Deep subseafloor sediments in Guaymas Basin harbor cosmopolitan microbiota and traces of hydrothermal populations

Environmental factors shape subsurface microbial ecosystems, and well-characterized sites are ideal for determining how environmental parameters shape sediment communities. Sediments from eight geologically and thermally distinct sites were drilled during International Ocean Discovery Program Expedition 385 in Guaymas Basin, an expedition focused on the hydrothermal deep biosphere. Using high-throughput 16S ribosomal nucleic acid sequencing, cell counts, phylogenetics, metatranscriptomics, and mineralogical/elemental X-ray spectroscopy, we examine linkages and feedbacks between mineral composition, temperature, geochemistry, and microbial populations. We show subsurface life is dominated by heterotrophic, cosmopolitan prokaryotes that thrive within a range of sediments and temperature conditions across Guaymas Basin. Hydrothermally-affiliated lineages are detected in low numbers at sites with steepest temperature gradients, within communities of mesophilic taxa that occur throughout Guaymas Basin and in other marine subsurface habitats. Thus, hydrothermal lineages do not replace the cosmopolitan, mesophilic subsurface community, but remain specific to sites where volcanic intrusions drive hydrothermal circulation. “Subsurface bacteria and archaea in the Guaymas Basin, Gulf of California, thrive within a wide range of sediments and temperature conditions, according to geobiological, geochemical, and mineralogical studies on microbial populations and sediment samples.”