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Project Progress

This project examines relationship between hydrological and biological diversity within a mesophilic, sufide-rich spring system. We are focusing on a set of springs in which the water composition, temperature and discharge are variable because of the mixing of groundwater from different sources. These springs are terrestrial analogues for late-stage groundwater discharge at the Martian surface. The site was chosen chosen based on geologic history, extant biology, and the accretion of large calcite ‘mounds’ created by spring water discharge. The mounds allow us to relate the extant biological communities to that preserved in the calcite mounds and to discern taphonomic processes affecting biosignature preservation. This allows us to identify the potential and challenge of finding a fossil record of life at spring deposits on other planets.

Even though the springs all lie within a few tens of meters of each other there is a wide range of hydrogeochemical properties and this is reflected in the biological communities that inhabit the springs. The dominant biology present at each spring is composed of sulfur-oxidizing members of both the Epsilon- and Gammaproteobacteria as revealed by 16S rRNA analysis; lipid analysis of the biomass confirms this observation. To date wee have been monitoring the hydrology of these springs for two years (discharge, temperature, geochemistry, water source as identified with stable isotopes of O and H). These measurements allow us to develop theoretical models for the hydrogeology associated with the springs and hence to understand their evolution in time, and the origin of spatial variability, of water temperature and geochemistry. We also have biological samples from a year period. In addition to differences between individual springs, we also see seasonal variations in the biological communities at a given spring.

A second site was chosen which we believe may be more analogous to Martian springs during periods of high discharge because the springs originate is largely unweathered basalt. They may also represent a possible terrestrial analog for Fe-based microbial ecosystems on Mars. This site (Box Canyon, Idaho) has been the subject of geomorphological and hydrological research by our NAI team (see subproject 1). We have focused on enumeration, enrichment, and isolation of lithoautotrophic Fe(II)-oxidizing and dissimilatory Fe(III)-reducing microorganisms from this circumneutral pH groundwater seep environment. At present we have several highly-purified enrichment cultures, and are preparing to isolate organisms in pure culture. The phylogenetic position of the pure culture isolates will be compared to in situ microbial community composition at the two sites as determined by 16S rRNA gene clone libraries (currently under construction) in order to assess whether the cultures are representative of dominant Fe redox-metabolism organisms in situ.

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