Field and laboratory studies on the bioconversion of coal to methane in the San Juan Basin

The bioconversion of coal to methane in the San Juan Basin, New Mexico, was investigated. Production waters were analyzed via enrichment studies, metabolite-profiling, and culture-independent methods. Analysis of 16S rRNA gene sequences indicated the presence of methanogens potentially capable of acetoclastic, hydrogenotrophic, and methylotrophic metabolisms, predominantly belonging to the Methanosarcinales and Methanomicrobiales. Incubations of produced water and coal readily produced methane, but there was no correlation between the thermal maturity and methanogenesis. Coal methanogenesis was greater when samples with a greater richness of Firmicutes were utilized. A greater archaeal diversity was observed in the presence of several aromatic and short-chain fatty acid metabolites. Incubations amended with lactate, hydrogen, formate, and short-chain alcohols produced methane above un-amended controls. Methanogenesis from acetate was not observed. Metabolite profiling showed the widespread occurrence of putative aromatic ring intermediates including benzoate, toluic acids, phthalic acids, and cresols. The detection of saturated and unsaturated alkylsuccinic acids indicated n-alkane and cyclic alkane/alkene metabolism. Microarray analysis complemented observations based on hybridization to functional genes related to the anaerobic metabolism of aromatic and aliphatic substrates. These data suggest that coal methanogenesis is unlikely to be limited by methanogen biomass, but rather the activation and degradation of coal constituents.