Abnormal growth of polyamine-deficient Escherichia coli mutant is partially caused by oxidative stress-induced damage

Polyamines participate in numerous cellular processes and are required for normal cell growth in Escherichia coli. In this study, we constructed a new polyamine-deficient E. coli mutant and investigated the physiological function of polyamines during normal aerobic growth conditions. We showed that the requirement for sulfur-containing, branched chain, and aromatic amino acids, which was exhibited in the sodA sodB double mutant faced with severe oxidative stress, was also true of the polyamine-deficient mutant during normal aerobic cell growth. Sorbitol, sucrose, mannose, 1,2-dihydroxybenzene-3,5-disulfonic acid (Tiron), an antioxidant that functions as an oxygen radical scavenger including O2−, and thiamine partially relieved the cell growth defect caused by polyamine depletion in a dose-dependent manner. As was the case for the cells treated with paraquat, the mutant had an elongated shape compared with the polyamine-proficient wild type. Decreased aeration also relieved the cell growth defect of the polyamine-deficient mutant. Finally, we confirmed that chloromethyl-2′,7′-dichlorofluorescin diacetate (DCFH-DA), which is oxidized in a fluorescent product in the presence of various oxidants, also fluoresce in the polyamine-deficient cells. These results showed that abnormal growth of the polyamine-deficient E. coli mutant results partially from oxidative stress-induced damage and the mutant thus exhibits the requirement for antioxidant or specific nutritional amino acid during normal aerobic growth.