A mutant in one of two exbD loci of a TonB system in Flavobacterium psychrophilum shows attenuated virulence and confers protection against cold water disease
A mutant in one of two exbD loci of a TonB system in Flavobacterium psychrophilum shows attenuated virulence and confers protection against cold water disease
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DOI：
10.1099/mic.0.2007/010900-0
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发表时间：
2008-04-01
期刊：
影响因子：
2.8
通讯作者：
Guijarro, Jose A.
中科院分区：
文献类型：
--
作者：
Alvarez, Beatriz;Alvarez, Javier;Guijarro, Jose A.
嗜冷黄杆菌（Flavobacterium psychrophilum）是一种引起鲑鱼冷水病（CWD）的嗜冷鱼类病原菌。通过Tn 4351诱变，先前分离到一种在缺铁培养基上生长缺陷的突变体，命名为FP 1033。FP 1033在铁的存在下恢复了亲本表型。在该突变体中被转座子破坏的基因编码与ExbD蛋白相似的蛋白质，ExbD蛋白是参与铁载体介导的铁摄取的TonB复合物系统的成员。对转座子插入周围的DNA的分析表明存在由exbB、两个exbD（exbD 1和exbD 2）和tonB基因座组成的tonB基因簇。RT-PCR分析和互补研究表明，这些基因被转录为操纵子，并且exbD 2：：Tn 4351表型是由缺乏ExbD 2引起的。FP 1033在虹鳟鱼苗中表现出降低的毒力，并在接种后赋予高水平的保护。这被认为是F.嗜冷菌减毒菌株，诱导虹鳟鱼对CWD的保护性免疫应答。这些结果表明，来自该特定TonB系统的exbD 2基因座是产生减毒活疫苗的合适靶标。
Flavobacterium psychrophilum is a psychrotrophic fish-pathogenic bacterium that causes cold water disease (CWD) in salmonids. By means of Tn4351 mutagenesis a mutant named FP1033, deficient in growth on iron-depleted medium, was previously isolated. FP1033 recovered the parental phenotype in the presence of iron. The gene disrupted by the transposon in this mutant encoded a protein with similarity to ExbD proteins, which are members of the TonB complex system involved in iron uptake mediated by siderophores. Analysis of the DNA surrounding the transposon insertion showed the presence of a tonB cluster of genes composed of exbB, two exbD (exbD1 and exbD2) and tonB loci. RT-PCR analysis and complementation studies indicated that these genes are transcribed as an operon and that the exbD2:: Tn4351 phenotype was caused by the lack of ExbD2. FP1033 showed decreased virulence and conferred a high level of protection in rainbow trout fry after vaccination. This is believed to be the first report of a F. psychrophilum attenuated strain that induces a protective immune response in rainbow trout against CWD. These results suggest that the exbD2 locus from this particular TonB system is a suitable target to generate a live attenuated vaccine.