Mechanisms of Secondary Biogenic Coalbed Methane Formation in Bituminous Coal Seams: A Joint Experimental and Multi-Omics Study

Abstract

Coal seam microbes, as endogenous drivers of secondary biogenic gas production in coal seams, might be related to methane production in coal seams. In this study, we carried out anaerobic indoor culture experiments of microorganisms from three different depths of bituminous coal seams in Huainan mining area, and revealed the secondary biogas generation mechanism of bituminous coal seams by using the combined analysis of macro-genome and metabolism multi-omics. The results showed that the cumulative mass molar concentrations (Molality) of biomethane production increased with the increase of the coal seam depth in two consecutive cycles; At the genus level, there were significant differences in the bacterial and archaeal community structures corresponding to the three coal seams 1#, 6#, and 9#, with correlations of R _bacterial = 0.368 and R _archaeal = 0.463, respectively; V_ad and V_i of coal were significantly correlated with differences in genus-level composition of bacteria and archaea; the largest difference in functional genes related to the methanogenic metabolic pathway was observed before and after incubation of coal bed microorganisms, with an average positive growth of 42%; meanwhile, a total of 11 classes of carbon metabolism homologues closely related to methanogenesis were detected in the liquid metabolites of coal bed microbes after 60 days of incubation. Finally, the fatty acid, amino acid and carbohydrate synergistic methanogenic metabolic pathway was reconstructed based on KEGG database; the expression level of mcrA gene within the metabolic pathway of the 1# deep coal sample was significantly higher than that of the other two groups (p < 0.05 for significance), and the efficient expression of this functional gene at the front end of the methanogenic pathway facilitates the conversion of bituminous coal organic matter to methane. Therefore, coal quality (V_ad) is likely to be one of the key factors causing diversity in microbial community composition and metabolic function differences in different coal seams.