Jean-luc Mouget | Universite du Maine (original) (raw)

Papers by Jean-luc Mouget

The application of ‘booster biocides’ Diuron, Tolylfluanid and Copper thiocyanate inbantifouling ... more The application of ‘booster biocides’ Diuron, Tolylfluanid and Copper thiocyanate inbantifouling paints, used to prevent development of biofouling, needs to be monitored before assessing their impacts on the environment. An alternative approach aims to propose eco-friendly and effective antifoulants isolated from marine organisms such as seaweeds. In this study, the effects of ‘booster biocides’ and the ethanol and dichloromethane extracts from a brown (Sargassum muticum) and a red alga (Ceramium botryocarpum) have been compared by algal growth inhibition tests of marine diatoms. The most efficient extracts were ethanol fraction of S. muticum and C. botryocarpum extracts with growth EC50 = 4.74 and 5.3 μg mL−1 respectively, with reversible diatom growth effect. The booster biocides are more efficient EC50 = 0.52 μg mL−1, but are highly toxic. Results validate the use of macroalgal extracts as non toxic antifouling compounds, and they represent valuable environmentally friendly alternatives in comparison with currently used biocides.

The photoinitiated polymerization of epoxidized hydroxytelechelic cis-1,4-polyisoprene and of a d... more The photoinitiated polymerization of epoxidized hydroxytelechelic cis-1,4-polyisoprene and of a dual system (epoxidized/ acrylated) telechelic cis-1,4-polyisoprene in the presence of 2,2-dimethyl-1,2-hydroxyacetophenone or/and hexafluoro-phosphate triarylsulfonium salt has been studied by real-time infrared spectroscopy. The synthesis of photosensitives oligoisoprenes was achieved by chemical modifications of hydroxytelechelic cis-1,4-polyisoprene obtained by controlled degradation of high molecular weight cis-1,4polyisoprene. Then, the effect of light intensity, photoinitiator concentration, addition of reactive diluent and concentration of functional groups on the photopolymerization process was evaluated. Concerning the cationic process, the results showed that the kinetic profile improves when photoinitiator concentration and light intensity increase. The optimum concentration of triarylsulfonium salt used as photoinitiator was determined as 5% (w/w) and the optimum light intensity was 50 mW cm À2 . Reactive diluent (3-ethyl-3hydroxymethyl oxetane) addition greatly improves the ultimate conversion and the polymerization rate. Subsequently, the photopolymerization kinetic of a dual epoxidized/acrylated system was studied. The results obtained using different photoinitiator mixtures and different intensity of irradiation showed that the crosslinking of acrylate functions at the chain-end prevents the progression of the cationic process at the oxirane groups along the chain. Thus, the mobility of the cationic reactive centers was restricted by the crosslinking at the high conversion of the acrylate double bonds.

Journal of Applied Polymer Science, 2013

New photosensitive oligoisoprenes were synthesized by controlled degradation of high molecular we... more New photosensitive oligoisoprenes were synthesized by controlled degradation of high molecular weight cis-1,4-polyisoprene and successive chemical modification of the chain-ends. Oligomers with diacrylate extremities were synthesized, characterized, and used in photocrosslinking reactions in different conditions. The photoinitiated polymerization of the diacrylate oligoisoprenes was carried out using 2,2-dimethyl-2-hydroxyacetophenone (Darocur 1173) as initiator and the reaction was monitored by photocalorimetry-DSC and real time FTIR spectroscopy. The influence of oxygen, photoinitiator concentration, light intensity, diluting agent, and oligomers molecular weight on the reaction rate was investigated. It was found that the presence of oxygen does not influence the photopolymerization kinetics of the diacrylate oligoisoprenes. Maximum conversion was obtained for a photoinitiator concentration of 5% (w/w) and for a light intensity of 13.5 mW/cm 2 . Decreasing the formulation viscosity by addition of a diluent (1,6-hexanediol diacrylate) raised the photopolymerization rate, by increasing the reactive species mobility.

Journal of Applied Phycology, 2002

This study reports further information on “mareninne,” awater-soluble blue-green pigment synthesi... more This study reports further information on “mareninne,” awater-soluble blue-green pigment synthesized by the diatom Hasleaostrearia, which is essential to the greening of maturing oysters inFrench production areas. The extraction process is reported, as well aspreliminary characterization of a partially purified marennine extract,including quantitative spectrophotometric analysis of intracellular pigment. Amean specific extinction coefficient, E 1%1cm = 17.2 at 669 nm, is

Advances in Botanical Research, 2014

Marine Drugs, 2014

In diatoms, the main photosynthetic pigments are chlorophylls a and c, fucoxanthin, diadinoxanthi... more In diatoms, the main photosynthetic pigments are chlorophylls a and c, fucoxanthin, diadinoxanthin and diatoxanthin. The marine pennate diatom Haslea ostrearia has long been known for producing, in addition to these generic pigments, a water-soluble blue pigment, marennine. This pigment, responsible for the greening of oysters in western France, presents different biological activities: allelopathic, antioxidant, antibacterial, antiviral, and growth-inhibiting. A method to extract and purify marennine has been developed, but its chemical structure could hitherto not be resolved. For decades, H. ostrearia was the only organism known to produce marennine, and can be found worldwide. Our knowledge about H. ostrearia-like diatom biodiversity has recently been extended with the discovery of several new species of blue diatoms, the recently described H. karadagensis, H. silbo sp. inedit. and H. provincialis sp. inedit. These blue diatoms produce different marennine-like pigments, which belong to the same chemical family and present similar biological activities. Aside from being a potential source of natural blue pigments, H. ostrearia-like diatoms thus present a commercial potential for aquaculture, cosmetics, food and health industries.

Protist, 2013

We present the first study examining mtDNA transmission in diatoms, using sexual progeny of the p... more We present the first study examining mtDNA transmission in diatoms, using sexual progeny of the pennate species Haslea ostrearia (Naviculaceae). A fragment of the cytochrome oxidase subunit I gene (cox1) with 7 nucleic substitutions between parental clones was used as a parental tracer in 16 F1 clones obtained from two pairs of mating crosses. Each cross involved a parental clone isolated from France (Bay of Bourgneuf) and Sweden (Kattegat Bay). We determined that all progeny possessed only one cox1 parental haplotype. These results suggest that the mitochondrial DNA transmission in H. ostrearia is uniparental. Implications and new topics of investigation are discussed.

Journal of Phycology, 2008

Analysis of reflectance spectra was used to monitor the conversion of diadinoxanthin (DD) into di... more Analysis of reflectance spectra was used to monitor the conversion of diadinoxanthin (DD) into diatoxanthin (DT) in two benthic diatom species, Amphora coffeaeformis (C. Agardh) Kütz. and Cylindrotheca closterium (Ehrenb.) J. C. Lewin et Reiman, cultured at high light (HL, 400 lmol AE m )2 AE s )1 PAR) and low light (LL, 25 lmol AE m )2 AE s )1 PAR). Cultures were exposed to saturating light for 32 min. HL cultures of both species showed higher (DT + DD) content, whereas LL cultures exhibited higher chl a and fucoxanthin content. DD to DT conversion, measured by HPLC, occurred mainly in the first 2 min (LL) or 5 min (HL) after exposure to saturating light. Nonphotochemical quenching (NPQ), measured by PAM fluorescence, showed the same pattern as DT ⁄ (DD + DT), resulting in a linear relationship between these parameters. Addition of dithiothreitol (DTT) blocked the conversion of DD into DT and significantly reduced NPQ induction. Reflectance spectra showed no obvious change after light exposure. However, second derivative spectra (dd) showed a shift in reflectance from 487 to 508 nm, which was not present for DTT-treated samples. Changes in dd 487 were strongly correlated with changes in DD (r = 0.76), while changes in dd 508 were strongly correlated with changes in DT (r = 0.94). The best index to estimate DD to DT conversion was dd 508 /dd 630 (r = 0.87). This index was very sensitive to minute changes that occurred immediately after exposure to light and was species insensitive. Good relationships were observed between indices for xanthophyll cycle activation (DD to DT conversion and NPQ induction) and the second derivative spectra. With further in situ validation, this index may prove to be highly useful for investigation into aquatic global photoregulation mechanisms in diatom-dominated samples.

Journal of Photochemistry and Photobiology B: Biology, 2007

This study reports comparison of two techniques measuring photosynthesis in the ubiquitous diatom... more This study reports comparison of two techniques measuring photosynthesis in the ubiquitous diatom Skeletonema costatum, i.e., the classical oximetry and the recent modulated fluorimetry. Microalgae in semi-continuous cultures were exposed to five different environmental conditions simulating a seasonal effect with co-varying temperature, photoperiod and incident light. Photosynthesis was assessed by gross rate of oxygen evolution (P B ) and the electron transport rate (ETR) measurements. The two techniques were linearly related within seasonal treatments along the course of the P/E curves. The light saturation intensity parameters (E k and E ETR k ), and the maximum electron transport rate increased significantly with the progression of the season while the maximum light utilization efficiency for ETR (a ETR ) was constant. By contrast, the maximum gross oxygen photosynthetic capacity ðP B max Þ and the maximum light utilization efficiency for P B (a B ) increased from December to May treatment but decreased from May to July treatment. Both techniques showed clear photoacclimation in microalgae with the progression of the season, as illustrated by changes in photosynthetic parameters. The relationship between the two techniques changed when high temperature, photoperiod and incident light were combined, possibly due to an overestimation of the PAR-averaged chlorophyll-specific absorption cross-section. Despite this change, our results illustrate the strong suitability of in vivo chlorophyll fluorimetry to estimate primary production in the field.

Journal of Photochemistry and Photobiology B: Biology, 2007

In order to investigate the dynamics of the acclimation of marine diatoms to ultraviolet radiatio... more In order to investigate the dynamics of the acclimation of marine diatoms to ultraviolet radiation (UVR), Amphora coffeaeformis, Odontella aurita and Skeletonema costatum were exposed for 5 h per day to a combination of UVA and UVB (UVBR/UVAR ratio 4.5%) with a total UVR daily dose of 110 kJ m À2 , which is equivalent to that observed in the natural environment. This treatment was applied in the middle of the photoperiod and was repeated on five successive days.

Journal of Photochemistry and Photobiology B: Biology, 2013

The objective of the present study was to estimate in vivo pigment composition and to retrieve ab... more The objective of the present study was to estimate in vivo pigment composition and to retrieve absorption cross-section values, a ⁄ , of photosynthetic micro-organisms using a non-invasive technique of reflectance spectrometry. To test the methodology, organisms from different taxonomical groups and different pigment composition were used (Spirulina platensis a Cyanophyta, Porphyridium cruentum a Rhodophyta, Dunaliella tertiolecta a Chlorophyta and Entomoneis paludosa a Bacillariophyta) and photoacclimated to two different irradiance levels: 25 lmol photon m À2 s À1 (Low Light, LL) and 500 lmol photon m À2 s À1 (High Light, HL). Second derivative spectra from reflectance were used to identify pigment in vivo absorption bands that were linked to specific pigments detected by high performance liquid chromatography. Whereas some absorption bands such as those induced by Chlorophyll (Chl) a (416, 440, 625 and around 675 nm) were ubiquous, others were taxonomically specific (e.g. 636 nm for Chl c in E. paludosa) and/or photo-physiological dependent (e.g. 489 nm for zeaxanthin in the HL-acclimated S. platensis). The optical absorption cross-section, a ⁄ , was retrieved from reflectance data using a radiative transfer model previously developed for microphytobenthos. Despite the cellular Chl a decrease observed from LL to HL (up to 88% for S. platensis), the a ⁄ increased, except for P. cruentum. This was attributed to a 'package effect' and to a greater absorption by photoprotective carotenoids that did not contribute to the energy transfer to the core Chl a.

FEMS Microbiology Ecology, 2000

Sexual reproduction is an obligatory phase in the life cycle of most diatoms, as cell size decrea... more Sexual reproduction is an obligatory phase in the life cycle of most diatoms, as cell size decreases with successive vegetative divisions and the maximal cell size is only restored by a specialized cell, the auxospore, which follows zygote formation as a result of sexual reproduction. While in pennate diatoms the induction of sexual reproduction depends primarily on cell-cell interactions, the importance of different external factors for the induction of sexual reproduction is less well known. Here, we investigated the effects of light on sexualization in the marine benthic pennate diatom Haslea ostrearia (Gaillon) R. Simonsen. Compatible clones were crossed and exposed to different combinations of light levels, qualities, and photoperiods. Light was found to be a key factor for sexualization, and to a certain extent, to control auxosporulation in H. ostrearia. The light conditions most favorable for sexual reproduction were low irradiances (o50 mmol photons m À2 s À1 ) and short photoperiods (6-10 h), conditions that prevail during winter, and to a lesser extent, the higher irradiances and longer photoperiods that correspond to the spring and fall, when blooms of this organism form in the natural environment. Auxospore formation was very rare in continuous light, and maximum in presence of red radiation, while it was never observed in darkness or in radiation other than red.

European Journal of Phycology, 2012

2012): Haslea karadagensis (Bacillariophyta): a second blue diatom, recorded from the Black Sea a... more 2012): Haslea karadagensis (Bacillariophyta): a second blue diatom, recorded from the Black Sea and producing a novel blue pigment, European Journal of Phycology, 47:4, 469-479 To link to this article: http://dx.

European Journal of Phycology, 2009

Twelve clonal cultures of the marine pennate diatom Haslea ostrearia (Gaillon) Simonsen were used... more Twelve clonal cultures of the marine pennate diatom Haslea ostrearia (Gaillon) Simonsen were used to study sexual reproduction and auxosporulation. After crossing, compatible gametangia paired girdle to girdle, with no visible surrounding mucilage. Two gametes were formed per gametangium; these were not attached to the thecae of the parental frustule and gametes from one gametangium fused with the gametes from

Aquatic Toxicology, 2009

The tributyltin-based products and organic biocides which are incorporated into antifouling paint... more The tributyltin-based products and organic biocides which are incorporated into antifouling paints have had a negative impact on the marine environment, and the ban on tributyltin-based antifouling products has urged the industry to find substitutes to prevent the development of fouling on ship hulls. Natural antifouling agents could be isolated from marine resources, providing an alternative option for the industry. The effects of different marine seaweed extracts from Sargassum muticum and Ceramium botryocarpum on the growth, pigment content and photosynthetic apparatus of the marine diatom Fragilaria pinnata were compared with those of Diuron, a biocide widely used in antifouling paints. The addition of the macroalgal extracts in the culture medium resulted in an inhibition of the growth of F. pinnata, but this inhibition was lower than that obtained with Diuron. After transfer to a biocide-free medium, F. pinnata cells previously exposed to the macroalgal extracts exhibited normal growth, in contrast to Diuron-treated cells, which died, demonstrating that the effects of the natural antifouling agents were reversible. Macroalgal extracts and Diuron-induced modifications in F. pinnata cellular pigment content. Chlorophyll a, fucoxanthin, and the xanthophyll pool, diadinoxanthin and diatoxanthin, were the most affected. Changes in the structure and function of the photosynthetic apparatus were studied by microspectrofluorimetry, and provided a comprehensive evaluation of the inhibition of the diatom Photosystem II (PSII) by the biocides. This study confirms that natural extracts from the macroalgae studied have the potential to be used as a substitute to commercial biocides in antifouling paints.

Aquatic Microbial Ecology, 2012

ABSTRACT: The capacity of microphytobenthos to withstand the variable and extreme conditions of t... more ABSTRACT: The capacity of microphytobenthos to withstand the variable and extreme conditions of the intertidal environment, prone to cause photoinhibition, has been attributed to particularly efficient photoprotection. However, little is known regarding the capacity of this protection against photoinhibition or the mechanisms responsible for it. The present study quantified the photoprotective capacity and the extent of photoinhibition under excess light, estimated the contribution of vertical migration and the xanthophyll cycle to overall ...

Aquatic Botany, 2011

This study is the first field work that examines the use of rapid light curves (RLCs) for in situ... more This study is the first field work that examines the use of rapid light curves (RLCs) for in situ assessment of microphytobenthos (MPB) photosynthetic activity. The advantages offered by RLC methodology respond primarily to in situ constraints concerning MPB ecology and behaviour. In particular, the rapidity of RLCs allows for a high number of replicates during emersion, while preventing disturbance of the measurement due to MPB cell migration. It is necessary to maintain this feature in order to thoroughly assess the large spatial and temporal variability of in situ MPB biomass and photosynthetic activity. Consequently, working with intertidal mudflat MPB biofilms dominated by epipelic (motile) species, we investigated the effect of 10-s and 30-s irradiance steps: two durations commonly used for building RLCs. We compared the performance of 10-s and 30-s RLCs in determining the in situ MPB photosynthetic activity without dark acclimation and in high irradiances (summer). Although a similar trend of MPB cell photoacclimation was observed using the two procedures, there were differences, revealed by lower values of˛-10 s and rETR max -30 s compared with˛-30 s and rETR max -10 s on some experimental days (49% and 34%, respectively). Discrepancies could mainly be explained by the unbalanced Q A redox state and the occurrence of photoprotective non-photochemical quenching (NPQ) present prior to RLC, which impacted the 10-s and 30-s RLCs differently. The initial slope (˛) was strongly impacted by NPQ developed prior to RLCs. A correction performed a posteriori and based on the use of the maximum F m ′ obtained during the course of RLCs was not sufficient to remove the bias of pre-existing NPQ on the determination of˛completely. Consequently, a good, direct and simultaneous determination of rETR max and˛was virtually impossible in situ even when using RLCs. In contrast to published results from laboratory studies, the shorter irradiance steps (10 s) offers the better (i.e. the most reasonable) compromise for assessing MPB maximum photosynthetic capacity in situ using RLC.

Aquaculture, 2012

Haslea karadagensis is a recently-described diatom, the second species of blue diatom to be ident... more Haslea karadagensis is a recently-described diatom, the second species of blue diatom to be identified, after Haslea ostrearia, the type species of the genus Haslea, which produces marennine, the water soluble pigment involved in the greening of oysters. Haslea karadagensis also produces a blue grey pigment, with different spectral characteristics from marennine itself. This study demonstrates that the pigment from H. karadagensis can colour the gills of two oysters of economic importance, Crassostrea gigas and Ostrea edulis, when they are fed with a suspension of algae, in the same way as the marennine produced by H. ostrearia. Like marennine, the purified pigment produced by H. karadagensis displays several different biological activities. Both the intracellular and extracellular forms of the pigment have been shown to inhibit the growth of marine bacteria (Polaribacter irgensii, Vibrio aestuarianus, Pseudoalteromonas elyakowii) and fungi (Corollospora maritima, Lulworthia sp., and Dendryphiella salina). The pigment also displays antiviral activity against Herpes simplex virus type 1 (HSV-1). In light of these preliminary results, the use of H. karadagensis and putative applications of its pigment in aquaculture, food chemistry and ecophysiological research, are discussed.

Journal of Agricultural and Food Chemistry, 2012

Marennine, the blue pigment produced by the diatom Haslea ostrearia, exists in two different form... more Marennine, the blue pigment produced by the diatom Haslea ostrearia, exists in two different forms, the intra-and extracellular forms. We investigated the antibacterial, antiviral, and antiproliferative properties of both of these forms. Both forms of marennine inhibited the development of marine bacteria, in particular the pathogenic organism Vibrio aesturianus, at concentrations as low as 1 μg/mL, but they did not display any effect on a wide range of pathogenic bacteria that are relevant for food safety. Both forms of the pigment produced by H. ostrearia also exhibited antiviral activity against the HSV1 herpes virus, with intra-and extracellular marennine having EC 50 values of 24.0 and 27.0 μg/mL, respectively. These values are 2 orders of magnitude higher than the value for the reference drug, Zovirax. Moreover, both forms of marennine were effective in slowing or inhibiting the proliferation of cancer cells. This study confirms the potential of marennine as a biologically active organic molecule, which could have a protective effect on bivalves, which filter seawater and fix the pigment on their gills. Moreover, marennine could be used in food engineering and chemistry as a natural blue pigment. However, despite that it is eaten and possibly assimilated by green oyster consumers, it also deserves in depth evaluation before being considered for use as a nutraceutical.

The application of ‘booster biocides’ Diuron, Tolylfluanid and Copper thiocyanate inbantifouling ... more The application of ‘booster biocides’ Diuron, Tolylfluanid and Copper thiocyanate inbantifouling paints, used to prevent development of biofouling, needs to be monitored before assessing their impacts on the environment. An alternative approach aims to propose eco-friendly and effective antifoulants isolated from marine organisms such as seaweeds. In this study, the effects of ‘booster biocides’ and the ethanol and dichloromethane extracts from a brown (Sargassum muticum) and a red alga (Ceramium botryocarpum) have been compared by algal growth inhibition tests of marine diatoms. The most efficient extracts were ethanol fraction of S. muticum and C. botryocarpum extracts with growth EC50 = 4.74 and 5.3 μg mL−1 respectively, with reversible diatom growth effect. The booster biocides are more efficient EC50 = 0.52 μg mL−1, but are highly toxic. Results validate the use of macroalgal extracts as non toxic antifouling compounds, and they represent valuable environmentally friendly alternatives in comparison with currently used biocides.

The photoinitiated polymerization of epoxidized hydroxytelechelic cis-1,4-polyisoprene and of a d... more The photoinitiated polymerization of epoxidized hydroxytelechelic cis-1,4-polyisoprene and of a dual system (epoxidized/ acrylated) telechelic cis-1,4-polyisoprene in the presence of 2,2-dimethyl-1,2-hydroxyacetophenone or/and hexafluoro-phosphate triarylsulfonium salt has been studied by real-time infrared spectroscopy. The synthesis of photosensitives oligoisoprenes was achieved by chemical modifications of hydroxytelechelic cis-1,4-polyisoprene obtained by controlled degradation of high molecular weight cis-1,4polyisoprene. Then, the effect of light intensity, photoinitiator concentration, addition of reactive diluent and concentration of functional groups on the photopolymerization process was evaluated. Concerning the cationic process, the results showed that the kinetic profile improves when photoinitiator concentration and light intensity increase. The optimum concentration of triarylsulfonium salt used as photoinitiator was determined as 5% (w/w) and the optimum light intensity was 50 mW cm À2 . Reactive diluent (3-ethyl-3hydroxymethyl oxetane) addition greatly improves the ultimate conversion and the polymerization rate. Subsequently, the photopolymerization kinetic of a dual epoxidized/acrylated system was studied. The results obtained using different photoinitiator mixtures and different intensity of irradiation showed that the crosslinking of acrylate functions at the chain-end prevents the progression of the cationic process at the oxirane groups along the chain. Thus, the mobility of the cationic reactive centers was restricted by the crosslinking at the high conversion of the acrylate double bonds.

Journal of Applied Polymer Science, 2013

New photosensitive oligoisoprenes were synthesized by controlled degradation of high molecular we... more New photosensitive oligoisoprenes were synthesized by controlled degradation of high molecular weight cis-1,4-polyisoprene and successive chemical modification of the chain-ends. Oligomers with diacrylate extremities were synthesized, characterized, and used in photocrosslinking reactions in different conditions. The photoinitiated polymerization of the diacrylate oligoisoprenes was carried out using 2,2-dimethyl-2-hydroxyacetophenone (Darocur 1173) as initiator and the reaction was monitored by photocalorimetry-DSC and real time FTIR spectroscopy. The influence of oxygen, photoinitiator concentration, light intensity, diluting agent, and oligomers molecular weight on the reaction rate was investigated. It was found that the presence of oxygen does not influence the photopolymerization kinetics of the diacrylate oligoisoprenes. Maximum conversion was obtained for a photoinitiator concentration of 5% (w/w) and for a light intensity of 13.5 mW/cm 2 . Decreasing the formulation viscosity by addition of a diluent (1,6-hexanediol diacrylate) raised the photopolymerization rate, by increasing the reactive species mobility.

Journal of Applied Phycology, 2002

This study reports further information on “mareninne,” awater-soluble blue-green pigment synthesi... more This study reports further information on “mareninne,” awater-soluble blue-green pigment synthesized by the diatom Hasleaostrearia, which is essential to the greening of maturing oysters inFrench production areas. The extraction process is reported, as well aspreliminary characterization of a partially purified marennine extract,including quantitative spectrophotometric analysis of intracellular pigment. Amean specific extinction coefficient, E 1%1cm = 17.2 at 669 nm, is

Advances in Botanical Research, 2014

Marine Drugs, 2014

In diatoms, the main photosynthetic pigments are chlorophylls a and c, fucoxanthin, diadinoxanthi... more In diatoms, the main photosynthetic pigments are chlorophylls a and c, fucoxanthin, diadinoxanthin and diatoxanthin. The marine pennate diatom Haslea ostrearia has long been known for producing, in addition to these generic pigments, a water-soluble blue pigment, marennine. This pigment, responsible for the greening of oysters in western France, presents different biological activities: allelopathic, antioxidant, antibacterial, antiviral, and growth-inhibiting. A method to extract and purify marennine has been developed, but its chemical structure could hitherto not be resolved. For decades, H. ostrearia was the only organism known to produce marennine, and can be found worldwide. Our knowledge about H. ostrearia-like diatom biodiversity has recently been extended with the discovery of several new species of blue diatoms, the recently described H. karadagensis, H. silbo sp. inedit. and H. provincialis sp. inedit. These blue diatoms produce different marennine-like pigments, which belong to the same chemical family and present similar biological activities. Aside from being a potential source of natural blue pigments, H. ostrearia-like diatoms thus present a commercial potential for aquaculture, cosmetics, food and health industries.

Protist, 2013

We present the first study examining mtDNA transmission in diatoms, using sexual progeny of the p... more We present the first study examining mtDNA transmission in diatoms, using sexual progeny of the pennate species Haslea ostrearia (Naviculaceae). A fragment of the cytochrome oxidase subunit I gene (cox1) with 7 nucleic substitutions between parental clones was used as a parental tracer in 16 F1 clones obtained from two pairs of mating crosses. Each cross involved a parental clone isolated from France (Bay of Bourgneuf) and Sweden (Kattegat Bay). We determined that all progeny possessed only one cox1 parental haplotype. These results suggest that the mitochondrial DNA transmission in H. ostrearia is uniparental. Implications and new topics of investigation are discussed.

Journal of Phycology, 2008

Analysis of reflectance spectra was used to monitor the conversion of diadinoxanthin (DD) into di... more Analysis of reflectance spectra was used to monitor the conversion of diadinoxanthin (DD) into diatoxanthin (DT) in two benthic diatom species, Amphora coffeaeformis (C. Agardh) Kütz. and Cylindrotheca closterium (Ehrenb.) J. C. Lewin et Reiman, cultured at high light (HL, 400 lmol AE m )2 AE s )1 PAR) and low light (LL, 25 lmol AE m )2 AE s )1 PAR). Cultures were exposed to saturating light for 32 min. HL cultures of both species showed higher (DT + DD) content, whereas LL cultures exhibited higher chl a and fucoxanthin content. DD to DT conversion, measured by HPLC, occurred mainly in the first 2 min (LL) or 5 min (HL) after exposure to saturating light. Nonphotochemical quenching (NPQ), measured by PAM fluorescence, showed the same pattern as DT ⁄ (DD + DT), resulting in a linear relationship between these parameters. Addition of dithiothreitol (DTT) blocked the conversion of DD into DT and significantly reduced NPQ induction. Reflectance spectra showed no obvious change after light exposure. However, second derivative spectra (dd) showed a shift in reflectance from 487 to 508 nm, which was not present for DTT-treated samples. Changes in dd 487 were strongly correlated with changes in DD (r = 0.76), while changes in dd 508 were strongly correlated with changes in DT (r = 0.94). The best index to estimate DD to DT conversion was dd 508 /dd 630 (r = 0.87). This index was very sensitive to minute changes that occurred immediately after exposure to light and was species insensitive. Good relationships were observed between indices for xanthophyll cycle activation (DD to DT conversion and NPQ induction) and the second derivative spectra. With further in situ validation, this index may prove to be highly useful for investigation into aquatic global photoregulation mechanisms in diatom-dominated samples.

Journal of Photochemistry and Photobiology B: Biology, 2007

This study reports comparison of two techniques measuring photosynthesis in the ubiquitous diatom... more This study reports comparison of two techniques measuring photosynthesis in the ubiquitous diatom Skeletonema costatum, i.e., the classical oximetry and the recent modulated fluorimetry. Microalgae in semi-continuous cultures were exposed to five different environmental conditions simulating a seasonal effect with co-varying temperature, photoperiod and incident light. Photosynthesis was assessed by gross rate of oxygen evolution (P B ) and the electron transport rate (ETR) measurements. The two techniques were linearly related within seasonal treatments along the course of the P/E curves. The light saturation intensity parameters (E k and E ETR k ), and the maximum electron transport rate increased significantly with the progression of the season while the maximum light utilization efficiency for ETR (a ETR ) was constant. By contrast, the maximum gross oxygen photosynthetic capacity ðP B max Þ and the maximum light utilization efficiency for P B (a B ) increased from December to May treatment but decreased from May to July treatment. Both techniques showed clear photoacclimation in microalgae with the progression of the season, as illustrated by changes in photosynthetic parameters. The relationship between the two techniques changed when high temperature, photoperiod and incident light were combined, possibly due to an overestimation of the PAR-averaged chlorophyll-specific absorption cross-section. Despite this change, our results illustrate the strong suitability of in vivo chlorophyll fluorimetry to estimate primary production in the field.

Journal of Photochemistry and Photobiology B: Biology, 2007

In order to investigate the dynamics of the acclimation of marine diatoms to ultraviolet radiatio... more In order to investigate the dynamics of the acclimation of marine diatoms to ultraviolet radiation (UVR), Amphora coffeaeformis, Odontella aurita and Skeletonema costatum were exposed for 5 h per day to a combination of UVA and UVB (UVBR/UVAR ratio 4.5%) with a total UVR daily dose of 110 kJ m À2 , which is equivalent to that observed in the natural environment. This treatment was applied in the middle of the photoperiod and was repeated on five successive days.

Journal of Photochemistry and Photobiology B: Biology, 2013

The objective of the present study was to estimate in vivo pigment composition and to retrieve ab... more The objective of the present study was to estimate in vivo pigment composition and to retrieve absorption cross-section values, a ⁄ , of photosynthetic micro-organisms using a non-invasive technique of reflectance spectrometry. To test the methodology, organisms from different taxonomical groups and different pigment composition were used (Spirulina platensis a Cyanophyta, Porphyridium cruentum a Rhodophyta, Dunaliella tertiolecta a Chlorophyta and Entomoneis paludosa a Bacillariophyta) and photoacclimated to two different irradiance levels: 25 lmol photon m À2 s À1 (Low Light, LL) and 500 lmol photon m À2 s À1 (High Light, HL). Second derivative spectra from reflectance were used to identify pigment in vivo absorption bands that were linked to specific pigments detected by high performance liquid chromatography. Whereas some absorption bands such as those induced by Chlorophyll (Chl) a (416, 440, 625 and around 675 nm) were ubiquous, others were taxonomically specific (e.g. 636 nm for Chl c in E. paludosa) and/or photo-physiological dependent (e.g. 489 nm for zeaxanthin in the HL-acclimated S. platensis). The optical absorption cross-section, a ⁄ , was retrieved from reflectance data using a radiative transfer model previously developed for microphytobenthos. Despite the cellular Chl a decrease observed from LL to HL (up to 88% for S. platensis), the a ⁄ increased, except for P. cruentum. This was attributed to a 'package effect' and to a greater absorption by photoprotective carotenoids that did not contribute to the energy transfer to the core Chl a.

FEMS Microbiology Ecology, 2000

Sexual reproduction is an obligatory phase in the life cycle of most diatoms, as cell size decrea... more Sexual reproduction is an obligatory phase in the life cycle of most diatoms, as cell size decreases with successive vegetative divisions and the maximal cell size is only restored by a specialized cell, the auxospore, which follows zygote formation as a result of sexual reproduction. While in pennate diatoms the induction of sexual reproduction depends primarily on cell-cell interactions, the importance of different external factors for the induction of sexual reproduction is less well known. Here, we investigated the effects of light on sexualization in the marine benthic pennate diatom Haslea ostrearia (Gaillon) R. Simonsen. Compatible clones were crossed and exposed to different combinations of light levels, qualities, and photoperiods. Light was found to be a key factor for sexualization, and to a certain extent, to control auxosporulation in H. ostrearia. The light conditions most favorable for sexual reproduction were low irradiances (o50 mmol photons m À2 s À1 ) and short photoperiods (6-10 h), conditions that prevail during winter, and to a lesser extent, the higher irradiances and longer photoperiods that correspond to the spring and fall, when blooms of this organism form in the natural environment. Auxospore formation was very rare in continuous light, and maximum in presence of red radiation, while it was never observed in darkness or in radiation other than red.

European Journal of Phycology, 2012

2012): Haslea karadagensis (Bacillariophyta): a second blue diatom, recorded from the Black Sea a... more 2012): Haslea karadagensis (Bacillariophyta): a second blue diatom, recorded from the Black Sea and producing a novel blue pigment, European Journal of Phycology, 47:4, 469-479 To link to this article: http://dx.

European Journal of Phycology, 2009

Twelve clonal cultures of the marine pennate diatom Haslea ostrearia (Gaillon) Simonsen were used... more Twelve clonal cultures of the marine pennate diatom Haslea ostrearia (Gaillon) Simonsen were used to study sexual reproduction and auxosporulation. After crossing, compatible gametangia paired girdle to girdle, with no visible surrounding mucilage. Two gametes were formed per gametangium; these were not attached to the thecae of the parental frustule and gametes from one gametangium fused with the gametes from

Aquatic Toxicology, 2009

The tributyltin-based products and organic biocides which are incorporated into antifouling paint... more The tributyltin-based products and organic biocides which are incorporated into antifouling paints have had a negative impact on the marine environment, and the ban on tributyltin-based antifouling products has urged the industry to find substitutes to prevent the development of fouling on ship hulls. Natural antifouling agents could be isolated from marine resources, providing an alternative option for the industry. The effects of different marine seaweed extracts from Sargassum muticum and Ceramium botryocarpum on the growth, pigment content and photosynthetic apparatus of the marine diatom Fragilaria pinnata were compared with those of Diuron, a biocide widely used in antifouling paints. The addition of the macroalgal extracts in the culture medium resulted in an inhibition of the growth of F. pinnata, but this inhibition was lower than that obtained with Diuron. After transfer to a biocide-free medium, F. pinnata cells previously exposed to the macroalgal extracts exhibited normal growth, in contrast to Diuron-treated cells, which died, demonstrating that the effects of the natural antifouling agents were reversible. Macroalgal extracts and Diuron-induced modifications in F. pinnata cellular pigment content. Chlorophyll a, fucoxanthin, and the xanthophyll pool, diadinoxanthin and diatoxanthin, were the most affected. Changes in the structure and function of the photosynthetic apparatus were studied by microspectrofluorimetry, and provided a comprehensive evaluation of the inhibition of the diatom Photosystem II (PSII) by the biocides. This study confirms that natural extracts from the macroalgae studied have the potential to be used as a substitute to commercial biocides in antifouling paints.

Aquatic Microbial Ecology, 2012

ABSTRACT: The capacity of microphytobenthos to withstand the variable and extreme conditions of t... more ABSTRACT: The capacity of microphytobenthos to withstand the variable and extreme conditions of the intertidal environment, prone to cause photoinhibition, has been attributed to particularly efficient photoprotection. However, little is known regarding the capacity of this protection against photoinhibition or the mechanisms responsible for it. The present study quantified the photoprotective capacity and the extent of photoinhibition under excess light, estimated the contribution of vertical migration and the xanthophyll cycle to overall ...

Aquatic Botany, 2011

This study is the first field work that examines the use of rapid light curves (RLCs) for in situ... more This study is the first field work that examines the use of rapid light curves (RLCs) for in situ assessment of microphytobenthos (MPB) photosynthetic activity. The advantages offered by RLC methodology respond primarily to in situ constraints concerning MPB ecology and behaviour. In particular, the rapidity of RLCs allows for a high number of replicates during emersion, while preventing disturbance of the measurement due to MPB cell migration. It is necessary to maintain this feature in order to thoroughly assess the large spatial and temporal variability of in situ MPB biomass and photosynthetic activity. Consequently, working with intertidal mudflat MPB biofilms dominated by epipelic (motile) species, we investigated the effect of 10-s and 30-s irradiance steps: two durations commonly used for building RLCs. We compared the performance of 10-s and 30-s RLCs in determining the in situ MPB photosynthetic activity without dark acclimation and in high irradiances (summer). Although a similar trend of MPB cell photoacclimation was observed using the two procedures, there were differences, revealed by lower values of˛-10 s and rETR max -30 s compared with˛-30 s and rETR max -10 s on some experimental days (49% and 34%, respectively). Discrepancies could mainly be explained by the unbalanced Q A redox state and the occurrence of photoprotective non-photochemical quenching (NPQ) present prior to RLC, which impacted the 10-s and 30-s RLCs differently. The initial slope (˛) was strongly impacted by NPQ developed prior to RLCs. A correction performed a posteriori and based on the use of the maximum F m ′ obtained during the course of RLCs was not sufficient to remove the bias of pre-existing NPQ on the determination of˛completely. Consequently, a good, direct and simultaneous determination of rETR max and˛was virtually impossible in situ even when using RLCs. In contrast to published results from laboratory studies, the shorter irradiance steps (10 s) offers the better (i.e. the most reasonable) compromise for assessing MPB maximum photosynthetic capacity in situ using RLC.

Aquaculture, 2012

Haslea karadagensis is a recently-described diatom, the second species of blue diatom to be ident... more Haslea karadagensis is a recently-described diatom, the second species of blue diatom to be identified, after Haslea ostrearia, the type species of the genus Haslea, which produces marennine, the water soluble pigment involved in the greening of oysters. Haslea karadagensis also produces a blue grey pigment, with different spectral characteristics from marennine itself. This study demonstrates that the pigment from H. karadagensis can colour the gills of two oysters of economic importance, Crassostrea gigas and Ostrea edulis, when they are fed with a suspension of algae, in the same way as the marennine produced by H. ostrearia. Like marennine, the purified pigment produced by H. karadagensis displays several different biological activities. Both the intracellular and extracellular forms of the pigment have been shown to inhibit the growth of marine bacteria (Polaribacter irgensii, Vibrio aestuarianus, Pseudoalteromonas elyakowii) and fungi (Corollospora maritima, Lulworthia sp., and Dendryphiella salina). The pigment also displays antiviral activity against Herpes simplex virus type 1 (HSV-1). In light of these preliminary results, the use of H. karadagensis and putative applications of its pigment in aquaculture, food chemistry and ecophysiological research, are discussed.

Journal of Agricultural and Food Chemistry, 2012

Marennine, the blue pigment produced by the diatom Haslea ostrearia, exists in two different form... more Marennine, the blue pigment produced by the diatom Haslea ostrearia, exists in two different forms, the intra-and extracellular forms. We investigated the antibacterial, antiviral, and antiproliferative properties of both of these forms. Both forms of marennine inhibited the development of marine bacteria, in particular the pathogenic organism Vibrio aesturianus, at concentrations as low as 1 μg/mL, but they did not display any effect on a wide range of pathogenic bacteria that are relevant for food safety. Both forms of the pigment produced by H. ostrearia also exhibited antiviral activity against the HSV1 herpes virus, with intra-and extracellular marennine having EC 50 values of 24.0 and 27.0 μg/mL, respectively. These values are 2 orders of magnitude higher than the value for the reference drug, Zovirax. Moreover, both forms of marennine were effective in slowing or inhibiting the proliferation of cancer cells. This study confirms the potential of marennine as a biologically active organic molecule, which could have a protective effect on bivalves, which filter seawater and fix the pigment on their gills. Moreover, marennine could be used in food engineering and chemistry as a natural blue pigment. However, despite that it is eaten and possibly assimilated by green oyster consumers, it also deserves in depth evaluation before being considered for use as a nutraceutical.