Influence of Uranium on Bacterial Communities: A Comparison of Natural Uranium-Rich Soils with Controls

This study investigated the influence of uranium on the indigenous bacterial community structure in natural soils with high uranium content. Radioactive soil samples exhibiting 0.26% - 25.5% U in mass were analyzed and compared with nearby control soils containing trace uranium. EXAFS and XRD analyses of soils revealed the presence of U(VI) and uranium-phosphate mineral phases, identified as sabugalite and meta-autunite. A comparative analysis of bacterial community fingerprints using denaturing gradient gel electrophoresis (DGGE) revealed the presence of a complex population in both control and uranium-rich samples. However, bacterial communities inhabiting uraniferous soils exhibited specific fingerprints that were remarkably stable over time, in contrast to populations from nearby control samples. Representatives of Acidobacteria, Proteobacteria, and seven others phyla were detected in DGGE bands specific to uraniferous samples. In particular, sequences related to iron-reducing bacteria such as Geobacter and Geothrix were identified concomitantly with iron-oxidizing species such as Gallionella and Sideroxydans. All together, our results demonstrate that uranium exerts a permanent high pressure on soil bacterial communities and suggest the existence of a uranium redox cycle mediated by bacteria in the soil

Analysis and exploitation of bacterial population from natural uranium-rich soils : selection of a model specie

On sait que les sols et les populations bactériennes indigènes ont une influence sur la mobilité des métaux, donc sur leur toxicité. Cette étude a été menée sur des sols uranifères et contrôles collectés dans le Limousin (régions naturellement riches en uranium ). une analyse physico-chimique et minéralogique des échantillons de sol a été réalisée. La structure des communautés bactériennes a été étudiée par électrophorèse en gradient de dénaturant (DGGE). La structure des communautés est remarquablement stable dans les sols uranifères, ce qui indique que l'uranium exerce une forte pression de sélection. D'autre part, une collection de bactéries cultivables à été réalisée à partir des sols, puis criblée pour la résistance à l'uranium, dans le but d'étudier les interactions entre bactéries et uranium. Des observations en Microscopie Électronique à Balayage ont mis en évidence différents mécanismes de chélation de l'uranium à la surface cellulaireIt is well known that soils play a key role in controlling the mobility of toxic metals and this property is greatly influenced by indigeous bacterial communities. This study has been conducted on radioactive and controls soils, collected in natural uraniferous areas (Limousin). A physico-chemical and mineralogical analysis of soils samples was carried out.The structure of bacterial communities was etimated by Denaturing Gradient Gel Electrophoresis (DGGE). The community structure is remarkably more stable in the uranium-rich soils than in the control ones, indicating that uranium exerts a high selection from the soils was constructed and screened for uranium resistance in order to study basteria-uranium interactions. Scanning electron microscopy revealed that a phylogenetically diverse set of uranium-resistant species ware able to chelate uranium at the cell surface

Microbacterium lemovicicum sp. nov., a bacterium isolated from a natural uranium-rich soil.

International audienceAn actinobacterial strain, designated ViU22(T), was isolated from a natural uranium-rich soil and was studied using a polyphasic approach. Cells formed orange-pigmented colonies, were rod-shaped, Gram-positive (non-staining method), non-motile and non-spore-forming. This organism grew in 0-4.5 % (w/v) NaCl and at 15-37 °C, with optimal growth occurring in 0.5 % (w/v) NaCl and at 30 °C. Comparative 16S rRNA gene sequence analysis revealed that the strain ViU22(T) belonged to the genus Microbacterium. It exhibited highest 16S rRNA gene sequence similarity with the type strains of Microbacterium testaceum (98.14 %) and Microbacterium binotii (98.02 %). The DNA-DNA relatedness of strains ViU22(T) with the most closely related type strains Microbacterium testaceum and Microbacterium binotii DSM 19164(T) was 20.10 % (± 0.70) and 28.05 % (± 0.35), respectively. Strain ViU22(T) possessed a type B2β peptidoglycan with partial substitution of glutamic acid by 3-hydroxy glutamic acid. The major menaquinones were MK-11 and MK-12. Major polar lipids detected in the strain ViU22(T) were diphosphatidylglycerol, phosphatidylglycerol, an unknown phospholipid and unknown glycolipids. The predominant fatty acids were anteiso-C15 : 0, anteiso-C17 : 0 and iso-C16 : 0, a pattern reported for other Microbacterium species. The major cell-wall sugars were galactose, xylose and mannose and the DNA G+C content was 71 mol%. Together, the DNA-DNA hybridization results and the differentiating phenotypic characteristics, showed that strain ViU22(T) should be classified as the type strain of a novel species within the genus Microbacterium, for which the name Microbacterium lemovicicum sp. nov. is proposed. The type strain is ViU22(T) ( = ATCC BAA-2396(T) = CCUG 62198(T) = DSM 25044(T))

On-chip microbial culture for the specific detection of very low levels of bacteria.

International audienceMicrobial culture continues to be the most common protocol for bacterial detection and identification in medicine and agronomics. Using this process may take days to identify a specific pathogen for most bacterial strains. Surface Plasmon Resonance (SPR) detection is an emerging alternative technology that can be used for the detection of bacteria using protein microarrays although typical limits of detection are in the range of 10(3)-10(6) cfu mL(-1), which is not compatible with most Food Safety regulation requirements. In this work, we combine concomitant "on-chip" microbial culture with sensitive SPR detection of bacteria thus allowing rapid specific detection of bacteria pathogens - including Salmonella enterica serovar Enteritidis, Streptococcus pneumoniae and Escherichia coli O157:H7 - cultured on a protein microarray. This Culture-Capture-Measure (CCM) approach significantly decreases both the number of processing steps and the overall assay time for bacterial detection. Signal analysis of SPR responses allowed the fast and quantitative assessment of bacterial concentrations initially present in the sample as low as 2.8 ± 19.6 cfu per milliliter. Altogether, our results show how simple, easy-to-operate, fluidic-less and lo-tec microarrays can be used with unprocessed samples and yield - in a single assay - both qualitative and quantitative information regarding bacterial contamination