FERRIC UPTAKE REGULATOR (FUR) MUTANTS OF PSEUDOMONAS-AERUGINOSA DEMONSTRATE DEFECTIVE SIDEROPHORE-MEDIATED IRON UPTAKE, ALTERED AEROBIC GROWTH, AND DECREASED SUPEROXIDE-DISMUTASE AND CATALASE ACTIVITIES

Pseudomonas aeruginosa is considered a strict aerobe that possesses se veral enzymes important in the disposal of toxic oxygen reduction prod ucts including iron- and manganese-cofactored superoxide dismutase and catalase, At present, the nature of the regulation of these enzymes i n P. aeruginosa is not understood. To address these issues, we used tw o mutants called A4 and C6 which express altered Fur (named for ferric uptake regulation) proteins and constitutively produce the siderophor es pyochelin and pyoverdin. Both mutants required a significant lag ph ase prior to log-phase aerobic growth, but this lag was not as apparen t when the organisms were grown under microaerobic conditions, The add ition of iron salts to mutant A4 and, to a greater extent, C6 cultures allowed for an increased growth rate under both conditions relative t o that of bacteria without added iron. Increased manganese superoxide dismutase (Mn-SOD) and decreased catalase activities were also apparen t in the mutants, although the second catalase, KatB, was detected in cell extracts of each far mutant, Iron deprivation by the addition of the iron chelator 2,2'-dipyridyl to wild-type bacteria produced an inc rease in Mn-SOD activity and a decrease in total catalase activity, si milar to the fur mutant phenotype. Purified wild-type Fur bound more a vidly than mutant Fur to a PCR product containing two palindromic 19-b p ''iron box'' regions controlling expression of an operon containing the sodA gene that encodes Mn-SOD. All mutants were defective in both ferripyochelin- and ferripyoverdin-mediated iron uptake, Two mutants o f strain PAO1, defective in pyoverdin but not pyochelin biosynthesis, produced increased Mn-SOD activity. Sensitivity to both the redox-cycl ing agent paraquat and hydrogen peroxide was greater in each mutant th an in the wild-type strain. In summary, the results indicate that muta tions in the P. aeruginosa fur locus affect aerobic growth and SOD and catalase activities in P. aeruginosa, We postulate that reduced sider ophore-mediated iron uptake, especially that by pyoverdin, may be one possible mechanism contributing to such effects.