Abstract :
[en] Sediment associated microbial communities are known to influence the behaviour of metals in sediments, for example changing their speciation. Moreover, Horizontal Gene transfers (HGT) contribute to the dissemination of genes that provide adaptation of acterial communities to contaminant stress such as metals. In this present study, environmental plasmids in two different freshwater sediments were purified,characterized and compared. The stations were located at Férin in the Sensée River (northern France, low metal levels) and in the Deûle River near a former Pb/Zn smelter closed in 2003 (MetalEurop, northern France). Plasmids were extracted and sequenced by the Illumina technology (2 x 150 pb, shotgun sequencing). A quantity of ± 31 x 10Exp6 reads was obtained in each station. After MG-RAST analysis, it appeared that the proportion of reads assigned to Pseudomonas, Burkholderia, Stenotrophomonas,Cupriavidus and Ralstonia were very different in both stations, contrary to previous results obtained with total DNA. On the functional side, reads assigned to the SEED category Virulence, Disease and Defence (among which metal resistance genes) were over-represented in MetalEurop. Sediments from Férin have also been monitored in microcosms during six months with regular additions of Zn or a mix of Zn, Pb, Cu and Cd to finally reach concentrations found in MetalEurop. The evolution of the microbial community and the metaplasmidome were monitored through viable counts, DGGE and metagenomic analysis. Our study showed that the structure of the community changed significantly with a decrease in equitability. Interestingly, levels of some metal -resistance genes increased in metal-complemented microcosms.
