Spatial variability of bacterial community compositions in the Mariana Trench.

Hadal microorganisms play an important role in the biogeochemical processes in marine ecosystems and act as a valuable resource for industrial applications. This paper presents the bacterial community analysis of samples taken from the Challenger Deep within the Mariana Trench, which is the deepest site in the ocean. High-throughput 16S rRNA gene amplicon sequencing was used to reveal that the vertically sampled bacterial populations at eight stations varied at the surface to 10 km depth. The surface water samples harbored a distinct bacterial assemblage, while the mesopelagic and bathyal samples manifested different bacterial community composition, which was not consistent with previous studies. Gammaproteobacteria was the most abundant bacteria in the bathyal and hadal waters. The hadal bacterial community consisted mostly of Alteromonadales and Oceanospirillales. The former was widely spread in the water column, which might suggest habitat partitioning at the genus and operational taxonomic unit levels, while the latter might represent hadal-enriched hydrocarbon degraders. The present work complements the current knowledge and understanding of the bathyal and hadal bacterial communities of the Mariana Trench.