XANTHAN GUM ARE INVOLVED IN BIOFILM FORMATION AND PATHOGENICITY IN XANTHOMONAS AXONOPODIS PV. CITRI (XAC)-CITRUS LIMÓN INTERACTION.

RIGANO, LUCIANO1; SICILIANO, FLORENCIA3; SENDIN, LORENA2; ANGULO BIAZUTTI, ANA2; MARANO, MARÍA ROSA3; CASTAGNARO, ATILIO2; DANKERT, MARCELO1 AND VOJNOV

Pinamar, Argentina

Congreso; SAIB; 2005

The plant pathogen Xac is responsible for the canker disease affecting citrus plants throughout the world. Here we show the role of xanthan gum in biofilm formation and, the pathogenicity of the bacterium. The polymerisation and export of xanthan are directed by the gum gene cluster(12 genes, gumB to gumM). We obtained a Xac mutant trough a cassette insertion at the gumB gene, which resulted in a mutant defective in xanthan synthesis. We studied the in vitro biofilm formation of the mutant and of the wild type bacterium by tagging the cells with a constitutive GFP containing plasmid and confocal fluorescence microscopy. This experiment showed that the wild type bacteria formed bacterial populations enclosed in a matrix attached to the chamber, whereas the xanthan defective mutant simply attached to the chamber bottom in a incoherent fashion. In addition, this mutant showed a significant impairment in growth and virulence in lemon leaves. This result allows us to speculate that the xanthan is neccesary for the bacterial biofilm formation and pathogenicity. Since biofilm formation has been implicated in various plant-pathogen interactions, the loss of xanthan mutant fitness could be linked to the inability to produce a functional biofilm.