Response ofBacillus subtilis spores to dehydration and UV irradiation at extremely low temperatures

Abstract

Spores of Bacillus subtilis have been exposed to the conditions of extreme dehydration (argon/silica gel; simulated space vacuum) for up to 12 weeks at 298 K and 80 K in the dark. The inactivation has been correlated with the production of DNA-double strand-breaks. The temperature-dependence of the rate constants for inactivation or production of DNA-double strand-breaks is surprisingly low. Controls kept in the frozen state at 250 K for the same period of time showed no sign of deterioration. In another series of experiments the spores have been UV irradiated (253.7 nm) at 298 K, 200 K and 80 K after exposure to dehydrating conditions for 3 days. Fluence-effect relationships for inactivation, production of DNA-double strand-breaks and DNA-protein cross-links are presented. The corresponding F37-values for inactivation and production of DNA lesions are significantly increased only at 80 K (factor of 4 to 5). The data indicate that the low temperatures that prevail in the outer parts of the Solar System or at the nightside of Mars or the Moon are not sufficiently low to crucially inhibit inactivation by dehydration. Our data place further constraints on the panspermia hypothesis.

The Ultraviolet Environment of Mars: Biological Implications Past, Present, and Future

“…In many terrestrial microorganisms the detrimental effects of UV radiation may be synergistically increased by extremes such as desiccation and reduced atmospheric pressure (Lindberg and Horneck 1991, Dose et al 1991, Horneck 1993, Dose and Klein 1996. On the surface of Mars the existence of oxidants in the upper layers of the martian regolith (e.g., Hunten 1979) would also be a significant additional stress to a putative surface biota.…”

“…Recent data have been gathered on the effects of UV radiation on Bacillus subtilis spores exposed to vacuum and dehydration (Horneck 1993, Dose andKlein 1996). Bacillus subtilis is a good model for the examination of planetary protection issues since studies on the microbiological profile of the Viking landers (Puleo et al 1977) showed that Bacillus spp.…”

“…The graph of biologically weighted fluence versus survival at 235 nm was then used to calculate the loss of viability under the given martian UV fluences. Dose and Klein (1996) also measured loss of B. subtilis TKJ 3412 viability under UV radiation. They measured an F 37 value (37% of viability left) of 50 J/m 2 for spores in vacuum (3 × 10 −6 mbar) at 298 K exposed to radiation from a mercury vapor lamp emitting primarily at 254 nm.…”

Natural Transfer of Viable Microbes in Space 1. From Mars to Earth and Earth to Mars

“…Exposure of spores of B. subtilis and cells of D. radiodurans to extended periods of vacuum (3 × 10 −4 Pa) resulted in DNA strand breaks and crosslinking of DNA to proteins (Dose et al 1991, Dose andGill 1995). At low temperatures (e.g., 80 K) the rate constants for production of DNA strand breaks were reduced by approximately a factor of 2 compared to room temperature (Dose and Klein 1996). Unique tandem-base change mutations were observed in B. subtilis spores after forced dehydration of its DNA in vacuum of 10 −5 Pa (Munakata et al 1997).…”

Survival of Moss Reproductive Structures under Simulated Martian Environmental Conditions and Extreme Thermal Stress: Vibrational Spectroscopic Study and Astrobiological Implications

“…Important from an experimental point view, therefore, is the study of survival of terrestrial organisms under simulated extraterrestrial conditions and various conditions of stress [2]. For example, following this experimental approach, the survival of bacterial spores (e.g., Bacillus spores) under simulated martian environmental conditions (SMEC) has been reported [3,4] as well as their survival under extreme conditions of ultraviolet radiation [5,6], heavy ions [7], simulated Mars solar radiation [8][9][10][11], low-pressure plasma [12], microgravity [13], outer space [14,15], Martian atmospheric pressure and composition [16], space vacuum and ultraviolet irradiation [17], and the comparative effects of several stresses on vegetative cells and spores [18] as well as under the environmental conditions of Jupiter's moon, Europe [19]. Survival of other bacteria, including an acidophilic chemolithotroph isolated from the Rio Tinto (Spain) and belonging to the Acidithiobacillus genus and Deinococcus radiodurans has been studied under SMEC [20], as well as methanogens under conditions of extreme dryness [21].…”