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Oral: Bacterial Virulence Regulation


Construction of phosphodiesterase mutants in Erwinia amylovora to evaluate the role of cyclic di-GMP in virulence regulation
R. KHARADI (1), R. Kharadi (1), L. Castiblanco (1), G. Sundin (1) (1) Michigan State University, U.S.A.

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The second messenger molecule cyclic-di-GMP (c-di-GMP) is a key regulator of biofilm formation, motility and virulence in bacteria. Diguanylate cyclase (DGC) enzymes function in the synthesis of c-di-GMP and phosphodiesterase (PDE) enzymes are involved in the degradation of c-di-GMP. We have previously studied the role of DGCs in regulating virulence traits in the fire blight pathogen Erwinia amylovora. Here we demonstrate that all three predicted PDE genes (edp genes, for Erwinia diguanylate phosphodiesterase), edpA, edpB and edpC negatively regulate amylovoran production and biofilm formation. This was correlated with a significant increase in the volume of ooze produced and the amylovoran content of ooze in an immature-pear infection model using the single-gene deletion mutants DedpA, DedpB, and DedpC. We also observed a significant decrease in motility, virulence in immature pears, and systemic infection levels in apple shoots in the triple-gene deletion mutant DedpA/edpB/edpC. Gene expression levels of dspE and hrpL, both indicators of type III secretion in E. amylovora, were significantly reduced in DedpA/edpB/edpC compared to the wild type. Thus, c-di-GMP seems to be primarily involved in the positive regulation of amylovoran production and biofilm formation; in addition, increased levels of c-di-GMP also negatively regulate motility and type III secretion during the pathogenesis of E. amylovora.