Diversity, functional potential, and assembly of bacterial communities in metal(loid)-contaminated sediments from a coastal industrial basin. Sediment

Heavy metal(loid) accumulation has exerted increasing pressure on estuarine-coastal ecosystems due to industrial sewage discharge. Consequently, a comprehensive understanding of ecological processes related to microbial communities in these ecosystems is critical for improving the sustainability of estuarine-coastal ecosystem functions. However, the community composition, functional potential, and assembly mechanisms of microbial community in metal(loid)-contaminated estuarine-coastal habitats remain poorly understood, especially along lotic systems extending from rivers to estuaries and to bays. Here, we collected sediment samples associated with sewage outlets from rivers (upstream/midstream of sewage outlet), estuaries (sewage outlets), and Jinzhou Bay (downstream of sewage outlets) within Liaoning Province, China in order to evaluate the relationships between microbiome and metal(loid) contamination. Sewage discharge markedly increased the contents of metal(loid)s in sediments, including of As, Fe, Co, Pb, Cd, and Zn. Significant discrepancies in alpha diversity and community composition were observed among the sampling sites. Random forest and microbe-environment network demonstrated that the above dynamics were primarily caused by salinity and metal(loid) concentrations (i.e., of As, Zn, Cd, and Pb). Furthermore, metal(loid) stress significantly increased abundances of metal(loid)-resistant genes, but decreased abundances of denitrification genes (nirS/K, narG, and nasA). Gene-microbe network, microbe-microbe network, network module, mantel test, and metagenomic genomic binning analyses all suggested that Dechloromonas, Hydrogenophaga, Thiobacillus, and Leptothrix were denitrifying bacteria present within sediments of this estuarine-coastal ecosystem. Moreover, neutral model, null model, and niche breadth analyzes demonstrated that the stochastic processes dominated the community assembly in estuary offshore sites, while deterministic processes dominated river community assembly mechanisms. Thus, salinity and total nitrogen content, rather than metal(loid) contents, governed the assembly processes in these sites. Overall, these elucidate mechanisms involved in constraining community diversities, functional potential, and assembly, while promoting an understanding of the microbial ecology of metal(loid)-contaminated estuarine-coastal ecosystems.