Desulfotomaculum and methanobacterium spp. dominate a 4- to 5-kilometer-deep fault

Alkaline, sulfidic, 4 to 53 million-year-old meteoric water emanating from a borehole intersecting quartzite-hosted fractures greater than 3.3 kilometer beneath the surface have supported a microbial community dominated by a bacterial species with Desulfotomaculum spp. and an archaeal species related to Methanobacterium spp. These geochemical setting and microbial communities are notably different from microbial ecosystems reported for shallower continental subsurface environments.