COLLABORATIVE RESEARCH: Microbiology and Biogeochemistry of Autotrophic Microbes in the Subsurface at Hydrothermal Vents: Filamentous-Sulfur Producing Bacteria

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The recent discovery of microbial populations beneath the deep ocean floor has far reaching implications in biology and has a potentially strong influence on a variety of biogeochemical processes. Hydrothermal fluid flowing through cracks and pores within the oceanic crust provides a potentially rich environment for subseafloor biological communities. Several recently published observations of .microbial eruptions point to the existence of a subseafloor biosphere that might contribute considerably to the productivity of these hydrothermal systems: Extensive discharges from so-called blizzard or snowblower vents (e.g., 9 deg N East pacific Rise) released large amounts of white flocculent material which accumulated into mats of 5 cm thickness. This material has since been identified as filamentous sulfur produced by novel microbes of the genus Arcobacter. The PIs plan an integrated microbiological and geochemical study of the abundance, distribution, and diversity of these filamentous-S producing microbes, and assessment of their ecological role at 9deg N EPR. Previous observations and the high likelihood for observing eruptive events with output of subsurface biomass mean that this site is well suited to address these questions. The proposed studies will test the following general hypotheses: 1) The prime habitat of filamentous-S-forming microbes is the shallow subsurface, i.e., that part of the subsurface characterized by the active mixing of hydrothermal fluid with seawater, and snowblower vents represent a snapshot sample of that persistent biosphere. 2) A significant portion of CO2-fixation in the subsurface is carried out by epsilon proteobacteria related to Candidatus Arcobacter sulfidicus by means of the reductive TCA cycle, which has significant implications for primary production estimates and interpretation of stable carbon isotope measurements. 3) The organisms forming filamentous-S produce a distinctive geochemical signature (biomarker, isotope) that is deposited and becomes part of the geological record. The project will involve: sampling at various vent habitats with a new device for uncontaminated in situ microbial sampling; deployment and recovery of devices to provide new surfaces for quantifying in situ colonization by microbes; shipboard culturing to assess function; molecular methods to assess the composition of the microbial community in relation to environmental conditions; stable isotope and radiotracer studies to identify autotrophic subseafloor microorganisms and measure their rates of CO2-fixation; and lipid biomarker studies to provide an independent assessment of the diversity and relative abundances of microbes in this system. Stable isotope ratios of bulk organic carbon, specific lipid biomarkers and dissolved inorganic carbon will provide information on the carbon-fixation physiologies employed by specific types of vent microbes and the transfer of carbon within the system. The broader impacts of this project include establishment of an inter-disciplinary collaboration between two institutions in the field of geobiology. It is expected that results will be integrated into coursework and web pages existing either in the PI.s labs or at the respective institutions. The project will support training of one graduate student in the emerging field of geobiology and encourage participation of minority and female students in these roles. Through the Dive and Discover project, the PIs will also target middle-school students (Grades 6-8) and the general public. A BIOLIPID website will be created to disseminate results on this and several closely related projects to researchers and the wider community.