[en] Metal contamination of soil and sediments is a serious environmental issue as metals cannot be degraded. Despite elevated metal concentrations, river sedimentary microbial communities near the MetalEurop foundry (Northern France) display an unexpected high diversity in comparison with an upstream control site (Férin). Recent methodological improvements of 16S rRNA taxonomy profiling has enhanced analytical accuracy and revealed that metals act as drivers of the microbial community structure. In the present study, a follow-up of the evolution of sediment microbial communities sampled in Férin sediments was performed in microcosms with a periodic renewal of the supernatant water. Experimental microcosms were progressively exposed to a mixture of metals to finally reach concentrations observed in MetalEurop: Cd (38.1 mg/kg), Cu (100.0 mg/kg), Pb (913.8 mg/kg) and Zn (3218.5 mg/kg). Microcosms were followed using 16S rRNA gene Illumina sequencing. Functional insights on metal resistance were obtained by quantitative PCR targeting czcA and pbrA genes coding for metal efflux pumps. The broad host range incP plasmid content was also followed by quantitative PCR. Interestingly, taxonomical analyses revealed a higher specific richness and equitability in metal-contaminated microcosms. This increase can be explained by metals acting as a community-manager together with community coalescence (i.e., the gathering of two different microbial communities). Quantitative PCR analysis coupled with taxonomic evolution suggest a step by step adaptation through the selection of different metal-resistance mechanisms.
