A culture-independent survey of the bacterial community in a radon hot spring

Paralana is an active, radon-containing hot spring situated in a region of South Australia's Flinders Ranges with a long history of hydrothermal activity. Our aim was to determine the bacterial composition of Paralana using a culture-independent, 16S rRNA-based technique. The presence of a diverse bacterial community was strongly suggested by the large number (approximately 180) of different ribotypes obtained upon analysis of nine hot spring samples. DNA sequencing of Paralana 16S rRNA genes corroborated this observation, identifying representatives of seven confirmed and two candidate divisions of the domain Bacteria. These included Cyanobacteria, Proteobacteria (both beta and delta subdivisions), the Cytophaga-Flexibacter-Bacteroides group, Low G + C Gram-positives, Nitrospira, green non-sulfur bacteria, green sulfur bacteria, OP8, and OP12. No known ionizing radiation-resistant Bacteria were identified. Only one Paralana 16S rRNA sequence type (recombinant B5D) was homologous to a sequence previously identified from a radioactive environment.

Site selection for Mars exobiology

The selection of sites on Mars that have a high priority for exobiological research is fundamental for planning future exploration. The most immediate need is to identify targets for high resolution orbital imaging during the Mars Observer and Mars '94/'96 missions that can be used to refine site priorities for surface exploration. We present an objective approach to site selection whereby individual sites are selected and scored, based on the presence of key geological features which indicate high priority environments. Prime sites are those that show evidence for the prolonged activity of liquid water and which have sedimentary deposits that are likely to have accumulated in environments favorable for life. High priority areas include fluvio-lacustrine (stream-fed lake systems), springs, and periglacial environments. Sites where mineralization may have occurred in the presence of organisms (e.g. springs) are given high priority in the search for a fossil record on Mars. A systematic review of Viking data for 83 sites in the Mars Landing Site Catalog resulted in the selection of 13 as being of exobiological interest. The descriptions of these sites were expanded to address exobiological concerns. An additional five sites were identified for inclusion in the second edition of the MLSC. We plan to broaden our site selection activities to include a systematic global reconnaissance of Mars using Viking data, and will continue to refine site priorities for exobiological research based on data from future missions in order to define strategies for surface exploration.