Influence of Core Oligosaccharide of Lipopolysaccharide to Outer Membrane Behavior of Escherichia coli

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.

Keywords: Escherichia coli; auto-aggregation; biofilm formation; cell surface hydrophobicity; core oligosaccharide; lipopolysaccharide; outer membrane permeability.

Figure 1

Structure and biosynthesis of the core oligosaccharide of LPS in E. coli W3110. Organization of the waa locus is also shown. Glycosyltransferases that construct the inner core backbone and the genes encoding these enzymes are shown in blue; enzymes that modify the structure of inner core and the genes encoding them are shown in red. Glycosyltransferases that construct the outer core and the genes encoding them are shown in green.

Figure 2

Comparison of LPS structure and cell growth of different E. coli strains. (a) The expected LPS structure; (b) LPS mobility on a silver stained tricine-PAGE; and (c) growth curve of E. coli W3110, ΔwaaC, ΔwaaF, ΔwaaG, ΔwaaO, ΔwaaR, ΔwaaU, ΔwaaP, ΔwaaQ, ΔwaaY and ΔwaaB. The same residues in different LPS structures were shown in the same color and shape. Kdo, 3-deoxy-d-manno-octulosonic acid; Hep, l-glycero-d- manno-heptose; P, phosphate; Glc, d-glucose; and Gal, d-galactose.

Figure 3

Cell surface hydrophobicity (a) and outer membrane permeability (b) of LPS core OS mutants derived from W3110. The values represent the mean ± SD of results from three independent experiments. Statistical analysis was performed using ANOVA. ** P ＜ 0.01 and * P ＜ 0.05, against the control strain W3110.

Figure 4

Comparison of biofilm formation (a) and auto-aggregation (b) of E. coli strains W3110, ΔwaaC, ΔwaaF, ΔwaaG, ΔwaaO, ΔwaaR, ΔwaaU, ΔwaaP, ΔwaaQ, ΔwaaY and ΔwaaB.