Microbial dynamics and biogenic methane production responses to the addition of glycine betaine in shales

Abstract

Biogenic methane production depends on microbial community compositions in shale gas reservoirs, and glycine betaine plays an important role in methanogenic metabolic pathways. Previous studies have mainly focused on the microbial community dynamics in the water produced by shale hydraulic fracturing. Here, we used fresh shale as a sample and obtained the methane (CH4) and carbon dioxide (CO2) concentrations, microbial communities, and methanogenic functional gene numbers of solid and liquid groups in anaerobic bottles through gas chromatography, 16S rDNA sequencing (60 samples) and quantitative real-time PCR analysis in all culture stages. With glycine betaine addition, the total CH4 concentrations of the S1, S2 and Sw samples were 1.56, 1.05 and 4.48 times, while CO2 increased by 2.54-, 4.80- and 0.43-fold compared with samples without glycine betaine after 28 days of incubation, respectively. The alpha diversity was reduced when glycine betaine was added. The significant differences in bacterial community abundance at the genus level in samples with glycine betaine were Bacillus, Oceanobacillus, Acinetobacter, and Legionella. The bacterial and archaeal community changes implied that the addition of glycine betaine may promote CH4 production mainly by first forming CO2 and then generating CH4. The results of mrtA, mcrA, and pmoA gene numbers showed that the shale had great potential for producing methane. The addition of glycine betaine to shale changed the original microbial networks and increased the nodes and taxon connectedness of the Spearman association network. Our analyses indicate that the addition of glycine betaine enhances CH4 concentrations, causing the microbial network to be more complex and sustainable which supports the survival and adaptation of microbes in shale formations.