AN ACTIVE MICROBIOME IN OLD FAITHFUL GEYSER (Invited Presentation)

Geysers are rare thermal features that form in terrestrial hydrothermal systems when a water source, heat source, and a permeable rock substratum with an appropriate plumbing system converge, resulting in periodic eruptions. Terrestrial hot springs and mudpots have been extensively studied to better understand the taxonomy and function of microorganisms living within those systems and to gauge the limits of life. While geysers have also been extensively studied to understand their eruption dynamics, it remains unknown if geysers host microbial life. Like hot springs and mudpots, geysers supply all components necessary to support life (i.e., water, carbon, chemical disequilibria for energy production, trace elements). However, it is unclear if these environments are habitable to microbial life due to their dynamic, extreme nature. Here, we examined Old Faithful Geyser (OFG), located in the Upper Geyser Basin in Yellowstone National Park, U.S.A., to investigate the abundance, composition, and function of life in geysed waters. We report geochemical and microbiological data from erupted vent water and vent water that collects in a splash pool adjacent to OFG during eruptions. Both waters contained microbial cells and radiotracer studies showed they fixed carbon dioxide (CO₂) when incubated at 70°C and 90°C, the temperatures of sampled OFG pool and vent waters, respectively. 16S rDNA and metagenomic sequence data indicated that both communities are dominated by Thermocrinis, a chemoautotrophic bacterium that fixes inorganic carbon into biomass using chemical energy. Thermocrinis exhibited high strain level genomic diversity (putative ecotypes adapted to narrow temperature or chemical conditions) relative to populations from non-geysing hot springs. These findings show that OFG is habitable and that its eruption dynamics and the temporal variation in the geochemical conditions they create promote the generation of genomic diversity, while highlighting the need to further research the extent of life in geyser systems such as OFG. These results point to the habitability of geyser systems on other planets and their moons, such as those recently detected on Enceladus.