Replication of Deoxyribonucleic Acid in Escherichia coli under Limited Supply of Oxygen

DNA synthesis under limited supply of oxygen was studied using Escherichia coli 15T⁻ requiring thymine, methionine, arginine and tryptophan. When the culture grown aerobically in a succinate medium was brought at its logarithmic phase to a semi-anaerobic condition (1%, v/v, O₂ in N₂), DNA synthesis continued for about 2hr and terminated temporarily. Repeated changes from aerobic (30 min) to semianaerobic (120 min) conditions resulted in the synchronization of cell division. The inhibitory effect of oxygen deficiency on the DNA replication cycle was more marked in the initiation stage than in the course of DNA synthesis. This was confirmed by the use of KCN as an inhibitor, which also inhibited more strongly the former stage than the latter.