Microbial Community Composition and the Effects of Trace Elements on Methanogenesis Associated with Deep Subsurface Coal

Biogenic coalbed methane (CBM), an end product of anaerobic coal biodegradation, is a natural gas. It is generated and trapped in large quantities in deep, unmineable coalbeds. This dissertation describes a series of three integrated research studies to better understand the microbial players and trace element(s) limitations of methanogenic communities in this process. Microcosm experiments together with culture independent analyses demonstrated that hydrogenotrophic and methylotrophic methanogens are dominated by Euryarchaeota in CBM production water from our sampling site, Powder River Basin, Wyoming. Based on 16S rRNA gene clone libraries, Methanobacteria , Methanomicrobia , and Methanococci were major representatives of the methanogens. Betaproteobacteria and Gammaproteobacteria , Bacteroidetes , Firmicutes , and Actinobacteria were found as most abundant bacterial lineages. Trace elements are essential components of enzymes or cofactors of metabolic pathways associated with organic matter degradation and methanogenesis. CBM production water enrichments were amended with a mixture of eight essential trace elements (iron, nickel, cobalt, molybdenum, zinc, manganese, boron, and copper) at varying concentrations. Trace elements at optimized concentrations enhanced methane production by 37% relative to unamended controls. Furthermore, transcript levels of a molecular marker for methanogens, mcrA , correlated positively with elevated rates of methane production (R2 =0.95). Additionally, trace element amendments to enrichments caused a shift in the metabolically-active methanogenic community. The addition of individual iron, nickel, zinc, manganese, tungstate, and selenium at their respective concentration gradients produced either no significant enhancement or had negative effects on methane production. However, addition of molybdenum (143.0 μg/L), cobalt (45.0 μg/L), and copper (15 μg/L) enhanced methane production by 72%, 55%, and 34%, respectively. The study revealed that molybdenum, cobalt, and copper were at limited concentrations in the CBM production water. Furthermore, addition of cobalt, molybdenum, and copper at their optimum concentrations for methane production caused an increase in methanogenic diversity and in transcript levels of mcrA (