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

铜绿假单胞菌铁摄取基因表达的调控机制

基本信息

批准号：
07670314
负责人：
TSUDA Masataka
金额：
$ 1.47万
依托单位：
Okayama University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
1995
资助国家：
日本
起止时间：
1995 至 1996
项目状态：
已结题

项目摘要

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.

在铁限制下，铜绿假单胞菌分泌铁载体（绿脓菌荧光素）螯合和摄取三价铁。大多数绿脓菌荧光素生物合成（pvd）基因位于染色体103-kb区域，称为pvd区域，并且该区域还编码FpvA（充当铁-绿脓菌荧光素复合物的受体的外膜蛋白）和PvdS（pvd操纵子转录所需的激活剂）。这些操纵子的转录在富含铁的条件下被Fur进一步抑制，Fur是铁调节子的全局阻遏物。序列分析和Fur滴定实验表明，pvd启动子的3个区域均不存在与Fur结合的共有序列Fur box，而pvdS的启动子区域存在Fur box。这些结果强烈支持，没有在富铁条件下的pvd操纵子的转录是由于毛皮介导的pvdS基因的转录抑制。pvdS突变体产生的碱性蛋白酶的野生型菌株产生的量的四分之一。这表明PvdS在碱性蛋白酶的产生中发挥着重要的作用，尽管不是必需的。使用Tn 1722的位点特异性解析系统分离在染色体pvd区域中具有大的和确定的缺失的各种突变体。这种完全缺乏pvd区的突变体在基本培养基中正常生长，表明pvd区不携带任何必需基因或营养缺陷型基因。构建了保留和缺失fpvA基因的缺失突变体。前者的突变体，但不是后者，有能力吸收外部添加的铁-绿脓菌荧光素复合物，这意味着第二个低亲和力受体以外的FpvA似乎不存在于铜绿假单胞菌。