Astrobiology Workshop, Macquarie University July 12-13 2001

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Archaeal and bacterial diversity in a moderately acidic thermal spring.

Mary McHale, Nancy Hinman, and Thomas L. Kieft. (New Mexico Institute of Mining and Technology, University of Montana)

We have characterized microbial communities in a thermal spring (~700C, pH 4) in Yellowstone National Park in order to relate the dominant microbial metabolic potentials (inferred from phylogenetic data) to the changing geochemistry of the spring in August 1999 and June 2000. The high temperature and chemolithotrophic energy sources within this spring may be analogous to the conditions during early life on Earth and possibly Mars, making it an excellent environment to discern interactions between evolving biological and geological parameters. Sediment and water samples taken from the collecting pool and run off channels were subject to chemical analysis, direct DNA extraction, PCR amplification with universal Archaeal and Bacterial primers, cloning, RFLP screening, and sequencing of the 16S rRNA genes. During the first sampling event the spring had more reducing conditions, while the spring had more oxidizing conditions during the second sampling event. There were also significant differences in the concentrations of minor ions between the sampling events. Phylogenetic analysis revealed a diverse community mainly belonging to the sulfur-dependent thermoacidophilic Crenarchaeota branch of Archaea, which are apparently responding to the geochemical changes. A majority of the 16S rRNA genes we analyzed clustered in two distinct groups within Crenarchaeota with few close relatives. Several clones containing Bacterial inserts were collected; these mainly consisted of close phylogenetic relatives of Hydrogenobacter and Bacillus subtilis. Cluster analysis of RFLP ribotype frequencies grouped by sampling events, suggesting a correlation between the microbial community and the changing geochemistry. The phylogenetic positions of these ribotypes suggest that the biogeochemical reactions mediated by the microorganisms from which they are derived remain consistent with the geochemistry of the spring environment.