Polyamines Protect Escherichia coli Cells from the Toxic Effect of Oxygen

Wild-type Escherichia coli cells grow normally in 95%$O_2/5\%\>CO_2$. In contrast, cells that cannot make polyamines because of mutations in the biosynthetic pathway are rapidly killed by incubation in 95%$O_2/5\%\>CO_2$. Addition of polyamines prevents the toxic effect of oxygen, permitting cell survival and optimal growth. Oxygen toxicity can also be prevented if the growth medium contains an amino acid mixture or if the polyamine-deficient cells contain a manganese-superoxide dismutase (Mn-SOD) plasmid. Partial protection is afforded by the addition of 0.4 M sucrose or 0.4 M sorbitol to the growth medium. We also report that concentrations of H2O 2that are nontoxic to wild-type cells or to mutant cells pretreated with polyamines kill polyamine-deficient cells. These results show that polyamines are important in protecting cells from the toxic effects of oxygen.