Microbial Ecology and Resultant Biomarkers Preserved in a Terrestrial Analog of a Martian Spring System

Details Microbial Ecology and Resultant Biomarkers Preserved in a Terrestrial Analog of a Martian Spring System Microbial Ecology and Resultant Biomarkers Preserved in a Terrestrial Analog of a Martian Spring System

Dec 2005

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005agufm.p42b..08g&link_type=abstract

American Geophysical Union, Fall Meeting 2005, abstract #P42B-08

Biology

0424 Biosignatures And Proxies, 0448 Geomicrobiology

Scientific paper

On Mars, groundwater discharge, heated by geological processes at depth, represents a likely late-stage reservoir of liquid water available for biological activity. Photo-geological observations of the Martian surface support geologically, relatively young groundwater discharge via sapping and/or fault-controlled springs. Our approach to the investigation of the possible biological potential of such reservoirs has been to characterize analogous, terrestrial spring systems. Our study site is a fault-driven, mesophilic, sulfur spring system between the Hayward and Calaveras faults in California. We have examined hydro-geological variables, nutrient availability for microbial metabolism, differences in extant community structure, and the seasonal changes associated with these variables. The springs under study also precipitate calcite and form large mounds, offering the potential to evaluate the preservation of biosignatures. The geochemistry and isotopic composition (2H/18O) of spring waters indicate that the various springs discharge waters represent differing amounts of mixing between deeper, connate water with shallow meteoric inputs. Clone libraries of 16S rDNA and fluorescence in situ hybridization experiments suggest that oxidation of sulfur compounds by Epsilon- and Gammaproteobacteria is a significant process occurring in the springs, and lipid analyses support these observations. While the studied springs undergo seasonal shifts in their respective geochemistries, only the microbial community at one of the springs elicits a commensurate seasonal variation. During the dry season, the community at this spring shifts to a red, plaque-like biofilm and iron-cycling organisms from the Alphaproteobacteria class increase significantly in their relative abundance within the community. Preliminary chemical analysis of the calcite accretions indicates abundant organic carbon, and thus, suggests a possible record of prior microbial ecosystems. On-going investigations of recalcitrant lipid species such as bacteriohopanepolyols (BHPs), in both extant biology as well as the accreted calcite, is underway and should provide insight to the taphonomic processes affecting the viability of lipid biosignatures. Results emphasize the role of local geophysical history in spring microbial community structure and productivity.

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