Publications by authors named "Marshall W Bowles"

Humanity's search for extraterrestrial life is a modern manifestation of the exploratory and curious nature that has led us through millennia of scientific discoveries. With the ongoing exploration of extraterrestrial bodies, the potential for discovery of extraterrestrial life has expanded. We may better inform this search through an understanding of how life persists and flourishes on Earth in a myriad of environmental extremes.

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The characterization of metabolically active fungal isolates within the deep marine subsurface will alter current ecosystem models and living biomass estimates that are limited to bacterial and archaeal populations. Although marine fungi have been studied for over fifty years, a detailed description of fungal populations within the deep subsurface is lacking. Fungi possess metabolic pathways capable of utilizing previously considered non-bioavailable energy reserves.

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Marine sediments host an unexpectedly large microbial biosphere, suggesting unique microbial mechanisms for surviving burial and slow metabolic turnover. Although dormancy is generally considered an important survival strategy, its specific role in subsurface sediments remains unclear. We quantified dormant bacterial endospores in 331 marine sediment samples from diverse depositional types and geographical origins.

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Sulfate reduction is a globally important redox process in marine sediments, yet global rates are poorly quantified. We developed an artificial neural network trained with 199 sulfate profiles, constrained with geomorphological and geochemical maps to estimate global sulfate-reduction rate distributions. Globally, 11.

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Nitrogen (N2) fixation was investigated at Mound 12, Costa Rica, to determine its spatial distribution and biogeochemical controls in deep-sea methane seep sediment. Using (15)N2 tracer experiments and isotope ratio mass spectrometry analysis, we observed that seep N2 fixation is methane-dependent, and that N2 fixation rates peak in a narrow sediment depth horizon corresponding to increased abundance of aggregates of anaerobic methanotrophic archaea (ANME-2) and sulfate-reducing bacteria (SRB). Using fluorescence in situ hybridization coupled to nanoscale secondary ion mass spectrometry (FISH-NanoSIMS), we directly measured (15)N2 uptake by ANME-2/SRB aggregates (n = 26) and observed maximum (15)N incorporation within ANME-2-dominated areas of the aggregates, consistent with previous analyses.

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We measured potential nitrate removal and denitrification rates in hydrothermally altered sediments inhabited by Beggiatoa mats and adjacent brown oil stained sediments from the Guaymas Basin, Gulf of California. Sediments with Beggiatoa maintained slightly higher rates of potential denitrification than did brown sediments at 31.2 ± 12.

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