Acidic peat bogs are major sinks for global carbon and sources of the greenhouse gas methane. As part of an NSF Microbial Observatory project, we studied methanogenesis in McLean Bog (MB), a small bog near Cornell, as well as in other peatlands. When we began our studies, numerous attempts at culturing indigenous methanogens from acidic (pH 4) bogs had failed, and one of our goals was their culture. We were particularly interested in an uncultured clade called E2 in the order Methanomicrobiales, which 16S rRNA gene clone libraries and T-RFLP studies indicated was dominant in MB. Through a set of iterative investigations on physiochemical conditions that favored methanogenesis, we were able to culture and isolate "Methanoregula boonei", an H2/CO2-utilizing methanogen in the E2 group with a pH optimum near 5.0. We more recently isolated "Methanosphaerula palustrus" a member of the related E1 group that was dominant in more neutral pH peatlands. Acetate is the main methane precursor in most freshwater systems, but conversion of acetate to methane in bogs has been controversial. We found that acetate concentrations 2 mM were toxic, but multiple low doses of acetate were converted to methane and members of acetate-using clades were enriched. However, multiple lines of evidence suggest that acetate is only a minor methane precursor in MB, suggesting a novel pattern of carbon flow. We also recently succeeded in enriching a novel acidiphilic cellulolytic anaerobic culture that contains a deep-branching member of the Fibrobacteres. These studies contribute to our understanding of the microbiology of peat, an area pioneered by Selman Waksman at Rutgers in the 1930s.

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