Peroxide-inducible catalase in Aeromonas salmonicida subsp salmonicida protects against exogenous hydrogen peroxide and killing by activated rainbow trout, Oncorhynchus mykiss L, macrophages

Aeromonas salmonicida subsp. salmonicida expresses a single cytoplasmically located catalase which was found to be inducible by exposure to 20 mu M hy drogen peroxide in mid-exponential phase resulting in a 4 fold increase in activity. Subsequent exposure to 2 mM peroxide in late-exponential/early-st ationary phase resulted in further induction of catalase activity which inc reased to 20 fold higher levels than those found in uninduced cultures. Exp onentially induced cultures were protected against subsequent exposure to 1 0 mM peroxide which was lethal to non-induced cultures. Bacteria subjected to induction in mid-exponential and early-stationary phase were resistant t o 100 mM peroxide, although viability was greatly reduced. Growth of the ba cterium under iron-restricted conditions had no effect on the peroxide indu ction of catalase. As current evidence indicates, the latter is an iron-co- factored heme catalase, this result suggests that catalase induction has a high priority in the metabolism of iron. Furthermore, exposure to peroxide also induces expression of periplasmic MnSOD. A. salmonicida MT423 was resi stant to normal rainbow trout macrophages, but was susceptible to killing b y activated macrophages. However, if catalase was induced by prior exposure to 20 mu M peroxide during mid-exponential phase, A. salmonicida was resis tant to killing by activated macrophages. The ability of A. salmonicida to upregulate periplasmic MnSOD and cytoplasmic catalase production under iron restricted conditions and low level peroxide (conditions expected to exist during the early stages of an infection) may be vital for its ability to w ithstand attack by phagocytic cells in vivo. (C) 1999 Academic Press.