Insights into the composition and assembly mechanism of microbial communities on intertidal microsand grains

IntroductionMarine microorganisms are essential in marine ecosystems and have always been of interest. Currently, most marine microbial communities are studied at the bulk scale (millimeters to centimeters), and the composition, function and underlying assembly mechanism of microbial communities at the microscale (sub-100 micrometers) are unclear.MethodsThe microbial communities on microsand grains (40-100 mu m, n = 150) from marine sediment were investigated and compared with those on macrosand grains (400-1000 mu m, n = 60) and bulk sediments (n = 5) using amplicon sequencing technology.ResultsThe results revealed a significant difference between microsand grains and macrosand grains. Microsand grains had lower numbers of operational taxonomic units (OTUs(97%)) and predicted functional genes than macrosand grains and bulk-scale samples. Microsand grains also showed greater intersample differences in the community composition and predicted functional genes than macrosand grains, suggesting a high level of heterogeneity of microbial communities at the microscale. Analyses based on ecological models indicated that stochastic processes dominated the assembly of microbial communities on sand grains. Consistently, cooccurrence network analyses showed that most microbial cooccurrence associations on sand grains were highly unstable. Metagenomic sequencing and further genome-scale metabolic modeling revealed that only a small number (1.3%) of microbe pairs showed high cooperative potential.DiscussionThis study explored the microbial community of marine sediments at the sub-100 mu m scale, broadening the knowledge of the structure and assembly mechanism of marine microbial communities.