Comparative study of the roles of AhpC and KatE as respiratory antioxidants in Brucella abortus 2308.

Brucella strains are exposed to potentially toxic levels of H2O2 both as a consequence of their aerobic metabolism and through the respiratory burst of host phagocytes. To evaluate the relative contributions of the sole catalase KatE and the peroxiredoxin AhpC produced by these strains in defense against H2O2-mediated toxicity, isogenic katE, ahpC, and katE ahpC mutants were constructed and the phenotypic properties of these mutants compared with those of the virulent parental strain B. abortus 2308. The results of these studies indicate that AhpC is the primary detoxifier of endogenous H2O2 generated by aerobic metabolism. KatE, on the other hand, plays a major role in scavenging exogenous and supraphysiologic levels of H2O2, although this enzyme can play a supporting role in the detoxification of H2O2 of endogenous origin if AhpC is absent. B. abortus ahpC and katE mutants exhibit wild-type virulence in C57BL/6 and BALB/c mice, but the B. abortus ahpC katE double mutant is extremely attenuated, and this attenuation is not relieved in derivatives of C57BL/6 mice that lack NADPH oxidase (cybb) or inducible nitric oxide synthase (Nos2) activity. These experimental findings indicate that the generation of endogenous H2O2 represents a relevant environmental stress that B. abortus 2308 must deal with during its residence in the host and that AhpC and KatE perform compensatory roles in detoxifying this metabolic H2O2.