Biogeographical distribution and diversity of microbes in methane hydrate-bearing deep marine sediments on the Pacific Ocean Margin

TLDR

The deep subseafloor biosphere is among the least-understood habitats on Earth, yet its vast microbial biomass may exert long-term controls on global biogeochemical cycles. The study maps the vertical and geographic distribution and phylogenetic diversity of microbes in Pacific Ocean Margin sediments and compares prokaryotic patterns between methane‑hydrate and hydrate‑free cores using >2,800 16S rRNA gene clones. Sediment cores were collected from the Peru and Cascadia Margins during ODP Legs 201 and 204, and >2,800 16S rRNA gene clones (400–500 bp) plus 348 representative ~1 kbp sequences were analyzed to assess prokaryotic distribution. In methane‑hydrate‑bearing cores the uncultivated Deep‑Sea Archaeal Group dominated, bacterial communities were enriched in JS1, Planctomycetes, and Chloroflexi, while cores lacking hydrates showed few or no Deep‑Sea Archaeal Group phylotypes, and cluster and principal component analyses revealed distinct prokaryotic communities between hydrate‑bearing and hydrate‑free sediments, underscoring their potential role in biogeochemical processes.

Abstract

The deep subseafloor biosphere is among the least-understood habitats on Earth, even though the huge microbial biomass therein plays an important role for potential long-term controls on global biogeochemical cycles. We report here the vertical and geographical distribution of microbes and their phylogenetic diversities in deeply buried marine sediments of the Pacific Ocean Margins. During the Ocean Drilling Program Legs 201 and 204, we obtained sediment cores from the Peru and Cascadia Margins that varied with respect to the presence of dissolved methane and methane hydrate. To examine differences in prokaryotic distribution patterns in sediments with or without methane hydrates, we studied >2,800 clones possessing partial sequences (400–500 bp) of the 16S rRNA gene and 348 representative clone sequences (≈1 kbp) from the two geographically separated subseafloor environments. Archaea of the uncultivated Deep-Sea Archaeal Group were consistently the dominant phylotype in sediments associated with methane hydrate. Sediment cores lacking methane hydrates displayed few or no Deep-Sea Archaeal Group phylotypes. Bacterial communities in the methane hydrate-bearing sediments were dominated by members of the JS1 group, Planctomycetes, and Chloroflexi. Results from cluster and principal component analyses, which include previously reported data from the West and East Pacific Margins, suggest that, for these locations in the Pacific Ocean, prokaryotic communities from methane hydrate-bearing sediment cores are distinct from those in hydrate-free cores. The recognition of which microbial groups prevail under distinctive subseafloor environments is a significant step toward determining the role these communities play in Earth’s essential biogeochemical processes.