Absence of increased genomic variants in the cyanobacterium Chroococcidiopsis exposed to Mars-like conditions outside the space station

Abstract

Despite the increasing interest in using microbial-based technologies to support human space exploration, many unknowns remain not only on bioprocesses but also on microbial survivability and genetic stability under non-Earth conditions. Here the desert cyanobacterium Chroococcidiopsis sp. CCMEE 029 was investigated for robustness of the repair capability of DNA lesions accumulated under Mars-like conditions (UV radiation and atmosphere) simulated in low Earth orbit using the EXPOSE-R2 facility installed outside the International Space Station. Genomic alterations were determined in a space-derivate of Chroococcidiopsis sp. CCMEE 029 obtained upon reactivation on Earth of the space-exposed cells. Comparative analysis of whole-genome sequences showed no increased variant numbers in the space-derivate compared to triplicates of the reference strain maintained on the ground. This result advanced cyanobacteria-based technologies to support human space exploration.

Figure 1

Experimental design. During the BIOMEX space experiment, dried cells of Chroococcidiopsis sp. CCMEE 029 were exposed to cosmic ionizing radiation combined with a Mars-like environment (UV radiation and atmosphere) simulated in LEO by using the ESA EXPOSE-R2 facility installed outside the ISS. The space-derivate was obtained upon rehydration of the exposed sample after retrieval to Earth. Whole-genome comparative analyses were performed among liquid triplicates of the ground-reference strain and the space-derived strain.

Figure 2

Circular bar plots showing of single nucleotide variants (SNVs) in the ground-reference Chroococcidiopsis sp. CCMEE 029 and space-derivate. The yellow bar plot shows the SNV frequency in the ground-reference genome representing the sum, according to the set theory, of the SNVs of each ground-reference replicate (CCMEE 029 A, B and C). The light-blue bar plot shows SNVs frequency in the space-derived genome. Bars indicate the SNVs frequency in 50-kbp sectors, numbers show absolute frequency values.