Funahashi Tatsuya, Tanabe Tomotaka, Miyamoto Katsushiro, Tsujibo Hiroshi, Maki Jun, Yamamoto Shigeo
College of Pharmaceutical Sciences, Matsuyama University, Matsuyama, Japan.
Biosci Biotechnol Biochem. 2013;77(2):353-60. doi: 10.1271/bbb.120774. Epub 2013 Feb 7.
Aeromonas hydrophila ATCC 7966(T) produces a catecholate siderophore amonabactin in response to iron starvation. In this study, we determined that this strain utilizes exogenously supplied enterobactin (Ent) for growth under iron-limiting conditions. A homology search of the A. hydrophila ATCC 7966(T) genomic sequence revealed the existence of a candidate gene encoding a protein homologous to Vibrio parahaemolyticus IrgA that functions as the outer membrane receptor for ferric Ent. SDS-PAGE showed induction of IrgA under iron-limiting conditions. The growth of the double mutant of irgA and entA (one of the amonabactin biosynthetic genes) was restored when it was complemented with irgA in the presence of Ent. Moreover, a growth assay of three isogenic tonB mutants indicated that the tonB2 system exclusively provides energy for IrgA to transport ferric Ent. Finally, reverse transcriptase-quantitative PCR revealed that the transcription of irgA and the TonB2 system cluster genes is iron-regulated, consistently with the presence of a predicted Fur box in the promoter region.
嗜水气单胞菌ATCC 7966(T)在铁饥饿时会产生儿茶酚型铁载体amonabactin。在本研究中，我们确定该菌株在铁限制条件下利用外源提供的肠杆菌素（Ent）进行生长。对嗜水气单胞菌ATCC 7966(T)基因组序列进行同源性搜索，发现存在一个候选基因，其编码的蛋白质与副溶血性弧菌IrgA同源，IrgA作为铁离子Ent的外膜受体发挥作用。SDS-PAGE显示在铁限制条件下IrgA被诱导表达。irgA和entA（amonabactin生物合成基因之一）的双突变体在Ent存在下用irgA进行互补时，其生长得以恢复。此外，对三个同基因tonB突变体的生长测定表明，tonB2系统专门为IrgA转运铁离子Ent提供能量。最后，逆转录定量PCR显示irgA和TonB2系统簇基因的转录受铁调节，这与启动子区域存在预测的Fur框一致。
