Escherichia colt mutants sensitive to oxygen

In order to investigate cellular defenses against oxygen toxicity, fifteen oxygen-sensitive (Oxy^s) mutants of Escherichia coli were isolated. Genetic experiments indicate that the mutations map to six different chromosomal regions. The mutants do not form macroscopic colonies when plated aerobically. They do form macroscopic colonies anaerobically. Oxygen, introduced during log phase, inhibits growth of liquid cultures. The degree of inhibition has been used to separate the mutants into three phenotypic classes. Mutants in Class I do not grow after exposure to oxygen. Mutants in Class II are able to grow, but at a reduced rate and to a reduced final titer, when compared to the wild-type parent. Mutants in Class III form filaments in response to oxygen. The results of enzymatic assays indicate that seven of the ten mutants in Class I have low levels of catalase, peroxidase, superoxide dismutase, and respiratory enzymes when compared with the wild-type parent. Mutations in five of the seven mutants in Class I which have the low enzyme activities map within the region: 8-13.5 min. PI transduction data indicate that mutations in at least three of these five map to 8.4 min. The correlation of low enzyme levels with mapping data suggest that a single gene may regulate several enzymes in response to oxygen. The remaining three mutants in Class I have wild-type levels of catalase, peroxidase, and superoxide dismutase, but have decreased respiratory enzyme activity. The mutants in Class II and Class III have enzyme activities similar to the wild-type parent. These results demonstrate that mutations in at least six genes can be expressed as oxygen-sensitivity. Some of these genes may be involved directly in respiration, cell division, or may regulate the expression of several enzymes.