Identification des gènes impliqués dans la formation de biofilm chez une souche atypique de Streptococcus thermophilus

International audienc

Identification des gènes impliqués dans la formation de biofilm chez une souche atypique de Streptococcus thermophilus

International audienc

[i]Streptococcus thermopilus[/i] biofilm lifestyle : A remnant of commensal ancestral life?

Microorganisms have a long history of use in food production and preservation. Their adaptation to food environments has profoundly modified their features, mainly through genomic flux. Streptococcus thermophilus, one of the most frequent starter culture organisms consumed daily by humans emerged recently from a commensal ancestor. As such, it is a useful model for genomic studies of bacterial domestication processes. Many streptococcal species form biofilms, a key feature of the major lifestyle of these bacteria in nature. However, few descriptions of S. thermophilus biofilms have been reported. An analysis of the ability of a representative collection of natural isolates to form biofilms revealed that S. thermophilus was a poor biofilm producer and that this characteristic was associated with an inability to attach firmly to surfaces. The identification of three biofilm-associated genes in the strain producing the most biofilms shed light on the reasons for the rarity of this trait in this species. These genes encode proteins involved in crucial stages of biofilm formation and are heterogeneously distributed between strains. One of the biofilm genes appears to have been acquired by horizontal transfer. The other two are located in loci presenting features of reductive evolution, and are absent from most of the strains analyzed. Their orthologs in commensal bacteria are involved in adhesion to host cells, suggesting that they are remnants of ancestral functions. The biofilm phenotype appears to be a commensal trait that has been lost during the genetic domestication of S. thermophilus, consistent with its adaptation to the milk environment and the selection of starter strains for dairy fermentations

Variation of raw wastewater microbiological quality in dry and wet weather conditions.

International audience: The microbiological quality of urban wastewaters presents important environmental, sanitary, and political challenges. However, the variability of untreated wastewater quality is seldom known when it comes to microbial parameters. This study aims to evaluate the variability of microbiological quality in wastewater influents from different wastewater treatment plants connected to combined and partially separate sewer networks in the Parisian area and to evaluate the impact of this variability on the treatment efficiency and on the accuracy of wastewater effluent monitoring. The densities of fecal indicator bacteria (FIB), Escherichia coli and intestinal enterococci, and their partitioning on settleable particles were analyzed at the inlet of two wastewater treatment plants during dry weather (130 composite samples and 7 days sampled every 2 hours) and storm events (39 composite samples, and 7 rain courses) from 2008 to 2012. The results showed that fecal indicator densities vary according to the network characteristics and according to the meteorological conditions. During storm events, a significant dilution of E. coli and enterococci was observed, as well as a decrease in the settleable fraction of E. coli during the maximal impact of the storm. However, storm events did not significantly impact the regular FIB monitoring. FIB removals by primary and secondary treatment were significantly correlated with FIB densities in influent wastewater; however, meteorological conditions also influenced the removal of FIB

Variabilité de la qualité microbiologique des eaux usées brutes dans une grande agglomération

National audienceMicrobial quality of urban wastewater relates to several environmental, sanitary and political issues. However, there is a lack of knowledge concerning the variability of raw wastewater. Our study aims at evaluating the microbial variability of the influent of several wastewater treatment plants in the Paris area, as well as estimating this variability impact on the treatment efficiency. Faecal bacterial indicators (E. coli et intestinal entero cocci) and their partitioning on settleable and free phases were measured at three waste - water treatment plants (Marne Aval, Seine Amont et Seine Centre) during dry and storm periods. Our results show that faecal indicator levels fluctuate according to the type of sewer system and the hydrological conditions. During storm events, a significant dilution of faecal indicators can be observed, as well as an increase in the percentage of settleable bacteria. Enterococci removal by primary and secondary treatment is linked to the influent level of enterococci, however the removal of both indicators is also influenced by the management operation of the wastewater treatment plants

Variabilité de la qualité microbiologique des eaux usées brutes dans une grande agglomération

National audienceMicrobial quality of urban wastewater relates to several environmental, sanitary and political issues. However, there is a lack of knowledge concerning the variability of raw wastewater. Our study aims at evaluating the microbial variability of the influent of several wastewater treatment plants in the Paris area, as well as estimating this variability impact on the treatment efficiency. Faecal bacterial indicators (E. coli et intestinal entero cocci) and their partitioning on settleable and free phases were measured at three waste - water treatment plants (Marne Aval, Seine Amont et Seine Centre) during dry and storm periods. Our results show that faecal indicator levels fluctuate according to the type of sewer system and the hydrological conditions. During storm events, a significant dilution of faecal indicators can be observed, as well as an increase in the percentage of settleable bacteria. Enterococci removal by primary and secondary treatment is linked to the influent level of enterococci, however the removal of both indicators is also influenced by the management operation of the wastewater treatment plants

Neutral community model explains the bacterial community assembly in freshwater lakes

International audienceOver the past decade, neutral theory has gained attention and recognition for its capacity to explain bacterial community structure (BCS) in addition to deterministic processes. However, no clear consensus has been drawn so far on their relative importance. In a metacommunity analysis, we explored at the regional and local scale the effects of these processes on the bacterial community assembly within the water column of 49 freshwater lakes. The BCS was assessed using terminal restriction fragment length polymorphism (T-RFLP) of the 16S rRNA genes. At the regional scales, results indicated that the neutral community model well predicted the spatial community structure (R(2) mean = 76%) compared with the deterministic factors - which explained only a small fraction of the BCS total variance (less than 14%). This suggests that the bacterial compartment was notably driven by stochastic processes, through loss and gain of taxa. At the local scale, the bacterial community appeared to be spatially structured by stochastic processes (R(2) mean = 65%) and temporally governed by the water temperature, a deterministic factor, even if some bacterial taxa were driven by neutral dynamics. Therefore, at both regional and local scales the neutral community model appeared to be relevant in explaining the bacterial assemblage structure

Importance of Local and Regional Scales in Shaping Mycobacterial Abundance in Freshwater Lakes

International audienceBiogeographical studies considering the entire bacterial community may underestimate mechanisms of bacterial assemblages at lower taxonomic levels. In this context, the study aimed to identify factors affecting the spatial and temporal dynamic of the Mycobacterium, a genus widespread in aquatic ecosystems. Nontuberculous mycobacteria (NTM) density variations were quantified in the water column of freshwater lakes at the regional scale (annual monitoring of 49 lakes in the Paris area) and at the local scale (2-year monthly monitoring in Créteil Lake) by real-time quantitative PCR targeting the atpE gene. At the regional scale, mycobacteria densities in water samples ranged from 6.7 × 103 to 1.9 × 108 genome units per liter. Density variations were primarily explained by water pH, labile iron, and dispersal processes through the connection of the lakes to a river. In Créteil Lake, no spatial variation of mycobacterial densities was noticed over the 2-year monthly survey, except after large rainfall events. Indeed, storm sewer effluents locally and temporarily increased NTM densities in the water column. The temporal dynamic of the NTM densities in Créteil Lake was associated with suspended solid concentrations. No clear seasonal variation was noticed despite a shift in NTM densities observed over the 2012–2013 winter. Temporal NTM densities fluctuations were well predicted by the neutral community model, suggesting a random balance between loss and gain of mycobacterial taxa within Créteil Lake. This study highlights the importance of considering multiple spatial scales for understanding the spatio-temporal dynamic of bacterial populations in natural environments

Modélisation hydrodynamique 3D pour l’évaluation de la qualité de l’eau en milieu urbain – application au Bassin de La Villette (Paris, France)

International audienceThe spatiotemporal distribution of contaminants in watercourses is an important aspect to consider, particularly to anticipate decision-making for sanitary risk management. Discharge variation and thermal stratification impact this spatiotemporal distribution between an upstream monitoring point and a downstream area of interest. In our study site, Bassin de La Villette (Paris, France), a three-dimensional hydrodynamic model (TELEMAC-3D) was used to estimate the impact of hydro-meteorological conditions on the transport of a microbiological contamination from upstream to downstream, where a bathing area is open during Summer. The model was validated by comparing simulation results with high-frequency field data of water temperature and electrical conductivity. Two different periods of hot weather, and two with large conductivity variations were simulated. The modelling results of water temperature and conductivity were in good agreement with field data. Finally, a period of bacterial contamination following a rain episode was simulated to illustrate the model capability to reproduce the contamination transport.La distribution spatio-temporelle des contaminants dans les cours d'eau doit être prise en compte, notamment pour les prises de décision visant à réduire les risques sanitaires. Les variations de débit et la stratification thermique ont un impact sur cette distribution spatio-temporelle, entre un point de surveillance en amont et une zone d'intérêt en aval. Dans notre site d'étude, le Bassin de La Villette (Paris, France), un modèle hydrodynamique tridimensionnel (TELEMAC-3D) a été utilisé pour estimer l'impact des conditions hydro-météorologiques sur le transport d’une contamination microbiologique de l'amont vers l'aval, où une zone de baignade est ouverte en été. Le modèle a été validé en comparant les résultats de simulation de la température de l'eau et de la conductivité électrique avec des données de terrain à haute fréquence. Deux périodes estivales chaudes, et deux périodes montrant de grandes variations de conductivité ont été simulées. Les résultats de modélisation de la température de l'eau et de la conductivité ont montré un bon accord avec les données de terrain. Enfin, une période de contamination bactérienne survenant après un épisode de pluie a été simulée pour illustrer la capacité du modèle à reproduire le transport de la contamination

Spectroscopie de fluorescence de la matière organique dissoute pour la surveillance de la qualité de l'eau dans les plans d'eau urbains

Dissolved organic matter (DOM) plays a key role in the freshwater ecosystem function. Fluorescencespectroscopy can be used to monitor DOM in aquatic environments. In urban waterbodies, wastewater dischargeand runoff during rainfall events affect the water quality and change the DOM composition. Few data areavailable in urban waters. In this paper, we present fluorescence data obtained through field campaignsconducted during dry and wet weather, in watercourses in the Paris metropolitan region (France). Samples werecollected in two water bodies (Marne River and La Villette canal), two stormwater outlet and the outlet of awastewater treatment plant. Fluorescence indices, used in the literature to estimate the DOM composition, werecalculated. Based on these indices, assumptions on the DOM composition of the samples in wet weather weredone. After further validation, they could be used as indicators of microbiological contamination in the studiedwatercourses.La matière organique dissoute (MOD) joue un rôle essentiel dans le fonctionnement des milieux aquatiques. Laspectroscopie de fluorescence peut être utilisée pour la surveillance de la MOD en milieu aquatique. Dans lesmasses d'eau urbaines, les rejets d'eaux usées et le ruissellement pendant les événements pluvieux affectent laqualité de l'eau et modifient la composition de la MOD. Peu de données sont disponibles dans les eaux urbaines.Dans cet article, des mesures de fluorescence sur des échantillons collectés par temps sec et temps de pluie,dans des cours d’eau de la région métropolitaine de Paris (France), sont présentées. L’échantillonnage a étéréalisé dans deux cours d'eau (rivière Marne et canal de la Villette), deux exutoires de réseau de drainage pluvialet le rejet d'une station d'épuration des eaux usées. Des index de fluorescence, utilisés dans la littérature pourestimer l’origine de la MOD, ont été calculés. Basés sur les données de fluorescence, ils ont permis d’émettre deshypothèses sur l’évolution de la MOD par temps de pluie et pourront servir d’indicateurs de contaminationmicrobiologique dans les cours d’eau étudiés