EAPSI: Physical characterization of extreme, deep-subsurface microorganisms from Homestake Gold Mine

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Earth's deep subsurface is a typically extreme, energy-starved ecosystem. This vast biosphere represents the largest microbial habitat on Earth and is a similar environment to those found in the subsurface of other planets. This project aims to grow and characterize microbial life in Earth's deep continental subsurface, specifically at the former Homestake Mine, in South Dakota. It was recently discovered that the continental deep subsurface is a populated ecosystem where single-celled organisms survive. In the continental subsurface, microbial life has been detected 3.3 km below Earth's surface. Only a few deep subsurface microorganisms have been grown in the laboratory hence how they survive remains unclear. Biological samples from the deep subsurface will not grow using traditional microbiological cultivation techniques. Therefore, successfully cultivating its residents requires innovative technology. Dr. Hiroyuki Imachi at JAMSTEC-Yokosuka in Japan has designed low-flow bioreactors to cultivate fastidious, low energy-adapted anaerobes (organisms that use a terminal electron acceptor other than O2) from the subsurface. For the current study, water and rock samples collected from 5,000 feet below surface at Homestake Mine will be incubated in low-flow bioreactors. The bioreactors contain mineral substrates and media designed to mimic the deep subsurface environment from which samples were collected. Subsequent collections of effluent from the reactors have yielded enrichments of subsurface anaerobes, excellent for isolation and metabolic characterization of typically low-density, slow-growing microorganisms. The methods to taxonomically and metabolically characterize these previously unstudied microorganisms will include rRNA and functional gene sequencing, lipid analyses, metabolic substrate usage, and qPCR and FISH probe design for in situ environmental detection. Because Earth's subsurface is analogous to that of other planets, understanding how life exists in Earth's deep subsurface will help in the search for life in the subsurface of other planets. This NSF EAPSI award is funded in collaboration with the Japan Society for the Promotion of Science.