Zhao Q, Poole K
Department of Microbiology and Immunology, Queen's University, Kingston, Ont., Canada.
FEMS Microbiol Lett. 2000 Mar 1;184(1):127-32. doi: 10.1111/j.1574-6968.2000.tb09002.x.
The exbBD genes of Pseudomonas aeruginosa PAO were cloned by complementation of the growth defect of an Escherichia coli exbB tolQ double mutant on iron-restricted medium. Nucleotide sequence analysis confirmed that these genes are contiguous and preceded by a second tonB gene in this organism, which we have designated tonB2. lacZ promoter fusions confirmed that expression of the tonB2-exbB-exbD genes is increased under conditions of iron limitation. Deletions within any of these genes, in contrast to deletions in the first tonB gene, tonB1, did not adversely affect growth on iron-restricted medium. On the other hand, tonB1 tonB2 double mutants were more compromised as regards growth in an iron-restricted medium than a tonB1 deletion, indicating that TonB2 could partially replace TonB1 in its role in iron acquisition. TonB1 but not TonB2 deletion strains were also compromised as regards the utilization of hemin or hemoglobin as sole iron sources, indicating that heme transport requires TonB1.
通过对铁限制培养基上大肠杆菌exbB tolQ双突变体生长缺陷的互补作用，克隆了铜绿假单胞菌PAO的exbBD基因。核苷酸序列分析证实，这些基因是连续的，并且在该生物体中第二个tonB基因之前，我们将其命名为tonB2。lacZ启动子融合证实，在铁限制条件下，tonB2-exbB-exbD基因的表达增加。与第一个tonB基因（tonB1）中的缺失相反，这些基因中任何一个的缺失都不会对铁限制培养基上的生长产生不利影响。另一方面，tonB1 tonB2双突变体在铁限制培养基中的生长比tonB1缺失更受影响，这表明TonB2在铁获取中的作用可以部分替代TonB1。TonB1缺失菌株而非TonB2缺失菌株在以血红素或血红蛋白作为唯一铁源的利用方面也受到影响，这表明血红素转运需要TonB1。
