5) was tested as sensing electrodes of a two-electrode structure sensor. The results showed that the selectivity of the sensor is dependent on the operating temperature and on the V2O5 content of the sensing electrode. By increasing V2O5 content in sensing electrode from 15 wt.% to 50 wt.%, selective ammonia sensors were achieved at 550 °C with high ammonia sensitivity around (62 mV/decades for 12 mol.% O2 in the base gas). The sensors with Au-50wt.%V2O5 electrodes showed no cross-sensitivity to CO, NO2, NO, H2 and Hydrocarbons at 550 °C and also in gas mixtures of CO, NH3, NO2, and NO gases. The obtained responses from this sensor were modeled successfully according to Nernst and Butler-Volmer equations.

Fig. 1

 1 Fig. 1 Scheme of fabricated sensor by screen-printing technology.

Fig. 2

 2 Fig. 2 Schematic of experimental test bench.

3. Results and discussions 3 . 1

 31 Comparison between Au and Au-15%V2O5 sensing electrodes: influence of operating temperature Sensors with Au and Au-15%V2O5 sensing electrodes were exposed successively to 100 ppm CO, NO2, NO, and 20 ppm of NH3 at different working temperatures in the range 450-600°C.The base gas in this experiment was composed of 12 mol.% O2 balanced with N2 and 1.5 vol.% absolute humidity. First, to emphasize the interest of V2O5 based electrodes, responses of Pt/YSZ/Au-15%V2O5 sensors were compared to the ones of a Pt/YSZ/Au sensors already reported for NOx detection in our previous studies[START_REF] Gao | Improvement of the NOx selectivity for a planar YSZ sensor[END_REF][START_REF] Romanytsia | Application of advanced morphology Au-X (X=YSZ, ZrO2) composites as sensing electrode for solid state mixed-potential exhaust NOx sensor[END_REF]. With our definition of sensor signal (∆𝑉 𝑅𝐸 0 = VRE -VSE) and response, a typical behavior of such Pt/YSZ/Au sensors is a positive response to reducing gases (CO, NO and NH3), and a negative one to oxidants ones like NO2. Figure3showing the signal of an Au-15%V2O5 based sensor confirms that the substitution of Au by Au-15%V2O5 as sensing electrode does not modify qualitatively the behavior.

Fig. 3

 3 Fig. 3 Signals of sensors with Au (in blue) and Au-15%V2O5 (in red) sensing electrodes for 100 ppm CO, NO2, NO and 20 ppm of NH3 at 450, 500, 550, and 600 °C, in the base gas with 12 mol.% O2.

2

 2 Au-15%V2O5 electrodes in sensor responses to pulses of CO (100 ppm), NH3 (20 ppm), NO2 (100 ppm) and NO (100 ppm) in base gas at different temperaturesEffect of V2O5 content in Au-V2O5 sensing electrode In addition to 15 wt.% of V2O5, two other mass percentages of V2O5 were tested in the sensing electrode (30 wt.% and 50 wt.% of V2O5). The different sensors (Au-15%V2O5, Au-30%V2O5and Au-50%V2O5) were exposed to 100 ppm CO, NO2, NO, and 20 ppm of NH3 at four temperatures of 450, 500, 550 and 600 °C. The base gas was again composed of 12 mol.% O2 balanced with N2 and 1.5 vol.% absolute humidity. Gas responses of these sensors (absolute value for NO2) were compared with each other at the four temperatures in Fig.4. The results

Fig. 4

 4 Fig. 4 Gas sensor responses (absolute value for NO2) of Au-V2O5 based sensors with three mass percentages of 15%, 30% and 50% of V2O5 at (a) 450 °C, (b) 500°C, (c) 550 °C, and (d) 600°C.

Fig. 5 .

 5 Fig. 5. It can be seen that Au particles (white color) are well dispersed in the whole porous sensing electrode. Although the mass percentage of V2O5 and Au is 50-50 in this electrode, Au particles quantity seems to be lower than that of V2O5. In fact, 50 wt.% of V2O5 corresponds to 85 vol.% V2O5, due to the high density of gold compared to V2O5 (19.32 g.cm -³ for Au compared to 3.36 g.cm -³ for V2O5).

Fig. 5

 5 Fig. 5 Cross-section SEM micrograph of Au-50%V2O5 electrode on YSZ electrolyte.

Fig 6 .

 6 Fig 6. shows the response of a Au-50%V2O5 sensor to 100 ppm of CO, 20 ppm of NH3, 100ppm of NO, 100ppm of NO2, 100 ppm of CxHy (2 times) and 20 ppm of H2 (4 times). The results in Fig. 6 clearly show that sensors display no responses to CO, NO and NO2 as previously seen and neither to hydrocarbons nor to hydrogen at 550 °C.

Fig. 6

 6 Fig. 6 Au-50%V2O5 sensor signal for 100 ppm CO, 20 ppm of NH3, 100 ppm of NO, 100 ppm of NO2, 100 ppm of CxHy (2 times), and 20 ppm of H2 (4 times) at 550 °C.

Fig. 7

 7 Fig.7Au-50% V2O5 sensor signal in a single gas or gas mixtures of CO, NH3, NO2, and NO at 550 °C with gas analysis at the cell exit.

  content can vary suddenly in a great range. Hence, sensing performances were studied at 550 °C by stepwise change in the NH3 concentration from 2 to 40 ppm (2, 4, 8, 16, 32, and 40 ppm) at four different concentrations of oxygen (2%, 5%, 12%, and 16.4 mol.%). The results are shown in Fig. 8. It can be seen that the sensor baseline (when there is no NH3), decreases with increasing O2 concentration. The results also indicate that the sensor has a high sensitivity to ammonia, even at low concentrations (2 ppm), but it is influenced by the oxygen concentration. This phenomenon indicates competitive adsorption between NH3 and O2 on the sensing electrode, which is modeled in the next part.

Fig. 8

 8 Fig. 8 Au-50%V2O5 sensors signal for different concentrations of NH3 (2, 4, 8, 16, 32, and 40 ppm) at four oxygen concentrations (2, 5, 12, and 16.4 mol.%) at 550 °C.

Fig. 9

 9 Fig. 9 Variations of Au-50%V2O5 sensor signals as a function of log(CNH3) at 550 °C, for the four studied oxygen concentrations.

Fig. 10

 10 Fig. 10 Comparing modeling and experimental results for Au-50%V2O5 sensor to different concentration of NH3 (2, 4, 8, 16, 32, and 40 ppm) and four concentrations of oxygen (2%, 5%, 12%, and 16.4%) at 550 °C.

Table 2

 2 Calculated oxygen concentrations on the sensing electrode at 550°C.

	O2 concentration in gas stream 𝐶 𝑂2 (RE) (mol.%)	∆V RE 0 (𝐶 𝑁𝐻3 = 0) (V) Calculated O2 concentration on sensing electrode 𝐶 𝑂2 (SE) (mol.%)
	2	0.012	1
	5	0.009	3
	12	0.008	7.7
	16.4	0.007	11

Table 3

 3 Parameter used for the sensor response modeling, issued from the literature[START_REF] Halim | Semi-Aerobic Landfill Leachate Treatment Using Carbon-Minerals Composite Adsorbent[END_REF][START_REF] Zhang | An ammonia electrolytic cell with NiCu/C as anode catalyst for hydrogen production[END_REF][33]. 𝐶 𝑂2 and 𝐶 𝑁𝐻3 ), and optimizing 𝛼 1 and 𝛼 2 by means of a solver (Excel Solver, minimizing the sum of error squares), all values are determined and listed in Table4. The obtained total mean square error is equal to 1.3×10 - 4 . From these calculated parameters, it is now possible to estimate the sensor signal for different NH3 injections (∆𝑉 𝑅𝐸 0 (𝐶 𝑁𝐻3 ≠ 0) ).

	Parameter	Value (unit)
	𝐸 𝑂 2 0 ′	1.22 (V)
	𝐸 𝑁𝐻 3 0 ′	-0.77 (V)
	m	0.5
	n	0.885
	B2	0.0642
	B1	0.4227
	Then, using the experimental results (∆𝑉 𝑅𝐸 0 as a function of

Table 4

 4 Parameter values issued from experimental results fitting.

	Parameter	Obtained value (unit)
	α1	0.92
	α2	0.32
	𝐸 0	-0.312 (V)
	𝐴 "	0.029


Eglantine Mathieu-Bégné
email: eglantine.mb@gmail.com

Géraldine Loot
email: geraldine.loot@univ-tlse3.fr

Simon Blanchet
email: simon.blanchet@sete.cnrs.fr

Eve Toulza
email: eve.toulza@univ-perp.fr

Clémence Genthon

Olivier Rey

Mathieu-Begne Eglantine

Blanchet Simon

Toulza Eve

Genthon Clemence
email: clemence.genthon@inra.fr

Rey Olivier

De novo transcriptome assembly for Tracheliastes polycolpus, an invasive

Keywords: Copepods, Monoxenous parasite, Parasite specificity, Curation

à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Introduction

Tracheliastes polycolpus (Copepoda, Neocopepoda, Podoplea, Siphonostomatoida, Lerneaopodidae) is a monoxene ectoparasitic copepod of freshwater fish [START_REF] Fryer | The parasitic copepoda and branchiura of British freshwater fishes. A handbook and key[END_REF]. Only adult females have a parasitic lifestyle, whereas males are microscopic and free-living organisms [START_REF] Kabata | Redescriptions of and comments on four little-known Lernaeopodidae (Crustacea: Copepoda)[END_REF]. Adult females anchor on fish fins and feed on their epidermal cells. This causes partial to total fin degradation, which generally favours secondary infections by bacteria or/and viruses [START_REF] Fryer | The parasitic copepoda and branchiura of British freshwater fishes. A handbook and key[END_REF], and ultimately reduces the fitness of their hosts [START_REF] Loot | The effects of the ectoparasite Tracheliastes polycolpus (Copepoda: Lernaeopodidae) on the fins of rostrum dace (Leuciscus leuciscus burdigalensis)[END_REF][START_REF] Blanchet | Why do parasitized hosts look different? Resolving the "chicken-egg" dilemma[END_REF].

In the 1920s, T. polycolpus was introduced from eastern Eurasia to western Europe through fish trades, and has since spread over several watersheds in England, France and Spain [START_REF] Rey | Elucidating the spatiotemporal dynamics of an emerging wildlife pathogen using approximate Bayesian computation[END_REF]. In France, T. polycolpus is primarily associated with the common dace and the rostrum dace (Leuciscus leuciscus and L. burdigalensis), but is also commonly observed on several alternative cyprinid species [START_REF] Lootvoet | Patterns and processes of alternative host use in a generalist parasite: insights from a natural host-parasite interaction[END_REF]. The recent invasion history of T. polycolpus, together with its switch to new alternative host species, constitutes an unprecedented opportunity to study the mechanisms underlying parasite specificity and the rapid adaptive processes associated with host shifts [START_REF] Lootvoet | Patterns and processes of alternative host use in a generalist parasite: insights from a natural host-parasite interaction[END_REF][START_REF] Dybdahl | Identifying the Molecular Basis of Host-Parasite Coevolution: Merging Models and Mechanisms[END_REF][START_REF] Fine | Does pathogen plasticity facilitate host shifts? Round JL[END_REF]. Developing"-omics" resources is a key step towards a better understanding of the molecular bases of such processes, notably the role of plasticity and/or selection associated with host shift based on gene expression profiles [START_REF] Fine | Does pathogen plasticity facilitate host shifts? Round JL[END_REF][START_REF] Hébert | Major host transitions are modulated through transcriptome-wide reprogramming events in Schistocephalus solidus , a threespine stickleback parasite[END_REF].

Here, we built a curated de novo transcriptome assembly for this species. More specifically, we present the first non-redundant and protein-coding transcriptome assembly together with functional annotations for T. polycolpus obtained from fifteen adult female parasites sampled on three different host species. Only a few assemblies exist for copepods and notably for parasitic copepods, although some have led to novel discoveries (including mechanisms for toxin resistance, gene expression patterns associated with molting or development) [START_REF] Lenz | De Novo Assembly of a Transcriptome for Calanus finmarchicus (Crustacea, Copepoda) -The Dominant Zooplankter of the North Atlantic Ocean. Ianora A[END_REF][START_REF] Nuñez-Acuña | High-throughput SNP discovery and transcriptome expression profiles from the salmon louse Caligus rogercresseyi (Copepoda: Caligidae)[END_REF][START_REF] Carmona-Antoñanzas | A Survey of the ATP-Binding Cassette (ABC) Gene Superfamily in the Salmon Louse (Lepeophtheirus salmonis). Corsi I[END_REF]. Consequently, this database constitutes an important genomic resource for an emerging parasite in wild populations and for the diverse group of Crustacean copepods.

Data description

Sampling

Fifteen adult females of T. polycolpus were sampled on three different fish host species at a single location in the Salat River in southwestern France on a single day to limit confounding environmental effects (Table 1). The three host species were the rostrum dace (L. burdigalensis) and two alternative hosts; the Occitan gudgeon (Gobio occitaniae) and the European minnow (Phoxinus phoxinus). Fish were caught by electric fishing using a DEKA® 7000, anaesthetized according to a standardized protocol, and inspected for the presence of parasites. Parasites were collected using sterile forceps as follows: five parasites were sampled on five dace, five parasites were sampled on four gudgeons, and five parasites were sampled on four minnows. The fifteen parasites were immediately stored in RNAlater for 24 hours and then conditioned at -80°C (to stabilize and protect cellular RNAs) until RNA extraction.

Sequencing

Total RNA from each parasite was extracted using the RNeasy Plus Mini Kit (Qiagen) following the manufacturer's instructions from the parasite trunk only-to minimize possible contamination with host RNA-with a final elution volume of 40 µL RNAse-free water. The quantity and quality of RNA extractions were assessed using a nanodrop ND-8000 (Thermo Scientific) and a BioAnalyser (Agilent Technologies), respectively. The individual RNA-seq libraries were prepared on a Tecan EVO2000 using the IlluminaTruSeq Stranded mRNA protocol.

The individual libraries obtained were multiplexed then pooled and sequenced on two lanes of an Illumina HiSeq 2000 (High Throughput mode) using a paired-end read length of 2x100 bp. The reads were demultiplexed, those that did not pass the chastity filter (i.e., internal filtering procedure from Illumina sequencers) were filtered out (about 7% of the total reads), and the adapters were trimmed automatically at this stage. The sequencing resulted in approximately 420 million 2 x 100 bp paired-end reads, with an average of 28 million paired-end reads per sample. The library preparation, sequencing and pre-processing automatic filtering steps were performed at the GeT-PlaGe core facility (Toulouse, France).

De novo transcriptome assembly and curation

Based on the reads obtained from all individuals, we first assembled a raw de novo transcriptome using the Trinity pipeline (version 2014-07-17) [START_REF] Haas | De novo transcript sequence reconstruction from RNA-seq using the Trinity platform for reference generation and analysis[END_REF]. Reads were trimmed using Trimmomatic [START_REF] Bolger | Trimmomatic: a flexible trimmer for Illumina sequence data[END_REF] with default parameters to discard low-quality and/or poorly informative reads.

Then, each sample was parsed separately as Trinity input, and the option "--SS_lib_type" was selected to keep strand specificity information. Other parameters were set to the default values. At this step the assembly contained a total of 101 636 contigs.

To curate the raw transcriptome assembly from non-protein-coding contigs, we discarded contigs lacking an open reading frame (ORF) or having an ORF shorter than 100 amino acids using the Trinity plugin TransDecoder [START_REF] Haas | De novo transcript sequence reconstruction from RNA-seq using the Trinity platform for reference generation and analysis[END_REF]. This filtering step resulted in 33 984 contigs enriched with only messenger RNAs (putative protein-coding genes). Finally, to reduce redundancy, we ran CD-HIT-EST (Version 4.6, [START_REF] Huang | CD-HIT Suite: a web server for clustering and comparing biological sequences[END_REF]) to cluster the resulting transcripts according to their similarity with a minimum sequence identity set to 95%, (options -c 0.95 -n 8, where c and n are "similarity threshold" and "word size" parameters respectively). These filtering steps resulted in a final protein-coding and non-redundant assembly containing17 157 transcripts corresponding to as many putative unique protein-coding genes.

Annotation

Transcriptome functional annotation was performed using the software suite Trinotate (version 3.1.0, [START_REF] Haas | De novo transcript sequence reconstruction from RNA-seq using the Trinity platform for reference generation and analysis[END_REF]). Translated sequences from the final assembly were used to perform a blastp search on the Swiss-Prot database and a protein domain search on the Pfam database (both uploaded from Trinotate version 3.1.10 on 07/03/2016). Results were then integrated in Trinotate to retrieve functional annotations leveraging eggNOG, GO and Kegg databases [START_REF] Huerta-Cepas | eggNOG 4.5: a hierarchical orthology framework with improved functional annotations for eukaryotic, prokaryotic and viral sequences[END_REF][START_REF]The Gene Ontology (GO) database and informatics resource[END_REF][START_REF] Kanehisa | KEGG: Kyoto Encyclopedia of Genes and Genomes[END_REF]. Only highly significant matches were reported in the annotation file (i.e., those with an e-value < 10 -5 for the blast hits and the domain noise cut-off for the Pfam domains). Overall, 13093 contigs were annotated from at least one database. Details about the number of contigs annotated on each database are given in Table 1. Transcript nucleotide and amino acid sequences are also provided in the annotation file (Supplementary S1).

Data validation and quality control

Quality of our final transcriptome assembly was evaluated based on three main criterions (Table 2 and Fig. 1, [START_REF] Haas | De novo transcript sequence reconstruction from RNA-seq using the Trinity platform for reference generation and analysis[END_REF][START_REF] Hara | Optimizing and benchmarking de novo transcriptome sequencing: from library preparation to assembly evaluation[END_REF]). 1. The representativeness criterion refers to raw read content represented by the assembly. 2. The completeness criterion is based on evolutionary expectations of nearuniversal gene content that the assembly includes. 3. Specificity refers to the number of genes that are specific to T. polycolpus when compared to closely related species.

Representativeness

Representativeness was evaluated by measuring the percentage of quality filtered reads that were properly re-aligned against the assembly. To do so, the software Bowtie 2 (version 2.1.0, [START_REF] Langmead | Fast gapped-read alignment with Bowtie 2[END_REF]) was used with default "end-to-end" alignment parameters. We estimated representativeness as the percentage of paired reads that aligned back to the assembly exactly once and with respect to the forward and reverse directions [START_REF] Langmead | Fast gapped-read alignment with Bowtie 2[END_REF]. We also reported the percentage of reads that mapped back more than once (as an indication of redundancy or repeated sequences) and the percentage of reads that did not map back to the final assembly (i.e., the proportion of non-represented reads within the assembly).

Completeness

Completeness was assessed by counting the percentage of orthologues conserved across arthropods that are present in the assembly using the software BUSCO [21]. However, if more than one transcript was found to be aligned with the same orthologous gene, then the assembly was therefore considered partially redundant. Thus, to account for both the number of orthologues and redundancy, we quantified the number of orthologues conserved across arthropods that were of a single copy within the assembly (i.e., BUSCOs: "Benchmarking Universal Single-Copy Orthologs", [21]).

Specificity

Specificity was assessed by quantifying the number of non-homologous transcripts obtained for T. polycolpus when compared to Lepeophtheirus salmonis and Caligus rogercresseyi, two parasitic copepod species sharing the same order with T. polycolpus and for which transcriptomic resources exist (available on Genbank under Bioproject numbers PRJEB1804 and PRJNA234316 respectively). These transcriptomes were obtained with comparable technologies to those we used in this study and from different development stages including adult females [START_REF] Nuñez-Acuña | High-throughput SNP discovery and transcriptome expression profiles from the salmon louse Caligus rogercresseyi (Copepoda: Caligidae)[END_REF][START_REF] Carmona-Antoñanzas | A Survey of the ATP-Binding Cassette (ABC) Gene Superfamily in the Salmon Louse (Lepeophtheirus salmonis). Corsi I[END_REF], which make the comparison relevant. We expect to find common orthologs between the three species, but also a large amount of development stage specific genes in the two sea lice species. We searched for reciprocal blast hit (RBH) between the assembly of T. polycolpus (after in silico RNA translation)

and that of each of the two copepods species using "tblastx". The e-value threshold was set to 0.001 in order to select the most significant matches [START_REF] Camacho | Manuel de l'utilisateur des applications BLAST en ligne de commande[END_REF], and transcripts not having a reciprocal match according to this criteria were considered specific to T. polycolpus.

Quality control results & discussion

Regarding representativeness, we obtained a mapping rate of 65.8%, which is lower than expected for a Trinity assemblage (i.e., approximately 90% [START_REF] Clarke | Comparative analysis of de novo transcriptome assembly[END_REF]). Importantly, a large proportion of raw reads (27.3%) could not be mapped back to the non-redundant and protein-coding assembly (Table 2) likely because some unique contigs were also lost during the filtering steps. Given that the raw assembly size was reduced by almost a factor of six in the non-redundant and proteincoding assembly, this assembly still displays a good compromise between its informative content (representativeness) and its complexity reduction. Indeed, when limiting redundancy and removing chimaera contigs, usually up to 47% of reference genes are retrieved in de novo assemblies conducted with several assemblers [START_REF] Yang | Optimizing de novo assembly of short-read RNA-seq data for phylogenomics[END_REF]. Furthermore, high completeness was achieved with overall 90.5% of BUSCOs retrieved in the assembly and only 2.6% of conserved orthologues across arthropods having being missed (Table 2). Interestingly, the BUSCO analysis also confirmed that we significantly limited redundancy during the curation process, as 37.7% of BUSCOs were duplicated in the raw assembly and only 5.7% of duplicated BUSCOs were found in the final assembly (Table 2). Finally, we found 6 910 potentially specific transcripts in our T.

polycolpus assembly compared with the two most closely related species currently available (Fig. 1). This high number of specific transcripts might be partly explained by the fact that the three species are from the same order but different families, except for L. salmonis and C. rogercresseyi that share the same family, which may explain their higher number of shared genes (see also Supplementary Fig. S2 for similarity histograms of the shared genes between the three species).

Overall, this highlights that this assembly constitutes an original specific resource of interest. Our quality assessment thus clearly revealed that the resulting non-redundant and protein-coding assembly fulfilled the three criteria we evaluated (i.e., representativeness, completeness and specificity). As such, we propose this non-redundant and protein-coding transcriptome assembly as a reference transcriptome assembly for T. polycolpus.

Conclusion

The transcriptome assembly reconstructed in this study is the most complete genomic/transcriptomic resource available for T.polycolpus, and more generally for freshwater copepods [START_REF] Bron | Copepod Genome Initiative[END_REF]. As such, this paves the way for future studies on this species, notably about the molecular bases of host shift by this parasite. Beyond the studies on this targeted species, this

transcriptome will also open new avenues for studying freshwater copepods that constitute cornerstone elements for the biological functioning of freshwater ecosystems.

Table 1 MIxS specifications, Assembly description and Annotation statistics for T. polycolpus de novo transcriptome assembly.

Table 2 Quality scores for the raw assembly and the final assembly of Tracheliastes polycopus.

a

  Tracheliastes polycolpus assembly generated from Trinity only b Tracheliastes polycolpus reference assembly, resulting from curation steps

Acknowledgements

We warmly thank all the students involved in field sampling.

Funding

This work was funded by the Agence Nationale de la Recherche (project INCLIMPAR, grant no. ANR-11-JSV7-0010), BiodivERsA (project PROBIS) and the Institut Universitaire de France.

EMB was supported by a PhD grant from the French Ministry for Education and Sciences. This work was performed in collaboration with the GeT core facility, Toulouse, France (http://get.genotoul.fr), and was supported by France Génomique National infrastructure, funded as part of "Investissement d'avenir" program managed by Agence Nationale pour la Recherche (contract ANR-10-INBS-09). This work was undertaken in laboratories being part of the "Laboratoire d'Excellence" (LABEX) entitled TULIP (ANR-10-LABX-41).

Availability of supporting data

Raw reads are deposited in Sequence Read Archive (GenBank) under project number PRJNA476682. Accession numbers are SRR7411022, SRR7411021, SRR7411024, SRR7411023, SRR7411026, SRR7411025, SRR7411028, SRR7411027, SRR7411030, SRR7411029, SRR7411019, SRR7411018, SRR7411017, SRR7411016, and SRR7411020. This Transcriptome Shotgun Assembly project has been deposited at DDBJ/EMBL/GenBank under the accession GGQW00000000. The version described in this paper is the first version, GGQW01000000.

Figure 1

Venn plot showing the number of specific and shared genes between T. polycolpus, C. rogercresseyi and L. salmonis, resulting from the RBH analysis.

Ethics statement

Fish carrying the parasites used in this study were caught under prefectoral order and in accordance to current ethical laws in France.

Competing interests

None.

Authors' contributions

GL, SB and OR designed the experiment and sampled the specimens. OR and CG performed molecular analyses and sequencing. EMB, OR and ET assembled and evaluated the transcriptome assembly. EMB, GL, ET, OR and SB wrote the paper. All authors read and approved the final version of the manuscript.