title: Appropriate Regulation of the σE-Dependent Envelope Stress Response Is Necessary To Maintain Cell Envelope Integrity and Stationary-Phase Survival in Escherichia coli.
abstract: The alternative sigma factor σEis a key component of theEscherichia coliresponse to cell envelope stress and is required for viability even in the absence of stress. The activity of σEincreases during entry into stationary phase, suggesting an important role for σEwhen nutrients are limiting. Elevated σEactivity has been proposed to activate a pathway leading to the lysis of nonculturable cells that accumulate during early stationary phase. To better understand σE-directed cell lysis and the role of σEin stationary phase, we investigated the effects of elevated σEactivity in cultures grown for 10 days. We demonstrate that high σEactivity is lethal for all cells in stationary phase, not only those that are nonculturable. Spontaneous mutants with reduced σEactivity, due primarily to point mutations in the region of σEthat binds the -35 promoter motif, arise and take over cultures within 5 to 6 days after entry into stationary phase. High σEactivity leads to large reductions in the levels of outer membrane porins and increased membrane permeability, indicating membrane defects. These defects can be counteracted and stationary-phase lethality delayed significantly by stabilizing membranes with Mg2+and buffering the growth medium or by deleting the σE-dependent small RNAs (sRNAs) MicA, RybB, and MicL, which inhibit the expression of porins and Lpp. Expression of these sRNAs also reverses the loss of viability following depletion of σEactivity. Our results demonstrate that appropriate regulation of σEactivity, ensuring that it is neither too high nor too low, is critical for envelope integrity and cell viability.IMPORTANCEThe Gram-negative cell envelope and cytoplasm differ significantly, and separate responses have evolved to combat stress in each compartment. An array of cell envelope stress responses exist, each of which is focused on different parts of the envelope. The σEresponse is conserved in many enterobacteria and is tuned to monitor pathways for the maturation and delivery of outer membrane porins, lipoproteins, and lipopolysaccharide to the outer membrane. The activity of σEis tightly regulated to match the production of σEregulon members to the needs of the cell. InE. coli, loss of σEresults in lethality. Here we demonstrate that excessive σEactivity is also lethal and results in decreased membrane integrity, the very phenotype the system is designed to prevent.
authors.affiliation: Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, Pennsylvania, USA.
authors.forename: Hervé
authors.initials: H
authors.lastname: Nicoloff
authors.affiliation: Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, Pennsylvania, USA.
authors.forename: Saumya
authors.initials: S
authors.lastname: Gopalkrishnan
authors.affiliation: Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, Pennsylvania, USA ades@psu.edu.
authors.forename: Sarah E
authors.identifier: http://orcid.org/0000-0003-4042-1283
authors.initials: SE
authors.lastname: Ades
mesh_terms: D000135:Acid Phosphatase / Q000235:genetics / Q000378:metabolism*; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D029968:Escherichia coli Proteins / Q000235:genetics / Q000378:metabolism*; D015964:Gene Expression Regulation, Bacterial; D050296:Microbial Viability; D018272:Porins / Q000378:metabolism; D012808:Sigma Factor / Q000235:genetics / Q000378:metabolism*
chemical_list: D029968:Escherichia coli Proteins; D018272:Porins; D012808:Sigma Factor; C063202:sporulation-specific sigma factors; D000135:Acid Phosphatase; C089634:umpG protein, E coli
keywords: cell envelope; stress response; transcriptional regulation