Phase Variation in Helicobacter pylori Lipopolysaccharide

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American Society for Microbiology

RESUMO

Helicobacter pylori NCTC 11637 lipopolysaccharide (LPS) expresses the human blood group antigen Lewis x (Lex) in a polymeric form. Lex is β-d-galactose-(1-4)-[α-l-fucose-(1-3)]-β-d-acetylglucosamine. Schematically the LPS structure is (Lex)n-core-lipid A. In this report, we show that Lex expression is not a stable trait but that LPS displays a high frequency (0.2 to 0.5%) of phase variation, resulting in the presence of several LPS variants in one bacterial cell population. One type of phase variation implied the loss of α1,3-linked fucose, resulting in variants that expressed nonsubstituted polylactosamines (also called the i antigen), i.e., Lex minus fucose; LPS: (lactosamine)n-core-lipid A. The switch of Lex to i antigen was reversible. A second group of variants arose by loss of polymeric main chain which resulted in expression of monomeric Ley; LPS: (Ley)-core-lipid A. A third group of variants arose by acquisition of α1,2-linked fucose which hence expressed Lex plus Ley; LPS: (Ley)(Lex)n-core-lipid A. The second and third group of variants switched back to the parental phenotype [(Lex)n-core-lipid A] in lower frequencies. Part of the variation can be ascribed to altered expression levels of glycosyltransferase levels as assessed by assaying the activities of galactosyl-, fucosyl-, and N-acetylglucosaminyltransferases. Clearly phase variation increases the heterogeneity of H. pylori, and this process may be involved in generating the very closely related yet genetically slightly different strains that have been isolated from one patient.

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