Dimethylsulfoniopropionate Metabolism by Marine Bacteria

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Intellectual Merit: Dimethylsulfoniopropionate (DMSP) accounts for up to 10% of the carbon fixed by marine phytoplankton in surface waters of the ocean and is the precursor to the potent anti-greenhouse gas dimethylsulfide (DMS), the largest natural source of sulfur to the atmosphere. Two competing pathways for DMSP metabolism operate in marine microbial communities. Most of the DMSP is processed by marine bacteria through the "demethylation" pathway, which leads to formation of methanethiol (MeSH) and other sulfur compounds. A smaller portion is metabolized via the "cleavage" pathway to DMS, resulting in sulfur emissions to the atmosphere. The point at which DMSP is directed to one of these pathways, referred to as "the bacterial switch", represents one of the critical regulatory points in the global sulfur cycle. Based upon recent discoveries of the genes necessary for these pathways, this research will examine the physiological and biochemical basis the bacterial switch in the model marine bacterium, Ruegeria pomeroyi. Research will examine the enzymes of the pathways to further understand how they function in cells. Other environmental and physiological controls of DMSP metabolism will be characterized in whole cells. Four roles will be specifically tested: DMSP as a carbon and sulfur source, as a compatible solute, and as an antioxidant. In addition, many of the genes of the demethylation pathway are widespread in terrestrial and other habitats where DMSP is not abundant and have been hypothesized to function in methionine metabolism. This potential role will also be tested. In conclusion, bacterial DMSP metabolism plays a fundamental role in the global sulfur cycle. This research seeks to understand why the bacteria metabolize DMSP. Broader Impacts: The broader impacts of the project include the training of two doctoral students and one postdoctoral research associate in the departments of Microbiology and Marine Sciences at the University of Georgia and providing research opportunities and mentoring for one undergraduate student per year. Students will obtain interdisciplinary training in microbial physiology, microbial ecology, enzymology and environmental sciences. Outreach activities at local elementary and high schools will emphasize prokaryotic diversity, decomposition and the carbon cycle, photosynthetic bacteria, and the role of bacteria in forming the earth's atmosphere. It will provide students opportunities for hands on work with modern techniques of molecular microbial ecology. By improving our knowledge of the microbial control of the evolution of DMS to the atmosphere, this research will provide understanding how these processes will respond to the predicted climate changes as well as potential opportunities for mitigation of global climate change.