A Single Nucleotide Exchange in the wzy Gene Is Responsible for the Semirough O6 Lipopolysaccharide Phenotype and Serum Sensitivity of Escherichia coli Strain Nissle 1917
Open Access
- 1 November 2002
- journal article
- research article
- Published by American Society for Microbiology in Journal of Bacteriology
- Vol. 184 (21), 5912-5925
- https://doi.org/10.1128/jb.184.21.5912-5925.2002
Abstract
Structural analysis of lipopolysaccharide (LPS) isolated from semirough, serum-sensitive Escherichia coli strain Nissle 1917 (DSM 6601, serotype O6:K5:H1) revealed that this strain's LPS contains a bisphosphorylated hexaacyl lipid A and a tetradecasaccharide consisting of one E . coli O6 antigen repeating unit attached to the R1-type core. Configuration of the GlcNAc glycosidic linkage between O-antigen oligosaccharide and core (β) differs from that interlinking the repeating units in the E . coli O6 antigen polysaccharide (α). The wa∗ and wb∗ gene clusters of strain Nissle 1917, required for LPS core and O6 repeating unit biosyntheses, were subcloned and sequenced. The DNA sequence of the wa∗ determinant (11.8 kb) shows 97% identity to other R1 core type-specific wa∗ gene clusters. The DNA sequence of the wb∗ gene cluster (11 kb) exhibits no homology to known DNA sequences except manC and manB . Comparison of the genetic structures of the wb∗ O6 ( wb∗ from serotype O6) determinants of strain Nissle 1917 and of smooth and serum-resistant uropathogenic E . coli O6 strain 536 demonstrated that the putative open reading frame encoding the O-antigen polymerase Wzy of strain Nissle 1917 was truncated due to a point mutation. Complementation with a functional wzy copy of E . coli strain 536 confirmed that the semirough phenotype of strain Nissle 1917 is due to the nonfunctional wzy gene. Expression of a functional wzy gene in E . coli strain Nissle 1917 increased its ability to withstand antibacterial defense mechanisms of blood serum. These results underline the importance of LPS for serum resistance or sensitivity of E . coli .Keywords
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