Quinolobactin, a new siderophore of Pseudomonas fluorescens ATCC 17400, the production of which is repressed by the cognate pyoverdine

Transposon mutant strain 3G6 of Pseudomonas fluorescens ATCC 17400 which wa s deficient in pyoverdine production, was found to produce another iron-che lating molecule; this molecule was identified as 8-hydroxy-4-methoxy-quinal dic acid (designated quinolobactin). The pyoverdine-deficient mutant produc ed a supplementary 75-kDa iron-repressed outer membrane protein (IROMP) in addition to the 85-kDa IROMP present in the wild type. The mutant was also characterized by substantially increased uptake of Fe-59-quinolobactin. The 75-kDa IROMP was produced by the wild type after induction by quinolobacti n-containing culture supernatants obtained from the pyoverdine-negative mut ant or by purified quinolobactin. Conversely, adding purified,wild-type pyo verdine to the growth medium resulted in suppression of the 75-M IROMP in t he pyoverdine-deficient mutant; however, suppression was not observed when Pseudomonas aeruginosa PAO1 pyoverdine, a siderophore utilized by strain 3G 6, was added to the culture. Therefore, we assume that the quinolobactin re ceptor is the 75-kDa IROMP and that the quinolobactin-mediated iron uptake system is repressed by the cognate pyoverdine.