Penicillin-binding Proteins Are Regulated by RpoS During Transitions in Growth States of Escherichia Coli

Attention has been recently focused on the role of the rpoS (formerly katF) gene product as a regulator during the transition from the exponential growth phase to the stationary phase as well as during nutritional starvation. It has been demonstrated that RpoS is an alternate sigma factor which would bind to promoters of genes induced at these times. It was previously noted that rpoS mutants do not undergo a transition to short rods during entry into the stationary phase. Because of their well-established role in morphogenesis, we investigated the status of the penicillin-binding proteins (PBPs) in Escherichia coli wild-type and isogenic rpoS mutants. Samples from cultures of E. coli ZK126 and ZK1000 (rpoS::kan) were taken in the midlogarithmic, early stationary, and late (24 h) stationary phases. The increase in PBP 6 seen upon entry of the wild-type strain into the stationary phase was not observed with the rpoS::kan cells, even after 24 h. There was also a marked decrease of PBP 3 in wild-type stationary-phase cells; PBP 3 has a known influence on morphogenesis. This decrease in PBP 3 was found to be markedly affected by the disruption of rpoS. Similar observations were made after prolonged starvation of the two strains for either glucose or a required amino acid. Inasmuch as PBPs are involved in peptidoglycan synthesis, we also examined two properties of peptidoglycan, autolysis and cross-linkage, that might be altered by the PBP differences. However, neither of these properties, which are known to undergo changes in the stationary phase, appeared to be influenced by the status of RpoS.