Fluctuations in populations of subsurface methane oxidizers in coordination with changes in electron acceptor availability

The concentrations of electron donors and acceptors in the terrestrial subsurface biosphere fluctuate due to migration and mixing of subsurface fluids, but the mechanisms and rates at which microbial communities respond to these changes are largely unknown. Subsurface microbial communities exhibit long cellular turnover times and are often considered relatively static—generating just enough ATP for cellular maintenance. Here, we investigated how subsurface populations of CH 4 oxidizers respond to changes in electron acceptor availability by monitoring the biological and geochemical composition in a 1,339 meters-below-land-surface (mbls) fluid-filled fracture over the course of both longer (2.5 year) and shorter (2-week) time scales. Using a combination of metagenomic, metatranscriptomic, and metaproteomic analyses, we observe that the CH 4 oxidizers within the subsurface microbial community change in coordination with electron acceptor availability over time. We then validate these findings through a series of 13 C-CH 4 laboratory incubation experiments, highlighting a connection between composition of subsurface CH 4 oxidizing communities and electron acceptor availability.