While microbial communities in marine sediments are generally sustained by sedimentation of organic matter from the water column, the Guaymas Basin hydrothermal sediments provide a model system for the microbial utilization and transformation of thermally released microbial substrates from deeply buried marine organic matter. As a working hypothesis, the physiologically distinct, layered microbial communities force the geothermally produced substrates through a double "microbial gauntlet" of anaerobic metabolism and autotrophic carbon fixation, where terminal anaerobic degradation of organic matter is performed by methanogenic and methane-oxidizing archaea, by sulfate-reducing bacteria and archaea, and potentially by novel subsurface archaeal populations within the upper sediments, while inorganic and organic remineralization products are assimilated by sulfur-oxidizing Beggiatoa mats at the sediment surface. This project will provide a quantitative understanding of how the dense and highly active benthic microbial populations of the Guaymas system utilize and recycle organic and inorganic carbon and sulfur of subsurface origin, how geochemical controls affect the community structure, and how uncultured, globally occurring subsurface archaea and bacteria thrive in their sediment habitat. To analyze the complex interplay of thermogenic and biogenic carbon sources and sinks, and the role of uncultured microbial populations in these processes, geochemical and molecular-biological approaches will be undertaken. The microbial community composition and activity patterns will be analyzed quantitatively. Carbon substrate profiles and microbial process rates (sulfate reduction, methanogenesis, methane oxidation) across hydrothermally active sediment sites will be measured and correlated to variations in microbial populations. The Guaymas Basin vents can serve as a model system for key linkages of the microbial and geological carbon and sulfur cycles, and shed new light on the roles of microorganisms as chemical catalysts of the marine environment and the marine subsurface. To tap into the great potential of Guaymas for teaching of biological-geological linkages in marine science, this project has initiated outreach projects with the Biodiversity Education and Public Outreach (BEPO) team and its Micros*cope resource at the Marine Biological Laboratory in Woods Hole, which also targets science educators and schools of non-english speaking minority communities. In addition, the Guaymas project will enhance undergraduate and graduate teaching, and provide hands-on research opportunities for graduate and undergraduate students.
