Enhancement of the viability of irradiated bacteria by chromosome transfer.

The effect of x-irradiating recipient cells of Escherichia coli K-12 before mating on the formation of recombinants and on the distribution of parental genetic material among recombinants was investigated in both the wild-type (Rec+) and a recombination-deficient (Rec-) mutant. In crosses involving Rec- recipients, recombinants selected for a late donor marker were formed in almost normal numbers. Rec- cells exposed to otherwise lethal doses of x-rays were still able to form viable recombinants for a distal male marker. These recombinants had inherited almost all the transferred donor chromosome, as evidenced by the preponderance of male markers in the recombinants. In contrast, the recombinant-forming ability was about as x-ray-sensitive as the colony-forming ability in Rec+ cells. No preference for donor chromosomal material was observed in recombinants from crosses involving x-irradiated Rec+ cells.