The basaltic ocean crust is the largest aquifer system on Earth, with a volume of water equal to the entire ocean cycling through it every 100,000-500,000 years.  However, the identities of the resident microbial communities, the rates at which they are active, and the reactions that they catalyze and the corresponding biogeochemical processes remain poorly understood.  We will discuss results from an ongoing investigation into the basement fluid sampled at the Juan de Fuca Ridge flank system off the western coast of North America.  We measured microbial sulfate reduction rates in laboratory incubations and showed a close correlation to decreasing availability of organic electron donors in the higher temperature, more altered fluids.  Using nanocalorimetry, we concluded that the heat signal produced during an isothermal scan from 35-85 °C likely resulted from the germination and subsequent metabolic activity of thermophilic endospores.  We also retrieved nearly 100 genomes from a metagenome analysis of these fluids, with &gt;30 of the genomes estimated to be &gt;90% complete.  Phylogenomic analysis revealed approximately an equal number of bacterial and archaeal genomes, most of which are only distantly related to known cultivars.  One near-complete archaeal genome (from the Archaeoglobi) points to a vast array of autotrophic and heterotrophic strategies, including fermentation of amino acids, methane cycling, and iron redox chemistry.

Activity and phylogenetic diversity of microorganisms in subsurface fluids in the upper ocean crust

253rd National Meeting (2017)

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