A Helicobacter hepaticus catalase mutant is hypersensitive to oxidative stress and suffers increased DNA damage

Catalase (KatA) is known to play an important role in oxidative stress resistance in many bacterial species and a homologue exists in Helicobacter hepaticus, a member of the enterohepatic Helicobacter species. Here, a katA mutant was constructed by insertional mutagenesis and its oxidative stress phenotype was investigated. Catalase activity was readily detected [196 units (mg protein crude cell extract)(-1)] in the wild-type, whereas the mutant strain was deficient in, but not devoid of, activity. In contrast, Helicobacter pylori katA strains lack detectable catalase activity and wild-type H. pylori generally contains higher specific activity than H. hepaticus. Wild-type H. hepaticus cells tolerated 6 % O2 for growth, whilst the katA mutant could not survive at this oxygen level. Even at the optimal O2 level, the growth of the H. hepaticus katA strain was severely inhibited, which is also in contrast to H. pylori katA strains. Wild-type H. hepaticus cells withstood exposure to 100 mM H(2)O(2) but the katA mutant cells were killed by the same treatment. Wild-type cells suffered no significant DNA damage by H(2)O(2) treatment (100 mM for 6 min), whilst the same treatment resulted in severe DNA fragmentation in the katA mutant. Thus H. hepaticus KatA plays an important role as an antioxidant protein.