Protection and Damage Repair Mechanisms Contributed To the Survival of sp. Exposed To a Mars-Like Near Space Environment.

spp. can withstand extremely harsh environments, including a Mars-like environment. However, studies are lacking on the molecular mechanisms of sp. surviving in Mars-like environments. In the HH-21-5 mission, the desert cyanobacterium sp. was exposed to a Mars-like environment (near space; 35 km altitude) for 4 h, and a single-factor environment of near space was simulated on the ground. We investigated the survival and endurance mechanisms of sp. ASB-02 after exposing it to near space by studying its physiological and transcriptional properties. After the exposure, sp. ASB-02 exhibited high cell viability, although photosystem II activity decreased and the levels of reactive oxygen species increased. The single-factor simulation experiments revealed that for the survival of sp. ASB-02 in near space, UV radiation was the most important limiting factor, and it was followed by temperature. The near space environment triggered multiple metabolic pathway responses in sp. ASB-02. The upregulation of extracellular polysaccharides as well as carotenoid and scytonemin biosynthesis genes in response to UV radiation attenuated the extent of radiation reaching the cells. At the same time, genes related to protein synthesis were upregulated in response to the low temperature, overcoming the decrease in metabolic activity that was caused by the low temperature. In near space and after rehydration, the genes involved in various DNA and photosystem II repair pathways were upregulated. This reflected the damage to the DNA and photosystem II protein subunits in cells during the flight and suggested that repair mechanisms play an important role in the recovery of sp. ASB-02. This study reported that the protective and repair mechanisms of sp. ASB-02 contributed to its endurance ability in a Mars-like near space environment. In sp. ASB-02, a Mars-like near space environment activated the expression of genes involved in extracellular polysaccharides (EPS), carotenoid, scytonemin, and protein syntheses, which provided additional protection. Additionally, the cell damage repair process enhanced the recovery rate of sp. ASB-02 after the flight. This study will help to enhance the understanding of the tolerance mechanism of sp. and to provide important guidance as to the survival requirements for microbial life in a Mars-like environment.