OXYGEN SENSITIVITY OF AN ESCHERICHIA-COLI MUTANT

Genetic evidence indicates that Oxy(s)-6, an oxygen-sensitive mutant o f Escherichia coli AB1157, is defective in the region of the hemB locu s. Oxy(s)-6 is capable of growth under aerobic conditions only if cult ures are initiated at low-inoculum levels. Aerobic liquid cultures are limited to a cell density of 10(7) cells per ml by the accumulation o f a metabolically produced, low-molecular-weight, heat-stable material in complex organic media. Both Oxy(s)-6 and AB1157 cells produce the material, but only aerobic cultures of the mutant are inhibited by it. The material is produced by both intact cell and cell extracts in com plex media. This reaction also occurs when the amino acid L-lysine is substituted for complex media.