Biology subjects

Desmarais, M.

Publications and source records attributed to Desmarais, M..

3 recordsLinked to original sources

bioRxiv2026

Seafloor topography structures subseafloor microbial communities in the Puerto Rico Trench

The influence of seafloor topography on subseafloor microbial communities is poorly understood. In this study, we systematically sampled subseafloor sedimentary microbial communities and pore-water geochemistry at bathyal, abyssal, and hadal water depths of the Puerto Rico Trench. The Puerto Rico Trench exhibits vertical relief of over 8 km with seafloor topography shaped by active plate tectonics and characterized by a very steep southern wall and active mass wasting. Sampling across these features, we find that subseafloor microbial communities are influenced by topography in the following two ways. First, subseafloor sediment in the deepest part of the trench is anoxic, enriched in organic matter due to mass transport of sediment from shallower water depths, and contains an anaerobic subseafloor community that is quite distinct from the anaerobic subseafloor community in anoxic sediment at bathyal depths. The difference between these bathyal and hadal subseafloor anaerobic communities is consistent with influence of water-depth-related physical properties on subseafloor community composition. Second, subseafloor sediment remains oxygenated for meters below seafloor on steep slopes within the bathyal zone, an abyssal topographic high within the trench, and the abyssal plain seaward of the trench subseafloor, likely due to limited sediment accumulation, which selects for the presence of aerobic microbial communities. The difference between these bathyal and abyssal aerobic subseafloor communities and the anaerobic communities at bathyal and hadal depths reflects the role of seafloor topography in structuring subseafloor availability of redox reactants, which in turn drives the activities and composition of subseafloor microbial communities.

microbiology↗

bioRxiv2026

Piezophilic activity dominates the Puerto Rico Trench deep subseafloor biosphere

Hydrostatic pressure is a defining feature of the deep ocean, yet how it structures microbial activity across the subseafloor biosphere is poorly understood. Here, we assess pressure effects on anabolic activity in seafloor and subseafloor communities across a margin-to-hadal-to-abyssal transect of the Puerto Rico Trench region (493-8,385 m water depth). Community-level responses to pressure reverse with burial, revealing a previously unrecognized shift toward piezophily in resident subseafloor communities down to 20 meters below seafloor (mbsf). In pressure-incubation experiments, atmospheric pressure yielded higher proportions of active cells in surficial sediments, whereas in situ pressure yielded higher proportions in the subseafloor. Pressure also structured active-community composition; in trench-axis sediments extending to 8.35 mbsf, JS1/Atribacterota populations belonging to geographically widespread hadal lineages exhibited a physiological response to in situ pressure, indicative of subseafloor piezophily. These findings suggest that hydrostatic pressure acts as an ecological filter after burial, favoring piezophilic traits that may support microbial persistence in the deep subseafloor biosphere.

microbiology↗

bioRxiv2026

Anaerobic methane oxidation by ANME-2a at two molar chloride in Orca Basin

Anaerobic methane oxidation, typically mediated by consortia of archaea and bacteria, is a key process in the global methane cycle, but little is known about its upper salinity limits. We characterized the microbial methane cycle in the anoxic, hypersaline Orca Basin using metagenomics, metatranscriptomics, fluorescence in situ hybridization, and geochemical measurements at sub-meter resolution. In the brine, we detected transcriptional activity of the halophilic methylotrophic methanogen Methanohalophilus, consistent with a biological source for Orca Basin methane. In the particle-rich halocline ([~]2 M Cl-; [~]2235 meters depth), high mcrA transcription by a novel ANME-2a species was co-located with a positive shift in {delta}13C-CH4 indicative of anaerobic oxidation of methane. ANME-2a also transcribed genes for biosynthesis of the osmolyte N({varepsilon})-acetyl-{beta}-L-lysine, supporting adaptation for hypersaline conditions. At the same depth, consortia of sarcina-like archaea, likely ANME-2a, were observed in association with vibrioid and filamentous bacteria, potentially members of a halotolerant genus in the order Desulfobulbales (family SURF-16, which includes the previously identified ANME partner Seep-DBB) that were active at the same depth. At and above the oxic-anoxic interface, aerobic methane oxidation appears to be mediated by three genera of uncultivated Methylococcales bacteria. Our results double the upper salinity range of ANME-2a to [~]2 M Cl- and reveal the key microbial players in the methane bio-filter between the Orca Basin brine and overlying seawater.

microbiology↗