Biogeographic Patterns and Ecological Roles of Microorganisms in Sediments Along an Estuarine Salinity Gradient

The distribution patterns and driving mechanisms of microbial biogeographic patterns are fundamental questions in microbiology. This study analysed and compared the bacterial biogeographic patterns in the coastal environment, focusing on the Yangtze Estuary and its adjacent coastal zone. The purpose is to explore the driving mechanisms under spatial distribution, the community assembly processes and potential functions. Our results revealed that the sediment bacterial community structure exhibited a distinct geographical pattern and was significantly influenced by environmental factors. The microbial community displayed a non-random co-occurrence pattern, and the biogeographic patterns were shaped not only by environmental constraints (deterministic processes) but also by stochastic processes resulting from dispersal limitation. The metagenome sequencing analysis revealed a pronounced salinity gradient in the nitrogen-cycling function of the bacterial community. This functional difference appears to be driven by microbial diversity changes from the estuarine region to the ocean, highlighting the key role of microbial ecological characteristics. The findings of this study contribute to a deeper understanding of microbial ecology in estuarine environments, emphasizing the complex interplay between environmental factors and microbial community dynamics in shaping the function of estuarine sediment bacterial communities.