COORDINATE REGULATION OF SIDEROPHORE AND EXOTOXIN-A PRODUCTION - MOLECULAR-CLONING AND SEQUENCING OF THE PSEUDOMONAS-AERUGINOSA FUR GENE

A 5.9-kb DNA fragment was cloned from Pseudomonas aeruginosa PA103 by its ability to functionally complement a fur mutation in Escherichia c oli. A fur null mutant E. coli strain that contains multiple copies of the 5.9-kb DNA fragment produces a 15-kDa protein which cross-reacts with a polyclonal anti-E. coli Fur serum. Sequencing of a subclone of the 5.9-kb DNA fragment identified an open reading frame predicted to encode a protein 53% identical to E. coli Fur and 49% identical to Vib rio cholerae Fur and Yersinia pestis Fur. While there is extensive hom ology among these Fur proteins, Fur from P. aeruginosa differs markedl y at its carboxy terminus from all of the other Fur proteins. It has b een proposed that this region is a metal-binding domain in E. coli Fur . A positive selection procedure involving the isolation of manganese- resistant mutants was used to isolate mutants of strain PA103 that pro duce altered Fur proteins. These manganese-resistant Fur mutants const itutively produce siderophores and exotoxin A when grown in concentrat ions of iron that normally repress their production. A multicopy plasm id carrying the P. aeruginosa fur gene restores manganese susceptibili ty and wild-type regulation of exotoxin A and siderophore production i n these Fur mutants.