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As a postdoctoral researcher in the Schrenk lab, I’m currently involved in multiple projects relating to serpentinization: a low temperature geochemical reaction in which the minerals olivine and pyroxene (found in ultramafic rock in the lower crust and upper mantle) chemically react with water. This reaction results in the release of hydrogen gas, the production of methane and small-chain hydrocarbons, and the precipitation of insoluable minerals. The reducing power supplied by serpentinizing environments, when mixed with oxidants from surface and subsurface sources, creates chemical disequilibria that provide a strong thermodynamic drive that microbial populations can harness. Besides promoting abiotic synthesis of simple carbon compounds, these environments are characterized by the presence of strong gradients in temperature, redox potential, geochemistry, and pH, which improve the thermodynamic favorability of key prebiotic reactions. Under the high pH conditions observed in serpentinizing rock, much of the available inorganic carbon in these environments is precipitated as calcite and aragonite, resulting in low concentrations of dissolved inorganic carbon. In situ microbial communities appear to be utilizing the products of serpentinization (such as CH4, H2, CO, and small organic molecules) as sources of carbon and energy. However, the life strategies of the microbes that currently live in serpentinizing environments are still unknown, and it is difficult to distinguish biotic from abiotic processes. The process of serpentinization has a prominent place in Earth’s history, and is implicated in the origins and early evolution of life on this planet, and on other worlds in our solar system such as Mars and the icy moons of Saturn and Jupiter.
Coast Range Ophiolite Microbial Observatory (CROMO), California, USA
The Coast Range Ophiolite was formed by the obduction of oceanic crust onto land during the Jurassic period. Metamorphosed peridotite in the form of serpentine rock characterizes this formation. CROMO is a subsurface observatory funded by the NASA Astrobiology Institute (NAI), the Sloan Foundation, and the Deep Carbon Observatory, consisting of a series of eight wells drilled at strategic locations and depths into the ophiolite. The boreholes have been outfitted for a program of long-term observation and experimentation via submerged data loggers and seasonal groundwater sampling. My work at CROMO uses a combination of cultivation and biogeochemistry approaches to study microbial and organic carbon samples obtained from the wells. Past studies of serpentinite-hosted microbes have focused on genomics techniques to elucidate metabolic potential. I am taking this work a step further and using an untargeted metabolomics approach to assess microbial activity in action, by quantifying the metabolites consumed and produced by these microbial communities. I use metabolomics to study microbial adaptations and responses to varying environmental conditions, such as pH and redox potential, by comparing the metabolome to genomic and transcriptomic datasets and identifying ongoing metabolic processes in the microbial community. Since the techniques are highly parallel to organic geochemistry approaches, these data can also provide insight into biogeochemical processes, such as carbon turnover.
Semail Ophiolite, Oman
The Semail Ophiolite, like the Coast Range Ophiolite, is composed of oceanic crust and upper mantle that was overthrust onto continental crust, during the late Cretaceous period. It is located on the eastern corner of the Arabian Peninsula and, at 100,000 km2, is the largest and most extensively studied ophiolite in the world. As part of the NAI Rock Powered Life team, and with additional funding from the Deep Carbon Observatory, the Schrenk lab is using a combined enrichment culturing and environmental metabolomics approach to better understand the metabolism of microbes living in this actively serpentiniing environment. I took part in an expedition to the Semail Ophiolite in February 2017 and directed the Schrenk lab’s involvement in the microbiolgical portion of the Oman Drilling Project on site. Culturing efforts and metabolite characterization are currently underway.
Lost City Hydrothermal Field, Atlantis Massif
In addition to terrestrial serpentine sites, our lab is also involving in ongoing efforts to characterize the microbial activity and biogeochemistry of the Lost City Hydrothermal Field, an active site of serpentinization-driven hydrothermal activity on the Atlantis Massif oceanic core complex. The carbonate towers of Lost City are inhabited by low-diversity microbial biofilms dominated by a single archaeal phylotype called Lost City Methanosarcinales (LCMS). While members of the LCMS share highly similar 16S ribosomal RNA gene sequences, sequencing of the V6 hypervariable region of the 16S rRNA gene and intergenic transcribed spacer region between the 16S and 23S rRNA genes revealed multiple closely related, coexisting strains. The biofilms are capable of both methanogenesis and methanotrophy, and in microcosm experiments both processes proceeded at similar rates and were stimulated by the addition of H2. The simultaneous consumption of H2 and CH4 is thermodynamically unfavorable; cell differentiation and syntrophy, however, may have evolved in the LCMS biofilms to allow the community to maximize the potential of the H2- and CH4-rich serpentinizing fluids in Lost City. The metabolic strategies utilized here are similar to those envisioned for life in early Earth hydrothermal systems.
In collaboration with Jan Amend at the University of Southern California and Laurie Barge at the NASA Jet Propulsion Laboratory, I am using our work at Lost City to develop culturing platforms that support conditions resembling those hypothesized to exist at the origin of life, in order to observe microbial populations and the products and kinetics of biochemical and geochemical pathways in an early life scenario. This project utilizes custom-made flow reactors mimicking early mineral catalytic systems in hydrothermal chimneys/sediments to compare biogenic and abiogenic outputs from these systems, using metabolomics/organic geochemical techniques to characterize the metabolic processes that occur in this environment in relation to abiotic reactions occurring in tandem. The project represents a novel system for culturing serpentinization-fueled microbial communities, in order to observe the activity of organisms that may functionally resemble the Last Universal Commen Ancestor (LUCA), in a laboratory environment replicating the conditions available on early Earth.