Subseafloor sediments, 85% of which are found in the deep sea (<1000 mbsl), host nearly one-third of Earth’s microbial biomass, making them one of the largest ecosystems on our planet. These communities, largely dominated by sulfate reducers and methanogens (>1.5 mbsf), experience extreme environmental conditions including high hydrostatic pressure. However, the impact of pressure on microbial activities and the molecular mechanisms of adaptation to life under these conditions are poorly understood. We collected sediment cores from the hadal, abyssal, and bathyal water-depth zones of the Puerto Rico Trench and hypothesize that 1) microbial communities within these samples are adapted to in situ pressure and 2) anaerobic activities proceed at the same rates observed in shallower waters. To assess this, replicate microcosms were established targeting the enrichment of sulfate reducers and methanogens and incubated at atmospheric (0.1 MPa) and in situ pressure (5-84 MPa, equivalent to 500-8400 mbsl). Differential gene expression (DGE) analyses will be performed to identify genes that potentially contribute to microbial adaptation to high pressure. In addition, sediments were incubated with the methionine analog L-homopropargylglycine to determine microbial activity across water-depth and redox zones using bioorthogonal non-canonical amino acid tagging. Initial results show that 78 microcosms contain elevated cell counts and sulfide concentrations, suggesting enrichment of sulfate reducers. Methanogenic microcosm monitoring, DGE analyses, and activity measurements are ongoing.

Primary Presenter: Miguel Desmarais, Scripps Institution of Oceanography (mdesmarais@ucsd.edu)

Authors:

Miguel Desmarais, Scripps Institution of Oceanography  (mdesmarais@ucsd.edu)

Alvaro Munoz Plominsky, Scripps Institution of Oceanography  (alm067@ucsd.edu)

Steven D'Hondt, University of Rhode Island  (dhondt@uri.edu)

Douglas Bartlett, Scripps Institution of Oceanography  (dbartlett@ucsd.edu)