High concentrations of bioavailable heavy metals impact freshwater sediment microbial communities

Heavy metal concentrations within freshwater systems can increase as a result of anthropogenic inputs, which in turn can influence microbial community composition and community function. In this study, lake sediments collected from two historically heavy metal impacted geographical regions [Poyang Lake, People's Republic of China (PRC), and sites adjacent to the Muskegon Watershed, MI (USA)] were analyzed for total and available heavy metals (Cd, Cr, Cu, Pb, and Zn), as well as microbial community structure using high-throughput sequencing technology. In PRC tributaries leading into Poyang Lake, Zn was found to be the most available metal species. In USA sites, available Cd was higher in Mona Lake sites than alternate USA sites. In both regions, results indicate a weak influence of metals on microbial alpha and beta diversity, but strong positive and negative correlations of available heavy metals with specific taxonomic groups of bacteria and archaea. Further, individual metal species impacted microbial groups and operational taxonomic units differently, suggesting that individual metal species are important in determining which microbial groups and species prevail under heavy metal stress, particularly in the case of bioavailable metals. In PRC, several taxonomic groups were correlated positively with Zn, including Actinobacteria, Bacteroidetes, Proteobacteria, and Verrucomicrobia. Geobacter and Pedosphaerales were both correlated positively to Cr in the same sites, while other correlations with microbial groups were negative. In sites from the USA, Deltaproteobacteria were correlated positively with Cd, while Betaproteobacteria were negatively correlated, suggesting that Cd resistance may differ at the level of Class within Proteobacteria. This study highlights the importance of analyzing available metals when examining the impact of this disturbance on microbial community structure within aquatic sediments.