Regulatory Mechanism for Expression of Genes for Iron Uptake in Pseudomonas aeruginosa

点击翻译按钮获取中文摘要

Under iron limitation, Pseudomonas aeruginosa secretes siderophore (pyoverdin) to chelate and uptake the ferric iron. Most of the pyoverdin biosynthetic (pvd) genes are located in a chromosomal 103-kb region, termed as pvd region, and this region also encodes FpvA,an outer membrane protein that serves as a receptor for ferri-pyoverdin complex, and PvdS,an activator required for transcription of the pvd operons. Transcription of these operons is further repressed under iron-rich conditions by Fur, a global repressor of the iron regulon. Sequence analysis and Fur titration assay demonstrated that the Fur box, a consensus sequence for binding of Fur, is absent in the three pvd promoter regions but present at the promoter region of pvdS.Transcription of pvdS was repressed and depressed under iron-rich and -limiting conditions, respectively. These results strongly support that no transcription of the pvd operons under iron-rich conditions is due to the Fur-mediated transcriptional repression of the pvdS gene. The pvdS mutant produced alkaline proteinase one-fourth in amount of that the wild type strain produced. This indicates that PvdS plays an important, albeit not essential, role in production of alkaline proteinase. Various mutants having large and defined deletion in the chromosomal pvd region were isolated using a site-specific resolution system of Tn1722. Such a mutant completely lacking the pvd region grew normally in minimal media, demonstrating that the pvd region does not carry any essential or auxotrophic genes. The deletion mutanats were constructed that retained and lacked the fpvA gene. The former mutanat, but not the latter one, had the ability to uptake the externally added ferri-pyoverdin complex, implying that a second low-affinity receptor other than FpvA appears not to exist in P.aeruginosa.