Lake Meta-Community Adaption to Heavy Metal Contamination: Thresholds, Sweeps and Switches in Short-Term Evolution

Heavy metals and metalloids are major industrial pollutants of soil and water ecosystems. Heavy metal contamination shapes species abundance and interactions within microbial communities, and also accelerates evolutionary processes. Signatures of selection are left among the functional repertoire of genes in the meta-community, especially those involved in heavy metal tolerance. In the current work, we study five lakes located in Abitibi (Quebec). Among them three are interconnected and lie along a heavy metal contamination gradient (Cadmium, Mercury) caused by historic mining activities (< 60 years of exposure). Using a meta-genomic shotgun sequencing approach (Illumina HiSeq) we generated 30Tbp of data from five lake samples to explore thresholds for community disturbance. We distinguish whether adaptive processes occur at the level of the individual (selective sweeps) or the gene (horizontal transfer) via comparisons of SNP variation between lakes at heavy metal tolerance, house keeping, and taxonomic marker loci. Our work provides insights into meta-community plasticity in response to environmental change, revealing thresholds between transient and permanent shifts in their composition and genetic repertoire. Furthermore, our study contributes to the discovery of environmental remediation strategies to target resistant-metal microorganisms genes in order to detoxify heavy metals, and therefore, minimize human impact on biodiversity.