Phase Variation in H Type I and Lewis a Epitopes of Helicobacter pylori Lipopolysaccharide

Abstract

ABSTRACT Helicobacter pylori NCTC 11637 lipopolysaccharide (LPS) expresses the human blood group antigens Lewis x (Le x ), Le y , and H type I. In this report, we demonstrate that the H type I epitope displays high-frequency phase variation. One variant expressed Le x and Le y and no H type I as determined by serology; this switch was reversible. Insertional mutagenesis in NCTC 11637 of JHP563 (a poly(C) tract containing an open reading frame homologous to glycosyltransferases) yielded a transformant with a serotype similar to the phase variant. Structural analysis of the NCTC 11637 LPS confirmed the loss of the H type I epitope. Sequencing of JHP563 in strains NCTC 11637, an H type I-negative variant, and an H type I-positive switchback variant showed a C14 (gene on), C13 (gene off), and C14 tract, respectively. Inactivation of strain G27, which expresses Le x , Le y , H type I, and Le a , yielded a transformant that expressed Le x and Le y . We conclude that JHP563 encodes a β3-galactosyltransferase involved in the biosynthesis of H type I and Le a and that phase variation in H type I is due to C-tract changes in this gene. A second H type I-negative variant (variant 3a) expressed Le x and Le a and had lost both H type I and Le y expression. Inactivation of HP093-HP094 resulted in a transformant expressing Le x and lacking Le y and H type I. Structural analysis of a mutant LPS confirmed the serological data. We conclude that the HP093-HP094 α2-fucosyltransferase (α2-FucT) gene product is involved in the biosynthesis of both Le y and Le x . Finally, we inactivated HP0379 in strain 3a. The transformant had lost both Le x and Le a expression, which demonstrates that the HP0379 gene product is both an α3- and an α4-FucT. Our data provide understanding at the molecular level of how H. pylori is able to diversify in the host, a requirement likely essential for successful colonization and transmission.