A mutant Escherichia coli that attaches peptidoglycan to lipopolysaccharide and displays cell wall on its surface.

Marcin Grabowicz,Thomas J Silhavy,Daniel Kahne,Matthew D Lebar,Dorothee Andres,Goran Malojčić

doi:10.7554/elife.05334

Abstract

The lipopolysaccharide (LPS) forms the surface-exposed leaflet of the outer membrane (OM) of Gram-negative bacteria, an organelle that shields the underlying peptidoglycan (PG) cell wall. Both LPS and PG are essential cell envelope components that are synthesized independently and assembled by dedicated transenvelope multiprotein complexes. We have identified a point-mutation in the gene for O-antigen ligase (WaaL) in Escherichia coli that causes LPS to be modified with PG subunits, intersecting these two pathways. Synthesis of the PG-modified LPS (LPS*) requires ready access to the small PG precursor pool but does not weaken cell wall integrity, challenging models of precursor sequestration at PG assembly machinery. LPS* is efficiently transported to the cell surface without impairing OM function. Because LPS* contains the canonical vancomycin binding site, these surface-exposed molecules confer increased vancomycin-resistance by functioning as molecular decoys that titrate the antibiotic away from its intracellular target. This unexpected LPS glycosylation fuses two potent pathogen-associated molecular patterns (PAMPs).

Highlights

A peptidoglycan (PG) cell wall is an essential extracytoplasmic feature of most bacteria (Singer et al, 1989); this essentiality has made its biogenesis a fruitful target for antibiotics, including vancomycin and penicillin
The cell wall is directly exposed to the extracellular milieu in Gram-positive bacteria, but is shielded in Escherichia coli and other Gram-negative species by a highly selective permeability barrier formed by the outer membrane (OM)
The search revealed that a mutation in a gene called waaL increases E. coli's resistance to vancomycin, but not to other antibiotics

Summary

Introduction

A peptidoglycan (PG) cell wall is an essential extracytoplasmic feature of most bacteria (Singer et al, 1989); this essentiality has made its biogenesis a fruitful target for antibiotics, including vancomycin and penicillin. One such vancomycin-resistant suppressor mapped to the waaL gene, the product of which is an IM glycosyltransferase that attaches The search revealed that a mutation in a gene called waaL increases E. coli's resistance to vancomycin, but not to other antibiotics.

Results

Conclusion