Investigation of the tolerance of various sulfate-reducing bacteria to Marsrelevant conditions

Abstract

The Mars, commonly referred to as the Red Planet, is considered the most Earth-like planet in our solar system and has always captivated humanity. One of the key questions in Mars exploration is whether life exists or has existed on the planet. With the increasing number of research missions to Mars, planetary protection has gained significant importance to prevent contamination with terrestrial microorganisms. Spore-forming sulfate-reducing bacteria represent a group of obligate anaerobic organisms that can be found on Earth under extreme conditions at depths of up to 3000 meters. In addition to their ability to form endospores, they are capable of chemolithoautotrophic growth using sulfate, H₂, and CO₂. This characteristic, combined with their adaptability to extreme conditions, theoretically positions them as potential candidates to survive the harsh environment of present-day Mars in the form of spores. In this study, seven representatives from different genera of the Peptococcaceae family were examined with regard to these questions. The results demonstrate that two species, Desulforamulus putei TH-11T and Desulfosporosinus lacus STP12T, are capable of growing without difficulty in the presence of the Mars regolith simulant MGS-1S. They utilize the sulfate within it as an electron acceptor in their metabolism and can also grow autotrophically in an H₂/CO₂ atmosphere. Furthermore, spores formed during growth in MGS-1S showed significant resistance to elevated temperatures, oxygen, and desiccation. These spores could thus serve as suitable survival stages to endure temporarily unfavorable conditions on Mars or potentially survive as stowaways during a journey to Mars. The results provide an initial insight into the potential and risks of spore-forming sulfate-reducing bacteria regarding the planetary protection of Mars. Additionally, they aim to stimulate further research activities and increased attention to this group of organisms in this field.