Redefining the requisite lipopolysaccharide structure in Escherichia coli.
Gram-negative bacteria possess an asymmetric lipid bilayer surrounding the cell wall, the outer membrane (OM). The OM inner leaflet is primarily composed of various glycerophospholipids, whereas the outer leaflet predominantly contains the unique amphiphilic macromolecule, lipopolysaccharide (LPS or endotoxin). The majority of all gram-negative bacteria elaborate LPS containing at least one 2-keto 3-deoxy-D-manno-octulosonate (Kdo) molecule. The minimal LPS structure required for growth of Escherichia coli has long been recognized as two Kdo residues attached to lipid A, inextricably linking viability to toxicity. Here we report the construction and characterization of the nonconditional E. coli K-12 suppressor strain KPM22 that lacks Kdo and is viable despite predominantly elaborating the endotoxically inactive LPS precursor lipid IV(A). Our results challenge the established E. coli Kdo2-lipid A dogma, indicating that the previously observed and well-documented dependence of cell viability on the synthesis of Kdo stems from a lethal pleiotropy precipitated after the depletion of the carbohydrate, rather than an inherent need for the Kdo molecule itself as an indispensable structural component of the OM LPS layer. Inclusion of the inner membrane LPS transporter MsbA on a multicopy plasmid partially suppresses the lethal deltaKdo phenotype directly in the auxotrophic parent strain, suggesting increased rates of nonglycosylated lipid A transport can, in part, compensate for Kdo depletion. The unprecedented nature of a lipid IV(A) OM redefines the requisite LPS structure for viability in E. coli.
Meredith
Timothy C
TC
Department of Medicinal Chemistry, College of Pharmacy, University of Michigan, 428 Church Street, Ann Arbor, Michigan 48109-1065, USA.
Aggarwal
Parag
P
Mamat
Uwe
U
Lindner
Buko
B
Woodard
Ronald W
RW
D002240:Carbohydrate Sequence; D002462:Cell Membrane / Q000201:enzymology; D004731:Endotoxins / Q000737:chemistry; D004926:Escherichia coli / Q000737:chemistry*; D006090:Gram-Negative Bacteria / Q000737:chemistry; D008050:Lipid A / Q000737:chemistry; D008051:Lipid Bilayers; D008070:Lipopolysaccharides / Q000737:chemistry* / Q000302:isolation & purification; D008969:Molecular Sequence Data; D010740:Phospholipases / Q000378:metabolism; D013400:Sugar Acids / Q000737:chemistry; D013816:Thermodynamics
D004731:Endotoxins; D008050:Lipid A; D008051:Lipid Bilayers; D008070:Lipopolysaccharides; D013400:Sugar Acids; C002532:2-keto-3-deoxyoctonate; D010740:Phospholipases