Survivability of Soil and Permafrost Microbial Communities after Irradiation with Accelerated Electrons under Simulated Martian and Open Space Conditions

Abstract

Abstract:One of the prior current astrobiological tasks is revealing the limits of microbial resistance to extraterrestrial conditions. Much attention is paid to ionizing radiation, since it can prevent the preservation and spread of life outside the Earth. The aim of this research was to study the impact of accelerated electrons (~1 MeV) as component of space radiation on microbial communities in their natural habitat-the arid soil and ancient permafrost, and also on the pure bacterial cultures that were isolated from these ecotopes. The irradiation was carried out at low pressure (~0.01 Torr) and low temperature (−130 • C) to simulate the conditions of Mars or outer space. High doses of 10 kGy and 100 kGy were used to assess the effect of dose accumulation in inactive and hypometabolic cells, depending on environmental conditions under long-term irradiation estimated on a geological time scale. It was shown that irradiation with accelerated electrons in the applied doses did not sterilize native samples from Earth extreme habitats. The data obtained suggests that viable Earth-like microorganisms can be preserved in the anabiotic state for at least 1.3 and 20 million years in the regolith of modern Mars in the shallow subsurface layer and at a 5 m depth, respectively. In addition, the results of the study indicate the possibility of maintaining terrestrial like life in the ice of Europa at a 10 cm depth for at least~170 years or for at least 400 thousand years in open space within meteorites. It is established that bacteria in natural habitat has a much higher resistance to in situ irradiation with accelerated electrons when compared to their stability in pure isolated cultures. Thanks to the protective properties of the heterophase environment and the interaction between microbial populations even radiosensitive microorganisms as members of the native microbial communities are able to withstand very high doses of ionizing radiation.

Survival of Radioresistant Bacteria on Europa’s Surface after Pulse Ejection of Subsurface Ocean Water

“…This is the result of the decrease of radiation damages under irradiation at a low temperature and low pressure. This effect was discussed by us previously in detail [14,20,21]. Our result is in general accordance with studies of radioresistance of Deinococcus radiodurans carried out previously with high doses of γ-ray irradiation at −79 • C [22,23].…”

“…There might be two possible causes for this. It might be that the MeV-electrons produce deadly damages more effectively than γ-rays [20], or it could be the difference in composition of the ice samples used, because salts and minerals may be sources of free radicals at radiolysis (e.g., [24]). Authors of the abovementioned papers [22,23] used an ordinary nutrient solution, while we used a special solution simulating the composition of Europa's ice.…”

“…Microbial communities of Earth glaciers could be proposed, like terrestrial analogs of Europa ice, for such studies [4,26,27]. We should note that we studied pure bacteria culture, while in nature, microorganisms exist in communities, and inter-and intrapopulation interactions as well as interactions with the environment can significantly increase microbial radioresistance [20,25]. Thus, studies of natural microbial communities' radioresistance would be eligible to specify putative life survivability on Europa under the accumulation of radiation dose.…”

“…This effect might not be real case, but it has no significant impact on the main goals and conclusions of It should be noted that the irradiation intensity used in the experiment was several orders of magnitude higher than on Europa (see Section 3.2). The effect of such differences on the microorganisms' viability was discussed by us in detail earlier [20,21]. Briefly, the effectiveness of a sparsely ionizing radiation (including accelerated electrons) dose is reduced with irradiation intensity decreasing as a result of recovery phenomena [28].…”

Stress-Tolerance and Taxonomy of Culturable Bacterial Communities Isolated from a Central Mojave Desert Soil Sample

“…Representatives of the genus Cellulomonas are often isolated from soil [69] with some of them known to be halotolerant species [70]. Bacteria of the genus Pontibacter have been previously isolated from arid soils [71,72].…”