Thierry Bouvier

Université Montpellier 2 Sciences et Techniques, Montpelhièr, Languedoc-Roussillon, France

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Publications (49)248.52 Total impact

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    ABSTRACT: Abstract. Size fractionation was performed using water from the Great Reef of Toliara (Madagascar) taken from two different habitats (ocean and lagoon) during the dry and wet seasons, to study the growth and mortality rates of bacterioplankton. Experiments were conducted with 1 and 100% of heterotrophic nanoflagellate (HNF) concentrations and virus-free water was obtained by tangential filtration (10 kDa). During the dry season, in both environments, bacterial abundance and production were significantly lower than values recorded during the wet season. Bacterial growth rates without grazers were 0.88 day �1 in the lagoon and 0.58 day �1 in the ocean. However, growth rates were statistically higher without grazers and viruses (1.58 day �1 and 1.27 day �1). An estimate of virus-induced bacterial mortality revealed the important role played by viruses in the lagoon (0.70 day �1) and the ocean (0.69 day �1). During the wet season, bacterial growth rates without grazers were significantly higher in both environments than were values obtained in the dry season. However, the bacterial growth rates were paradoxally lower in the absence of viruses than with viruses in both environments. Our results suggest that changes in nutrient concentrations can play an important role in the balance between viral lysis and HNF grazing in the bacterial mortality. However, virus-mediated bacterial mortality is likely to act simultaneously with nanoflagellates pressure in their effects on bacterial communities.
    Marine and Freshwater Research 04/2015; DOI:10.1071/MF14253 · 2.25 Impact Factor
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    ABSTRACT: N2-fixing cyanobacteria represent a major source of new nitrogen and carbon for marine microbial communities, but little is known about their ecological interactions with associated microbiota. In this study we investigated the interactions between the unicellular N2-fixing cyanobacterium Cyanothece sp. Miami BG043511 and its associated free-living chemotrophic bacteria at different concentrations of nitrate and dissolved organic carbon and different temperatures. High temperature strongly stimulated the growth of Cyanothece, but had less effect on the growth and community composition of the chemotrophic bacteria. Conversely, nitrate and carbon addition did not significantly increase the abundance of Cyanothece, but strongly affected the abundance and species composition of the associated chemotrophic bacteria. In nitrate-free medium the associated bacterial community was co-dominated by the putative diazotroph Mesorhizobium and the putative aerobic anoxygenic phototroph Erythrobacter and after addition of organic carbon also by the Flavobacterium Muricauda. Addition of nitrate shifted the composition toward co-dominance by Erythrobacter and the Gammaproteobacterium Marinobacter. Our results indicate that Cyanothece modified the species composition of its associated bacteria through a combination of competition and facilitation. Furthermore, within the bacterial community, niche differentiation appeared to play an important role, contributing to the coexistence of a variety of different functional groups. An important implication of these findings is that changes in nitrogen and carbon availability due to, e.g., eutrophication and climate change are likely to have a major impact on the species composition of the bacterial community associated with N2-fixing cyanobacteria.
    Frontiers in Microbiology 01/2015; 5:795. DOI:10.3389/fmicb.2014.00795 · 3.94 Impact Factor
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    ABSTRACT: Phytoplankton diversity and abundance in estuarine systems are controlled by many factors. Salinity, turbidity, and inorganic nutrient concentrations and their respective ratios have all been proposed as principal factors that structure phytoplankton diversity and influence the emergence of potentially toxic species. Although much work has been conducted on temperate estuaries, less is known about how phytoplankton diversity is controlled in tropical, monsoonal systems that are subject to large, seasonal shifts in hydrology and to rapidly changing land use. Here, we present the results of an investigation into the factors controlling phytoplankton species composition and distribution in a tropical, monsoonal estuary (Bach Dang estuary, North Vietnam). A total of 245 taxa, 89 genera from six algal divisions were observed. Bacillariophyceae were the most diverse group contributing to 51.4 % of the microalgal assemblage, followed by Dinophyceae (29.8 %), Chlorophyceae (10.2 %), Cyanophyceae (3.7 %), Euglenophyceae (3.7 %) and Dictyochophyceae (1.2 %). The phytoplankton community was structured by inorganic nutrient ratios (DSi:DIP and DIN:DIP) as well as by salinity and turbidity. Evidence of a decrease in phytoplankton diversity concomitant with an increase in abundance and dominance of certain species (e.g., Skeletonema costatum) and the appearance of some potentially toxic species over the last two decades was also found. These changes in phytoplankton diversity are probably due to a combination of land use change resulting in changes in nutrient ratios and concentrations and global change as both rainfall and temperature have increased over the last two decades. It is therefore probable in the future that phytoplankton diversity will continue to change, potentially favoring the emergence of toxic species in this system.
    Environmental Monitoring and Assessment 09/2014; DOI:10.1007/s10661-014-4024-y · 1.68 Impact Factor
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    ABSTRACT: A recent hypothesis considers that many coral pathologies are the result of a sudden structural alteration of the epibiotic bacterial communities in response to environmental disturbances. However, the ecological mechanisms that lead to shifts in their composition are still unclear. In the ocean, viruses represent a major bactericidal agent but little is known on their occurrence within the coral holobiont. Recent reports have revealed that viruses are abundant and diversified within the coral mucus and therefore could be decisive for coral health. However, their mode of action is still unknown, and there is now an urgent need to shed light on the nature of the relationships they might have with the other prokaryotic and eukaryotic members of the holobiont. In this opinion letter, we are putting forward the hypothesis that coral-associated viruses (mostly bacterial and algal viruses), depending on the environmental conditions might either reinforce coral stability or conversely fasten their decline. We propose that these processes are presumably based on an environmentally driven shift in infection strategies allowing viruses to regulate, circumstantially, both coral symbionts (bacteria or Symbiodinium) and surrounding pathogens.
    Environmental Microbiology 08/2014; DOI:10.1111/1462-2920.12579 · 6.24 Impact Factor
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    ABSTRACT: Viruses attract increasing interest from environmental microbiologists seeking to understand their function and role in coral health. However, little is known about their main ecological traits within the coral holobiont. In this study, a quantitative and qualitative characterization of viral and bacterial communities was conducted on the mucus of 7 different coral species of the Van Phong Bay (Viet Nam). On average, the concentrations of viruses and bacteria were respectively 17 and 2-fold higher in the mucus than in the surrounding water. The examination of bacterial community composition also showed remarkable differences between mucus and water samples. The percentage of active respiring cells was nearly 3-fold higher in mucus (m= 24.8%) than in water (m= 8.6%). Interestingly, a positive and highly significant correlation was observed between the proportion of active cells and viral abundance in the mucus, suggesting that the metabolism of the bacterial associates is probably a strong determinant of the distribution of viruses within the coral holobiont. Overall, coral mucus, given its unique physico-chemical characteristics and sticking properties, can be regarded as a highly selective biotope for abundant, diversified and specialized symbiotic microbial and viral organisms.
    Environmental Microbiology Reports 06/2014; 6(6). DOI:10.1111/1758-2229.12185 · 3.26 Impact Factor
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    ABSTRACT: The effects of grazing pressure and inorganic nutrient availability on the direct carbon transfer from freshly produced phytoplankton exudates to heterotrophic bacteria biomass production were studied in Mediterranean coastal waters. The short-term incorporation of ¹³C (H¹³CO₃) in phytoplankton and bacterial lipid biomarkers was measured as well as the total bacterial carbon production (BP), viral lysis and the microbial community structure under three experimental conditions: (1) High inorganic Nutrient and High Grazing (HN + HG), (2) High inorganic Nutrient and Low Grazing (HN + LG) and (3) under natural in situ conditions with Low inorganic Nutrient and High Grazing (LN + HG) during spring. Under phytoplankton bloom conditions (HN + LG), the bacterial use of freshly produced phytoplankton exudates as a source of carbon, estimated from ¹³C enrichment of bacterial lipids, contributed more than half of the total bacterial production. However, under conditions of high grazing pressure on phytoplankton with or without the addition of inorganic nutrients (HN + HG and LN + HG), the ¹³C enrichment of bacterial lipids was low compared with the high total bacterial production. BP therefore seems to depend mainly on freshly produced phytoplankton exudates during the early phase of phytoplankton bloom period. However, BP seems mainly relying on recycled carbon from viral lysis and predators under high grazing pressure.
    FEMS Microbiology Ecology 03/2014; 87(3):757-69. DOI:10.1111/1574-6941.12262 · 3.88 Impact Factor
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    ABSTRACT: a b s t r a c t Vermicompost and biochar amendments are management practices which may contribute to sustain-able agroecosystems by reducing dependence on inorganic fertilizers. However, little is known about their impacts on soil microorganisms and their transfer and evolution in connected aquatic systems. The aim of this study was to determine the influence of organic manure (buffalo manure, compost or ver-micompost) and biochar amendments on bacterial and viral properties in soil and water. A three year experiment was carried out with terrestrial mesocosms which were used to test the effect of organic matter amendment on maize growth. In the last year of the experiment, runoff and infiltration waters from the terrestrial mesocosms were transferred to aquatic mesocosms. Organic fertilization improved soil properties (higher C, N content and pH H 2 O) and as a consequence increased soil bacterial and viral abundance. Bacterial diversity (Shannon 'H' and richness 'S' indices calculated from DGGE fingerprint) was also enhanced after the continuous application of organic amendments. Compared with compost, vermicompost reduced viral abundance and S but similar H and bacterial abundance were observed. The pH H 2 O , C content and bacterial and viral abundance increased in the aquatic mesocosms following organic fertilization. As a consequence, bacterial and viral diversity also increased in the water, although no dif-ferences were found between compost and vermicompost. Biochar increased soil bacterial abundance for the mineral fertilizer treatment but did not influence bacterial and viral abundance in water. However, the combination of biochar and vermicompost led to an increase of viruses in soil and a reduction of bacteria in water. Similarity dendrograms from the DGGE banding patterns showed that the structure of bacterial communities was mainly influenced by the fertilizer treatments in soil but by the presence of biochar in water. In conclusion, this study demonstrated that the nature of the organic amendment has important consequences on both soil and water microbial abundance and diversity.
    Applied Soil Ecology 01/2014; 73:78-86. DOI:10.1016/j.apsoil.2013.08.016 · 2.21 Impact Factor
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    ABSTRACT: a b s t r a c t The amendment of vermicompost is a management practice that may contribute to sustainable agro-ecosystems by making them less dependent on inorganic fertilizers. However, little is known about the impact of this practice on soil biota and the flow of microbes to the water system. Using a 30-days laboratory experiment, we investigated the development of the peregrine earthworm species, Dichogaster bolaui, in presence of compost or vermicompost, and assessed its impact on the flow of bacteria and viruses to the water system. The dynamics of soil bacterial diversity (assessed by DGGE) and concentration in water together with their viral parasites were also assessed through an incubation of solution during 5 days (comparison between T 0 and T 5). This study highlights the rapid development of D. bolaui after compost amendment. However, the low quality of vermicompost and the absence of organic amendment in the control treatment allowed the survival but not the development of D. bolaui. Higher bacterial and viral abundances in compost and vermicompost substrates led to more important transfer of these communities from the soil to the water system in comparison with the untreated soil, but no difference was observed between compost and vermicompost treatments. In terms of abundance, the bacterial to virus ratio was rather stable in the soil solution but no such a relation was observed in the soil. A reduction of bacterial diversity (OTU) was measured at the end of the incubation period for all the treatments. However, higher number of OTU at T 5 for the compost treatment suggested a better adaptation and/or resistance of soil bacteria to the aquatic system, in comparison with the control treatment. Vermicompost treatment led to intermediate conclusions. The presence of D. bolaui significantly reduced bacterial abundance in the soil organic layer (both compost and vermicompost treatments) but it did not influence bacterial and viral abundance in water, suggesting independent processes. Earthworms buffered bacterial DGGE patterns after five days of incubation, probably through a facilitation of soil bacterial groups more able to resist in solution.
    Soil Biology and Biochemistry 08/2013; 66:197-203. DOI:10.1016/j.soilbio.2013.07.007 · 4.41 Impact Factor
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    ABSTRACT: Recent developments of molecular tools have revolutionized our knowledge of microbial biodiversity by allowing detailed exploration of its different facets and generating unprecedented amount of data. One key issue with such large datasets is the development of diversity measures that cope with different data outputs and allow comparison of biodiversity across different scales. Diversity has indeed three components: local (α), regional (γ) and the overall difference between local communities (β). Current measures of microbial diversity, derived from several approaches, provide complementary but different views. They only capture the β component of diversity, compare communities in a pairwise way, consider all species as equivalent or lack a mathematically explicit relationship among the α, β and γ components. We propose a unified quantitative framework based on the Rao quadratic entropy, to obtain an additive decomposition of diversity (γ = α + β), so the three components can be compared, and that integrate the relationship (phylogenetic or functional) among Microbial Diversity Units that compose a microbial community. We show how this framework is adapted to all types of molecular data, and we highlight crucial issues in microbial ecology that would benefit from this framework and propose ready-to-use R-functions to easily set up our approach.
    Environmental Microbiology 05/2013; 15(10). DOI:10.1111/1462-2920.12156 · 6.24 Impact Factor
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    ABSTRACT: Changes in environmental conditions and prokaryote physiology can strongly affect the dynamics of both the lysogenic and lytic bacteriophage replication cycles in aquatic systems. However, it remains unclear whether it is the nature, amplitude or frequency of these changes that alter the phage replication cycles. We performed an annual survey of three Mediterranean lagoons with contrasting levels of chlorophyll a concentration and salinity to explore how these cues and their variability influence either replication cycle. The lytic cycle was always detected and showed seasonal patterns, whereas the lysogenic cycle was often undetected and highly variable. The lytic cycle was influenced by environmental and prokaryotic physiological cues, increasing with concentrations of dissolved organic carbon, chlorophyll a, and the proportion of respiring cells, and decreasing with the proportion of damaged cells. In contrast, lysogeny was not explained by the magnitude of any environmental or physiological parameter, but increased with the amplitude of change in prokaryote physiology. Our study suggests that both cycles are regulated by distinct factors: the lytic cycle is dependent on environmental parameters and host physiology, while lysogeny is dependent on the variability of prokaryote physiology. This could lead to the contrasting patterns observed between both cycles in aquatic systems.
    Environmental Microbiology 03/2013; 15(9). DOI:10.1111/1462-2920.12120 · 6.24 Impact Factor
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    ABSTRACT: Small size eukaryotes play a fundamental role in the functioning of coastal ecosystems, however, the way in which these micro-organisms respond to combined effects of water temperature, UVB radiations (UVBR) and nutrient availability is still poorly investigated. We coupled molecular tools (18S rRNA gene sequencing and fingerprinting) with microscope-based identification and counting to experimentally investigate the short-term responses of small eukaryotes (<6 μm; from a coastal Mediterranean lagoon) to a warming treatment (+3°C) and UVB radiation increases (+20%) at two different nutrient levels. Interestingly, the increase in temperature resulted in higher pigmented eukaryotes abundances and in community structure changes clearly illustrated by molecular analyses. For most of the phylogenetic groups, some rearrangements occurred at the OTUs level even when their relative proportion (microscope counting) did not change significantly. Temperature explained almost 20% of the total variance of the small eukaryote community structure (while UVB explained only 8.4%). However, complex cumulative effects were detected. Some antagonistic or non additive effects were detected between temperature and nutrients, especially for Dinophyceae and Cryptophyceae. This multifactorial experiment highlights the potential impacts, over short time scales, of changing environmental factors on the structure of various functional groups like small primary producers, parasites and saprotrophs which, in response, can modify energy flow in the planktonic food webs.
    BMC Microbiology 09/2012; 12:202. DOI:10.1186/1471-2180-12-202 · 2.98 Impact Factor
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    Amandine Leruste, Thierry Bouvier, Yvan Bettarel
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    ABSTRACT: The distribution of viruses inhabiting the coral mucus remains undetermined, as there is no suitable standardized procedure for their separation from this organic matrix, principally owing to its viscosity and autofluorescence. Seven protocols were tested, and the most efficient separations were obtained from a chemical treatment requiring potassium citrate.
    Applied and Environmental Microbiology 06/2012; 78(17):6377-9. DOI:10.1128/AEM.01141-12 · 3.95 Impact Factor
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    ABSTRACT: The ecological insurance hypothesis predicts a positive effect of species richness on ecosystem functioning in a variable environment. This effect stems from temporal and spatial complementarity among species within metacommunities coupled with optimal levels of dispersal. Despite its importance in the context of global change by human activities, empirical evidence for ecological insurance remains scarce and controversial. Here we use natural aquatic bacterial communities to explore some of the predictions of the spatial and temporal aspects of the ecological insurance hypothesis. Addressing ecological insurance with bacterioplankton is of strong relevance given their central role in fundamental ecosystem processes. Our experimental set up consisted of water and bacterioplankton communities from two contrasting coastal lagoons. In order to mimic environmental fluctuations, the bacterioplankton community from one lagoon was successively transferred between tanks containing water from each of the two lagoons. We manipulated initial bacterial diversity for experimental communities and immigration during the experiment. We found that the abundance and production of bacterioplankton communities was higher and more stable (lower temporal variance) for treatments with high initial bacterial diversity. Immigration was only marginally beneficial to bacterial communities, probably because microbial communities operate at different time scales compared to the frequency of perturbation selected in this study, and of their intrinsic high physiologic plasticity. Such local "physiological insurance" may have a strong significance for the maintenance of bacterial abundance and production in the face of environmental perturbations.
    PLoS ONE 06/2012; 7(6):e37620. DOI:10.1371/journal.pone.0037620 · 3.53 Impact Factor
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    ABSTRACT: Variations of the sticking properties of transparent exopolymeric particles (TEP) were investigated by studying the interactions between latex beads and TEP precursors collected along a salinity gradient in the Bach Dang estuary, North Vietnam. For each sampling station, a suspension of TEP and beads was prepared and the formation of mixed aggregates was monitored in the laboratory under controlled turbulence intensity. The number of beads attached to TEP per volume of TEP increased from 0.22 x 10-3 ±0.15 x 10-3 µm-3 to 5.33 x 10-3 ±1.61 x 10-3 µm-3, from low (<1) to high (>28) salinities, respectively. The sudden increase in TEP sticking properties from salinity 10 to 15 suggests the occurrence of an “aggregation web” resulting of the stimulation of aggregation processes. For a given turbulence level, the formation of large aggregates should be enhanced seaward. The presence of a higher fraction of large aggregates seaward is supported by the increase of the slope of the particle size spectra measured in situ. The observed increase in TEP sticking properties toward high salinities may affect the vertical export pump in estuaries. This study suggests that the transition from a low to a high physico-chemical reactivity of TEP along estuaries may result in a succession from recycling for salinity <10 to enhanced aggregation/sedimentation processes and export dominated systems for salinity >10.
    Estuarine Coastal and Shelf Science 02/2012; 96(1):151-158. DOI:10.1016/j.ecss.2011.10.028 · 2.25 Impact Factor
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    ABSTRACT: Virus-like particles were observed in thin sections of partially bleaching colonies of the scleractinian Acropora cytherea, collected in the Hon Mun Marine Protected Area (Vietnam). The most common particles were found in the cytoplasm of epidermal cells, exhibiting icosahedral symmetry and measuring 90–140 nm in diameter. Some had a tail-like structure resembling that of certain Hepadnaviridae such as the hepatitis B virus. Some others were tailless with a virion size. Overall, less than 10% of the cells showed obvious signs of infection. Images of virally-parasitized tissues of A. cytherea provide further evidence that corals are a target for viral infection. However, more research is required into their pathogenicity and involvement in bleaching events.
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    ABSTRACT: Considering the major involvement of gut microflora in the digestive function of various macro-organisms, bacterial communities inhabiting fish guts may be the main actors of organic matter degradation by fish. Nevertheless, the extent and the sources of variability in the degradation potential of gut bacterial communities are largely overlooked. Using Biolog Ecoplate™ and denaturing gradient gel electrophoresis (DGGE), we explored functional (i.e. the ability to degrade organic matter) and genetic (i.e. identification of DGGE banding patterns) diversity of fish gut bacterial communities, respectively. Gut bacterial communities were extracted from fish species characterized by different diets sampled along a salinity gradient in the Patos-Mirim lagoons complex (Brazil). We found that functional diversity was surprisingly unrelated to genetic diversity of gut bacterial communities. Functional diversity was not affected by the sampling site but by fish species and diet, whereas genetic diversity was significantly influenced by all three factors. Overall, the functional diversity was consistently high across fish individuals and species, suggesting a wide functional niche breadth and a high potential of organic matter degradation. We conclude that fish gut bacterial communities may strongly contribute to nutrient cycling regardless of their genetic diversity and environment.
    FEMS Microbiology Ecology 11/2011; 79(3):568-80. DOI:10.1111/j.1574-6941.2011.01241.x · 3.88 Impact Factor
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    ABSTRACT: Phytoplankton diversity, primary and bacterial production, nutrients and metallic contaminants were measured during the wet season (July) and dry season (March) in the Bach Dang Estuary, a sub-estuary of the Red River system, Northern Vietnam. Using canonical correspondence analysis we show that phytoplankton community structure is potentially influenced by both organometallic species (Hg and Sn) and inorganic metal (Hg) concentrations. During March, dissolved methylmercury and inorganic mercury were important factors for determining phytoplankton community composition at most of the stations. In contrast, during July, low salinity phytoplankton community composition was associated with particulate methylmercury concentrations, whereas phytoplankton community composition in the higher salinity stations was more related to dissolved inorganic mercury and dissolved mono and tributyltin concentrations. These results highlight the importance of taking into account factors other than light and nutrients, such as eco-toxic heavy metals, in understanding phytoplankton diversity and activity in estuarine ecosystems.
    Marine Pollution Bulletin 09/2011; 62(11):2317-29. DOI:10.1016/j.marpolbul.2011.08.044 · 2.79 Impact Factor

Publication Stats

1k Citations
248.52 Total Impact Points

Institutions

  • 2007–2015
    • Université Montpellier 2 Sciences et Techniques
      Montpelhièr, Languedoc-Roussillon, France
  • 2011–2014
    • French National Centre for Scientific Research
      Lutetia Parisorum, Île-de-France, France
    • Institute of Research for Development
      Marsiglia, Provence-Alpes-Côte d'Azur, France
  • 1997–2014
    • Université de Montpellier 1
      • ECOSYM (Ecologie des systèmes marins côtiers) - UMR 5119
      Montpelhièr, Languedoc-Roussillon, France
  • 2010
    • Observatoire Océanologique de Villefranche sur Mer
      • Laboratoire d'Océanographie de Villefranche-sur-Mer
      Villefranche, Provence-Alpes-Côte d'Azur, France
  • 2003
    • Université du Québec à Montréal
      • Department of Biological Sciences
      Montréal, Quebec, Canada
  • 2001–2002
    • Université Libre de Bruxelles
      • Laboratory of Aquatic Systems Ecology
      Bruxelles, Brussels Capital Region, Belgium