Abstract: 【Objective】Catalase（KatA）is an important virulence factor encoded by Helicobacter pylori, and plays an important role in bacterial resistance to host immune killing and vaccine development. The objective of this study is to identify the enzymatic properties of H.pylori catalase and to analyze its function in H. pylori oxidation tolerance.【Method】Firstly, katA gene was isolated from the genome of clinical drug-resistant strain Hp_G272, and KatAG272 protein was cloned and expressed in Escherichia coli. Then, the catalase activity of KatAG272 was analyzed in vitro with CAT detection kit. Secondly, katA genetic engineering strains were constructed by homologous recombination, including knockout strains and complemented strains. Finally, the function of katA gene and its role in tolerance to oxidative damage of H. pylori were analyzed by comparing the differences in growth phenotype, decomposition and tolerance of hydrogen peroxide between wild and engineered strains.【Result】KatAG272 was successfully cloned, expressed and purified from E. coli. Enzymatic analysis showed that KatAG272 was a class of eosinophilic catalase. Gene knockout analysis showed that H. pylori lost its ability to decompose and tolerate hydrogen peroxide, while regained its ability to decompose and tolerate hydrogen peroxide after gene complement.【Conclusion】katA is the only functional gene that decomposes and tolerates hydrogen peroxide in H. pylori, and plays an important role in the oxidative tolerance of H. pylori. This study lays a foundation for the study of the virulence and pathogenic mechanism of H. pylori.

Key words: Helicobacter pylori, catalase, katA, tolerance, clone and expression, gene knockout