| Summary: | <i>Helicobacter pylori</i> infection is associated with several gastric diseases, including gastritis, peptic ulcer, gastric adenocarcinoma and mucosa-associated lymphatic tissue (MALT) lymphoma. Due to the prevalence and severeness of <i>H. pylori</i> infection, a thorough understanding of this pathogen is necessary. Lipopolysaccharide, one of the major virulence factors of <i>H. pylori</i>, can exert immunomodulating and immunostimulating functions on the host. In this study, the <i>HP0044</i> and <i>HP1275</i> genes were under investigation. These two genes potentially encode GDP-D-mannose dehydratase (GMD) and phosphomannomutase (PMM)/phosphoglucomutase (PGM), respectively, and are involved in the biosynthesis of fucose. <i>HP0044</i> and <i>HP1275</i> knockout mutants were generated; both mutants displayed a truncated LPS, suggesting that the encoded enzymes are not only involved in fucose production but are also important for LPS construction. In addition, these two gene knockout mutants exhibited retarded growth, increased surface hydrophobicity and autoaggregation as well as being more sensitive to the detergent SDS and the antibiotic novobiocin. Furthermore, the LPS-defective mutants also had significantly reduced bacterial infection, adhesion and internalization in the in vitro cell line model. Moreover, disruptions of the <i>HP0044</i> and <i>HP1275</i> genes in <i>H. pylori</i> altered protein sorting into outer membrane vesicles. The critical roles of <i>HP0044</i> and <i>HP1275</i> in LPS biosynthesis, bacterial fitness and pathogenesis make them attractive candidates for drug inventions against <i>H. pylori</i> infection.
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