Interactions between surface properties of pristine coals and the intrinsic microbial communities involved in methane formation

As climate change continues, there is growing interest in the biological, in situ conversion of coal to methane, which is a cleaner and more efficient source of energy. The purpose of this study was to reveal the relationship between the surface properties of coals and the intrinsic microbial communities involved in methane formation. The material examined included nine coals varying in maturity and methane-bearing capacity. Compilation of data on wettability (θw) (measured by a sessile drop method) and microbial community composition (next-generation sequencing (NGS)) revealed that the occurrence of Bacteroidetes, Firmicutes and methanogenic Euryarchaeota was significantly, positively (P < 0.05) correlated with θw of coal. The dependence was the opposite for Actinobacteria. These results suggest that the groups of microorganisms responsible for the decomposition of organic matter in bituminous coals (hydrophobic) and lignites (hydrophilic) differ, which may impact methane formation in the seams. This is because Bacteroidetes and Firmicutes stimulate this process, while the influence of Actinobacteria is the opposite. Our work demonstrates for the first time the links between the surface properties of coals, geotectonic conditions, microbial ecophysiology and the methane-bearing capacity of the coals.