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中文摘要：
瓜类细菌性果斑病（bacteria lfruit blotch，BFB）是由西瓜噬酸菌（Acidovorax citrulli，Ac）引起的一种病害，严重为害西瓜、甜瓜的叶片和果实，造成大量减产。迄今，对该病害的研究主要集中在病原菌鉴定、病原菌检测技术、病害防治方法、品种抗病性鉴定等方面，而对病原菌的致病机理仍然知之甚少。本实验以西瓜噬酸菌xjli2菌株为背景构建转座子（mini—Tn51插入的突变体文库，以哈密瓜（Cucumismelovar．saccharinus）为实验材料，通过对哈密瓜种子浸种处理和子叶注射接种的方法筛选突变体，而后利用同源重组的方法获得插入突变体，并对所得的突变株及野生型、互补等各个菌株进行致病性、游动性等相关表型进行测定。研究结果表明，通过文库筛选得到的1株致病力明显下降的突变体，亚克隆鉴定可知该突变体△妒25的Mini—Tn5插入位点为吡哆醛磷酸生物合成蛋白基IN（pdxJ基因），其功能主要与吡哆醛磷酸（俗称VB6）生物合成蛋白相关。突变菌株APdxJ致病性显著下降，生长能力、游动性明显降低，无法正常形成鞭毛和产生生物膜。通过外源添加VB6可恢复其致病性和生长能力等主要表型。本研究证明VB6生物合成在致病性、生长能力以及鞭毛的合成等方面发挥着重要作用，为降低病原菌侵害提供了一个新的思路。
英文摘要：
Bacterial fruit blotch（BFB） is a threatening disease caused by Acidovorax citrulli and it can seriously damage leaves and fruit of watermelons and melons, resulting in reduction of production. So far, the research on this disease has mainly been concentrated in the advances in the identification of pathogens, detection, prevention and the identification of cultivar resistance. However, pathogenesis of pathogens is still poorly understood. In this study, we generated a transposon （Tn5） mutant library on the background of strain xjll2 of Acidovorax citruUi and screened it for reduced virulence by seed-transmission and injectioninoculation with melons （Cucumis melo var. saccharinus）. Meanwhile, we obtained mutant and complementary type and determined pathogenicity, growth, motility, etc, in order to explain the pathogenic mechanism from the perspective of molecular genetics. The results showed that the identification of a Tn5 mutant with reduced virulence was impaired in pdxJ, which was involved in pyridoxal phosphate biosynthetic protein. Further characterization of this mutant revealed that Acidovorax citrulli required pdxJ for pathogenicity, flagellar, growth capacity and levels of biofilm formation. By exogenous VB6 the mutant could recover capacity for pathogenicity and growth. Therefore, it is demonstrated that biosynthesis of pyridoxal phosphate （commonly known as VB6） plays an important part in pathogenicity, growth, formation of flagellar and so on.
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