Role of an Escherichia coli stress-response operon in stationary-phase survival.

Abstract

The phage shock protein operon (pspABCE) ofEscherichia coli is strongly expressed in response to stress environmental conditions, such as heat shock, ethanol treatment, osmotic shock, and filamentous phage infection. We show that bacteria lacking the pspABC genes exhibit a substantial decrease in the ability to survive prolonged incubation in stationary phase under alkaline conditions (pH 9). The psp mutant bacteria grow approximately as well as wild-type strains in the alkaline medium, and stationary-phase survival of the psp mutants improves substantially at pH values closer to the optimal growth range (pH 6-8). In late statoar-phase (1-to 2-day-old) cells, the operon can be strongly induced under certain conditions, and PspA can become one ofthe most highly expressed bacterial proteins. The combination of stationary-phase starvation and alkaline pH is likely to place a severe strain on the maintenance ofendogenous energy sources, and, consistent with these effects, we find that psp expression is also induced by uncouplers of oxidative phosphorylation and other agents that interfere with energy production. (1)], and the existence of a multifactor network tightly regulating psp expression, led us to assume that the operon serves a protective or beneficial function. We have suggested that the lack of a stress-related, logarithmic-phase psp phenotype is due to a functional overlap ofthe Psps with the cr32-controlled regulon (6). Both PspA and the o-32-dependent heat shock system turn off psp expression, and this negative regulation may result from similar or overlapping activities.We report here that the psp operon is required for prolonged survival in stationary phase at alkaline pH (pH 9) and that the expression of the psp genes can be strongly induced during stationary phase under certain conditions. MATERIALS AND METHODSBacterial Strains and Plasmids. Strains K561, J134 (K561 ApspABC), L1, and L24 (L1 ApspABC) have been described (6, 10). SG20045 (cps-5::TnlO Alon-100) (11) was kindly provided by Susan Gottesman (National Institutes of Health). SK5022 (zci-604: :TnlO) was from the E. coli Genetic Stock Center (CGSC no. 6666). L104 (K561 cps-S::TnlO), L102 (J134 cps-S::TnJO), and L96 (J134 psp+ zci-604:: TnlO) were generated by transduction (12). The plasmid pBRPS-1, which carries the complete psp operon, was constructed by ligating the 4.5-kb EcoRI fragment of pPS-1 (5)

The Escherichia coli phage‐shock‐protein (psp) operon

“…Nonetheless, the absence of the psp genes does have effects. E. coli lacking PspA-C survive much more poorly in stationary phase at alkaline pH (Weiner and Model, 1994), are somewhat more motile than psp þ cells (our unpublished results), are slower to export proteins via the sec pathway (Kleerebezem et al, 1996;Kleerebezem and Tommassen, 1993), and are less able to maintain their membrane potential when stressed (Kleerebezem et al, 1996). Both the inducing stimuli and the nature of these phenotypes suggest that the psp genes constitute a stress-response operon which may respond to alterations in the energy charge of the cell.…”

“…The phenotypes that have been reported for cells in which the operon is deleted are as follows: lowered survival at alkaline pH in stationary phase (Weiner and Model, 1994), slower protein translocation (Kleerebezem et al, 1996;Kleerebezem and Tommassen, 1993), greater motility, and the loss of membrane potential when cells are subjected to a specific, proton-motive force (pmf)-depleting stress (Kleerebezem et al, 1996). Overexpression of pspA diminishes motility (our unpublished results), and this is more marked than the increase in motility observed in the absence of the psp operon.…”

“…Stresses, such as extreme heat shock or treatment with 10% ethanol and hyper-(but not hypo-) osmotic shock are also inducers (Brissette et al, 1990), but it is not clear whether these stimuli, many of which are lethal to the cell, elicit a normal induction response or short-circuit the normal controls on psp expression. The psp genes are also induced by media downshifts, and are induced very strongly by proton ionophores such as CCCP or other uncouplers (dinitrophenol or free fatty acids) (Weiner and Model, 1994), and by disruption of fatty acid biosynthesis, either by mutation or with the inhibitors diazaborine or cerulenin (Bergler et al, 1994). In addition, PspA protein is a major component of the limited protein synthesis that occurs during late stationary phase (Weiner and Model, 1994).…”

“…The psp genes are also induced by media downshifts, and are induced very strongly by proton ionophores such as CCCP or other uncouplers (dinitrophenol or free fatty acids) (Weiner and Model, 1994), and by disruption of fatty acid biosynthesis, either by mutation or with the inhibitors diazaborine or cerulenin (Bergler et al, 1994). In addition, PspA protein is a major component of the limited protein synthesis that occurs during late stationary phase (Weiner and Model, 1994). Other than expression of gene IV or infection with filamentous phage, all the inducing stimuli also induce the 32 -dependent heat-shock genes (groE, dnaK, dnaJ, grpE (Lindquist and Craig, 1988;Yura et al, 1993)), but psp-operon transcription does not require 32 and hence none of the other components of the canonical heat-shock response; indeed, shift of a 32ts mutant to the non-permissive temperature intensifies the psp response, and for the stimuli that induce psp transiently, such as heat and exposure to ethanol, this prolongs the response (Brissette et al, 1990;Weiner et al, 1991).…”

Habituation of Foodborne Pathogens Exposed to Extreme pH Conditions: Genetic Basis and Implications in Foods and Food Processing Environments

“…Unlike other genes that have been expressed under high pH conditions, surA is not transcribed by the alternate sigma factor. Phage shock proteins (PSPs) are also required for survival of stationary phase E. coli cells at pH 9 (Weiner & Model, 1994). Mutants that lacked the operon psp-ABCE that encodes PSPs showed a significant decrease in survival under the same conditions.…”