title: Disruption of lipid homeostasis in the Gram-negative cell envelope activates a novel cell death pathway.
abstract: Gram-negative bacteria balance synthesis of the outer membrane (OM), cell wall, and cytoplasmic contents during growth via unknown mechanisms. Here, we show that a dominant mutation (designated mlaA*, maintenance of lipid asymmetry) that alters MlaA, a lipoprotein that removes phospholipids from the outer leaflet of the OM of Escherichia coli, increases OM permeability, lipopolysaccharide levels, drug sensitivity, and cell death in stationary phase. Surprisingly, single-cell imaging revealed that death occurs after protracted loss of OM material through vesiculation and blebbing at cell-division sites and compensatory shrinkage of the inner membrane, eventually resulting in rupture and slow leakage of cytoplasmic contents. The death of mlaA* cells was linked to fatty acid depletion and was not affected by membrane depolarization, suggesting that lipids flow from the inner membrane to the OM in an energy-independent manner. Suppressor analysis suggested that the dominant mlaA* mutation activates phospholipase A, resulting in increased levels of lipopolysaccharide and OM vesiculation that ultimately undermine the integrity of the cell envelope by depleting the inner membrane of phospholipids. This novel cell-death pathway suggests that balanced synthesis across both membranes is key to the mechanical integrity of the Gram-negative cell envelope.
authors.affiliation: Department of Molecular Biology, Princeton University, Princeton, NJ 08544;
authors.forename: Holly A
authors.initials: HA
authors.lastname: Sutterlin
authors.affiliation: Department of Bioengineering, Stanford University, Stanford, CA 94305;
authors.forename: Handuo
authors.initials: H
authors.lastname: Shi
authors.affiliation: Department of Molecular Biology, Princeton University, Princeton, NJ 08544;
authors.forename: Kerrie L
authors.initials: KL
authors.lastname: May
authors.affiliation: Department of Bioengineering, Stanford University, Stanford, CA 94305;
authors.forename: Amanda
authors.initials: A
authors.lastname: Miguel
authors.affiliation: Department of Bioengineering, Stanford University, Stanford, CA 94305; Lynbrook High School, San Jose, CA 95129;
authors.forename: Somya
authors.initials: S
authors.lastname: Khare
authors.affiliation: Department of Bioengineering, Stanford University, Stanford, CA 94305; Department of Microbiology and Immunology, Stanford University School of Medicine, Stanford, CA 94305 tsilhavy@princeton.edu kchuang@stanford.edu.
authors.forename: Kerwyn Casey
authors.initials: KC
authors.lastname: Huang
authors.affiliation: Department of Molecular Biology, Princeton University, Princeton, NJ 08544; tsilhavy@princeton.edu kchuang@stanford.edu.
authors.forename: Thomas J
authors.initials: TJ
authors.lastname: Silhavy
mesh_terms: D001425:Bacterial Outer Membrane Proteins / Q000235:genetics / Q000378:metabolism; D002462:Cell Membrane / Q000737:chemistry / Q000378:metabolism; D002473:Cell Wall / Q000378:metabolism*; D004926:Escherichia coli / Q000166:cytology / Q000187:drug effects / Q000235:genetics / Q000378:metabolism; D029968:Escherichia coli Proteins / Q000235:genetics / Q000378:metabolism*; D005227:Fatty Acids / Q000378:metabolism; D050356:Lipid Metabolism / Q000235:genetics*; D008070:Lipopolysaccharides / Q000378:metabolism; D008274:Magnesium / Q000378:metabolism / Q000494:pharmacology; D009154:Mutation; D010539:Permeability; D054466:Phospholipases A1 / Q000378:metabolism; D010743:Phospholipids / Q000378:metabolism*
chemical_list: D001425:Bacterial Outer Membrane Proteins; D029968:Escherichia coli Proteins; D005227:Fatty Acids; D008070:Lipopolysaccharides; D010743:Phospholipids; D054466:Phospholipases A1; C412876:outer membrane phospholipase A; D008274:Magnesium
keywords: lipid transport; lipopolysaccharide; lysophospholipids; outer membrane; single-cell imaging