Elemental sulfur, S(0), is a common chemical species involved in a wide range of environmental and industrial reactions. S(0) is a non-toxic, relatively inert, immobile solid under most conditions. It is the "Yellow" in Yellowstone National Park, it is applied as a slow release fertilizer in agriculture, and it is the desired end product for industrial processes that remove toxic hydrogen sulfide from waste. The cycling of S(0) is driven by microbial activity. Broadly this project seeks to provide new insights into microbe-mineral interactions by addressing the following question:How does a single microbe both synthesize and degrade an insoluble inorganic compound?
The model system for this project is the phototrophic green sulfur bacterium Chlorobaculum tepidum. While some microbes either form or consume extracellular minerals, Cba. tepidum is unusual as it both forms S(0) from hydrogen sulfide and consumes S(0) when hydrogen sulfide is not present. Tools of nanoscale imaging, analytical chemistry and molecular biology will be applied to identify how Cba. tepidum interacts with S(0) during its formation and consumption. The project seeks to identify specific gene products required for both S(0) formation and consumption. It will then address how these gene products tailor both Cba. tepidum and S(0) surfaces for productive interaction. The availability of energy and nutrients are critical parameters that define microbial niches and the success of microbial communities in a given environment. The vast majority of cultured microbes obtain energy and nutrients from compounds soluble in aqueous media. However, many resources are bound as insoluble minerals, like S(0). The understanding of mechanisms for cellular interactions with insoluble minerals developed in this project will provide an instructive comparison to other microbe-mineral systems (i.e. Fe/Mn oxidizing and reducing bacteria) and allow us to discriminate between unique and universal features.
Broader Impacts The study of microbe-mineral interactions provides an excellent opportunity to train students and junior scientists at the interface of chemistry, biology, and environmental science. The project will provide interdisciplinary training for at least two Ph.D. students, one postdoctoral scholar and three undergraduates over the duration of the project. This includes technical training in bacterial molecular genetics, "omics" techniques, anaerobic culturing, and nanoscale imaging and elemental analysis techniques. The participation of under-represented groups will be facilitated by the PI's role as a Co-PI on an IGERT (DGE-1144726) that is establishing undergraduate-to-graduate bridge programs with local minority serving institutions. Results and information generated by this project will be disseminated to the public through the University of Delaware's Coast Day, which attracts >10,000 visitors each year, lifelong learning seminars, science cafés, and public group visits to the Delaware Biotechnology Institute. The goal of these public interactions is to impart the critical role of environmental microbes as beneficial biogeochemical engines and not solely agents of disease. K-12 educators will specifically be targeted by PI and Co-PI participation in "in service day" training seminars.
