Physico-chemical limit of microbial life. Studies with novel haloarchaeal isolates from Permian salt deposits

Since the Viking missions in 1976/77, which were designed for the detection of microbes on the surface of Mars, our perception of the physico-chemical limits of life has expanded considerably. So-called extremophilic microorganisms, which are capable of thriving in the presence of one or more factors once considered inimical to life - e.g. high or low temperatures, alkaline or acidic environments, high pressure, high salinity - were discovered in various locations around the globe. An example are novel extremely halophilic archaebacteria (haloarchaea), which were isolated by the applicant from 250 million year old Alpine salt deposits, and also from Permian salt sediments in England, Poland and Germany. These microorganisms appear, besides being resistant to salt and desiccation, capable of extreme longevity. In addition, a wide range of haloarchaeal ribosomal genes were found in ancient rock salt. Such data support the hypothesis of a long survival of these microorganisms. Since there is now multiple evidence for extraterrestrial halite, it appears plausible to include into the search for life in outer space specifically a search for halophilic microorganisms. However, the "exobiological potential" of haloarchaea needs to be assessed in detail, as well as their tolerance to tectonic movements during the folding of the Alps. This proposal will determine the limiting ranges of several physico-chemical factors with respect to haloarchaeal survival and viability. The experiments will be carried out predominantly with novel haloarchaeal isolates from Permian salt and some other type strains. Treatments of cells will include high pressures and elevated temperatures (produced by a cold seal pressure vessel), and Mars-like environments, e.g. low temperatures, low pressures, a carbon dioxide atmosphere and UV irradiation, as can be produced in a Martian simulation chamber. Analysis of microorganisms following these stress conditions will be by molecular, biochemical and microbiological methods. The expected results should allow an estimation of the tolerance of extreme geological forces by salt-enclosed haloarchaea, as well as a reasonable forecast about the feasibility of considering haloarchaea as analogues for extraterrestrial forms of life.