Microbial community analysis in the terrestrial subsurface lignite seam of the Tempoku coalfield, Hokkaido, Japan.

Groundwater sampling is one of the critical steps when we study the microbial ecology in the subsurface environment. Exposure of anoxic groundwater to aerobic atmosphere may have irreversible detrimental effect on anaerobic microorganisms, leading to a possible misunderstanding about in situ microbial community structure. In this project, we attempted to install a new groundwater sampling system using Argon gas pressure into the headspace of borehole by which we could obtain in-situ groundwater from a lignite layer by minimizing exposure to aerobic atmosphere. We evaluated the microbial community structure in groundwater samples taken by this sampling system, comparing to a method using disposable bailors. Microbial community analysis revealed that the former sampling method made a difference compared to the latter ones, in which the percentage of methanogenic archaea increased. Our results demonstrated that the former one was more favorable for obtaining groundwater unperturbed by the exposure to aerobic atmosphere than the latter ones, and the improvement of sampling method significantly affected the microbial community structure in the investigated subterranean lignite layer.