Multiple Envelope Stress Response Pathways Are Activated in an Escherichia coli Strain with Mutations in Two Members of the DedA Membrane Protein Family

ABSTRACTThe ability to persist and grow under alkaline conditions is an important characteristic of many bacteria. In order to survive at alkaline pH,Escherichia colimust maintain a stable cytoplasmic pH of about 7.6. Membrane cation/proton antiporters play a major role in alkaline pH homeostasis by catalyzing active inward proton transport. The DedA/Tvp38 family is a highly conserved membrane protein family of unknown function present in most sequenced genomes. YqjA and YghB are members of theE. coliDedA family with 62% amino acid identity and partially redundant functions. We have shown thatE. coliwith ΔyqjAand ΔyghBmutations cannot properly maintain the proton motive force (PMF) and is compromised in PMF-dependent drug efflux and other PMF-dependent functions. Furthermore, the functions of YqjA and YghB are dependent upon membrane-embedded acidic amino acids, a hallmark of several families of proton-dependent transporters. Here, we show that the ΔyqjAmutant (but not ΔyghB) cannot grow under alkaline conditions (ranging from pH 8.5 to 9.5), unlike the parentE. coli. Overexpression ofyqjArestores growth at alkaline pH, but only when more than ∼100 mM sodium or potassium is present in the growth medium. Increasing the osmotic pressure by the addition of sucrose enhances the ability of YqjA to support growth under alkaline conditions in the presence of low salt concentrations, consistent with YqjA functioning as an osmosensor. We suggest that YqjA possesses proton-dependent transport activity that is stimulated by osmolarity and that it plays a significant role in the survival ofE. coliat alkaline pH.IMPORTANCEThe ability to survive under alkaline conditions is important for many species of bacteria.Escherichia colican grow at pH 5.5 to 9.5 while maintaining a constant cytoplasmic pH of about 7.6. Under alkaline conditions, bacteria rely upon proton-dependent transporters to maintain a constant cytoplasmic pH. The DedA/Tvp38 protein family is a highly conserved but poorly characterized family of membrane proteins. Here, we show that the DedA/Tvp38 protein YqjA is critical forE. colito survive at pH 8.5 to 9.5. YqjA requires sodium and potassium for this function. At low cation concentrations, osmolytes, including sucrose, can facilitate rescue ofE. coligrowth by YqjA at high pH. These data are consistent with YqjA functioning as an osmosensing cation-dependent proton transporter.

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The Cpx Envelope Stress Response Is Controlled by Amplification and Feedback Inhibition

Journal of Bacteriology ◽

10.1128/jb.181.17.5263-5272.1999 ◽

1999 ◽

Vol 181 (17) ◽

pp. 5263-5272 ◽

Cited By ~ 161

Author(s):

Tracy L. Raivio ◽

Daniel L. Popkin ◽

Thomas J. Silhavy

Keyword(s):

Escherichia Coli ◽

Stress Response ◽

Virulence Factors ◽

Histidine Kinase ◽

Feedback Inhibition ◽

Response Regulator ◽

Regulatory System ◽

Concomitant Increase ◽

Envelope Stress ◽

Two Component

ABSTRACT In Escherichia coli, the Cpx two-component regulatory system activates expression of protein folding and degrading factors in response to misfolded proteins in the bacterial envelope (inner membrane, periplasm, and outer membrane). It is comprised of the histidine kinase CpxA and the response regulator CpxR. This response plays a role in protection from stresses, such as elevated pH, as well as in the biogenesis of virulence factors. Here, we show that the Cpx periplasmic stress response is subject to amplification and repression through positive and negative autofeedback mechanisms. Western blot and operon fusion analyses demonstrated that the cpxRA operon is autoactivated. Conditions that lead to elevated levels of phosphorylated CpxR cause a concomitant increase in transcription ofcpxRA. Conversely, overproduction of CpxP, a small, Cpx-regulated protein of previously unknown function, represses the regulon and can block activation of the pathway. This repression is dependent on an intact CpxA sensing domain. The ability to autoactivate and then subsequently repress allows for a temporary amplification of the Cpx response that may be important in rescuing cells from transitory stresses and cueing the appropriately timed elaboration of virulence factors.

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Overlapping stimulons arising in response to divergent stresses in Escherichia coli

10.1101/2021.12.17.473201 ◽

2021 ◽

Author(s):

Huijing Wang ◽

GW McElfresh ◽

Nishantha Wijesuriya ◽

Adam Podgorny ◽

Andrew D Hecht ◽

...

Keyword(s):

Escherichia Coli ◽

Stress Response ◽

Stress Responses ◽

Differential Expression Analysis ◽

Stringent Response ◽

Coli Strain ◽

Growth Media ◽

Overflow Metabolism ◽

Rna Seq ◽

E Coli

Cellular responses to stress can cause a similar change in some facets of fitness even if the stresses are different. Lactose as a sole carbon source for Escherichia coli is an established example: too little causes starvation while excessive lactose import causes toxicity as a side-effect. In an E. coli strain that is robust to osmotic and ionic differences in growth media, B REL606, the rate of antibiotic-tolerant persister formation is elevated in both starvation-inducing and toxicity-inducing concentrations of lactose in comparison to less stressful intermediate concentrations. Such similarities between starvation and toxification raise the question of how much the global stress response stimulon differs between them. We hypothesized that a common stress response is conserved between the two conditions, but that a previously shown threshold driving growth rate heterogeneity in a lactose-toxifying medium would reveal that the growing fraction of cells in that medium to be missing key stress responses that curb growth. To test this, we performed RNA-seq in three representative conditions for differential expression analysis. In comparison to nominally unstressed cultures, both stress conditions showed global shifts in gene expression, with informative similarities and differences. Functional analysis of pathways, gene ontology terms, and clusters of orthogonal groups revealed signatures of overflow metabolism, membrane component shifts, and altered cytosolic and periplasmic contents in toxified cultures. Starving cultures showed an increased tendency toward stringent response-like regulatory signatures. Along with other emerging evidence, our results show multiple possible pathways to stress responses, persistence, and possibly other phenotypes. These results suggest a set of overlapping responses that drives emergence of stress-tolerant phenotypes in diverse conditions.

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