Prokaryotic Community of the Ancient Antarctic Permafrost after Irradiation with Gamma Rays under Simulated Martian Conditions

Ionizing radiation is an important environmental factor affecting the dynamics of biospheric processes in the past and present, as well as limiting the spread of life outside the Earth. The effect of radiation on microorganisms has been studied for decades, but studies of the response of natural microbial ecosystems are still scarce. We have studied the effect of 100 kGy gamma irradiation under low pressure (1 Torr) and low temperature (–50°C) on microbial community of the ancient Antarctic permafrost sedimentary rock. After irradiation, the total number of prokaryotic cells determined by epifluorescence microscopy, as well as the number of metabolically active bacterial and archaeal cells detected by fluorescence in situ hybridization remained at the control level, while the number of cultured heterotrophic bacteria decreased by an order of magnitude. Using the multisubstrate testing method, it has been found that the microbial complex retained a high potential metabolic activity and functional diversity after exposure to a combination of extreme physical factors. The resistance demonstrated by the microbial community significantly exceeded the generally accepted estimates of the prokaryotes’ radioresistance and indicated an underestimation of the microorganisms' radioresistance in natural habitats and the important role of mineral heterophase environment and irradiation conditions (pressure, temperature). The study confirmed the potential for long-term cryopreservation of viable terrestrial-like microorganisms in the Martian regolith, as well as the possibility of transferring anabiotic life forms as a part of small bodies in the space environment.