Vertical variation in prokaryotic community composition and co-occurrence patterns in sediments of the Three Gorges Reservoir, China.

Archaea and bacteria are distributed throughout the sediment; however, our understanding of their biodiversity patterns, community composition, and interactions is primarily limited to the surface horizons (0-20 cm). In this research, sediment samples were collected from three vertical sediment profiles (depths of 0-295 cm) in the Three Gorges Reservoir (TGR), one of the largest reservoirs in the world. Through 16S rRNA sequencing, it was shown that sediment microbial diversity did not significantly vary across the sediment. Nevertheless, a decline in the similarity of archaeal and bacterial communities over distance along sediment vertical profiles was noted. Nonmetric multidimensional scaling (NMDS) analysis revealed that archaeal and bacterial communities could be clearly separated into two groups, located in the upper sediments (0-135 cm) and deep sediments (155-295 cm). Meanwhile, at the fine-scale of the vertical section, noteworthy variations were observed in the relative abundance of prominent archaea (e.g., Euryarchaeota) and bacteria (e.g., Proteobacteria). The linear discriminant analysis effect size (LEfSe) demonstrated that twenty-four bacterial and twenty-six archaeal biomarker microbes exist in the upper and deep sediment layers. Each layer exhibited distinctive microbial divisions, suggesting that microbes with diverse biological functions are capable of thriving and propagating along the sediment profile. Co-occurrence network analysis further indicated that the microbial network in the upper sediments was more complex than that in the deep sediments. Additionally, the newly discovered anaerobic methanotrophic archaeon Candidatus Methanoperedens was identified as the most abundant keystone archaeal taxon in both sediment layers, highlighting the significance of methane oxidation in material cycling within the TGR ecosystem. In summary, our study examined the biodiversity and coexistence patterns of benthic microbial communities throughout the vertical sediment profile, providing detailed insights into the vertical geography of archaeal and bacterial communities in typical deep-water reservoir ecosystems.