Abstract：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 xjl12 of Acidovorax citrulli and screened it for reduced virulence by seed-transmission and injection inoculation 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.
