Physiological interactions of silica, iron oxide, and coal particulates on microbial growth and isolation of coalbed-derived microorganisms

Coal beds are anoxic, subsurface environments containing many complex, cross-linked, macromolecular, and primarily indeterminate organic structures of geological origin. Although some studies have examined coalbed community structures using culture-independent methods, few reports have focused on the isolation and characterization of coalbed microorganisms. It is not unlikely that communities with unique metabolic properties have evolved over time due to constant exposure to the unique chemical composition of coal and the generally anoxic environment in coal beds. Using a variety of anaerobic culturing techniques, we isolated a new genus of sulfate-reducing bacteria, Desulfocarbo indianensis SCBM, and a new species of iron-, sulfur-, and Mn(IV)-reducing bacteria, Desulfuromonas carbonis ICBM, from co-produced water extracted from a coal bed in Indiana. Our isolation of novel microbes suggests that long-term exposure to unique subsurface coal environments has selected novel microorganisms.;Most microorganisms in coal beds, as well as microorganisms in other natural systems, are attached to solid surfaces or in particle-microbe aggregates, rather than present as planktonic cells. Interactions of microorganisms with fine particles have been reported to affect microbial physiology and metabolism. However, very little is known about the mechanisms underlying microbial growth enhancement or inhibition. Here, we investigated the effects of hydrous ferric oxide, a high-purity silica, and ground coal on Acidovorax sp. 2AN growth. We systematically evaluated hypothetical mechanisms previously proposed by others about how particulates affect microbial growth. Our results indicate that growth enhancement did not result from particulates serving as an additional electron acceptor (Fe(III)), nutrient source (Fe or Si), or a pH buffer. Enhanced growth was also not a result of alteration of proton motive force due to proximity to a negatively-charged surface leading to changes in ATP generation. The stimulatory effect was potentially the result of greater microbial access to sorbed substrates or a more generalized effect on gene expression from cell-particle association.