Anaerobic incubation enhances the colony formation of a polA recB strain of Escherichia coli K-12.

Escherichia coli strain E247 (polA1 recB21) has reduced colony formation (even at the permissive temperature of 30 degrees C) because of a poor suppressor mutation (sup-126). The colony formation was enhanced in the absence of oxygen about 3-fold at 30 degrees C and 10(6)-fold at 43 degrees C, suggesting that a polA recB strain was inviable due to oxygen toxicity. Colony formation was also increased by incubation in an agar medium containing the reducing agent thioglycolate and incubation in the presence of chloroform-killed Saccharomyces cerevisiae pet+ cells, but not pet cells. Since the E247 strain viability was inversely dependent on the oxygen pressure and since the strain was more sensitive to superoxide radical than either the polA or the recB mutant, it seems likely that the polA and recB genes play a role in repairing DNA damage during respiration.