Methanogenic Archaea in the Space Environment

Abstract

Next phase of experiment TEST is aimed to evaluate microbial viability after a prolonged external exposure on the International space station (ISS). Methanogenic archaea isolated from various habitats have been tested in ground facilities for the ability to survive exposure to such open space factors as UV and vacuum. Methanosarcina mazei S-6T (VKM B-1636T) was found to be the most viable and, therefore, suitable for the experiment. Our investigations showed that the Methanosarcina mazei population maintained viability in the course of 24-month exposure. On this evidence we conclude that genome of this metanogenic archaea possesses mechanisms against the space vacuum, UV and thermal differences that, probably, underlie the ability of the strain to form peculiar cyst-like dormant cells.

Survival of microorganisms during two-year exposure in outer space near the ISS

“…3 a), characterized by the presence of a multilayer thickened cell membrane, which has never been observed in strains of this species on Earth, as well as in the control strain in our experiments (Fig. 3 b) 16 .

Figure 3 SEM images of M. mazei S-6 T cells: ( a ) ultra of Methanosarcina cell from the isolate obtained after the 24-mos exposure; ( b ) ultrafine of Methanosarcina cell control.

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“…The growth of the archaea population was determined by the methane formation during cultivation on a nutrient medium. As a result, a 14-day delay in the appearance of methane was revealed during cultivation of the Methanosarcina mazei S-6 T strain after exposure, which was not observed in the ground control strain 16 .…”

“…The main selection criteria were considered to be the largest number of surviving microorganisms after exposure to the maximum dose of ultraviolet radiation and the largest number of microorganisms preserved on the surface after a pressure drop. As a result of the conducted studies, the following microorganisms were selected for subsequent tests in outer space with an exposure duration of 12 and 24 months—bacterial spores of the B. subtilis species isolated from the outer surface of the ISS porthole 15 , fungal spores of the A. pullulans species, isolated from the outer surface of the radiator of the ISS temperature control system 15 , archaea of the M. mazei S-6 T species, collection strain VKM B-1636T 16 .…”

“…The number of surviving spores of bacteria and fungi was determined by the viable colony-forming units (CFU) that grew during surface sowing on solid nutrient media. The number of surviving methanogenic archaea was determined by the methane formation 16 . Figure 2 shows the decrease in the number of viable colony-forming units (CFU) of microorganisms vs. exposure time in open space.…”

“…Based on the literature above, radiation resistance of microorganisms can increase at low temperatures. It is known that the radiation resistance of bacteria spores is higher than that of fungi spores 16 . Most fungi are more sensitive to ionizing radiation and are completely inactivated in the dose range from 1 to 10 kGy, however, the limit of their stability is not reliably determined 28 .…”