microbial diversity in marine sediment near Yangtze river estuary

Yangtze river estuary is the most developed area in China, and would affect nearby marine sediment. However, the environmental factors of marine sediments near Yangtze river estuary and their effects on the marine microbial distribution are rarely reported. In this study, we collected 48 marine sediment samples near Yangtze river estuary and assigned them into 4 different groups of MG1 to MG4 based on their environmental factors. The environment factors of these 4 groups are significantly different, showing the group assignment is rational. The alpha diversity of MG1 to MG3 are similar, and MG4 is slightly different with the other 3 groups. Most microbes are predicted to be derived from ocean, and the most abundant microbes of these 4 groups are Proteobacteria, Acidobacteria and Actinobacteria. Moreover, the microbial distribution in each group are similar, further indicating the group assignment is rational. Most microbes could not be assigned at the genus level, suggesting most microbes in the marine sediment are uncultured. Among the samples, the Nitrosopumilus microbes are abundant, showing the nitrogen might be limited in marine environment. The microbial distribution of these 4 groups are different. Especially, MG1 and MG3, MG2 and MG3 showed significant difference with each other on several different genus. These differences might be derived from the environmental factors, such as total nitrogen content. The co-occurrence analysis of these 4 groups showed that the keystone taxa in each group is not the most dominant microbe. The keystone taxa of each group are different, suggesting these 4 marine groups are different at the OTU-level. In summary, the dominant environmental factors sharping the microbial distribution of the samples are complex, and the microbial communities of these samples might be mainly affected by the Yangtze river.