Ferric Uptake Regulator (FurA) is Required for Virulence on Watermelon.

is the causal agent of bacterial fruit blotch, a serious threat to commercial watermelon and melon crop production worldwide. Ferric uptake regulator (Fur) is a global transcription factor that affects a number of virulence-related functions in phytopathogenic bacteria; however, the role of has not been determined for . Hence, we constructed an deletion mutant and a corresponding complement in the background of strain xlj12 to investigate the role of the gene in siderophore production, concentration of intracellular Fe, bacterial sensitivity to hydrogen peroxide, biofilm formation, swimming motility, hypersensitive response induction, and virulence on melon seedlings. The deletion mutant displayed increased siderophore production, intracellular Fe concentration, and increased sensitivity to hydrogen peroxide. In contrast, biofilm formation, swimming motility, and virulence on melon seedlings were significantly reduced in the mutant. As expected, complementation of the deletion mutant restored all phenotypes to wild-type levels. In accordance with the phenotypic results, the expression levels of and that encode bacterioferritin, that encodes iron/manganese superoxide dismutase, that encodes a flagellar protein, that encodes the type III secretion system (T3SS) ATPase, and that encodes the T3SS outer membrane ring protein were significantly downregulated in the deletion mutant. In addition, the expression of -related genes and and was significantly upregulated in the mutant. Overall, these results indicated that, in , FurA contributes to the regulation of the iron balance system, and affects a variety of virulence-related traits.