Collaborative Research: Tracking Chemical, Isotopic, and Molecular Signatures of Tightly Coupled Sulfur Cycling in Phototrophic and Chemosynthetic Microbial Ecosystems

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The metabolic activity of microorganisms dominates the biogeochemical evolution of the Earth over geologic time. One of the fundamental questions facing scientists seeking to understand global biogeochemistry is: What is the relationship between microbial community composition (who¡¦s there?), metabolic activity (what are they doing?), and ambient environmental conditions (e.g., pH, sulfate levels) (how are they impacted?). Sulfur cycling, particularly the coupling between sulfate reduction and sulfide oxidation, is one of the dominant geochemical pathways driving carbon mineralization within many diverse microbial ecosystems today. Isotopic and mineralogical evidence recovered from ancient rocks suggest biological sulfate reduction played an important role on early Earth as well. In attempt to better understand this globally important process and the corresponding biosignatures of active sulfur cycling microorganisms, we are proposing a multi-disciplinary, high-resolution geochemical and molecular biological investigation of closely coupled microbial sulfur cycling in three representative microbial ecosystems. These include a 3-4 member synergistic anoxygenic phototrophic consortium, moderately diverse chemosynthetic sulfur-oxidizing mats, and highly complex benthic oxygenic photosynthetic microbial mats. These systems differ in terms of biological complexity and in the major sulfur cycling pathways, that collectively will provide fundamental information regarding light-dependent and -independent sulfur metabolisms. Our work combines analyses at high spatial (?Ým-scale) resolution of sulfur and carbon isotopic data using secondary ion mass spectrometry (SIMS) and FISH-nanoSIMS, microvoltammetic sulfur species measurements, and CARD-FISH molecular imaging to investigate the linkage among microbial spatial organization, metabolic activity, and establishment of geochemical gradients by coupled sulfur cycling communities. Together, the data from this combined laboratory and field study will develop a new toolset that can be used to study tightly coupled sulfur cycling on an unprecedented scale within microbially dominated sedimentary environments. This project will inform scientists about the fundamental chemistry and biology governing sulfur in the environment, past and present. This is important because sulfur plays a critical role in processes controlling not only how we view the evolution of life on this planet, but also about ore deposits as sources of metal resources, oil and gas formation and their economic recovery, soil nutrient availability affecting crop yields and the quality of water resources, and the transport of many contaminants in ground and surface waters. Additionally this project will help train the next generation of scientists with the scientific and technical knowledge to work in high tech and scientific industry, research, and education fields.