Identification and Characterization of Early Mission Phase Microorganisms Residing on the Mars Science Laboratory and Assessment of Their Potential to Survive Mars-like Conditions

Abstract

Planetary protection is governed by the Outer Space Treaty and includes the practice of protecting planetary bodies from contamination by Earth life. Although studies are constantly expanding our knowledge about life in extreme environments, it is still unclear what the probability is for terrestrial organisms to survive and grow on Mars. Having this knowledge is paramount to addressing whether microorganisms transported from Earth could negatively impact future space exploration. The objectives of this study were to identify cultivable microorganisms collected from the surface of the Mars Science Laboratory, to distinguish which of the cultivable microorganisms can utilize energy sources potentially available on Mars, and to determine the survival of the cultivable microorganisms upon exposure to physiological stresses present on the martian surface. Approximately 66% (237) of the 358 microorganisms identified are related to members of the Bacillus genus, although surprisingly, 22% of all isolates belong to non-spore-forming genera. A small number could grow by reduction of potential growth substrates found on Mars, such as perchlorate and sulfate, and many were resistant to desiccation and ultraviolet radiation (UVC). While most isolates either grew in media containing ‡10% NaCl or at 4°C, many grew when multiple physiological stresses were applied. The study yields details about the microorganisms that inhabit the surfaces of spacecraft after microbial reduction measures, information that will help gauge whether microorganisms from Earth pose a forward contamination risk that could impact future planetary protection policy.

Silicates Eroded under Simulated Martian Conditions Effectively Kill Bacteria—A Challenge for Life on Mars

“…Bacillus sp . spores are of particular interest and concern, as they are common contaminants in cleanrooms used for assembly of spacecraft (Puleo et al, 1977 ; La Duc et al, 2009 ; Smith et al, 2017 ) and thus likely agents of forward contamination.…”

Habitability of Mars: How Welcoming Are the Surface and Subsurface to Life on the Red Planet?

“…If life existed or currently exists on Mars, it would most likely be in the form of microbial communities that could be supported by Martian conditions, especially in the deep subsurface [24]. Studies on the survival of microorganisms in simulated Martian conditions include experiments on microbial survival in Mars soil analogs [125,126], on spacecraft surface materials [124], and in predefined laboratory media [127]. Even though the latter two do not refer directly to the surface or subsurface of Mars and their associated parameters (pH, oxidation, temperature, water activity), they are discussed in this review to cover the spectrum of microorganisms and their survival capabilities in simulated Martian conditions.…”

“…B. pumilus is one of the most often isolated strains from the SAF with high tolerance of both its vegetative cells and spores to UV and hydrogen peroxide [147]. In a study by Smith et al [127], the isolates that were retrieved from surfaces of the MSL (n = 358) were tested for growth and survival under aerobic conditions with exposure to various environmental factors, such as low temperature (4 • C), high salt concentrations (0.5%, 5%, 10%, 20% NaCl), pH ranges (7,8,9,10,11,12), desiccation, UVC, hydrogen peroxide, and growth under anaerobic conditions with various sources of energy (perchlorate, sulfate, and arsenate). Various microorganisms were found to be resistant when exposed to single environmental stresses, but there were also microorganisms that survived as many as four conditions independently.…”

“…These species included Bacillus safensis, Bacillus aerius, Bacillus sp. T14, and Staphylococcus pastuerii (20% NaCl, 4 • C, 5% H 2 O 2 or at pH 9.0), Staphylococcus epidermidis (20% NaCl, 4 • C, 5% H 2 O 2 , pH 8), and Paenibacillus lautus (20% NaCl, 4 • C, 5% H 2 O 2 , pH 10.0) [127].…”

“…Moderate to strong growth was observed in media containing up to 1 M of perchlorate salt, while for chlorate salts, growth was observed in solutions containing up to 2.75 M. Among the tested isolates, the most common species included Halomonas venusta, Planococcus salnarum, and Bacillus licheniformis. Isolates that were collected from the surface of the MSL were tested for growth under a 10 mM concentration of Na perchlorate salt with acetate or lactate as an electron donor (20 mM) [127]. These isolates included Bacillus sp.…”