Successful colonization of plant tissue by Pseudomonas syringae appears to require the ability to cope with oxidative stree caused by the HOOH produced during early phases of the interaction. P. syringae strains were found to contain 10 to 100-fold higher levels of catalase activity than their nonpathogenic relatives, P. fluorescens and P. putida. At least 8 catalase isozymes were detected in lysates of P. syringae pv. glycinea race 4. Two of these isozymes were unique to the periplasm. Catalase activity in P. syringae strains was dependent on the growth phase of the culture. The specific activity of cytoplasmic catalases increased during the transition to stationary phase. These results are consistent with the involvement of multiple catalase isozymes in the reduction of oxidative stress during pathogenesis by these bacteria.
