nai

Project Progress

In January 2015, Templeton and PhD students Miller and Rempfert conducted multiple weeks of field sampling with RPL collaborators Juerg Matter and Peter Kelemen to obtain fluids, gases and biomass from 9 deep wells drilled into peridotites and gabbros that host a deep subsurface hydrological system. Fluids were obtained from a range of pH (7.5 to 11.2), dissolved hydrogen and methane concentrations (0-3mM). These samples were used for the targeted culturing of several metabolic groups from these fluids, most notably methanogenic, sulfate reducing, and iron reducing consortia that can function under simulated in-situ conditions of hyperalkaline pH, high H₂, low sulfate and low CO₂. In Year 1, we have made the greatest progress so far in our efforts to study microbial methanogenesis at high pH, by isolating cultures of Methanobacterium sp. that we detect by 16S rRNA amplicon sequencing methods in biomass recovered from the most methane-rich fluids hosted in highly altered peridotites (see Theme 1 Physiology project report).

We have utilized isotopic analyses of the δD of hydrogen and water to infer that the millimolar H₂ detected in the Oman fluids exhibits an equilibrium formation temperature of ~50oC. We have also demonstrated that the subsurface CH₄ exhibits the heaviest δ¹³C CH₄ ever measured in experimental or natural systems (Miller et al., in press). We currently infer from a combination of field and experimental measurements that significant methane production and consumption are occurring in the subsurface. Co-investigator Shuhei Ono has also measured the clumped isotopologues of one deep subsurface methane sample in order to gain insight into the methane formation pathways.

In order to determine the water/rock reactions that may be occurring in the modern acquifer, giving rise to H₂ production, we are utilizing a integrated suite of of synchrotron-based x-ray fluorescence mapping of Fe speciation, coupled with QEMSCAN imaging and Raman microscale mapping of serpentinized rocks with Co-I Lisa Mayhew and co-investiagor Eric Ellison. Co-I Tominaga has also measured changes in the magnetic properties of the serpentinites to help detect the formation and loss of magnetite within subsurface zones of variable serpentinization (see Theme 1 Mineralogy project report).

Using high-throughput DNA sequencing approaches, we have determined that the subsurface serpentinite-hosted fluids contain microbial communities that differ relative to communities detected at hyperalkaline surface seeps in ophiolite systems worldwide. For example, in Oman, the subsurface microbial community is dominated by Meiothermus, candidate phylum OP1, and the family Thermodesulfovibrionaceae. We do also detect abundant Proteobacteria, including Hydrogenophaga (e.g. “Serpentinomonas”), as well as Firmicutes and candidate phylum OD1, which indicates some similarity to other serpentinizing systems such as the Cedars. Current metagenomic analysis of the DNA will be critical to infer potential metabolisms utilized by these microbial communities, particularly given the abundance of Candidate divisions with no known cultured representatives.

In Year 2, the RPL team will deploy members from 7 member labs to Oman to conduct a coordinated deep subsurface sampling campaign, targeting the collection of DNA, RNA, lipids, aqueous geochemistry and mineral products that can be used for an integrated suite of metabolomics, metagenomics and biosignature studies designed to elucidate the function of a serpentinite-hosted biosphere.