NASA Astrobiology Institute (NAI)

We are working to cultivate and characterize microorganisms which directly derive energy from reactions between mafic rocks and water. We are particularly targeting organisms that colonize the surfaces of the rocks during alteration. Thus we are also developing high-resolution chemical measurements capable of detecting reaction fronts and mineral by-products that form over time at the microbe-mineral interface.

Our focus is to identify forms of microbial life that are chemosynthetically supported by water-rock interaction, and to develop high-resolution geochemical techniques capable of measuring the biological signatures of their activity. We are specifically interrogating microbial interactions with the crust in the deep ocean and subsurface, which together comprise the largest unexplored habitats on Earth. During the past year, we have extended our work on the oxidative alteration of basalts to new studies focused on highly reducing systems where reactions between fluids and ultramafic rocks generate H₂ as a byproduct (i.e. serpentinization reactions).

One of our initial objectives was to use vent fluids and oceanic serpentinites as materials for inoculation to culture thermophilic consortia of microorganisms adapted to utilizing H₂ produced slowly over time. Graduate student Lisa Mayhew has been optimizing a cultivation system that reacts seawater with various substrates such as olivine, basalt and Fe0. Preliminary H₂-generating vials were first inoculated with hydrothermal fluids and microbial mats collected at Loihi Seamount in Oct. 2007. These systems were then reoptimized for use in July 2008 for samples collected along the Mid-Atlantic Ridge (MAR08), specifically at Rainbow and Lost City hydrothermal fields, which are hosted at depth in ultramafic rocks and generate fluids modulated by serpentinization reactions.

Preliminary experiments were also conducted to use microscale synchrotron-based x-ray microprobe mapping measurements to map the distribution and oxidation states of Fe on the rims of basalts and olivines reacted with anoxic seawater in laboratory incubations. The goal is to identify the nano- and micro-scale reaction products that are generated in the presence and absence of microbial consortia during H₂ generation. These feasibility experiments were conducted at the Stanford Synchrotron Radiation laboratory in June 2008 and were sufficiently successful to provide new approaches to characterize the laboratory experiments and partially serpentinized rocks associated with the MAR08 endeavor.