Microbial diversity and functional profiling in coastal tidal flat sediment with pollution of nutrients and potentially toxic elements

Purpose The coastal tidal flat is one of the most dynamic environments in the biosphere and provides an important habitat for marine organisms. Pollution by excessive nutrients and potentially toxic elements (PTEs) can threaten microbial processes. The objective of this study was to investigate the effects of environmental properties on microbial diversity and functional profiling, and uncover the correlations between communities, nutrients, and PTEs, laying theoretical support for ecological studies of coastal tidal flat. Materials and methods Surface sediments from the typical coastal tidal flat zones (including Longshan Wharf (LS), Gaobeipu (GBP), and Shuiyunpu (SYP)) at the South Bank of Hangzhou Bay in Zhejiang Province, China, were investigated using Illumina sequencing and metagenome sequencing for the diversity and function of the microbial communities. Water quality and sediment monitoring were performed to assess the environment of the coastal tidal flat. Results and discussion The concentrations of water chemical oxygen demand (COD), available phosphorus (AP), dissolved inorganic nitrogen (DIN), and sediment Cr indicated that the coastal tidal flat was mainly polluted by nutrients and PTEs. The dominant microorganisms of the sediment samples were bacteria, of which 32 known phyla and 26 dominant classes were detected. Cr was positively correlated with Desulfuromonadia and Verrucomicrobiae, whereas it was negatively correlated with Gemmatimonadetes, Dadabacteriia, Gammaproteobacteria, and Dehalococcoidia, which showed opposite trends to Pb and AP. Metabolic functional genes were analyzed and differences in both N- and P-cycling processes were observed. Furthermore, multidrug resistance genes were the most abundant in sediment samples, whereas macB and tetA genes were more abundant than the whole antibiotic resistance genes. Network analysis revealed that Plactomycetia was the major bacterial host. Conclusions This study characterized the microbial diversity and functional profiling in the sediments of the coastal tidal flat, and revealed the effects of available nutrients and PTE pollution that may prompt the selection of dominant microbial members, which provides the theoretical support for future studies on monitoring and managing the coastal tidal flat ecosystems.