UNUSUAL GROWTH-PHASE AND OXYGEN-TENSION REGULATION OF OXIDATIVE STRESS PROTECTION ENZYMES, CATALASE AND SUPEROXIDE-DISMUTASE, IN THE PHYTOPATHOGEN XANTHOMONAS-ORYZAE PV ORYZAE

The enzymes catalase and superoxide dismutase play major roles in prot ecting phytopathogenic bacteria from oxidative stress. In Xanthomonas species, these enzymes are regulated by both growth phase and oxygen t ension. The highest enzyme levels were detected within 1 h of growth. Continued growth resulted in a decline of both enzyme activities. High oxygen tension was an inducing signal for both enzyme activities. An 80,000-Da monofunctional catalase and a manganese superoxide dismutase were the major forms of the enzymes detected at different stages of g rowth. The unusual regulatory patterns are common among several Xantho monas strains tested and may be advantageous to Xanthomonas species du ring the initial stage of plant-microorganism interactions.