R. Hernandez Martinez,2
C. Korsi Dumenyo,3
D. A. Cooksey,4 and
R. P. P. Almeida5
1Department of Entomology and Nematology, Citrus Research and Education Center, University of Florida, IFAS, 700 Experiment Station Road, Lake Alfred 33850, U.S.A.; 2Department of Microbiology, Center for Scientific Research and Higher Education of Ensenada, Km. 107 Ctra. Tijuana-Ensenada, 22860 Ensenada, Baja California, Mexico; 3Department of Agricultural and Environmental Science, Tennessee State University, Nashville 37209, U.S.A.; 4Department of Plant Pathology and Microbiology, University of California, Riverside 92521, U.S.A.; 5Department of Environmental Science, Policy, and Management, University of California, Berkeley 94720, U.S.A.
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Accepted 5 May 2013.
Exopolysaccharides (EPS) synthesized by plant-pathogenic bacteria are generally essential for virulence. The role of EPS produced by the vector-transmitted bacterium Xylella fastidiosa was investigated by knocking out two genes implicated in the EPS biosynthesis, gumD and gumH. Mutant strains were affected in growth characteristics in vitro, including adhesion to surfaces and biofilm formation. In addition, different assays were used to demonstrate that the mutant strains produced significantly less EPS compared with the wild type. Furthermore, gas chromatography–mass spectrometry showed that both mutant strains did not produce oligosaccharides. Biologically, the mutants were deficient in movement within plants, resulting in an avirulent phenotype. Additionally, mutant strains were affected in transmission by insects: they were very poorly transmitted by and retained within vectors. The gene expression profile indicated upregulation of genes implicated in cell-to-cell signaling and adhesins while downregulation in genes was required for within-plant movement in EPS-deficient strains. These results suggest an essential role for EPS in X. fastidiosa interactions with both plants and insects.
This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 2013.