[show abstract][hide abstract] ABSTRACT: Faecal indicator bacteria (thermotolerant coliform and faecal streptococci) were enumerated in a Mediterranean coastal river to
evaluate bacterial contamination levels in relation to hydrological conditions, to estimate delivery of bacterial loads to transitional and
coastal waters (Thau lagoon) and to identify bacterial sources of pollution and their contribution to the bacterial flow. Results showed
that (1) in low flow conditions,mean bacterial concentrations were higher than EU guidelines for bathing waters; (2) floods had higher
concentrations of indicator bacteria than low flows; (3) low flow conditions represented a negligible proportion of bacterial loads
compared with high flow and flood periods; (4) during medium and low flow conditions, bacteria were stored in riverbed fine
sediments forming in-stream stores that may be flushed during floods; (5) the first flush effect was highlighted during an early autumn
flood as was the role of in-stream stores during the course of the flood; and (6) point sources that continuously feed the river are
contributing to the pool of bacteria accumulated in the riverbed sediment.
[show abstract][hide abstract] ABSTRACT: In marine invertebrates that acquire their symbionts from the environment, these are generally only taken up during early developmental stages. In the symbiosis between lucinid clams and their intracellular sulfur-oxidizing bacteria, it has been shown that the juveniles acquire their symbionts from an environmental stock of free-living symbiont forms, but it is not known if adult clams are still competent to take up symbiotic bacteria from the environment. In this study, we investigated symbiont acquisition in adult specimens of the lucinid clam Codakia orbiculata, using transmission electron microscopy, fluorescence in situ hybridization, immunohistochemistry and PCR. We show here that adults that had no detectable symbionts after starvation in aquaria for 6 months, rapidly reacquired symbionts within days after being returned to their natural environments in the field. Control specimens that were starved and then exposed to seawater aquaria with sulfide did not reacquire symbionts. This indicates that the reacquisition of symbionts in the starved clams returned to the field was not caused by high division rates of a small pool of remaining symbionts that we were not able to detect with the methods used here. Immunohistochemistry with an antibody against actin, a protein involved in the phagocytosis of intracellular bacteria, showed that actin was expressed at the apical ends of the gill cells that took up symbionts, providing further evidence that the symbionts were acquired from the environment. Interestingly, actin expression was also observed in symbiont-containing cells of untreated lucinids freshly collected from the environment, indicating that symbiont acquisition from the environment occurs continuously in these clams throughout their lifetime.
[show abstract][hide abstract] ABSTRACT: In intermittent rivers, characterised by a specific hydrological behaviour, sedimentâ€“water column interactions may influence water quality during low flows. The main objective of this work was to assess the extent of anthropogenic pollution (organotins, faecal indicator bacteria and nutrients) in the river sediment of an intermittent river and its impact on the downstream water bodies: The VÃ¨ne River, main tributary of the Thau lagoon. We first investigated anthropogenic pollution from water and sediment samples collected in situ along the river course (1.5 km); then, during laboratory experiments, we assessed the survival of faecal bacteria and quantified the degradation rates of organotins on the same sediments. The results indicate the presence of anthropogenic pollution all along the study reach. The waste water treatment plant effluent is a direct pollution input source for anthropogenic pollution. The sediment data points to an urban drainage ditch as a secondary point pollution source while the organotins data highlights the presence of other diffuse sources, specific to this substance. The results of the laboratory experiments show that both faecal bacteria and organotins may persist in the river sediments for up to two months in summer and even longer in winter. This indicates that sediments may, under favourable conditions, become important pollutant stores which may later be released and transported to the Thau lagoon during floods.
[show abstract][hide abstract] ABSTRACT: OmpU porins are increasingly recognized as key determinants of pathogenic host Vibrio interactions. Although mechanisms remain incompletely understood, various species, including the human pathogen Vibrio cholera, require OmpU for host colonization and virulence. We have shown previously that OmpU is essential for virulence in the oyster pathogen Vibrio splendidus LGP32. Here, we showed that V. splendidus LGP32 invades the oyster immune cells, the hemocytes, through subversion of host-cell actin cytoskeleton. In this process, OmpU serves as an adhesin/invasin required for β-integrin recognition and host cell invasion. Furthermore, the major protein of oyster plasma, the extracellular superoxide dismutase Cg-EcSOD, is used as an opsonin mediating the OmpU-promoted phagocytosis through its RGD sequence. Finally, the endocytosed bacteria were found to survive intracellularly, evading the host defense by preventing acidic vacuole formation and limiting reactive oxygen species production. We conclude that (i) V. splendidus is a facultative intracellular pathogen that manipulates host defense mechanisms to enter and survive in host immune cells, and (ii) that OmpU is a major determinant of host cell invasion in Vibrio species, used by V. splendidus LGP32 to attach and invade oyster hemocytes through opsonisation by the oyster plasma Cg-EcSOD.
Proceedings of the National Academy of Sciences 02/2011; 108(7):2993-8. · 9.74 Impact Factor
[show abstract][hide abstract] ABSTRACT: In Mediterranean coastal rivers, floods last often less than a few hours but supply large amounts of contaminants to transitional and coastal waters. Estimating flood loads requires appropriate sampling strategies. We applied flood-scale sampling for the survey of two rivers flowing into the Thau lagoon (France). Two bacterial indicators were considered, thermotolerant coliforms (TTC) and faecal streptococci (FC). During floods, concentrations of indicator bacteria associated with non-mineral suspended solids increased quickly with the rising flow, their decrease during the recession period was slow and erratic. Statistical analysis was performed on total bacterial flood loads measured during 20 floods, versus hydrological variables and land-use characteristics. The analysis highlighted the significant impacts of human pollution sources together with the magnitude of the flood. Regarding the results, the best linear regression models linked total bacterial flood loads to peak discharge for both TTC and FS, reinforcing the assumption that in-stream bacterial stores play an important role in the level of bacterial flood loads in Mediterranean coastal rivers. At an annual scale, between 13.9 and 16.6 log10cfu of TTC could be supplied depending on the hydrological conditions during the year. Over the 12 year period, from 1994 to 2006 it was shown that the flood loads were responsible for at least 98% of the TTC total annual load and in 8 of 12 years the floods contributed to at least 99.9% of the annual loads. Over the same period on average the single major flood represents 74% of the total annual load. The contribution of in-stream bacterial stores was demonstrated but spatial variations in total flood loads showed that this contribution is difficult to evaluate. Bacteria from land stores appeared to be negligible in both catchments.Highlights► We analyze temporal dynamics and spatial evolution of bacterial loads during Mediterranean flood events. ► The peak discharge and flood volume are of primary importance to characterize bacterial flood loads. ► The best linear regression models linked total bacterial flood loads to peak discharge. ► Bacterial load of the major flood of the year could represent 99% of the total annual load. ► Within intermittent river, bacterial in-stream stores and overflows of sewage systems contribute largely to bacterial load.
Journal of Hydrology 01/2011; 405:501-511. · 2.96 Impact Factor
[show abstract][hide abstract] ABSTRACT: The sanitary microbiological condition of Mediterranean coastal rivers is a growing concern because of its impacts on the compliance of receiving coastal and transitional waters which are of high recreational and economic values. Due to strong anthropogenic pressures, coastal rivers do not often meet the required standards and guidelines, expressed in terms of coliforms and streptococci abundances. These indicator bacteria themselves are usually not pathogenic, but they allow the tracking of recent faecal contamination and the possible presence of pathogenic micro-organisms in rivers, in an easier and less costly way. Mediterranean coastal rivers are subject to long dry periods cut by short duration flush flood events. During dry and low flow period, faecal bacteria often bound to particulate matter tend to settle in the riverbed and to constitute an in-stream store in which bacteria are able to survive for long durations and even to multiply. During intense rainfall events and floods, peaks of faecal contamination occur in rivers due to entrainment of stored bacteria in river channels by the flood. Modelling these intermittent rivers poses a numerical challenge due to the high spatial and temporal gradients and proximity of zero value. These conditions are not well handled or not simulated at all in most of the currently available watershed and rivers models. The objective of this work is to simulate the transfer and fate of faecal coliforms and faecal streptococci in an intermittent river, considering a dry period followed by a flash flood. The river considered is the French river "La Vène", close to Montpellier, for which data of several dry periods and floods are available. The model considered is Mohid River Network (MRN), (www.mohid.com). MRN is a 1D hydrodynamic model that considers a network of tributaries and allows for dynamic time step. It can also compute properties transport, such as faecal bacteria, and compute water storage in pools, transmission losses and evaporation fluxes with the fine spatial and temporal discretisation required by temporary waters. In a first step an analysis of sensibility has been performed to assess the effect of the uncertainties in the input data on the results of the model. These uncertainties can for example be due to insufficient temporal and/or spatial resolution. For dry periods, we have then adapted the decay laws of the bacteria in the bed and the surface water to better simulate the fate of the bacteria. During flash floods, the hypothesis that the bacteria will be transferred from the river bed to the surface water and from the surface water to the river bed according to the sediments erosion and deposition fluxes leds to relatively good results. An important parameter for the simulation is however the particular / dissolved ratio of CTT and SF in the surface water.
[show abstract][hide abstract] ABSTRACT: Vibrio splendidus, strain LGP32, is an oyster pathogen associated with the summer mortalities affecting the production of Crassostrea gigas oysters worldwide. Vibrio splendidus LGP32 was shown to resist to up to 10 microM Cg-Def defensin and Cg-BPI bactericidal permeability increasing protein, two antimicrobial peptides/proteins (AMPs) involved in C. gigas immunity. The resistance to both oyster Cg-Def and Cg-BPI and standard AMPs (polymyxin B, protegrin, human BPI) was dependent on the ompU gene. Indeed, upon ompU inactivation, minimal bactericidal concentrations decreased by up to fourfold. AMP resistance was restored upon ectopic expression of ompU. The susceptibility of bacterial membranes to AMP-induced damages was independent of the ompU-mediated AMP resistance. Besides its role in AMP resistance, ompU proved to be essential for the adherence of V. splendidus LGP32 to fibronectin. Interestingly, in vivo, ompU was identified as a major determinant of V. splendidus pathogenicity in oyster experimental infections. Indeed, the V. splendidus-induced oyster mortalities dropped from 56% to 11% upon ompU mutation (Kaplan-Meier survival curves, P < 0.01). Moreover, in co-infection assays, the ompU mutant was out competed by the wild-type strain with competitive indexes in the range of 0.1-0.2. From this study, ompU is required for virulence of V. splendidus. Contributing to AMP resistance, conferring adhesive properties to V. splendidus, and being essential for in vivo fitness, the OmpU porin appears as an essential effector of the C. gigas/V. splendidus interaction.
[show abstract][hide abstract] ABSTRACT: The bivalve Codakia orbicularis, hosting sulfur-oxidizing gill endosymbionts, was starved (in artificial seawater filtered through a 0.22-mum-pore-size membrane) for a long-term experiment (4 months). The effects of starvation were observed using transmission electron microscopy, fluorescence in situ hybridization and catalyzed reporter deposition (CARD-FISH), and flow cytometry to monitor the anatomical and physiological modifications in the gill organization of the host and in the symbiotic population housed in bacteriocytes. The abundance of the symbiotic population decreased through starvation, with a loss of one-third of the bacterial population each month, as shown by CARD-FISH. At the same time, flow cytometry revealed significant changes in the physiology of symbiotic cells, with a decrease in cell size and modifications to the nucleic acid content, while most of the symbionts maintained a high respiratory activity (measured using the 5-cyano-2,3-ditolyl tetrazolium chloride method). Progressively, the number of symbiont subpopulations was reduced, and the subsequent multigenomic state, characteristic of this symbiont in freshly collected clams, turned into one and five equivalent genome copies for the two remaining subpopulations after 3 months. Concomitant structural modifications appeared in the gill organization. Lysosymes became visible in the bacteriocytes, while large symbionts disappeared, and bacteriocytes were gradually replaced by granule cells throughout the entire lateral zone. Those data suggested that host survival under these starvation conditions was linked to symbiont digestion as the main nutritional source.
Applied and environmental microbiology 05/2009; 75(10):3304-13. · 3.69 Impact Factor
[show abstract][hide abstract] ABSTRACT: We investigated the characteristics of the sulfur-oxidizing symbiont hosted in the gills of Codakia orbicularis, a bivalve living in shallow marine tropical environments. Special attention was paid to describing the heterogeneity of the population by using single-cell approaches including flow cytometry (FCM) and different microscopic techniques and by analyzing a cell size fractionation experiment. Up to seven different subpopulations were distinguished by FCM based on nucleic acid content and light side scattering of the cells. The cell size analysis of symbionts showed that the symbiotic population was very heterogeneous in size, i.e., ranging from 0.5 to 5 mum in length, with variable amounts of intracellular sulfur. The side-scatter signal analyzed by FCM, which is often taken as a proxy of cell size, was greatly influenced by the sulfur content of the symbionts. FCM revealed an important heterogeneity in the relative nucleic acid content among the subclasses. The larger cells contained exceptionally high levels of nucleic acids, suggesting that these cells contained multiple copies of their genome, i.e., ranging from one copy for the smaller cells to more than four copies for the larger cells. The proportion of respiring symbionts (5-cyano-2,3-ditolyl-terazolium chloride positive) in the bacteriocytes of Codakia revealed that around 80% of the symbionts hosted by Codakia maintain respiratory activity throughout the year. These data allowed us to gain insight into the functioning of the symbionts within the host and to propose some hypotheses on how the growth of the symbionts is controlled by the host.
Applied and Environmental Microbiology 05/2007; 73(7):2101-9. · 3.68 Impact Factor
[show abstract][hide abstract] ABSTRACT: The large tropical lucinid clam Codakia orbicularis has a symbiotic relationship with intracellular, sulfide-oxidizing chemoautotrophic bacteria. The respiration strategies utilized by the symbiont were explored using integrative techniques on mechanically purified symbionts and intact clam-symbiont associations along with habitat analysis. Previous work on a related symbiont species found in the host lucinid Lucinoma aequizonata showed that the symbionts obligately used nitrate as an electron acceptor, even under oxygenated conditions. In contrast, the symbionts of C. orbicularis use oxygen as the primary electron acceptor while evidence for nitrate respiration was lacking. Direct measurements obtained by using microelectrodes in purified symbiont suspensions showed that the symbionts consumed oxygen; this intracellular respiration was confirmed by using the redox dye CTC (5-cyano-2,3-ditolyl tetrazolium chloride). In the few intact chemosymbioses tested in previous studies, hydrogen sulfide production was shown to occur when the animal-symbiont association was exposed to anoxia and elemental sulfur stored in the thioautotrophic symbionts was proposed to serve as an electron sink in the absence of oxygen and nitrate. However, this is the first study to show by direct measurements using sulfide microelectrodes in enriched symbiont suspensions that the symbionts are the actual source of sulfide under anoxic conditions.
Applied and Environmental Microbiology 08/2004; 70(7):4144-50. · 3.68 Impact Factor
[show abstract][hide abstract] ABSTRACT: The effects of starvation and salinity on the physiology of Salmonella typhimurium were investigated in a microcosm study. The physiological changes were monitored by using fluorochromes dyes such as DAPI (4',6-diamidino-2-phenylindole) for evaluation of the genomic content, CTC (5-cyano-2,3-ditolyl tetrazolium chloride) for respiratory activity and syto 9 and propidium iodide for cytoplasmic membrane damages. The metabolic activity of the cellular population was assessed with the method of Kogure (direct viable count), to enumerate the substrate-responsive cells. These different staining procedures were objectively analysed by an image analysis system. This paper describes the progressive alteration of Salmonella typhimurium physiology under salinity and starvation conditions.
[show abstract][hide abstract] ABSTRACT: Maintenance of pathogenicity of viable but nonculturable Salmonella typhimurium cells experimentally stressed with UV-C and seawater, was investigated relative to the viability level of the cellular population. Pathogenicity, tested in a mouse model, was lost concomitantly with culturability, whereas cell viability remained undamaged, as determined by respiratory activity and cytoplasmic membrane and genomic integrities.
Applied and Environmental Microbiology 08/1999; 65(7):3229-32. · 3.68 Impact Factor
[show abstract][hide abstract] ABSTRACT: The release of enteric pathogenic bacteria in aquatic environments poses the problem of the fate of these bacteria under the effects of environmental factors (solar radiation, salt concentration, temperature, nutrient level, pH, competition). Frequently, these bacterial cells, potentially pathogenic, enter into a non-culturable state on routine bacteriological plating media. However, the use of direct detection methods DAPI stained cells allows the visualization of these Viable but Non Culturable cells VNC. But, beyond the characterization of the viability of the cells electron transport activity, metabolic activity, membrane integrity, structure and/or quantity of DNA, what happens with the virulence of these cells? This problem was experimentally investigated according to the bacterial model Salmonella Typhimurium. The virulence of this strain, which is the agent of the murine typhoid, was evaluated on a mouse model. Experimentally, the effects of some environmental factors on the survival and on the maintenance of virulence of Salmonella Typhimurium were measured in microcosms exposed to UV radiation (four germicidal lamps 8 mW s−1 cm−2, wave length: 254 nm, salt concentration (Sea Salt Sigma, 37, nutrient starvation. The microcosms were simultaneously submitted to these three factors, with variable exposure times. For each of those times, the viability of the nonculturable cells which became nonculturable because of the exposure to the three factors was measured through different physiological states notable in the cells, after using different fluorescent dyes. The stained cells were observed by epifluorescence microscopy and analysed by image cytometry. So, the cellular populations are characterised by enumeration of respiring bacteria CTC, , metabolising bacteria YEK,  modified, bacteria owning an undamaged cytoplasmic membrane LD, Live/Dead BacLight Viability Kit. Molecular Probes Inc.; we also determined the quantity and/or structure of DNA of the cells fluorescence level of DAPI stained cells), After exposure to the three factors for one hour 13.56 J cm−2, while the plate count cell density rapidly decreased from #107 cells mL−1 to0.1 cell mL−1, physiological states of these viable but non-culturable cells are similar to those of non-exposed cells. On the other hand, after exposure for three hours, only 10 % of the cells deposit a CTC formazan-crystal and 20 % are substrate responsive cells enlarged cells in presence of Yeast Extract and Cephalexin: YEC. Half of the cellular population presents an undamaged cytoplasmic membrane and the level of fluorecence of DAPI stained cells is close to 85 %, which shows that the DNA of these cells is weakly damaged. After exposure to the three experimental factors for24 hours 315 J cm−2, weak replies to the physiological tests used in this study to characterize the viability of the non-culturable cellular population are observed CTC: 4 %; YEC: 2 %; LD: 11.8 % while the fluorescence level of DAPI stained cells remains firm at 80 %. At the same time, the virulence expression of VNC cells of Salmonella Typhimurium, evaluated by intraperitoneal injection to the mouse route which excludes uncontrolled parameters, unlike the per os route does not seem to be correlated with the cellular viability such as it has been evaluated in this study. A 30 min exposure (6.73 J cm−2) to the three environmental factors, leading to the non-culturability of almost the entire exposed cell population 0.08 culturable cell mL−1 whereas the level of viability of those culturable cells is closed to the one of non-exposed cells. The injection of 1000 of those cells 0.001 culturable cells in 100 μL inoculated into the mouse a group of ten mice does not cause any mortality four weeks post-inoculation, whereas the injection of the same dose of non-exposed cells leads to the death of all mice in the group one week post-inoculation. According to our preliminary experiments on Salmonella Typhimurium, the loss of the state of culturability and the loss of virulence towards mice by intra-peritoneal route, because of the exposure to associated effects of UV irradiation 254 nm, salinity 37 and nutrient starvation, seem to be concomitant.RésuméLe rejet de bactéries entériques pathogènes dans l'environnement aquatique pose le problème du devenir de ces microorganismes sous les effets des facteurs environnementaux (rayonnement solaire, salinité, température, oligotrophie, pH, compétition). L'évolution fréquente de ces cellules bactériennes potentiellement pathogènes vers un état non cultivable implique l'absence de détection de celles-ci par des méthodes traditionnelles. Cependant, l'utilisation des méthodes de détection directes permet de visualiser ces cellules non cultivables. Au stade suivant, il est nécessaire de caractériser le niveau de viabilité de ces cellules non cultivables. Mais au-delà de la caractérisation de l'état viable de la cellule (activité des chaînes respiratoires, activité métabolique, intégrilé membranaire, structure et/ou quantité d'ADN) se pose parallèlement le problème du maintien du pouvoir pathogène de ces bactéries. Cette problématique a été abordée expérimentalement sur le modèle bactérien Salmonella Typhimurium. Pour évaluer le pouvoir pathogène de cette souche, il est fait appel au modèle souris, Salmonella Typhimurium étant l'agent de la typhoïde murine. Pour évaluer les effets de certains facteurs environnementaux sur cette souche pathogène, il a été fait appel sur le plan expérimental en microcosmes au rayonnement UV (quatre lampes germicides 8 mW s−1 cm −2à 254 nm), à la salinité (SeaSalt Sigma, 37) et à l'oligotrophie. Ces trois facteurs sont appliqués simultanément avec des temps d'exposition variables. Pour chaque temps d'exposition, le niveau de viabilité des cellules qui ont perdu le pouvoir de cultiver sous les effets de ces facteurs est mesuré à travers différents états physiologiques, au moyen de marqueurs fluorochromiques. La réaction marqueur-cellule est observée par microscopic en épifluorescence et analysée par cytométrie en images. Ainsi, les populations cellulaires sont caractérisées sur le plan de la respiration (CTC, ), de la capacité à métaboliser un nutriment (YEC,  modifié), de l'intégrité membranaire (LD, Kit Live/Dead Baclight-Molecular Probes Inc) et de la structure et/ou quantité d'ADN . Alors que la disparition du pouvoir de cultiver de toutes les cellules exposées (zéro cultivabilité) se réalise en 1 h (13,56 J cm−2), les états physiologiques que présentent ces cellules non cultivables sont proches de ceux présentés par les cellules d'une culture non exposée. Par contre, après 3 h d'exposition, 10 % seulement des cellules présentent une activité de leur chaîne respiratoire (CTC) et 20 % présentent une activité métabolique (extrait de levure en présence de céphalexine). La moitié des cellules présente une atteinte de la membrane cytoplasmique et le niveau de fluorescence de la population cellulaire est voisin de 85 % montrant par là que ces cellules ne présentent à ce stade qu'une faible atteinte de l'ADN. Après 24 h d'exposition (315 J cm−2) à ces trois facteurs stressants expérimentaux, les tests physiologiques appliqués dans cette étude sur les cellules non cultivables sont quasiment négatifs alors que le niveau de fluorescence de leur ADN marqué se maintient à 80 %. En parallèle, le suivi du pouvoir pathogène de ces cellules de Salmonella Typhimurium, évalué par injection intrapéritonéale à la souris (voie permettant de s'affranchir de paramètres non contrôlés comme la voie per os), ne paraît pas évoluer en fonction de la disparition de la viabilité cellulaire mesurée par les tests utilisés dans cette étude. Une exposition de 30 min (6,73 J cm−2) aux trois facteurs stressants expérimentaux fait disparaître le pouvoir de cultiver de la quasi-totalité des cellules exposées (0,08 cellules cultivables mL−1) alors que ces cellules présentent un état de viabilité proche de celui d'une souche non exposée. L'injection de 1000 de ces cellules ( 0,001 cellule cultivable dans 100 μL injecté) à la souris (un lot de dix souris) n'entraîne aucun état pathologique ni mortalité sur quatre semaines d'observations alors que l'injection du même nombre de cellules non exposées aux trois facteurs stressants entraîne la mort du lot de souris en une semaine.D'après ces quelques expérimentations préliminaires sur Salmonella Typhimurium, la perte du pouvoir de cultiver paraît s'accompagner de la perte de la virulence testée chez la souris par voie intrapéritonéale après exposition aux effets associés de l'irradiation UV, de la salinité 37 et de l'oligotrophie.
[show abstract][hide abstract] ABSTRACT: Intermittent Mediterranean rivers show long draught periods interrupted by floods of high intensity and short duration. Their channel network structure is also highly variable in space and time. Water quality dynamics in these rivers is highly impacted by this specific hydrological behaviour. During the dry period, the river channel may dry up completely except in some reaches where anthropogenic point-source inputs (mainly waste water treatment plant effluents) contribute to maintain pools. Accumulation of pollutants is observed in these reaches. During the first floods, flow is rarely continuous all along the channel network, because of the existence of transmission losses. At the beginning of a storm, propagation of flood waves is limited by infiltration in the channel bed, but also by filling-up of localized storage zones. Total flood volumes therefore do not increase very much, and even decrease downstream. Some floods observed in the upstream part of the river are not transferred to the outlet. This, in turn, influences the spatial and temporal dynamics of pollutant fluxes. Along the river course, pollutograph shapes show significant differences. Intense autumn floods flush away suddenly the pollutants from the soils and the river bed, but large amounts of pollutants remain trapped in the riverbed, if transmission losses are significant. Due to this peculiar Mediterranean hydrological regime, specific observation networks must be set up to assess the temporal and spatial variability of pollutant fluxes in the river, the processes governing pollutant transport, as well as the ranking of the origins of the pollutants. All these phenomena are illustrated here on the case of the Vène River (67 km², South of France) over the observation period: from September 2003 to August 2006, on suspended solids, nutrients and faecal bacteria. The combination of continuous and event based monitoring coupled with the multi-scale sampling strategy allows a global understanding of the factors and processes influencing water quality at the catchment scale: concentration data are used to assess the contamination levels of the river and the bio-availability of pollutants, while by analysing the instantaneous fluxes the various contributions to the river might be established. Finally total flood loads are calculated in order to evaluate the exports at the catchment outlet. The multi-disciplinary approach followed herein improved our knowledge of the integrated catchment response and its impact for downstream environments.
[show abstract][hide abstract] ABSTRACT: Sphaeroma serratum is a marine isopod species that inhabits seashores from Europe
to West Africa. The individuals live under stones in direct contact with reduced sediments and
harbour a diverse bacterial community on the cuticle of their pleopods. We investigated the
diversity of these epibiotic bacteria on male (pubescent and senescent) and female specimens with
electron microscopic obser vations and molecular tools. The microbial community of S. serratum
was shown to be composed of at least 5 bacterial morphotypes observed on the pleopodal cuticle
in all male specimens. Using fluorescence in situ hybridization, we identified 5 major phylogenetic
groups (α-, β-, γ- and δ-Proteobacteria and Archaea) whereas denaturing gradient gel electro -
phoresis (DGGE) of PCR-amplified 16S rRNA gene fragments of epibiotic bacteria revealed
50 bands. The bacterial community associated with S. serratum seems more diverse than in other
marine crustaceans, such as Rimicaris. The relative diversity of this bacterial community was also
studied in relation to the molt cycle. The comparison of DGGE band patterns of several individuals
from female, pubescent male and senescent male groups revealed that the bacterial community
diversity was dependent on the sex and the age of the individuals and more generally on the
Marine Ecology Progress Series 457:11-27. · 2.55 Impact Factor