Comparative genomics of space-resilient Chroococcidiopsis cyanobacteria reveals a core genetic repertoire supporting extreme tolerance towards desert and non-Earth conditions

Desert cyanobacteria of the Chroococcidiopsis genus, due to their remarkable desiccation and radiation tolerance, are considered model candidates in the field of astrobiology. For this reason, three strains, namely Chroococcidiopsis sp. CCMEE 029, 057 and 064 have been exposed in the dried state to space- and Mars-like conditions throughout laboratory simulations and real space exposure using the EXPOSE facility installed outside the International Space Station. However, how they can recover upon rehydration and repair the damage accumulated under extreme conditions on Earth and in space remains to be fully elucidated through omics-based investigations. Hence, comparative genomics of these three Chroococcidiopsis strains offered a powerful lens to explore the genetic components of their capability to persist under extreme conditions. The analysis of newly obtained gapless genome assemblies of the laboratory-maintained reference strains of CCMEE 029, 057 and 064 allowed the identification of conserved and non-shared genes involved in reactive oxygen species detoxification, desiccation tolerance, DNA protection and repair. Moreover, a biosynthetic gene cluster for scytonemin production was identified in every strain, while strain CCMEE 057 also harbored the genes for the biosynthesis of a mycosporine-like amino-acid. Such insights are crucial for understanding the adaptation strategies employed by microorganisms to survive in dry, radiation-intense environments, offering clues about the potential for life beyond Earth.