Acquired Radioresistance Through Adaptive Evolution with Gamma Radiation as Selection Pressure: Increased Expression and Induction of Anti-Stress Genes.

Elucidating the mechanisms of radioresistance in highly radiotolerant organisms can provide valuable insights into the adaptation and evolution of organisms. However, research has been limited on many naturally occurring radioresistant organisms due to a lack of information regarding their genetic and biochemical characteristics and the difficulty of handling them experimentally. To address this, we conducted an experiment on adaptive evolution using gamma radiation as the selection pressure to generate evolved Escherichia coli with gamma radiation resistance approximately one order of magnitude greater than that of wild-type E. coli. Gene expressions in all wild-type and evolved radioresistant E. coli in the presence or absence of gamma irradiation were analyzed and compared using RNA sequencing. Under steady-state conditions, the genes involved in survival, cell recovery, DNA repair, and response following stress exposure were upregulated in evolved E. coli compared with those in wild-type E. coli. Furthermore, the evolved E. coli induced these genes more efficiently following gamma irradiation and greater DNA repair activity than that in the wild-type E. coli. Our results indicate that an increased steady-state expression of various anti-stress genes, including DNA repair-related genes, and their highly efficient induction under irradiation are responsible for the remarkable radioresistance of evolved E. coli.