Aerobic bacterial methane synthesis.

Reports of biogenic methane (CH) synthesis associated with a range of organisms have steadily accumulated in the literature. This has not happened without controversy and in most cases the process is poorly understood at the gene and enzyme levels. In marine and freshwater environments, CH supersaturation of oxic surface waters has been termed the "methane paradox" because biological CH synthesis is viewed to be a strictly anaerobic process carried out by O-sensitive methanogens. Interest in this phenomenon has surged within the past decade because of the importance of understanding sources and sinks of this potent greenhouse gas. In our work on Yellowstone Lake in Yellowstone National Park, we demonstrate microbiological conversion of methylamine to CH and isolate and characterize an sp. capable of this activity. Furthermore, we identify and clone a gene critical to this process (encodes pyridoxylamine phosphate-dependent aspartate aminotransferase) and demonstrate that this property can be transferred to with this gene and will occur as a purified enzyme. This previously unrecognized process sheds light on environmental cycling of CH, suggesting that O-insensitive, ecologically relevant aerobic CH synthesis is likely of widespread distribution in the environment and should be considered in CH modeling efforts.