Iron-mediated regulation of alkaline proteinase production in Pseudomonas aeruginosa

We analyzed the regulation by iron of alkaline proteinase (AP) production i n Pseudomonas aeruginosa. Extracellular AP production was detected from the mid-logarithmic to the stationary phase by an antibody-based assay system, and was strongly repressed by iron in the medium. This repression was show n by Northern hybridization and primer extension to occur at the level of t ranscription. The primer extension analysis revealed that the start point o f transcription of AP gene was the nucleotide position -84 from the start p oint of translation. Furthermore, we investigated whether this transcriptio nal repression involved PvdS protein. Using the mutant strain of pvdS, the alternative cr factor gene revealed that the PvdS protein is required for t he full expression of AP, and a previous study showed that expression of pv dS is also repressed by iron. Therefore, we thought that one mechanism of r epression of AP production operated through reduction of the PvdS protein l evel. Purified AP decomposed the transferrin, and released iron from it. Pu rified AP added to the medium containing transferrin as the only iron sourc e enhanced the growth of R aeruginosa. Moreover, mutation in the AP gene de creased the growth rate in the medium containing the transferrin as the onl y iron source. These results clearly indicated that AP expression should oc cur in a free-iron-deficient environment and emphasized the importance of A P to iron acquisition in the infection site.