Mutation in Escherichia coli during substrate-accelerated death

Substrate-accelerated death was studied in lactose-limited cultures of Escherichia coli WP2 trp- and E. coli WP2 trp+. During starvation of E. coli WP2 trp- the viable count decreased while the number of trp+ revertants increased. Addition of 7.5 mM-cAMP to the starvation medium prevented the death of the trp-cells but not the increase in the number of trp+ revertants. As starvation of pure cultures of trp+ revertants did not result in death it suggests that the level of cAMP in trp- cells was lower that in trp+ cells. Addition of benzyl penicillin, nalidixic acid, novobiocin or rifampicin did not affect the viable counts thus indicating that neither cryptic growth not DNA replication occurred; however, in the presence of novobiocin there was no increase in the number of trp+ revertants. The possibility of a constitutive error-prone DNA repair mechanism is considered.