Abstract
Helicobacter pylori is an important gastroduodenal pathogen of humans whose survival in the gastric environment below pH 4 is dependent on bacterial production of urease, whereas above pH 4 urease-independent mechanisms are involved in survival, but that remain to be elucidated fully. Previous structural investigations on the lipopolysaccharides (LPSs) of H. pylori have shown that the majority of these surface glycolipids express partially fucosylated, glucosylated, or galactosylated N-acetyllactosamine (LacNAc) O-polysaccharide chains containing Lewis(x) (Le(x)) and/or Lewis(y) (Le(y)), although some strains also express type 1 determinants, Lewis(a), Lewis(b), and H-1 antigen. In this study, we investigated acid-induced changes in the structure and composition of LPS and cellular lipids of the genome-sequenced strain, H. pylori 26695. When grown in liquid medium at pH 7, the O-chain consisted of a type 2 LacNAc polysaccharide, which was glycosylated with alpha-1-fucose at O-3 of the majority of N-acetylglucosamine residues forming Le(x) units, including chain termination by a Le(x) unit. However, growth in liquid medium at pH 5 resulted in production of a more complex O-chain whose backbone of type 2 LacNAc units was partially glycosylated with alpha L-fucose, thus forming Le(x), whereas the majority of the nonfucosylated N-acetylglucosamine residues were substituted at O-6 by alpha-D-galactose residues, and the chain was terminated by a Le(y) unit. In contrast, detailed chemical analysis of the core and lipid A components of LPS and analysis of cellular lipids did not show significant differences between H. pylori 26695 grown at pH 5 and 7. Although putative molecular mechanisms affecting Le(x) and Le(y) expression have been investigated previously, this is the first report identifying an environmental trigger inducing phase variation of Le(x) and Le(y) in H. pylori that can aid adaptation of the bacterium to its ecological niche.
Highlights
Helicobacter pylori is an important gastroduodenal pathogen of humans whose survival in the gastric environment below pH 4 is dependent on bacterial production of urease, whereas above pH 4 urease-independent mechanisms are involved in survival, but that remain to be elucidated fully
Growth in liquid medium at pH 5 resulted in production of a more complex O-chain whose backbone of type 2 LacNAc units was partially glycosylated with ␣-L-fucose, forming Lex, whereas the majority of the nonfucosylated N-acetylglucosamine residues were substituted at O-6 by ␣-D-galactose residues, and the chain was terminated by a Ley unit
Detailed chemical analysis of the core and lipid A components of LPS and analysis of cellular lipids did not show significant differences between H. pylori 26695 grown at pH 5 and 7
Summary
Bacterial Strain and Growth Conditions—H. pylori strain 26695, whose complete genome sequence has been determined, was originally isolated from a patient with gastritis [40]. The water-soluble LPS preparations were purified by treatment with RNase A, DNase II, and proteinase K (Sigma) as described previously [15, 45] and subsequently by gel-permeation chromatography on a column of Bio-Gel P2 (1 m ϫ 1 cm) with water as the eluent [22]. After treatment with 0.1 M HCl (100 °C, 30 min), lipid A was reduced with NaBH4 and subjected to hydrazinolysis (100 °C, 48 h) and N-acetylation with acetic anhydride/NaOH [47], and subsequently the product was purified by gel-permeation chromatography on columns of Sephadex G-25 (50 ϫ 2 cm) and TSK-HW40S (24 ϫ 1 cm; Merck) [45]. Electrophoretic and Serological Analyses—For analysis of the macromolecular heterogeneity of H. pylori LPS by gel electrophoresis, proteinase K-treated whole-cell lysates were prepared as described [48]. Free dephosphorylated lipid A was mixed with either NaI or CsI to obtain fragments as well as molecular ions in the positive ion mode as described [45, 65]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
