Hydrogen and bioenergetics in the Yellowstone geothermal ecosystem

TLDR

Geochemical energy budgets for high‑temperature microbial ecosystems at Yellowstone National Park have been unclear. The study aims to determine the relative contributions of different geochemistries to the energy demands of these ecosystems by integrating three lines of inference. Researchers examined the phylogenetic composition of >70 °C hot‑spring communities with distinct chemistries, performed parallel chemical analyses, and applied thermodynamic modeling. Molecular analyses and thermodynamic modeling show that most biomass derives energy from hydrogen oxidation, with H₂ concentrations up to >300 nM, indicating that hydrogen is the primary energy source for primary production even in sulfide‑rich conditions.

Abstract

The geochemical energy budgets for high-temperature microbial ecosystems such as occur at Yellowstone National Park have been unclear. To address the relative contributions of different geochemistries to the energy demands of these ecosystems, we draw together three lines of inference. We studied the phylogenetic compositions of high-temperature (>70°C) communities in Yellowstone hot springs with distinct chemistries, conducted parallel chemical analyses, and carried out thermodynamic modeling. Results of extensive molecular analyses, taken with previous results, show that most microbial biomass in these systems, as reflected by rRNA gene abundance, is comprised of organisms of the kinds that derive energy for primary productivity from the oxidation of molecular hydrogen, H 2 . The apparent dominance by H 2 -metabolizing organisms indicates that H 2 is the main source of energy for primary production in the Yellowstone high-temperature ecosystem. Hydrogen concentrations in the hot springs were measured and found to range up to >300 nM, consistent with this hypothesis. Thermodynamic modeling with environmental concentrations of potential energy sources also is consistent with the proposed microaerophilic, hydrogen-based energy economy for this geothermal ecosystem, even in the presence of high concentrations of sulfide.