Abstract
Lipopolysaccharides, major molecules in the outer membrane of Gram-negative bacteria, play important roles on membrane integrity of the cell. However, how the core oligosaccharide of lipopolysaccharide affect the membrane behavior is not well understood. In this study, the relationship between the core oligosaccharide of lipopolysaccharide and the membrane behavior was investigated using a series of Escherichia coli mutants defective in genes to affect the biosynthesis of core oligosaccharide of lipopolysaccharide. Cell surface hydrophobicity, outer membrane permeability, biofilm formation and auto-aggregation of these mutant cells were compared. Compared to the wild type W3110, cell surface hydrophobicities of mutant ΔwaaC, ΔwaaF, ΔwaaG, ΔwaaO, ΔwaaP, ΔwaaY and ΔwaaB were enhanced, outer membrane permeabilities of ΔwaaC, ΔwaaF, ΔwaaG and ΔwaaP were significantly increased, abilities of biofilm formation by ΔwaaC, ΔwaaF, ΔwaaG, ΔwaaO, ΔwaaR, ΔwaaP, ΔwaaQ and ΔwaaY decreased, and auto-aggregation abilities of ΔwaaC, ΔwaaF, ΔwaaG, ΔwaaO, ΔwaaR, ΔwaaU, ΔwaaP and ΔwaaY were strongly enhanced. These results give new insight into the influence of core oligosaccharide of lipopolysaccharide on bacterial cell membrane behavior.
Highlights
In most Gram-negative bacteria, lipopolysaccharide (LPS), the major component in the outer leaflet of outer membrane, provides the structural integrity of the outer membrane [1,2]
In Escherichia coli, LPS typically consists of a hydrophobic domain known as lipid A, a nonrepeating core oligosaccharide, and a distal polysaccharide known as O-antigen repeats [2]
Ten genes involved in LPS outer core biosynthesis were individually deleted from the chromosome of E. coli W3110, resulting in E. coli mutant strains ΔwaaC, ΔwaaF, ΔwaaG, ΔwaaO, ΔwaaR, ΔwaaU, ΔwaaP, ΔwaaQ, ΔwaaY and ΔwaaB, respectively
Summary
In most Gram-negative bacteria, lipopolysaccharide (LPS), the major component in the outer leaflet of outer membrane, provides the structural integrity of the outer membrane [1,2]. The gmhD operon contains genes waaC and waaF required for addition of Hep. The waaQ operon contains eight genes necessary for biosynthesis of the outer core and its modification. The heptosyltransferases, WaaC and WaaF, add Hep residues in the inner core of LPS. Glucosyltransferase WaaG adds the first Glc residue, the first sugar in the outer core of LPS, to the second. Heptosyltransferase WaaU adds the fourth Hep to the third Glc. The outer membrane of Gram-negative bacteria is a barrier to many antibiotics and host defense factors [8], it is important for nutrient absorption and waste discharge of the cell. To understand the effect of core OS on membrane behavior, a whole set of deletion mutations of single genes in the waa locus of E. coli were constructed, and their membrane behavior were investigated. Glycosyltransferases that construct the outer core and the genes encoding them are shown in green
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