Employees of the Department of Soil Biology, Faculty of Soil Science, Moscow State University, for the first time studied the effect of high concentration perchlorates on terrestrial analogs of hypothetical microbial communities of Mars. It turned out that a high concentration of perchlorates does not lead to death, but contributes to an increase in the number of many microorganisms. This testifies in favor of the possibility of survival of terrestrial microorganisms in the Mars regolith. The work was published in the International Journal of Astrobiology.
One of the main obstacles to the development of terrestrial microorganisms in the conditions of Mars is the lack of liquid water. The average annual temperature on the planet is about –50 ° С, with fluctuations from approximately –150 ° С to + 30 ° С, depending on the region, season, time of day. At low temperatures, water is in the form of ice, while at higher temperatures, water sublimes, i.e. immediately turns into vapor, since the atmospheric pressure on Mars is about 100 times lower than Earth’s.
Thanks to space missions, it was found that the regolith (residual soil is a product of space weathering of rock in situ) of Mars contains perchlorates in concentrations of about 0.5-1%. Scientists speculate that perchlorates may contribute to the formation and storage of liquid water on Mars, as their solutions have low freezing points. The formation of relatively recently discovered geomorphological structures on Mars, similar to streams, as well as subsurface water bodies, may be associated with the formation of perchlorate-containing solutions. At the same time, perchlorates are strong oxidants and can be harmful to microorganisms. Previous studies have shown that some microorganisms can grow in the presence of very high perchlorate concentrations (over 10%). Nonetheless, the limits of resistance of microorganisms to perchlorates are not defined. Similar studies were previously carried out with individual microorganisms, while microorganisms, as a rule, exist in the form of microbial communities in which different organisms interact both with each other and with a heterogeneous environment.
Employees of the Faculty of Soil Science of Moscow State University studied the effect of perchlorates in high concentrations (5%) on the microbial communities of desert soil and ancient frozen rocks. Such microbial communities are considered as terrestrial analogs of hypothetical microbial communities on Mars, since they exist in extreme conditions. Samples of soils and rocks were moistened with a perchlorate solution or water, then incubated for 10 days, and after that the number and diversity of microorganisms were examined in the samples. Scientists used methods of cultivation, epifluorescence microscopy, in situ fluorescence hybridization, multisubstrate testing, and lipid gas chromatography and mass spectrometry. Sample preparation and incubation and most microbiological analyzes were performed at Moscow State University.
It turned out that the presence of such a high concentration of perchlorates did not lead to the death of the microbial community. Moreover, there was an increase in the abundance of many microorganisms, and the conservation of a large biodiversity, comparable to that in the samples without perchlorates. “Thus, it has been shown that the presence of 5% perchlorate in soils and rocks does not lead to the death or significant inhibition of microbial communities. This testifies to the possibility of survival of terrestrial microorganisms in the regolith of Mars, ”said Vladimir Cheptsov , junior researcher at the laboratory of soil microbiology, faculty of soil science, Moscow State University.
The results of such studies are necessary to assess the possibility of detecting life on various space bodies, to select regions and / or types of rocks and landforms where it is possible to detect organisms or their traces. This, in turn, is required for the planning of space missions, for the development of methods and equipment for these missions, as well as for the development of planetary quarantine measures (i.e., preventing the pollution of other planets and satellites by terrestrial microorganisms and vice versa).
“In continuation of the work, it is planned to study the effect of higher concentrations of perchlorates on microbial communities and to search for the limiting concentrations at which the survival of microbial communities is possible,” added Vladimir Cheptsov.