Study on Iron Regulon Pseudomonas aeruginosa

在铁限制下，铜绿假单胞菌分泌pyoverdin，这是一种低分子量的铁载体，能够以非常高的亲和力捕获铁离子，并将其吸收到细胞中。在染色体遗传图谱的47 min区（pvd区）发现了许多与pyoverdin产生有关的pvd基因聚集和组织在许多操作子中。对三个pvd操纵子的遗传分析表明，它们的转录(1)在富铁条件下受到抑制，(2)需要一个编码在pvd区域的正调节因子PvdS。根据uncleotide测序和随后的同源性搜索，推断PvdS是调节“胞质外功能”的RNA聚合酶sigma因子亚家族的成员。pvdS的启动子区域包含与铁调控的全局抑制因子Fur的一致结合序列匹配的序列。与该序列（Fur box）的存在一致，pvdS的转录在富铁条件下受到抑制。本研究获得的数据表明：(1)富铁条件下Fur的活性形式与pvdS启动子处的Fur box结合，抑制pvdS的转录；(2)pvdS不产生后，不允许其他结构pvd基因的转录。由于毛皮最有可能参与pyoverdin的产生，因此进行了等位基因交换诱变以分离染色体突变的毛皮。我们多次尝试获得这样的突变是不成功的，这表明Fur对铜绿假单胞菌的生存能力至关重要的作用。

Under iron limitation, Pseudomonas aeruginosa secretes pyoverdin, a low-molecular-weight siderophore able to capture ferric iron with a very high affinity for uptake of this ion into the cell. A number of pvd genes involved in pyoverdin production were found to be clustered and organized in many operons at the 47 min region (pvd region) on the chromosomal genetic map. Genetic analysis of the three pvd operons demonstrated that their transcription (1) was repressed under iron-rich conditions and (2) required a positive regulator, PvdS,that was encoded in the pvd region. Based on uncleotide sequencing and subsequent homology search, it was inferred that PvdS is a member of subfamily of RNA polymerase sigma factors regulating "extracytoplasmic functions" . The promoter region of pvdS contained the sequence that matched well with the consensus binding sequence of Fur, a global repressor of the iron regulon. Consistent with the presence of such a sequence (Fur box) , transcription of pvdS was repressed under iron-rich conditions. The data obtained in this study leads to the proposal that (i) an active form of Fur under an iron-rich condition binds to the Fur box at the pvdS promoter to repress the transcription of pvdS and (ii) no production of PvdS thereafter does not permit the transcription of other structural pvd genes. Because of the most probable involvement of Fur in pyoverdin production, allelic exchange mutagenesis was carried out to isolate a chromosomal fur mutation. Our repeated attempt to obtain such a mutation was unsuccessful, suggesting the essential role of Fur on the viability of P.aeruginosa.