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Proc Natl Acad Sci U S A. 2016 Mar 15;113(11):E1565-74. doi: 10.1073/pnas.1601375113. Epub 2016 Feb 29.

Disruption of lipid homeostasis in the Gram-negative cell envelope activates a novel cell death pathway.

Author information

1
Department of Molecular Biology, Princeton University, Princeton, NJ 08544;
2
Department of Bioengineering, Stanford University, Stanford, CA 94305;
3
Department of Bioengineering, Stanford University, Stanford, CA 94305; Lynbrook High School, San Jose, CA 95129;
4
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.
5
Department of Molecular Biology, Princeton University, Princeton, NJ 08544; tsilhavy@princeton.edu kchuang@stanford.edu.

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.

KEYWORDS:

lipid transport; lipopolysaccharide; lysophospholipids; outer membrane; single-cell imaging

PMID:
26929379
PMCID:
PMC4801249
DOI:
10.1073/pnas.1601375113
[Indexed for MEDLINE]
Free PMC Article

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