My research program is focused on the physiology, biochemistry, and genetics of the strictly anaerobic methane-producing archaea (methanogens). Methanogens are found in virtually every anaerobic environment and are the only organisms capable of biological methane production. Methane produced by methanogens is critical to the global cycling of carbon, a potent greenhouse gas, and a valuable biofuel. The pathways and enzymes involved in methanogenesis have been identified and well-characterized. However, much less is known about how methanogens respond to environmental change, including stressors. Because many methanogenesis enzymes contain oxygen-labile cofactors such as iron-sulfur clusters (1), we are particularly interested in understanding how methanogens sense and respond to oxygen and oxidative stress. We are using Methanosarcina acetivorans as a model organism, due to its metabolic diversity and robust genetic system. Two primary projects are focused on M. acetivorans proteins that contain regulatory iron-sulfur clusters. In each protein, the iron-sulfur clusters are proposed to function by modulating the structure and activity of the protein in response to oxygen or reactive oxygen species. The results obtained will provide insight into the function of iron-sulfur clusters in proteins involved in response to oxidative stress. Overall, an understanding of the oxidative stress response in methanogens will lead to better methods for modulating biological methane production, as well as providing insight into how anaerobes and archaea in general cope with oxidative stress. A third project is focused on utilizing the established M. acetivorans genetic system to develop methanogen strains with improved capabilities, including increased substrate utilization and oxygen tolerance.