Effects of overproduction of superoxide dismutases in Escherichia coli on inhibition of growth and on induction of glucose-6-phosphate dehydrogenase by paraquat.

Stationary phase inocula were more susceptible to the growth inhibitory effect of paraquat than were log phase inocula and this difference was exacerbated in strains overproducing superoxide dismutases (SOD). Glucose-6-phosphate dehydrogenase (G-6-PD), a member of the soxR regulon, was induced by paraquat promptly in the case of log phase cells; but only after a lag in stationary phase cells and this difference was also exaggerated in strains overproducing SOD. The negative consequences of overproduction of SOD on the adaptation of stationary phase cells to paraquat may be attributed to competition for cellular resources with an attendant delay in biosynthesis of other components of soxR. Since overproduction of SOD did not prevent log phase cells from inducing G-6-PD in response to paraquat, it appears likely that soxR can respond to aspects of redox status other than O2-. This conclusion is in accord with data which is already in the literature.