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Project Progress

Our investigation focuses on two areas:

1. Production of volatile and stable organic biosignatures in photosynthetic ecosystems.

We conducted a field expedition to Guerrero Negro, Mexico , to collect intertidal and subtidal hypersaline microbial mats, as analogs for Earth’s early microbial communities. The mats are being maintained in a greenhouse facility under quasi in situ conditions. We have constructed a theoretical model predicting flows of substrate, and harvesting of energy, by various microbial guilds within the mat community. These models predict substantial production of volatile fatty acids and hydrogen, which have now been demonstrated experimentally. We have documented the diversity of Archaea within subtidal mats, with a particular emphasis on production of methane (as a volatile product of metabolism in photosynthetic systems). Detailed work has identified a novel methanogen in this system, and has documented the depth-dependence of methane production. We have identified an isoprenoid lipid that may serve as a biomarker characteristic of hypersaline environments. This isoprenoid is hypothesized to be a diagenetic precursor of a widespread biomarker found in ancient oils. In collaboration with University of Colorado investigators, we documented the diversity of bacterial, archeal, and eukaryal domains within the subtidal mat system. This work expands the known division-level diversity of bacteria by about 40%, and has identified a novel eukaryote that branches at the kingdom level.

2. Viability of microbial communities in ophiolite-hosted alkaline springs (as possible analogs for early terrestrial or Martian habitats).

We identified and characterized a series of spring systems hosted in northern California ophiolites. Samples from Complexion Spring were prepared in thin section and mineralogy was characterized via electron microscopy and ion microprobe analysis. These samples were found to consist of approximately one-half primary olivine mineralogy and one-half secondary alteration (i.e., serpentine) minerals, suggesting that serpentinization (to yield the potenial biological substrate, H₂ ), is active at the relatively low temperatures encountered by this ophiolite during its history, but that the process is not complete even after more than 100 Myr.