ROLE OF THE ESCHERICHIA-COLI SURA PROTEIN IN STATIONARY-PHASE SURVIVAL

SurA is a periplasmic peptidyl-prolyl isomerase required for the effic ient folding of extracytoplasmic proteins. Although the surA gene had been identified in a screen for mutants that failed to survive! in sta tionary phase, the role played by SurA in stationary-phase survival re mained unknown. The results presented here demonstrate that the surviv al defect of surA mutants is due to their inability to grow at elevate d pH in the absence of sigma(S). When cultures of Escherichia coli wer e grown in peptide-rich Luria-Bertani medium, the majority of the cell s lost viability during the first two to three days of incubation in s tationary phase as the pH rose to pH 9, At this time the surviving cel ls resumed growth. In cultures of surA rpoS double mutants the survivo rs lysed as they attempted to resume growth at the elevated pH, Cells lacking penicillin binding protein 3 and sigma(S) had a survival defec t similar to that of surA rpoS double mutants, suggesting that SurA fo ldase activity is important for the proper assembly of the cell wall-s ynthesizing apparatus.