Functional Analysis Of Type â…£ Pili Related Genes Pilo And Pilq In Acidovorax Citrulli

Bacterial fruit blotch of melons is a disease which is caused by Acidovorax citrulli. Since now it has been reported that this disease can cause serious damages of local melons in United States, Australia, Brazil, China and many other countries. For preventing bacterial fruit blotch of melons fundamentally,we should find out the mechanism of Acidovorax citrulli.In2009, Bahar reported that type IV pili existed in Acidovorax citrulli and also was an important virulence factor. Type IV pili are proteinaceous, flexible filaments with a diameter of5-8nm which can be found in both Gram-negative and Gram-positive bacteria. They are generally located at one or both poles of a cell, where they mediate twitching motility. Type â…£ pili have also been shown to be involved in a variety of other bacterial activities and features, including surface adhesion, colonization, biofilm formation, genetic material uptake and virulence. Synthetic proteins of type â…£ pili take a high homology with â…¡ type secretion system proteins, including fimbrial protein pilA, pilE, pseudobacterium pilin, fimbrial prosoma leader peptidases pilD, ATPase pilM, multilayer proteins across the membrane and secretion element out of membrane pilQ, pilMIN/O/P proteins are also involved in the synthesis of type â…£ pili.In this experiment, we obtained two mutant strains pilO and pilQ with dramatically reduced virulence by seed-transmission assays. By transmission electron microscopy, we found that wild type and pilO mutant could form type â…£ pili, whereas pilQ mutant lost type â…£ pili. Results of optical microscope observation showed that pilO and pilQ mutants, compared with wild type, lost twitching motility completely, meanwhile their swimming ability, biofilm formation and virulence also reduced significantly. For complementary strains, virulence, twitching motility, swimming ability and biofilm formation recovered partly. Compared with wild-type, the growth of mutants showed no significant difference in MMX medium, and they can also stimulate HR in non-host. PilO mutant still can form type â…£ pili but completely lost twitching ability, which showed that pilO gene was not directly involved in synthesis of type IV pili but was functional gene of type â…£ pili in Acidovorax citrulli; PilQ mutant could not form type IV pili and lost twitching motility showed that pilQ gene was directly involved in synthesis of type â…£ pili and was the synthetic gene of type â…£ pili. Type â…£ pili of Acidovorax citrulli was related to twitching motility, virulence, swimming ability and biofilm formation.