[Departement_IRSTEA]Eaux [TR1_IRSTEA]BELCA | This study is a first attempt to investigate the impact of urban contamination on metal tolerance of heterotrophic river biofilms using a short-term test based on β-glucosidase activity. Tolerance levels to Cu, Cd, Zn, Ni and Pb were evaluated for biofilms collected at three sites along an urban gradient in the Seine river (France). Metallic pollution increased along the river, but concentrations remained low compared to environmental quality standards. Biofilm metal tolerance increased downstream from the urban area. Multivariate analysis confirmed the correlation between tolerance and contamination and between multi-metallic and physico-chemical gradients. Therefore, tolerance levels have to be interpreted in relation to the whole chemical and physical characteristics and not solely metal exposure. We conclude that community tolerance is a sensitive biological response to urban pressure and that mixtures of contaminants at levels lower than quality standards might have a significant impact on periphytic communities.

International audience | Mangroves are threatened ecosystems that provide numerous ecosystem services, especially through their wide biodiversity, and their bioremediation capacity is a challenging question in tropical areas. In a mangrove in Mayotte, we studied the potential role of microbial biofilm communities in removing nutrient loads from pre-treated wastewater. Microbial community samples were collected from tree roots, sediments, water, and from a colonization device, and their structure and dynamics were compared in two areas: one exposed to sewage and the other not. The samples from the colonization devices accurately reflected the natural communities in terms of diversity. Communities in the zone exposed to sewage were characterized by more green algae and diatoms, higher bacteria densities, as well as different compositions. In the area exposed to sewage, the higher cell densities associated with specific diversity patterns highlighted adapted communities that may play a significant role in the fate of nutrients.

International audience | Mangroves are threatened ecosystems that provide numerous ecosystem services, especially through their wide biodiversity, and their bioremediation capacity is a challenging question in tropical areas. In a mangrove in Mayotte, we studied the potential role of microbial biofilm communities in removing nutrient loads from pre-treated wastewater. Microbial community samples were collected from tree roots, sediments, water, and from a colonization device, and their structure and dynamics were compared in two areas: one exposed to sewage and the other not. The samples from the colonization devices accurately reflected the natural communities in terms of diversity. Communities in the zone exposed to sewage were characterized by more green algae and diatoms, higher bacteria densities, as well as different compositions. In the area exposed to sewage, the higher cell densities associated with specific diversity patterns highlighted adapted communities that may play a significant role in the fate of nutrients.

International audience | Biofilm development in wastewater treatment system by soil infiltration is often mentioned for its participation to purification efficiency and clogging zone formation. It appears necessary to understand its evolution in order to better control the operation of these systems. The objective of this study was to improve knowledge about the temporal evolution of the biofilm structure in the first centimetres of infiltration system. For this purpose, metabolic fingerprints by Biolog EcoPlate (TM) and molecular fingerprints by Ribosomal Intergenic Spacer Analysis (RISA) were carried out on sand, septic effluent and treated effluent samples from two experimental reactors supplied with different hydraulic loads collected at different times. The metabolic capabilities of sand microflora decreased in time. In the same way, molecular structure of the biofilm community changed and converged to similar structure in time. Principal components analysis on RISA gel revealed a ''buffering effect'' of the sand filter on the genetic structure of the bacterial community from treated effluent. The kinetics of evolution of the both metabolic and genetic fingerprints showed a reduction of the metabolic and genetic potentials of septic and treated effluents for the same times. The population dynamic within the biofilms appears interesting evidence in the comprehension of the operation of the treatment systems.

International audience | Biofilm development in wastewater treatment system by soil infiltration is often mentioned for its participation to purification efficiency and clogging zone formation. It appears necessary to understand its evolution in order to better control the operation of these systems. The objective of this study was to improve knowledge about the temporal evolution of the biofilm structure in the first centimetres of infiltration system. For this purpose, metabolic fingerprints by Biolog EcoPlate (TM) and molecular fingerprints by Ribosomal Intergenic Spacer Analysis (RISA) were carried out on sand, septic effluent and treated effluent samples from two experimental reactors supplied with different hydraulic loads collected at different times. The metabolic capabilities of sand microflora decreased in time. In the same way, molecular structure of the biofilm community changed and converged to similar structure in time. Principal components analysis on RISA gel revealed a ''buffering effect'' of the sand filter on the genetic structure of the bacterial community from treated effluent. The kinetics of evolution of the both metabolic and genetic fingerprints showed a reduction of the metabolic and genetic potentials of septic and treated effluents for the same times. The population dynamic within the biofilms appears interesting evidence in the comprehension of the operation of the treatment systems.

The work was done in collaboration with V. Lecomte (GRAIE). We thank B. Montuelle, F. Rimet, R. Sommaruga, and anonymous reviewers for their constructive comments on the manuscript. | International audience | Wastewater treatment plants (WWTP) are the main sources of a broad spectrum of pharmaceuticals found in freshwater ecosystems. These pollutants raise environmental health concerns because of their highly bioactive nature and their chronic releases. Despite this, pharmaceuticals' effects on aquatic environments are poorly defined. Biofilms represent a major part of the microbial life in rivers and streams. They can drive key metabolic cycles and their organizations reflect exposures to changing chemical, physical, and biological constraints. This study estimated the concentrations, over a 3-year period, of ten pharmaceuticals and five nutrients in a river contaminated by a conventional WWTP fed by urban and hospital wastewaters. Variations in these concentrations were related to biofilm bacterial community dynamics. Rock biofilms had developed over defined periods and were harvested at four locations in the river from the up- and downstream WWTP discharge point. Pharmaceuticals were found in all locations in concentrations ranging from not being detected to 192 ng L-1. Despite the high dilution factor of the WWTP effluents by the receiving river, pharmaceuticals were found more concentrated downstream than upstream the WWTP. Shifts in bacterial community structures linked to the environmental emission of pharmaceuticals were superior to seasonal community changes. A community structure from a site located downstream but close to the WWTP was more strongly associated with high pharmaceutical loads and different from those of biofilm samples from the WWTP upstream or far downstream sites. These latter sites were more strongly associated with high nutrient contents. Low environmental concentrations of pharmaceuticals can thus be transferred from WWTP effluents to a connected stream and induce bacterial aquatic community changes over time.

National audience | In this work, the behavior in tomato rhizosphere of Bacillus velezensis FZB42 was analyzed taking into account the surfactin production, the use of tomato roots exudate as substrates, and the biofilm formation. B. velezensis FZB42 and B. amyloliquefaciens S499 have a similar capability to colonize tomato rhizosphere. Little difference in this colonization was observed with surfactin non producing B. velezensis FZB42 mutant strains. B. velezensis is able to grow in the presence of root exudate and used preferentially sucrose, maltose, glutamic, and malic acids as carbon sources. A mutant enable to produce exopolysaccharide (EPS-) was constructed to demonstrate the main importance of biofilm formation on rhizosphere colonization. This mutant had completely lost its ability to form biofilm whatever the substrate present in the culture medium and was unable to efficiently colonize tomato rhizosphere.