[B-BG01] Earth and Planetary Science Frontiers for Life and Global Environment

[BBG01-05] Culture-independent sequencing analysis of microbial community in deep-sea sediment

★Invited Papers

*Satoshi Hiraoka¹ (1.Japan Agency for Marine-Earth Science and Technology)

Keywords:Deep-sea sediment, Microbes, Metagenomics

Hadal trench bottom (>6000 m below sea level [mbsl]) sediments harbor higher microbial cell abundance compared with adjacent abyssal plain (3000-6000 mbsl) sediments. This is supported by the accumulation of sedimentary organic matter (OM), facilitated by trench topography. However, the benthic microbes in trench systems has not been well understood yet. The recent development of DNA sequencing technologies and bioinformatics allows us to investigate the taxonomic distributions and genomic diversity of microbes in the deep-sea sediment without cultivation. Using the technology, our group previously reported the analysis of small subunit ribosomal RNA gene tag sequencing for 92 sediment subsamples of seven abyssal and seven hadal sediment cores collected from three trench regions (the Japan, Izu-Ogasawara, and Mariana Trenches). Tag-sequencing analyses revealed specific distribution patterns of several phyla associated with oxygen and nitrate. The community structure was distinct between abyssal and hadal sediments, following geographic locations and factors represented by sediment depth. Co-occurrence network revealed six potential prokaryotic consortia that covered across regions. Our results further support that the OM cycle is driven by hadal currents and/or rapid burial shapes microbial community structures at trench bottom sites, in addition to vertical deposition from the surface ocean. In addition, from the metagenomic analysis of abyssal sediments collected from the Izu-Ogasawara trench and subsequent searching of a public protein database, we recently discovered novel beta-N-acetylgalactosaminidases and beta-N-acetylhexosaminidase enzymes. Based on the phylogenetic and structural analyses, the enzymes likely belong to new (sub)families related to the glycoside hydrolase 123 (GH123) family that classified in CAZy database. Our sequencing-based analyses highlight unprecedented taxonomic, genetic, and genomic diversity of microbial assemblages in surface seafloor sediments, providing novel insights into deep-sea microbial ecology.