Modifications métaboliques et structurelles des communautés de bactéries marines exposées à différentes qualités de matière organique

Heterotrophic bacterial communities in marine environment are exposed to a heterogeneous mixture of dissolved organic compounds with different bioavailability that may control both their activities and their composition. In the frame of this thesis, we studied the response of different coastal bacterial communities to the single or combined addition of various natural dissolved organic matter (DOM) photo-oxidized or not, presenting different bioavailability characteristics. Firstly, we studied the effects of the addition of highly bioreactive DOM derived from jellyfish on bacterial activities and community structure in a Mediterranean coastal lagoon. We observed that resilience of the bacterial community after the addition of DOM from the jellyfish was higher for metabolic functions than diversity, suggesting that jellyfish blooms can induce durable changes in the bacterial community structure in coastal lagoons. Secondly, we investigated the occurrence of priming effect (increase in microbial degradation of refractory DOM upon the addition of labile DOM) on coastal marine environments. Experiments with single or combined additions of recalcitrant and labile DOM sources were performed with a Mediterranean and a Patagonian fjord bacterial communities. In both cases we observed a greater effect of combined addition on bacterial community composition. However we did not observe an increase in recalcitrant DOM degradation of recalcitrant DOM following the addition of labile compounds, suggesting that priming effect did not occur during our experiments. Finally, we studied the impact of contrasted DOM (i.e. recalcitrant riverine DOM, labile phytoplankton-derived DOM) photodegradation on coastal bacterial communities activity and composition. We observed that photodegradation of phytoplankton-derived DOM led to a lower bacterial growth and changes in bacterial community diversity, in favour of Alphaproteobacteria.En milieu marin, les communautés bactériennes hétérotrophes sont exposées à un mélange hétérogène de composés organiques dissous présentant différents degrés de labilité, qui peuvent contrôler à la fois leurs activités et leur composition. Dans le cadre de cette thèse, nous avons étudié la réponse de communautés bactériennes présentes dans des environnements côtiers contrastés à l’ajout simple ou combiné de différentes sources naturelles de matière organique dissoute (MOD), préalablement photo oxydée ou non et présentant différentes bio réactivités. Dans un premier temps, nous avons étudié l’impact d’ajout de MOD labile provenant de méduses sur l’activité et la diversité bactériennes d’une communauté d’une lagune côtière méditerranéenne. Nous avons observé que la résilience des communautés bactériennes suite à cet ajout était plus importante pour les fonctions métaboliques que pour la diversité. Ceci suggère que les efflorescences de méduses peuvent entrainer des changements durables de la structure des communautés bactériennes en environnement côtier. Dans un deuxième temps, nous nous sommes intéressés à la possibilité d’un priming effect (accélération de la dégradation bactérienne de la MOD réfractaire en présence de MOD labile) en milieu côtier. Des expériences d’ajout simple ou combiné de MOD labile et récalcitrante ont été réalisées sur des communautés bactériennes de Mer Méditerranée et d’un fjord de Patagonie chilienne. Dans les deux cas, nous avons observé des changements plus importants de la composition communautaire bactérienne suite à un ajout combiné. Cependant, nous n’avons pas observé une plus forte consommation de MOD récalcitrante suite à l’ajout de composés labiles, ce qui suggère que le priming effect n’a pas eu lieu au cours de nos expériences. Enfin, nous avons étudié l’impact de la photodégradation de différentes sources de MOD (i.e. MOD récalcitrante de rivière, MOD labile provenant de phytoplancton) sur l’activité et la diversité de communautés bactériennes côtières. Nous avons observé que la photodégradation de la MOD issue d’une culture de phytoplancton entrainait à la fois une croissance bactérienne plus faible et une modification de la diversité bactérienne en faveur des Alphaprotéobactéries

Metagenome sequencing of the microbial community of a solar saltern crystallizer pond at cáhuil lagoon, chile.

Cáhuil Lagoon in central Chile harbors distinct microbial communities in various solar salterns that are arranged as interconnected ponds with increasing salt concentrations. Here, we report the metagenome of the 3.0- to 0.2-µm fraction of the microbial community present in a crystallizer pond with 34% salinity

Modélisation interdisciplinaire de l'intercompréhension dans les interactions

National audienceNé en 2010, le projet MIAC - Modélisation interdisciplinaire de l'acceptabilité et de l'intercompréhension dans les interactions - s'est fixé le but de mieux comprendre l'intercompréhension dans les interactions d'un point de vue transversal aux hommes, aux animaux et aux machines. Nous proposons ici une modélisation interdisciplinaire de l'intercompréhension dans les interactions, dont nous faisons l'hypothèse qu'elle pourrait fonctionner quels que soit les partenaires impliqués. Pour cela, nous nous sommes basés sur la définition de modèle proposée par Mortensen (1972)

Habitat-mediated size selection in endangered Atlantic salmon fry: selectional restoration assessment

Preservation of adaptive variation is a top priority of many species restoration programs, but most restoration activities are conducted without direct knowledge of selection that might foster or impair adaptation and restoration goals. In this study, we quantified geographic variation in selection on fry size of endangered Atlantic salmon (Salmo salar) during the 6-week period immediately following stocking in the wild. We also used a model selection approach to assess whether habitat variables influence patterns of such selection. We found evidence for significant size-selection in five out of six selection trials. Interestingly, the strength and pattern of selection varied extensively among sites, and model selection suggested that this variation in phenotypic selection was related to geographic variation in the presence of large woody debris and the slope of the stream gradient. The strong selection differentials we observed should be a concern for endangered salmon restoration, whether they reflect natural processes and an opportunity to maintain adaptation, or an indicator of the potentially deleterious phenotypic consequences of hatchery practices

New aminosterol derivatives for antimicrobial use in veterinary medicine

Actuellement, le traitement des pathologies infectieuses chez les bovins et les animaux de compagnie est menacé par l’accroissement de l’antibiorésistance et des bactéries multirésistantes. Il est donc primordial pour les entreprises pharmaceutiques vétérinaires de développer de nouvelles gammes d’agents antibactériens spécifiques au domaine animale. Dans ce contexte, il a été montré que certains polyaminostérols naturels tels que la squalamine possèdent un fort potentiel antimicrobien. Ainsi, l’objectif de ce travail de thèse est de répondre à la problématique présentée par la société Virbac dans le traitement des mammites (bovins) et des otites/pyodermites (chien) par le développement d’une nouvelle classe de dérivés polyaminostéroïdiens synthétiques à large spectre antimicrobien. Pour cela, nous avons constitué une chimiothèque de composés originaux préparés à partir de différents acides biliaires selon des voies de synthèse inédites. Ces composés ont été évalués in vitro pour leur cytotoxicité et leurs activités antibactériennes contre diverses bactéries à Gram positif et à Gram négatif et nous avons pu établir la preuve de concept in vitro de leur potentiel thérapeutique en tant qu’agents antibactériens ou adjuvants d’antibiotiques. De plus, nous avons montré que l’un de ces nouveaux dérivés, la claramine A1, agit sur l’intégrité physique des membranes bactériennes et sur les performances d'efflux des pompes AcrAB-TolC. Ainsi, il apparaît finalement que ces dérivés polyaminostéroïdiens au mode d’action non conventionnel pourraient constituer une nouvelle classe d’agents antibactériens pour un usage en tant que substituts d’antibiotiques en médecine vétérinaire.Currently, the treatment of infectious pathologies in cattle and pets is threatened by the growing antimicrobial resistance and the development of multidrug-resistant bacteria. Thus it is necessary for the veterinary pharmaceutical firms to develop new lines of antibacterial agents. In this context, some natural polyaminosterols such as squalamine have gained interest due to their potent antimicrobial activities. Thus the aim of this PhD work is to provide an answer in the treatment of mastitis (cattle) and otitis/pyoderma (dog) by the development of a new class of synthetic polyaminosterols with a broad spectrum of antibacterial activity. In this purpose, a chemical library of original compounds has been prepared starting from various bile acids by using unprecedented synthesis procedures. These compounds were evaluated for their in vitro cytotoxicity on CHO cells as well as their antibacterial activities against Gram-positive and Gram-negative bacteria and we have establish the in vitro proof of concept of the therapeutic potential of this family of molecules as antibacterial agent or antibiotic adjuvant. Additional investigations were then conducted on one of these novel derivatives namely claramine A1 to deepen knowledge of its mechanism of action and showed that claramine A1 acts on the physical integrity of bacterial membranes and the efflux performance of AcrAB-TolC pumps. Based on the results of claramine A1, it finally appears that these new polyaminosterol derivatives possessing a non-classical mode of action pertain to a new class of antibacterial agents and could constitute a substitute for traditional antibiotics in veterinary medicine

Metabolic and composition changes in marine bacterial community esposed to variable natural organic matter bioreactivity

En milieu marin, les communautés bactériennes hétérotrophes sont exposées à un mélange hétérogène de composés organiques dissous présentant différents degrés de labilité, qui peuvent contrôler à la fois leurs activités et leur composition. Dans le cadre de cette thèse, nous avons étudié la réponse de communautés bactériennes présentes dans des environnements côtiers contrastés à l’ajout simple ou combiné de différentes sources naturelles de matière organique dissoute (MOD), préalablement photo oxydée ou non et présentant différentes bio réactivités. Dans un premier temps, nous avons étudié l’impact d’ajout de MOD labile provenant de méduses sur l’activité et la diversité bactériennes d’une communauté d’une lagune côtière méditerranéenne. Nous avons observé que la résilience des communautés bactériennes suite à cet ajout était plus importante pour les fonctions métaboliques que pour la diversité. Ceci suggère que les efflorescences de méduses peuvent entrainer des changements durables de la structure des communautés bactériennes en environnement côtier. Dans un deuxième temps, nous nous sommes intéressés à la possibilité d’un priming effect (accélération de la dégradation bactérienne de la MOD réfractaire en présence de MOD labile) en milieu côtier. Des expériences d’ajout simple ou combiné de MOD labile et récalcitrante ont été réalisées sur des communautés bactériennes de Mer Méditerranée et d’un fjord de Patagonie chilienne. Dans les deux cas, nous avons observé des changements plus importants de la composition communautaire bactérienne suite à un ajout combiné. Cependant, nous n’avons pas observé une plus forte consommation de MOD récalcitrante suite à l’ajout de composés labiles, ce qui suggère que le priming effect n’a pas eu lieu au cours de nos expériences. Enfin, nous avons étudié l’impact de la photodégradation de différentes sources de MOD (i.e. MOD récalcitrante de rivière, MOD labile provenant de phytoplancton) sur l’activité et la diversité de communautés bactériennes côtières. Nous avons observé que la photodégradation de la MOD issue d’une culture de phytoplancton entrainait à la fois une croissance bactérienne plus faible et une modification de la diversité bactérienne en faveur des Alphaprotéobactéries.Heterotrophic bacterial communities in marine environment are exposed to a heterogeneous mixture of dissolved organic compounds with different bioavailability that may control both their activities and their composition. In the frame of this thesis, we studied the response of different coastal bacterial communities to the single or combined addition of various natural dissolved organic matter (DOM) photo-oxidized or not, presenting different bioavailability characteristics. Firstly, we studied the effects of the addition of highly bioreactive DOM derived from jellyfish on bacterial activities and community structure in a Mediterranean coastal lagoon. We observed that resilience of the bacterial community after the addition of DOM from the jellyfish was higher for metabolic functions than diversity, suggesting that jellyfish blooms can induce durable changes in the bacterial community structure in coastal lagoons. Secondly, we investigated the occurrence of priming effect (increase in microbial degradation of refractory DOM upon the addition of labile DOM) on coastal marine environments. Experiments with single or combined additions of recalcitrant and labile DOM sources were performed with a Mediterranean and a Patagonian fjord bacterial communities. In both cases we observed a greater effect of combined addition on bacterial community composition. However we did not observe an increase in recalcitrant DOM degradation of recalcitrant DOM following the addition of labile compounds, suggesting that priming effect did not occur during our experiments. Finally, we studied the impact of contrasted DOM (i.e. recalcitrant riverine DOM, labile phytoplankton-derived DOM) photodegradation on coastal bacterial communities activity and composition. We observed that photodegradation of phytoplankton-derived DOM led to a lower bacterial growth and changes in bacterial community diversity, in favour of Alphaproteobacteria

Bile Acid Derivatives: From Old Molecules to a New Potent Therapeutic Use: An Overview

Bile acids or bile salts, belong to a large family of biological steroid derivatives found predominantly in the bile of mammals and other vertebrates. These amphipathic molecules possess numerous functions, including eliminating cholesterol from the body, driving the flow of bile to eliminate catabolites, emulsifying fat-soluble vitamins to enable their absorption, aiding in motility and in reducing the bacteria flora found in the small intestine and biliary tract. In this review, we investigate progress towards synthetic bile acid derivatives, with special emphasis on how they might be used for various biological applications and the challenges that remain in developing these compounds as potent drugs of the future especially in the field of microbiology (antimicrobial activities) and cancer (anticancer agents). We will emphasize the fact that even few researches are devoted around these peculiar structures. All the researches pointed out the important potential of such derivatives for the design of new classes of drugs

Photoreactivity of riverine and phytoplanktonic dissolved organic matter and its effects on the dynamics of a bacterial community from the coastal Mediterranean Sea

International audienceHigh solar radiation levels measured in the Mediterranean basin can result in photo-oxidation of dissolved organic matter (DOM) at the sea surface. The objective of the present study was to determine the effects of solar radiation on two contrasting sources of DOM (diatom-derived DOM and riverine DOM) and to evaluate its effect on the growth and the composition of a bacterial community from the Mediterranean Sea. DOM was sequentially exposed to artificial solar radiation or kept in the dark and then added to microcosms containing coastal seawater. For both sources of DOM, light exposure induced photo-alterations by decreasing absorbance and fluorescence of colored dissolved organic matter. However, resulting effects on bacteria were contrasted. Photo-alteration of phytoplankton-derived DOM resulted in a lower bacterial growth during the three first days, without modifying the total dissolved organic carbon consumption. Moreover, after 3 days of incubation, the bacterial diversity as determined by 16S rRNA gene pyrosequencing, revealed that DOM phototransformation led to a higher relative abundance of Alphaproteobacteria and a lower relative abundance of Gammaproteobacteria. A limited number of operational taxonomic units (OTUs) (n=44) explained 80% of the diversity changes between dark and the light treatments, with an equal number of positively and negatively affected OTUs. In contrast, the photobleaching measured on riverine DOM after sunlight exposure had no effect on both bacterial carbon cycling and composition during a 7-days biodegradation experiment. Our results demonstrate that the effects of solar radiation on DOM greatly differ according to the initial composition of DOM and that changes in bacterial composition, when occurred, showed diverse responses inside a same class of bacteria, underlying the necessity to use a sufficiently resolutive approach to describe them. A better understanding of the interactive effects of the biological degradation and the photoinduced degradation of DOM are required in the context of the global change affecting Mediterranean Sea

Changes in bacterial community metabolism and composition during the degradation of dissolved organic matter from the jellyfish Aurelia aurita in a Mediterranean coastal lagoon

Blanchet, Marine ... et. al.-- Special issue Microbial Ecology of the Continental and Coastal Environments.-- 16 pages, 8 figures, 2 tables, electronic supplementary material http://dx.doi.org/10.1007/s11356-014-3848-xSpatial increases and temporal shifts in outbreaks of gelatinous plankton have been observed over the past several decades in many estuarine and coastal ecosystems. The effects of these blooms on marine ecosystem functioning and particularly on the dynamics of the heterotrophic bacteria are still unclear. The response of the bacterial community from a Mediterranean coastal lagoon to the addition of dissolved organic matter (DOM) from the jellyfish Aurelia aurita, corresponding to an enrichment of dissolved organic carbon (DOC) by 1.4, was assessed for 22 days in microcosms (8 l). The high bioavailability of this material led to (i) a rapid mineralization of the DOC and dissolved organic nitrogen from the jellyfish and (ii) the accumulation of high concentrations of ammonium and orthophosphate in the water column. DOM from jellyfish greatly stimulated heterotrophic prokaryotic production and respiration rates during the first 2 days; then, these activities showed a continuous decay until reaching those measured in the control microcosms (lagoon water only) at the end of the experiment. Bacterial growth efficiency remained below 20 %, indicating that most of the DOM was respired and a minor part was channeled to biomass production. Changes in bacterial diversity were assessed by tag pyrosequencing of partial bacterial 16S rRNA genes, DNA fingerprints, and a cultivation approach. While bacterial diversity in control microcosms showed little changes during the experiment, the addition of DOM from the jellyfish induced a rapid growth of Pseudoalteromonas and Vibrio species that were isolated. After 9 days, the bacterial community was dominated by Bacteroidetes, which appeared more adapted to metabolize high-molecular-weight DOM. At the end of the experiment, the bacterial community shifted toward a higher proportion of Alphaproteobacteria. Resilience of the bacterial community after the addition of DOM from the jellyfish was higher for metabolic functions than diversity, suggesting that jellyfish blooms can induce durable changes in the bacterial community structure in coastal lagoons. © 2014, Springer-Verlag Berlin HeidelbergThis study was supported by the CNRS-EC2CO program through the GELPROC project (2010–2012): “Interactions between gelatinous plankton and dynamics of prokaryotic communities.”Peer Reviewe

Polyamine derivatives: a revival of an old neglected scaffold to fight resistant Gram-negative bacteria?

International audienceEmergence of multidrug resistant pathogens was responsible for microbial infections and inefficacy of numerous antimicrobial therapies has induced a need for the research of new classes of antibiotics. In this review, we will focus our interest towards the biological properties of polyamino antimicrobial agents