Improved formation of biogenic methane by cultivable bacteria in highly volatile bituminous coals

Biogenic gas production can be improved by activating coal microorganisms, which is of great significance and application value to increase the production of coalbed methane. However, it remains poorly understood about the biological mechanism of the cultivable bacteria in coals that enhance gas production. In this study, cultivable bacteria in coal were enriched by minimal salts plus yeast medium, and coal was cultured with these medium-removed bacteria cells in minimal salts medium. Metagenomics was used to analyze the differences in the microbial composition and function. The results showed that cultivable bacteria caused large changes in the microbial and functional structure in the coals, and the cultivable bacteria Bacillus dominated in the treated coal (88.74 ± 0.51%). Metagenomics analysis showed that the KEGG Orthologs from four methanogenesis pathways in cultivable bacteria treated coals were detected, these pathways were CO2 to methane, methanol to methane, acetate to methane, and using methyl-CoM as the terminal methyl carrier. Importantly, the cultivable bacteria mainly increased the functional genes related to the degradation of benzoate, fatty acids, fluorobenzoate, xylene and aromatic compound, and further increased the acetate content. In addition, metagenome-assembled genome analysis showed that the pta and cysK genes mainly originated from Bacillus, which was beneficial to acetate production. And the cultivable bacteria treated coals had a higher methane emission than the control groups. In summary, cultivable bacteria can enhance biogas production by enhancing organic matter degradation and acetate pathway, which is of great importance for increasing coalbed methane production by domestication.