Variability of Microbial Community Structure Distribution in Marine Shallow Surface Sediments in Shenhu Area

Due to the frequent exchange of matter and energy between living and non-living matter in seawater, the surface layer, particularly the distribution of microorganisms in centimeter-scale and element concentrations in surface sediments, demonstrates the important message of the local biogeochemical environment. This work probed the differences in microbial communities between two sampling cores obtained from the same area and the possible environmental factors, e.g., in situ component and concentration in porewater. Here, high-throughput sequencing (16S rRNA, Illumina sequencing) and quantitative PCR analysis were used to investigate the diversity of microorganisms in sediments of two push cores of L1 and S8 from Shenhu Area, South China Sea. Porewater concentration of components and isotopic fractionation were also obtained to explore the possible correlation between the microbial community and the chemical compositions of porewater. Q-PCR revealed bacteria play an important role in the geochemical cycle in the surface sediments, and archaea may be the main community in response to environmental changes and maintain the local marine ecosystem. The total gene copies of microorganisms in the study area were lower than nearby marine sediments. Microbial community compositions showed the dominant microbial phyla were similar on Phylum level in L1 and S8, with only different abundances. Firmicutes and Proteobacter were the main bacterial phyla, while Thaumarchaeota, Lokiarchaeota and Bathyarchaeota dominated the archaeal community. The abundance of the dominant class varied significantly between L1 and S8. Bacilli in Firmicutes and Gammaproteobacteria in Proteobacter were prevalent bacterial class, MGI in Thaumarchaeota was the predominant archaeal class in L1, while Thermoplasmata and Group-C3 dominated in S8. PCoA results showed a clear diversity of bacterial and archaeal communities between these two sites, as well as significant geographic variation in microbial communities. RDA results revealed that a complex combination of environmental factors might correlate to microbial communities in a marine dynamic environment. Here, δ13CDIC, DIC and SO42– were strongly correlated to the bacterial communities, whereas δ13CDIC, Fe2+ and SO42– concentration linked to archaeal communities. Microbial communities and RDA results suggested carbon may be the main factor related to the microbial community in L1, while Fe2+ correlated with microbial community composition in S8. SO42– concentration and the distribution of Gammaproteobacteria indicated that the sulfur cycle is probably active in this area.