Study on Iron Regulon Pseudomonas aeruginosa

在铁的限制下，铜绿假单胞菌会分泌氧化铁，这是一种低分子的铁载体，能够以非常高的亲和力捕捉铁，将这些离子吸收到细胞中。在染色体遗传图谱上的47min区(PVD区)，发现了一些与吡咯菌素产生有关的PVD基因在许多操纵子中聚集和组织。对三个PVD操纵子的遗传分析表明，它们的转录(1)在富铁的条件下被抑制，(2)需要在PVD区域编码的正调控因子PvdS。根据核苷酸序列测定和随后的同源性搜索，推测PvdS是调节“胞外功能”的RNA聚合酶西格玛因子亚家族的成员。PvdS的启动子区域含有与铁调节子的全局抑制因子Fur的共同结合序列很好匹配的序列。与这种序列(Fur Box)的存在一致，pvdS的转录在富铁的条件下被抑制。本研究中获得的数据导致了这样的假设：(1)在富铁的条件下，Fur的活性形式与pvdS启动子上的Fur盒结合，以抑制pvdS的转录；(Ii)此后不产生pvdS，不允许其他结构的PVD基因转录。由于毛皮最有可能参与吡咯菌素的生产，因此采用等位基因交换诱变的方法分离出了一个染色体上的毛皮突变。我们多次尝试获得这样一个突变，但都没有成功，这表明Fur对铜绿假单胞菌的生存起着至关重要的作用。

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.