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Biofilm Formation, Epiphytic Fitness, and Canker Development in Xanthomonas axonopodis pv. citri

¹Fundación Pablo Cassará, Centro de Ciencia y Tecnología “Dr. Cesar Milstein,” Saladillo 2468 C1440FFX, Ciudad de Buenos Aires, Argentina; ²Instituto de Biología Molecular y Celular de Rosario-CONICET, División Virología, Departamento Microbiología, Facultad de Ciencias Bioquímicas y Farmacéuticas, UNR. Suipacha 531, 2000. Rosario, Argentina; ³Estación Experimental Agroindustrial Obispo Colombres, Casilla No. 9, Las Talitas, 4101, Tucumán, Argentina; ⁴ BIOMERIT Research Centre, Department of Microbiology, National University of Ireland, Cork, Ireland

The phytopathogenic bacterium Xanthomonas axonopodis pv. citri is responsible for the canker disease affecting citrus plants throughout the world. Here, we have evaluated the role of bacterial attachment and biofilm formation in leaf colonization during canker development on lemon leaves. Crystal violet staining and confocal laser scanning microscopy analysis of X. axonopodis pv. citri strains expressing the green fluorescent protein were used to evaluate attachment and biofilm formation on abiotic and biotic (leaf) surfaces. Wild-type X. axonopodis pv. citri attached to and formed a complex, structured biofilm on glass in minimal medium containing glucose. Similar attachment and structured biofilm formation also were seen on lemon leaves. An X. axonopodis pv. citri gumB mutant strain, defective in production of the extracellular polysaccharide xanthan, did not form a structured biofilm on either abiotic or biotic surfaces. In addition, the X. axonopodis pv. citri gumB showed reduced growth and survival on leaf surfaces and reduced disease symptoms. These findings suggest an important role for formation of biofilms in the epiphytic survival of X. axonopodis pv. citri prior to development of canker disease.

Additional keywords: Citrus limon, EPS, GFP-labeled X. axonopodis pv. citri.