Life without Oxygen
Dr. James G. Ferry Center for Microbial Structural Biology

Anaerobes--microbes living without oxygen--comprise nearly one-fourth of all living protoplasm on earth and are found in a variety of habitats. They primarily convert biomass to methane in a process that is critical to the global carbon cycle. The conversion is accomplished by a syntrophic consortium of at least three metabolic groups (fermentative, obligate proton-reducing, and methanogenic). The methanogens produce CH4 from either the reduction of CO2 or the methyl group of acetate by two separate pathways. Elucidation of the pathway for CO2 reduction to CH4, the first to be investigated, has yielded several novel enzymes and cofactors; however, most of the CH4 produced in nature originates from the methyl group of acetate. Methanosarcina thermophila is a moderate thermophile which ferments acetate by reducing the methyl group to CH4 with electrons derived from oxidation of the carbonyl group to CO2. The pathway in M. thermophila is now understood on a biochemical and genetic level comparable to the understanding of the CO2-reducing pathway.

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