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Characterization of Regulatory Pathways in Xylella fastidiosa: Genes and Phenotypes Controlled by algU ^,

Xiang Yang Shi,¹ C. Korsi Dumenyo,² Rufina Hernandez-Martinez,^1, Hamid Azad,¹ and Donald A. Cooksey^1*

Department of Plant Pathology and Microbiology, University of California, Riverside, California 92521,¹ Institute of Agricultural and Environmental Research, Tennessee State University, Nashville, Tennessee 37209²

Received 2 June 2007/ Accepted 29 August 2007

Many virulence genes in plant bacterial pathogens are coordinately regulated by "global" regulatory genes. Conducting DNA microarray analysis of bacterial mutants of such genes, compared with the wild type, can help to refine the list of genes that may contribute to virulence in bacterial pathogens. The regulatory gene algU, with roles in stress response and regulation of the biosynthesis of the exopolysaccharide alginate in Pseudomonas aeruginosa and many other bacteria, has been extensively studied. The role of algU in Xylella fastidiosa, the cause of Pierce's disease of grapevines, was analyzed by mutation and whole-genome microarray analysis to define its involvement in aggregation, biofilm formation, and virulence. In this study, an algU::nptII mutant had reduced cell-cell aggregation, attachment, and biofilm formation and lower virulence in grapevines. Microarray analysis showed that 42 genes had significantly lower expression in the algU::nptII mutant than in the wild type. Among these are several genes that could contribute to cell aggregation and biofilm formation, as well as other physiological processes such as virulence, competition, and survival.

Published ahead of print on 7 September 2007.

Supplemental material for this article may be found at http://aem.asm.org/.

Present address: Department of Microbiology, Center for Scientific Research and Higher Education of Ensenada (CICESE), Km 107 Ctra. Tijuana-Ensenada, 22860 Ensenada, Baja California, México.