title: The rate of osmotic downshock determines the survival probability of bacterial mechanosensitive channel mutants.
abstract: Mechanosensitive (MS) channels allow cells to sense and respond to environmental changes. In bacteria, these channels are believed to protect against an osmotic shock. The physiological function of these channels has been characterized primarily by a standardized assay, where aliquots of batch-cultured cells are rapidly pipetted into a hypotonic medium. Under this method, it has been inferred many types of MS channels (MscS homologs in Escherichia coli) demonstrate limited effectiveness against shock, typically rescuing less than 10% of the cells when expressed at native levels. We introduce a single-cell-based assay which allows us to control how fast the osmolarity changes, over time scales ranging from a fraction of a second to several minutes. We find that the protection provided by MS channels depends strongly on the rate of osmotic change, revealing that, under a slow enough osmotic drop, MscS homologs can lead to survival rates comparable to those found in wild-type strains. Further, after the osmotic downshift, we observe multiple death phenotypes, which are inconsistent with the prevailing paradigm of how cells lyse. Both of these findings require a reevaluation of our basic understanding of the physiology of MS channels.
authors.affiliation: Departments of Biochemistry and Molecular Biophysics, California Institute of Technology, Pasadena, California, USA.
authors.forename: Maja
authors.initials: M
authors.lastname: Bialecka-Fornal
authors.affiliation: Department of Applied Physics, California Institute of Technology, Pasadena, California, USA.
authors.forename: Heun Jin
authors.initials: HJ
authors.lastname: Lee
authors.affiliation: Departments of Biochemistry and Molecular Biophysics, California Institute of Technology, Pasadena, California, USA Department of Applied Physics, California Institute of Technology, Pasadena, California, USA Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, California, USA phillips@pboc.caltech.edu.
authors.forename: Rob
authors.initials: R
authors.lastname: Phillips
mesh_terms: D002473:Cell Wall; D004926:Escherichia coli / Q000235:genetics / Q000502:physiology*; D029968:Escherichia coli Proteins / Q000235:genetics / Q000378:metabolism*; D015964:Gene Expression Regulation, Bacterial / Q000502:physiology; D040542:Mechanotransduction, Cellular / Q000235:genetics / Q000502:physiology*; D009154:Mutation; D009997:Osmotic Pressure / Q000502:physiology*
chemical_list: D029968:Escherichia coli Proteins