Geochemical and microbial insights into vertical distributions of genetic potential of N-cycling processes in deep-sea sediments

The exploration of the deep-sea sedimentary microbial communities could reveal the diversity, composition, as well as biogeochemical relationships. The West Philippine Basin, the world?s largest marginal basin plate which surrounded by subduction boundaries, has special location and geological significance, while few studies investigated deep-sea sedimentary microbial community especially functional groups and genes involved in N transformation in this area till now. Here, the combination of microbial community composition through 16S rRNA gene sequencing, N transformation functional genes quantification, and geochemical analysis were jointly employed, aiming to explore the vertical distributions of microbial community and N-transforming microorganisms in an intact sediment core (400 cm depth) from the West Philippine Basin (15.32 ?N, 133.23 ?E, water depth 4941.9 m). The results showed that phyla Proteobacteria and Thaumarchaeota had higher relative abundances in the surface sediments (0?5 cm), while the relative abundance of phylum Firmicutes increased with depth and became dominant in the deeper sediments (350?400 cm). Based on the sequencing and quantification results, the overall abundances of inferred N-cycling taxa and functional genes decreased with depth, and the archaeal ammonia oxidation and denitrification were the dominant N transformation processes in the surface and below the surface (5?400 cm) sediments, respectively. Depth and organic matter were the key environmental variables driving the microbial community structure and N transformation processes in deep-sea sediments. This study could potentially improve the consensus that N-cycling processes in deep-sea sediments are linked and complicated, which could aid to illuminate the understanding of the role of deep-sea microbes in N cycles.