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Besides the lethal effect of viruses on the microbial community (typically the bacteria and the phytoplankton), the viral activity can affect significantly not only the structure of this community but also the cycling of carbon and other nutrients within aquatic ecosystems. Due to their activities, viruses could maintain the prokaryotic community diversity by lysing the most dominant populations then allowing the development of the minor groups. Also, viruses constitute the major driver of horizontal gene transfer between bacterial species or genus and therefore they could be the principal actor in the diversification of microbial communities. The viral lysis which induces the transformation of the biomass into dissolved organic matter pool could stimulate the microbial respiration and reduce the transfer of carbon to higher trophic levels as well as the sedimentation of organic particles towards the bottom. At last, aquatic viruses may generate an important interest for applied issues, typically the phagotherapy for aquaculture, even if an important effort remains to be done in the comprehension of the real efficiency of this therapy and the possible underlying resistance phenomena.

The invasive bloody red mysid, Hemimysis anomala, has recently colonised peri-alpine lakes in Western Europe. During the last decade, scuba divers have regularly reported observations of substantial winter swarms of this animal in Lakes Bourget (France) and Geneva (Switzerland-France). During the last four years, we have regularly dived and observed such phenomena in a variety of habitats, revealing thousands to millions of individuals during the period between December and March, with maximal densities occurring in the water column and small open wrecks in January or February. Surprisingly, however, no swarm was observed during the winters of 2022–2023. This led to the hypothesis that temperature could be the main direct or indirect factor responsible for this lower abundance, resulting in the absence of significant gatherings. Some possible explanations are discussed.

Mating is rarely random in nature, but the effects of mate selection on offspring performance are still poorly understood, even in well-established models such as salmonid fish. We sampled wild lake char (Salvelinus umbla) and used their gametes to investigate the genetic consequences of different mating scenarios. In a first study, we used full-factorial breeding to experimentally separate additive genetic from maternal environmental effects. This led to 60 families and in total 1,073 embryos that were raised singly after sublethal exposures to the pathogen Aeromonas salmonicida, the common pollutant ethinylestradiol, or water only. Contrary to predictions of ‘good genes’ sexual selection, offspring of more yellow males were less tolerant to the pathogen than offspring of pale males, while male coloration did not predict offspring tolerance to ethinylestradiol. However, increased kinship between the parents had strong negative effects on embryo development in all treatment groups. In a second experiment, we monitored 1,464 singly-raised embryos that resulted from 70 pair-wise sperm competition trials. These embryos were raised in an environment that supports the growth of symbiotic microbes (sublethal stress) or in a clean environment. Offspring of yellow males were again less stress tolerant than those of pale males, and embryo development was again slowed down with increasing genetic similarity between the parents. We conclude that genetic benefits of mate selection would be strongest if females avoided genetic similarity during mate selection, for example based on MHC-linked signals, while male breeding colors seem more relevant in intra-sexual selection.

International audience; Almost sixty years ago, Bdellovibrio and like organisms (BALOs) were discovered as the first obligate bacterial predators of other bacteria known to science. Since then, they were shown to be diverse and ubiquitous in the environment, and to bear astonishing ecological, physiological, and metabolic capabilities. The last decade has seen important strides made in understanding the mechanistic basis of their life cycle, the dynamics of their interactions with prey, along with significant developments towards their use in medicine, agriculture, and industry. This review details these achievements, identify current understanding and knowledge gaps to encourage and guide future BALO research.

Lake Cadagno, a permanently stratified high-alpine lake with a persistent microbial bloom in its anoxic chemocline, has long been considered a model for the low-oxygen, high-sulfide Proterozoic ocean where early microbial life gave rise to Earth’s oxygenated atmosphere. Although the lake has been studied for over 25 years, the absence of concerted study of the bacteria, phytoplankton, and viruses, together with primary and secondary production, has hindered a comprehensive understanding of its microbial food web. Here, the identities, abundances, and productivity of microbes were evaluated in the context of Lake Cadagno biogeochemistry. Photo-synthetic pigments and chloroplast 16S rRNA gene phylogenies suggested high abundances of eukaryotic phytoplankton, primarilyChlorophyta, through the water column. Of these, a close relative ofAnkyra judayi, a high-alpine adapted chlorophyte, peaked with oxygen in the mixolimnion, whileClosteriopsis-related chlorophytes peaked in the chemocline and monimolimnion. Anoxygenic phototrophic sulfur bacteria, Chromatium, dominated the chemocline along withLentimicrobium, a newly observed genus of known fermenters. Secondary production peaked in the chemocline, suggesting anoxygenic primary producers depended on heterotrophic nutrient remineralization. Virus-to-microbe ratios spanned an order of magnitude, peaking with high phytoplankton abundances and at a minimum at the peak of Chromatium, dynamic trends that suggest viruses may play a role in the modulation of oxygenic and anoxygenic photo- and chemosynthesis in Lake Cadagno. Through the combined analysis of bacterial, eukaryotic, viral, and biogeochemical dynamics of Lake Cadagno, this study provides a new perspective on the biological and geochemical connections that comprised the food webs of the Proterozoic ocean.IMPORTANCEAs a window to the past, the study offers insights into the role of microbial guilds of Proterozoic ocean chemoclines in the production and recycling of organic matter of sulfur- and ammonia-containing ancient oceans. The new observations described here suggest that eukaryotic algae were persistent in the low oxygen upper-chemocline in association with purple and green sulfur bacteria in the lower half of the chemocline. Further, this study provides the first insights into Lake Cadagno viral ecology. High viral abundances suggested viruses may be essential components of the chemocline where their activity may result in the release and recycling of organic matter. The framework developed in this study through the integration of diverse geochemical and biological data types lays the foundation for future studies to quantitatively resolve the processes performed by discrete populations comprising the microbial loop in this early anoxic ocean analogue.

Meromictic Lake Cadagno, an ancient ocean analogue, is known for its permanent stratification and persistent anoxygenic microbial bloom within the chemocline. Although the anaerobic microbial ecology of the lake has been extensively studied for at least 25 years, a comprehensive picture of the microbial food web linking the bacterial layer to phytoplankton and viruses, with explicit measures of primary and secondary production, is still missing. This study sought to understand better the abundances and productivity of microbes in the context of nutrient biogeochemical cycling across the stratified zones of Lake Cadagno. Photosynthetic pigments and chloroplast 16S rRNA gene phylogenies suggested the presence of eukaryotic phytoplankton through the water column. Evidence supported high abundances of Ankyra judayi, a high-alpine adapted chlorophyte, in the oxic mixolimnion where oxygenic-primary production peaked. Through the low- and no-oxygen chemocline and monimolimnion, chlorophytes related to Closteriopsis acicularis, a known genus of meromictic lakes, and Parachlorella kessleri were observed. Chromatium, anoxygenic phototrophic sulfur bacteria, dominated the chemocline along with Lentimicrobium, a genus of known fermenters whose abundance was newly reported in Lake Cadagno. Secondary production peaked in the chemocline suggesting primary producers depend on heterotrophs for nutrient remineralization. As previously observed, sulfur-reducing bacteria (SRBs), especially Desulfocapsa and Desulfobulbus, were present in the chemocline and anoxic monimolimnion. Virus-to-microbe ratios (VMR) peaked in the zone of phytoplankton yet were at a minimum at the peak of Chromatium. These dynamic trends suggest viruses may play a role in the modulation of oxygenic and anoxygenic photo- and chemosynthesis in Lake Cadagno and other permanently stratified systems.ImportanceAs a window to the past, the study offers insights into the role of microbial guilds of Proterozoic ocean chemoclines in the production and recycling of organic matter of sulfur- and ammonia-containing ancient oceans. The new observations described here suggest that eukaryotic algae were persistent in the low oxygen upper-chemocline in association with purple and green sulfur bacteria in the lower half of the chemocline. Further, this study provides the first insights into Lake Cadagno viral ecology. High viral abundances suggested viruses may be essential components of the chemocline where their activity may result in the release and recycling of organic matter. The framework developed in this study through the integration of diverse geochemical and biological data types lays the foundation for future studies to quantitatively resolve the processes performed by discrete populations comprising the microbial loop in this early anoxic ocean analogue.

International audience; This dataset complement a previously published dataset [1] and corresponds to the physico-chemical parameters data series produced during the MESOLAC experimental project [2]. The presented dataset is composed of: 1. In situ profiles (0–3m) of temperature, conductivity, pH, dissolved oxygen (concentration and saturation). 2. In situ measurements of light spectral UV/VIS/IR irradiance (300–950 nm wavelength range) taken at 0, 0.25, 0.5, 1, 1.5, 2 and 2.5m. 3. Laboratory chemical analysis of samples collected at 0 and 2 m (conductivity, pH, total alkalinity, NH4, NO2, NO3, total and particulate nitrogen (Ntot, Npart), PO4, total and particulate phosphorus (Ptot, Ppart), total, organic particulate and total particulate carbon (Ctot, Cpart-org, Cpart-tot), Cl, SO4, SiO2. 4. Laboratory analysis of pigments extracted from samples collected at 0 and 2 m (Chla, Chlc, carotenoids, phaeopigments).The experimental design is the same as in Tran-Khac et al [1]. Briefly, it consisted of nine pelagic mesocosms (about 3000 L, 3m depth) deployed in July 2019 in Lake Geneva near the shore of Thonon les Bains (France) aiming to simulate predicted climate scenarios (i.e. extreme events) and assess the response of planktonic communities, ecosystem functioning and resilience.During the experiment, physical parameters were measured twice a week. At the same time, samples were collected at 0 and 2m of depth for subsequent chemical laboratory analyses. These data are presented in the dataset file, ordered by sampling event (numbered from S1 to S8), treatment (Control-C, High-H and Medium-M) and replicates (1 to 3). For each sampling point the measured parameters are listed in columns, missing data and values below the detection limit are marked as NA (not available).This data set aims to contribute to the understanding of the effect of environmental forcing on lake physico-chemical characteristics (such as temperature, oxygen and nutrient concentration) under simulated intense weather events. To a broader extent, the presented data can be used for a wide variety of applications, including monitoring of a large peri-alpine lake functioning under environmental stress and being included in further meta-analysis to generalise the effect of climate change on large lakes. The two complementary dataset differ in the acquired data and methods, temporal and spatial resolution. They complete each other in terms of physico-chemical characterization of the experimental treatments and together can allow comparison of the two different monitoring strategies (continuous vs punctual) during in situ experimental manipulations.

Supplemental Material for the Note "N3AF 2019 7(2), 1-25"

This review describes a unique functional bacterial group referred to as Bdellovibrio and like organisms (BALOs). These gram-negative bacteria are obligate predators of other bacteria, with, on one hand, different predation strategies, a remarkable predation spectrum to cope with any type of competitiveness, as well as a competent life cycle ensuring efficient multiplication. On the other hand, this group could fulfil a similar ecological role as bacteriophages concerning the control of bacterial populations. As potentially important natural bio agents, they are more and more considered as alternatives to antibiotics and are investigated for potential uses in medicine and biotechnologies. However, before relying on them to help and heal us, their role in complex and uncontrolled in vivo systems needs to be experimentally assessed, unlike classic broth medium in the laboratory. This review uncovers what lies behind this group and explores their place in natural systems as well as their applications to improve human and animal wellbeing against pathogens increasingly resistant to antibiotics.

Blooms of Planktothrix rubescens have been recorded for 15 years in Lake Bourget (France), from 1995 to 2009. Then, the presence of this filamentous and toxic cyanobacterium became anecdotic between 2010 and 2015 and it was clearly thought that such a proliferation was over. However, against all odds, blooms occurred again in 2016 and 2017 despite apparent very low phosphorus concentrations in surface waters of the lake. Aims of this study were thus to explain the reasons of this come back in order to propose scenarios likely to be helpful to stakeholders who need to know if such proliferations may occur again in the future. We show that phosphorus input, both from the main tributaries to the lake and possibly from the sediments, were likely the triggers of the new development of the cyanobacterium since a minimum autumn/winter inoculum of P. rubescens was detected the year before. Then, the bloom, that was observed deeper than previous years, was associated to a conjunction of factors already well-known to favour the development of this very competitive species (i.e. mild winter temperature, water column stability, available light at depth, surface water transparency, low predation, etc…). Although many factors and processes could account for the occurrence and bloom of the cyanobacterium, not observed, measured or taken into account here, a plausible scenario could be proposed and may be useful to deciders. One thing remains unclear: where do the cyanobacterium hides when it is not observed during the routine monitoring survey and thus from which place it could initiate its development (nearshore, in the pelagic zone, from the sediment?), unless it is simply not sampled and observed due to methodological bias.

International audience; Understanding temporal and spatial microbial community abundance and diversity variations is necessary to assess the functional roles played by microbial actors in the environment. In this study, we investigated spatial variability and temporal dynamics of two functional microbial sediment communities, methanogenic Archaea and methanotrophic bacteria, in Lake Bourget, France. Microbial communities were studied from 3 sites sampled 4 times over a year, with one core sampled at each site and date, and 5 sediment layers per core were considered. Microbial abundance in the sediment were determined using flow cytometry. Methanogens and methanotrophs community structures, diversity, and abundance were assessed using T-RFLP, sequencing, and real-time PCR targeting mcrA and pmoA genes, respectively. Changes both in structure and abundance were detected mainly at the water-sediment interface in relation to the lake seasonal oxygenation dynamics. Methanogen diversity was dominated by Methanomicrobiales (mainly Methanoregula) members, followed by Methanosarcinales and Methanobacteriales. For methanotrophs, diversity was dominated by Methylobacter in the deeper area and by Methylococcus in the shallow area. Organic matter appeared to be the main environmental parameter controlling methanogens, while oxygen availability influenced both the structure and abundance of the methanotrophic community.

Organic ligands such as exopolymeric substances (EPS) are known to form complexes with iron (Fe) and modulate phytoplankton growth. However, the effect of organic ligands on bacterial and viral communities remains largely unknown. Here, we assessed how Fe associated with organic ligands influences phytoplankton, microbial, and viral abundances and their diversity in the Southern Ocean. While the particulate organic carbon (POC) was modulated by Fe chemistry and bioavailability in the Drake Passage, the abundance and diversity of microbes and viruses were not governed by Fe bioavailability. Only following amendments with bacterial EPS did bacterial abundances increase, while phenotypic alpha diversity of bacterial and viral communities decreased. The latter was accompanied by significantly enhanced POC, pointing toward the relief of C limitation or other drivers of the microbial loop. Based on the literature and our findings, we propose a conceptual framework by which EPS may affect phytoplankton, bacteria, and viruses. Given the importance of the Southern Ocean for Earth&rsquo, s climate as well as the prevalence of viruses and their increasingly recognized impact on marine biogeochemistry and C cycling, the role of microbe&ndash, virus interactions on primary productivity in the Southern Ocean needs urgent attention.

Les tortues marines sont partout présentes dans la ceinture tropicale et subtropicale. Au-delà de leur grâce et du plaisir qu'elles procurent aux plongeurs qui ont la chance de les croiser, elles jouent des rôles écolo-giques majeurs : maintien et entretien des prairies ou herbiers sous-marins, participation à la (bonne) santé des récifs coralliens, prédation des méduses (régulation des populations), etc. Ces reptiles marins constituent également un fantastique bio-indicateur de l'état de santé des écosystèmes. Dès lors, étudier leur biologie et leur écologie revêt un enjeu d'importance pour mieux comprendre leur éthologie (comportement), et ce, d'autant plus, que les différentes populations de tortues ont régressé dramatiquement au cours des dernières décennies. Parmi les fautifs, évidemment ai-je envie de dire, l'Homme qui détruit leur environnement, sur-pêche, pollue… mais aussi le changement climatique qui vient en rajouter une couche en modifiant signifi-cativement l'environnement ! Aujourd'hui, le constat est sans appel : six des sept espèces de tortues marines sont classées par l'IUCN (Union internationale pour la conservation de la nature) comme étant menacées ou en danger d'extinction ! Le comportement des tortues marines a déjà été beaucoup étudié en termes de migration, alimentation et patterns (stratégie, manière, type) de reproduction, notamment pour aider à mieux les protéger et pour la mise en place des différentes mesures de conservation. Parmi les outils qui ont été utilisés dans ce but, on peut citer la surveillance visuelle des plages, le comptage des oeufs, le suivi dans l'eau par « snorkeling » ou PMT, la télémétrie (notamment satellitaire). LA CARAPACE DES TORTUES MARINES : SOURCE PRÉCIEUSE D'INFORMATIONS > Il y a deux ans une étude scientifique s'intéressant aux comportements et déplacements des tortues marines a été publiée. Dans des travaux inédits, Sinziana Rivera (1) et ses collègues se penchaient sur la complémentarité de deux méthodes, classique (la microscopie) et récente (la biologie moléculaire), pour identifier les microalgues présentes sur la carapace des tortues. À l'époque, je n'y avais pas prêté attention, mea culpa, mais cette analyse particulièrement originale restant d'actualité, je vous en propose une synthèse ci-après. Par Stéphan Jacquet. Photos Olivier Clot-Faybesse et Vincent Maran. S. JACQUET n MIEUX APPRÉHENDER LES DÉPLACEMENTS DES TORTUES GRÂCE AUX DIATOMÉES Plus original est le suivi qui peut être fait en étudiant la microflore présente sur la carapace de ces animaux. Certains micro-organismes ont la capacité de s'agré-ger et de constituer ce que l'on appelle des biofilms. Il s'agit d'une sorte de tapis, adhésif et protecteur, de taille variable constitué par une communauté plus ou moins complexe de plusieurs cellules, adhérant entre elles et à une surface (naturelle ou artificielle). Les dia-tomées sont, parmi les microalgues, les championnes du monde de la formation de biofilms sur tout type de support et dans tout type de milieu. La carapace des tortues ne leur a donc pas échappé tout comme aux chercheurs qui ont pu constater que ces diato-mées colonisent effectivement volontiers les écailles kératineuses de ces reptiles, y sont nombreuses et I N F O S R E C H E R C H E La composition des microalgues ou diatomées colonisant la carapace des tortues est riche d'enseignements sur leur mode de vie. © O. C.-F. Les tortues participent au maintien et à l'entretien des prairies et des herbiers sous-marins. © O. C.-F. Cocconeis sp. au microscope électronique (taille : 12 microns environ) sur un monocristal de sel. © Frédéric Bolze/Jacques Faerber Une tortue verte (Chelonia mydas) à la carapace bien recouverte de diatomées, en séance de nettoyage. © V. M. Comparaison du niveau d'identification (en pourcentages) atteint avec la microscopie (haut) et le métabarcoding (bas) des diatomées présentes dans les biofilms récoltés sur les carapaces de tortues. À noter que la classification d'un organisme s'écrit, du plus général au plus spécifique, ainsi : classe, ordre, famille, genre, espèce. Licmophora sp flabellata. © Hervé Limouzin LES TORTUES MARINES Il existe un peu plus de 300 espèces de tortues sur notre planète. Environ 250 vivent en eau douce, milieux humides et palustres, 60 sont exclu-sivement terrestres et seulement sept sont marines. Il s'agit de la tortue luth, la tortue caouanne, la tortue imbriquée, la tortue verte, la tortue à dos plat, la tortue olivâtre et la tortue de Kemp. Les six dernières appartiennent à la famille des cheloniidés et ont une carapace sans carène couverte d'écailles et une ou deux griffes sur les nageoires. Seule la tortue luth fait partie de la famille des dermochélyidées, caractérisée par l'absence de corne et d'écailles sur sa carapace. La tortue verte dont il est question dans cet article, Chelonia mydas, est la plus grande des cheloniidés (80 à 130 cm), pèse entre 160 et 250 kg et elle est végétarienne à l'état adulte (se nourrissant essentiellement de plantes marines qui donnent à sa chair la couleur verte imputable à son régime alimentaire).

International audience; This dataset corresponds to a data series produced from automated data loggers during the MESOLAC experimental project. Nine pelagic mesocosms (about 3000 L, 3 m depth) were deployed in July 2019 in Lake Geneva near the shore of Thonon les Bains (France), simulating predicted climate scenarios (i.e. intense weather events) by applying a combination of forcing. The design consisted of three treatments each replicated three times: a control treatment (named C - no treatment applied) and two different treatments simulating different intensities of weather events. The high intensity treatment (named H) aimed to reproduce short and intense weather events such as violent storms. It consisted of a short-term stress applied during the first week, with high pulse of dissolved organic carbon (5x increased concentration, i.e. total DOC similar to 6 mg L-1), transmitted light reduced to 15% and water column manual mixing. The medium intensity treatment (named M) simulated less intense and more prolonged exposures such as during flood events. It was maintained during the 4 weeks of the experiment and consisted of 1.5x increased concentration of dissolved organic carbon (i.e. total DOC similar to 2 mg L-1), 70% transmitted light and water column manual mixing. Automated data loggers were placed for the entire period of the experiment in the mesocosms and in the lake for comparison with natural conditions. Temperature, conductivity, dissolved oxygen and CO2 were monitored every 15 min at different depths (0.15, 0.25, 1 and 2 m). This data set aims to contribute our understanding of the effect of environmental forcing on lake ecosystem processes (such as production, respiration and CO2 exchange) under simulated intense weather events and the ability of the planktonic community to recover after perturbation. To a broader extent, the presented data can be used for a wide variety of applications, including monitoring of lake community functioning during a period of high productivity on a large peri-alpine lake and being included in further meta-analysis aiming at generalising the effect of climate change on large lakes.

International audience; When considering microbial biotic interactions, viruses as well as eukaryotic grazers are known to be important components of aquatic microbial food webs. It might be the same for bacterivorous bacteria but these groups have been comparatively less studied. This is typically the case of the Bdellovibrio and like organisms (BALOs), which are obligate bacterial predators of other bacteria. Recently, the abundance and distribution of three families of this functional group were investigated in perialpine lakes, revealing their presence and quantitative importance. Here, a more in-depth analysis is provided for Lake Geneva regarding the diversity of these bacterial predators at different seasons, sites and depths. We reveal a seasonal and spatial (vertical) pattern for BALOs. They were also found to be relatively diverse (especially Bdellovibrionaceae) and assigned to both known and unknown phylogenetic clusters. At last we found that most BALOs were positively correlated to other bacterial groups, mainly Gram-negative, in particular Myxococcales (among which many are predators of other microbes). This study is the first shedding light on this potentially important bacterial killing group in a large and deep lake.

A u beau milieu du Léman, le plus grand lac naturel pro-fond d'Europe occidentale, l'attaque a été foudroyante. Peu de chance d'en réchap-per ! La victime est une bac-térie aquatique, Limnohabitans planktonicus, dont la taille ne dépasse pas deux micromètres. Sa prédatrice… est aussi une bactérie, plus petite. Du genre Peredibacter, elle se délecte de ses semblables. La proie, qui se nourrissait de matière organique dissoute libérée par le phy-toplancton alentour, n'a rien senti venir. Force est de constater que la loi de la jungle s'applique aussi au monde microbien. Les bactéries aquatiques jouent un rôle fonctionnel clé au sein des écosystèmes, ce qui n'empêche pas qu'elles soient les proies de prédateurs ou de parasites très efficaces. Outre les bactériophages ou phages-des virus man-geurs de bactéries-, qui se sont révélés, au cours des trois dernières décennies, un facteur majeur de régulation de l'abondance des bac-téries dans les milieux aquatiques et de leur diversité, d'autres prédateurs, comme les Dans les profondeurs des grands lacs de montagne et ailleurs, des bactéries se nourrissent de leurs semblables avec une efficacité redoutable. Nommées Balo, ces bactéries prédatrices offrent une alternative prometteuse aux antibiotiques. Ces bactéries qui en dévorent d'autres organismes unicellulaires flagellés, les ciliés ou certains métazoaires appartenant au zooplanc-ton (ou plancton animal), sont bien connus des biologistes. Les bactéries qui se nour-rissent de leurs consoeurs le sont moins, mais depuis peu, on s'accorde à y voir un groupe qui compte aussi dans le contrôle des populations bactériennes. Certaines sont regroupées dans un groupe fonctionnel, les Bdellovibrio et orga-nismes apparentés ou Balo (pour Bdellovibrio and like organisms). Depuis quelques années, grâce aux nouvelles techniques de séquençage et de manipulation génétique, de bio-informatique et de microsco-pie, on commence à mieux connaître ces bacté-ries et leur impact écologique. Au point d'en faire de sérieux candidats dans la lutte antibac-térienne en aquaculture, mais aussi en agriculture et en médecine.

The vertical distribution of chlorophyll in stratified lakes and reservoirs frequently exhibits a maximum peak deep in the water column, referred to as the deep chlorophyll maximum (DCM). DCMs are ecologically important hot spots of primary production and nutrient cycling, and their location can determine vertical habitat gradients for primary consumers. Consequently, the drivers of DCM structure regulate many characteristics of aquatic food webs and biogeochemistry. Previous studies have identified light and thermal stratification as important drivers of summer DCM depth, but their relative importance across a broad range of lakes is not well resolved. We analyzed profiles of chlorophyll fluorescence, temperature, and light during summer stratification from 100 lakes in the Global Lake Ecological Observatory Network (GLEON) and quantified two characteristics of DCM structure: depth and thickness. While DCMs do form in oligotrophic lakes, we found that they can also form in eutrophic to dystrophic lakes. Using a random forest algorithm, we assessed the relative importance of variables associated with light attenuation vs. thermal stratification for predicting DCM structure in lakes that spanned broad gradients of morphometry and transparency. Our analyses revealed that light attenuation was a more important predictor of DCM depth than thermal stratification and that DCMs deepen with increasing lake clarity. DCM thickness was best predicted by lake size with larger lakes having thicker DCMs. Additionally, our analysis demonstrates that the relative importance of light and thermal stratification on DCM structure is not uniform across a diversity of lake types.

Obligate predatory bacteria, i.e. bacteria requiring a Gram negative prey cell in order to complete their cell cycle, belong to the polyphyletic group referred to as the Bdellovibrio And Like Organisms (BALO). Predatory interactions between bacteria are complex, yet their dynamics and impact on bacterial communities in the environment are becoming better understood. BALO have unique life cycles: they grow epibiotically with the predator remaining attached to the prey's envelope, dividing in a binary manner or periplasmically, i.e. by penetrating the prey's periplasm to generate a number of progeny cells. The periplasmic life cycle includes unique gene and protein patterns and unique signaling features. These ecological and cellular features, along with applications of the BALO in the medical, agricultural and environmental fields are surveyed.

International audience; The French National Committee for Scientific Diving (CNPS) is an inter-agency committee on scientific diving activities. French marine universities, research institutes (CNRS-INEE/INSU/INSHS, DRASSM, EPHE, IFREMER, INRA, INSERM, IPEV, IRD, IRSTEA) and the National Museum (MNHN) are involved or represented. The CNPS, created in 1999, is the scientific diving representative of the Ministry of Higher Education and Research to the Ministry of Labor. It includes personalities chosen for their expertise in the field of professional use of diving (scientific and technical diving, training), the law of the sea, the hyperbaric medicine and the European scientific diving panel (ESDP). The aims of this group of experts are: a) to observe the evolution of the professional scientific diving practices worldwide, b) to define common frameworks and promote the best practices, c) to provide high-level expertise and advices to Ministries of Labor and Research, d) to monitor the innovations in scientific diving, technology, field practices and hyperbaric medicine, e) to share informations and feedback with the French scientific divers community, f) to participate in the training of scientific divers, and g) to represent France at the ESDP. The CNPS has been fully involved since 2009 in the formulation of new laws and regulations dedicated to professional diving with the Ministry of Labor. The French scientific diving community is very diversified, for historical reasons, due to its 18 000 km long coastline and a strong presence overseas, through the involvement of researchers in global science issues and international collaborations. This poster presents the aims, activities and key results obtained by the CNPS. It also sets out some perspectives, especially actions in favour of a convergence of European practice patterns and standards.