Catalase has a novel protective role against electrophile killing of Xanthomonas

The ability of Xanthomonas campestris pv, phaseoli to protect itself agains t lethal concentrations of man-made (N-ethylmaleimide. NEM) and endogenousl y produced (methylglyoxal, MG) electrophiles was investigated. Pretreatment of X. c. pv. phaseoli with a low concentration of NEM induced protection a gainst lethal concentrations of NEM and MC, MG pretreatment weakly induced protection against NEM but not against MG itself. NEM-induced protection ag ainst electrophile killing required new protein synthesis and was abolished by the addition of a protein synthesis inhibitor. By contrast, MG-induced protection against NEM killing was independent of de novo protein synthesis . X, c, pv, phaseoli harbouring an expression vector carrying a catalase ge ne was over 100-fold more resistant to MG and NEM killing. High expression levels of genes for other peroxide-protective enzymes, such as those for al kyl hydroperoxide reductase (ahpC and ahpF) and ohr, failed to protect agai nst electrophile killing, Thus, catalase appears to have a novel protective role(s) against electrophile toxicity. This finding suggests that in X, c, pv, phaseoli NEM and MG toxicity might involve accumulation and/or increas ed production of H2O2, This idea was supported by the observation that addi tion of 10 mM sodium pyruvate. a compound that can react chemically with pe roxide or hydroxyl radical scavengers (DMSO and glycerol), was found to pro tect Xanthomonas from electrophile killing. The protective role of catalase and the role of H2O2 in electrophile toxicity are novel observations and c ould be generally important in other bacteria, In addition, unlike other ba cteria, Xanthomonas in stationary phase was more susceptible to electrophil e killing compared to cells in exponential phase.