Astrobiology Workshop, Macquarie University July 12-13 2001

workshop home page | workshop program

Radon-tolerant microbes from Paralana thermal spring, South Australia

Cherida Trott(1), Roberto P. Anitori(3), David J. Saul1, Louisa Tuiafitu(4), Peter L. Bergquist(2,3,5) and Malcolm Walter(2, 4)

1 School of Biological Sciences, Private Bag 90219, Auckland University, New Zeal and;
2 Australian Centre for Astrobiology, 3 Department of Biological Sciences, and 4 Department of Earth and Planetary Sciences, Macquarie University, North Ryde, 2109, Australia.
5 Division of Molecular Medicine, Auckland University Medical S chool, New Zealand.

In the search for extant or extinct microbial life on Mars, one of most critical questions is "where do we look?" Based on life here on Earth, sites with the highest probability of containing evidence of present or past life are those that may have been/are currently associated with water. An energy source is also important. Hydrothermal areas, such as putative ancient Martian hot springs, satisfy these criteria and therefore represent excellent potential targets. But what do we search for? Analysis of analogous terrestrial sites can help us in obtaining some answers.

We present initial results from an analysis of nine samples recovered from the Paralana hot spring in the Flinders Ranges, South Australia. Water temperatures at the sampling sites ranged from 48 - 63OC; pH was neutral. Also, the spring wat ers contain low levels of radon gas. We have used DNA-based techniques to survey all nine samples. Specifically, 16S ribosomal RNA (rRNA) genes were PCR amplified using degenerate eubacterial primers from genomic DNA extracted from the samples. The genes were analysed by Amplified Ribosomal DNA Restriction Analysis (ARDRA), which provides easily comparable fingerprints or 'molecular signatures', and DNA sequencing. The data were examined using phylogenetic software (PAUP*). Eight of the nine samples displayed a moderate to large number of different molecular signatures, including one to six 'dominant' (i.e. representing > 5% of the total analysed) ARDRA fingerprints. For each sample, the contribution of these dominant fingerprints ranged from 15% to 76%. The notable exception was sample F , in which 95% of the signatures were identical. When examined as one set, there were over 20 dominant groups across the nine samples. Examples of 16S rRNA gene s identified by DNA sequencing include those from a nitrite-oxidising bacterium (Nitrospira moscoviensis), and green sulfur and green non-sulfur bacteria. Finally, an optical microscopic examination of the samples revealed the presence of both prokaryotes (e.g. cyanobacteria) and eukaryotes (e.g. nematodes).