Survivability of Soil and Permafrost Microbial Communities after Irradiation with Accelerated Electrons under Simulated Martian and Open Space Conditions
Department of Soil Biology, Lomonosov Moscow State University, Moscow 119991, Russia
Space Research Institute, Russian Academy of Sciences, Moscow 117997, Russia
Ioffe Physical-Technical Institute, Russian Academy of Sciences, St. Petersburg 194021, Russia
Peter the Great St. Petersburg State Polytechnic University, St. Petersburg 194021, Russia
Petersburg Nuclear Physics Institute Named by B.P. Konstantinov of National Research Centre “Kurchatov Institute”, Gatchina 188300, Russia
Institute of Physics and Technology, Ural Federal University, Ekaterinburg 620002, Russia
Author to whom correspondence should be addressed.
Geosciences 2018, 8(8), 298; https://doi.org/10.3390/geosciences8080298
Received: 1 July 2018 / Revised: 17 July 2018 / Accepted: 6 August 2018 / Published: 8 August 2018
(This article belongs to the Special Issue Early Earth Environments and Biospheric Evolution)
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.