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J. Bacteriol. doi:10.1128/JB.01067-07
Copyright (c) 2007, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Global Genomic Analysis of Pseudomonas savastanoi pv. savastanoi Plasmids

Área de Genética, Universidad de Málaga, 29071 Málaga, Spain; Department of Crop Sciences, University of Illinois, Urbana, IL 61801, USA; Departamento de Producción Agraria, Universidad Pública de Navarra, 31006 Pamplona, Spain; Department of Plant Pathology, Michigan State University, East Lansing, MI 48824, USA

^* To whom correspondence should be addressed. Email: crr{at}uma.es.

	Abstract

Pseudomonas savastanoi pv. savastanoi (Psv) strains harbor native plasmids belonging to the pPT23A plasmid family (PFPs) which are detected in all pathovars examined of the related species P. syringae and contribute to the ecological and pathogenic fitness of their host. However, there is a general lack of information about the gene content of Psv plasmids and their role in the interaction of this pathogen with olive plants. We designed a DNA macroarray containing 135 plasmid-borne P. syringae genes to conduct a global genetic analysis of 32 plasmids obtained from 10 Psv strains. Hybridization results revealed that the number of plasmids belonging to the pPT23A-family plasmids (PFPs) per strain varied from one to four. Additionally, most strains contained at least one plasmid (designated non-PFP) that did not hybridize to the repA gene of pPT23A. Only three PFPs contained genes involved in the biosynthesis of the virulence factor indole-3-acetic acid (iaaM, iaaH and iaaL). In contrast, ptz, a gene involved in the biosynthesis of cytokinins, was found in five PFPs and one non-PFP. Genes encoding a type IVA secretion system (T4SS) were found in both PFPs and non-PFPs; however, type IVB genes were only found on PFPs. Nine plasmids encoded both T4SSs, whereas seven other plasmids carried none of these genes. Most PFPs and non-PFPs hybridized to at least one putative type III secretion system effector gene and to a variety of additional genes encoding known P. syringae virulence factors, and one or more insertion sequence transposase genes. These results indicate that non-PFP plasmids may contribute to the virulence and fitness of the Psv host. The overall gene content of Psv plasmids, with their repeated information, mosaic arrangement and insertion sequences, suggests a possible role in adaptation to a changing environment.