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Microbial population dynamics, metabolic diversity, and associated biomarkers within subsurface serpentinized fluids of the Samail ophiolite, Oman
Thieringer, Patrick H.
Thieringer, Patrick H.
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2023
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2024-11-29
Abstract
Microbial life hosted within deep subsurface serpentinization sites are candidates for the origin of life on Earth. These deep biospheres facilitate the investigation of the earliest forms of life and evolution on Earth and serve as analogue environments to locations of potential extraterrestrial habitability. Serpentinization is the hydrothermal alteration of ultramafic rock resulting in the hydration of olivine or pyroxene minerals producing highly reduced, hyperalkaline (>11 pH) fluids rich in dissolved H2. In the presence of appreciable amounts of H2, dissolved inorganic carbon (primarily CO2) is reduced to CH4 and other hydrocarbons that can readily serve as electron donors to support microbial metabolisms. These microorganisms employ diverse metabolic and physiological adaptation strategies to overcome nutrient restrictions and high pH conditions within these environments. This dissertation examines the individual species to community level dynamics of microbial life in the terrestrial serpentinizing subsurface at the Samail Ophiolite, Oman. This work disentangles the geochemical and spatial constraints shaping microbial diversity, metabolic pathways, and preservation potential of molecular biosignatures. The microbial communities were scrutinized through application of amplicon and metagenomic sequencing, geochemistry, and lipid biomarker analysis. First, a pangenomic approach was applied to methanogenic populations to assess the habitat-specific functional gene distribution across varying fluid conditions. Results demonstrate the niche differentiation of two Methanobacterium populations within the most hyperalkaline fluids to support co-existence strategies circumventing limitations imposed by serpentinization impacted fluids. Next, the distribution of metabolic potential across depth and geochemical regimes revealed that functional redundancy may support the role for metabolic auxotrophies in nutrient restricted conditions. Lastly, coupling biogeographic distribution of microbial communities with lipidomic biomarkers exposed that microorganisms within hyperalkaline fluids could potentially increase their cell membrane rigidity and compactness to overcome osmotic stress imposed by high pH conditions. Characterization of lipid profiles demonstrated distinct compounds may serve as relevant biosignatures preserved in the rock record to guide detection of ancient life at other sites of serpentinization. Altogether, this dissertation contributes to our understanding of microbial habitability at the species to community level in subsurface serpentinizing environments. Through greater comprehension of lifestyle adaptations and resolution of recalcitrant biosignatures, this work helps expand our ability to predict microbial life at analogue sites to aid our search for life on other planetary bodies.
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