Adaptive laboratory evolution of Micrococcus luteus and identification of genes associated with radioresistance through genome-wide association study

Micrococcus luteus (V017) is a Gram-positive bacterium that was isolated from a sterilization area exposed to Co-60 radiation. In this study, we performed an adaptive laboratory evolution experiment with M. luteus, exposing it to 24 continuous cycles of gamma irradiation at four different doses (1.5 kGy, 3.5 kGy, 5.5 kGy, and 7.5 kGy). This led to the creation of four evolved populations with different levels of radioresistance, which were positively correlated with the radiation dose applied. The survival rate of the evolved population that underwent adaptive treatment at the highest dose (7.5 kGy) was 0.69% after exposure to 5.5 kGy, which is about five orders of magnitude higher than that of the original strain V017. Furthermore, 76 evolved strains were selected from these populations, and their genomes were re-sequenced, uncovering a total of 3072 mutations. A genome-wide association study identified 56 single nucleotide polymorphisms (SNPs) significantly associated with radioresistance, linked to 62 candidate genes. Ultimately, 9 genes were selected for functional validation. Inactivating 6 of these genes, including H0H31_RS03855 (SMC family ATPase, SbcC), H0H31_RS04250 (ribonuclease HII), H0H31_RS04570 (endonuclease VIII), H0H31_RS07595 (bifunctional 3 '-5 ' exonuclease/DNA polymerase I), H0H31_RS00170 (serine/threonine phosphatase PPP), and H0H31_RS05860 (CBS-domain-containing protein), significantly increased sensitivity to gamma radiation, underscoring their importance in radioresistance.