Microbial consortia controlling biogenic gas formation in the Qaidam Basin of western China

Knowledge of what controls the activity of subsurface microbial communities is critical for assessing and managing biogenic methane resources. In this study, 19 formation waters and five gas samples were collected at depths of 800 to 1900 m from Quaternary biogenic gas fields of the Qaidam Basin, China. The formation waters were brines with chloride (Cl) concentrations from 1200 to 2700 mM. Bacterial 16S rRNA gene copies ranged from 3.75 × 104 to 2.23 × 106 copies mL−1 of water, and those of archaea ranged from 2.44 × 103 to 4.66 × 107 copies mL−1 of water. Both bacterial and archaea 16 s rRNA gene copies were negatively correlated with Cl concentration. The microbial community structure differed significantly depending on Cl concentrations. At high Cl waters (>1800 mM), the microbial community showed a halophilic signature made up of several abundant taxonomic groups within Firmicules, γ-Proteobacteria, and methylotrophic Methanosarcinales. At low Cl, Firmicules and hydrogenotrophic...