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Life Underground in the Sanford Underground Research Facility

Presenter: Jan Amend, University of Southern California
When: February 29, 2016 1PM PST

Quality samples from the marine deep subsurface biosphere are difficult to obtain, biomass there is often at very low concentrations, and slow metabolic activity thwarts many laboratory experiments. However, the host rock types are generally less diverse than their continental counterparts. The petrologic complexity of the continents is countered by the relative ease in access via mines, drill holes, and deeply-sourced springs.

The Life Underground team of the NAI is investigating the deep biosphere in the paleoproterozoic iron-rich metasediments at the Sanford Underground Research Facility (SURF) in South Dakota (USA). I will present recent results in metabolic reaction energetics, microbial diversity analysis, and in situ electrode cultivation. Gibbs energy calculations of ~100 inorganic redox reactions show that per mole of electrons transferred, reactions with O2, NO3-, and MnIV are the most exergonic (-120 to -40 kJ). When normalized per kg H2O, however, the most exergonic reactions are sulfur oxidation, essentially independent of the identity of the oxidant (including CO, CO2, and FeIII).

Metagenomic analysis of fluid samples led to nearly closed genomes of several novel lineages within candidate phyla, and 16S sequences of DNA extracted from fresh rock core via sterile cryo-drilling share very few taxa with fluid samples from the same mine level (~1500 m). Enrichments from 5-month-long in situ electrode incubation experiments led to the isolation at several reducing potentials of novel bacteria that are related to known Fe and Mn oxidizers and reducers.

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