title: Phylogenetic and Variable-Number Tandem-Repeat Analyses Identify Nonpathogenic Xanthomonas arboricola Lineages Lacking the Canonical Type III Secretion System.
abstract: Xanthomonas arboricola is conventionally known as a taxon of plant-pathogenic bacteria that includes seven pathovars. This study showed that X. arboricola also encompasses nonpathogenic bacteria that cause no apparent disease symptoms on their hosts. The aim of this study was to assess the X. arboricola population structure associated with walnut, including nonpathogenic strains, in order to gain a better understanding of the role of nonpathogenic xanthomonads in walnut microbiota. A multilocus sequence analysis (MLSA) was performed on a collection of 100 X. arboricola strains, including 27 nonpathogenic strains isolated from walnut. Nonpathogenic strains grouped outside clusters defined by pathovars and formed separate genetic lineages. A multilocus variable-number tandem-repeat analysis (MLVA) conducted on a collection of X. arboricola strains isolated from walnut showed that nonpathogenic strains clustered separately from clonal complexes containing Xanthomonas arboricola pv. juglandis strains. Some nonpathogenic strains of X. arboricola did not contain the canonical type III secretion system (T3SS) and harbored only one to three type III effector (T3E) genes. In the nonpathogenic strains CFBP 7640 and CFBP 7653, neither T3SS genes nor any of the analyzed T3E genes were detected. This finding raises a question about the origin of nonpathogenic strains and the evolution of plant pathogenicity in X. arboricola. T3E genes that were not detected in any nonpathogenic isolates studied represent excellent candidates to be those responsible for pathogenicity in X. arboricola.
authors.affiliation: INRA, UMR 1345, Institut de Recherche en Horticulture et Semences, Beaucouzé, France.
authors.forename: Salwa
authors.initials: S
authors.lastname: Essakhi
authors.affiliation: INRA, UMR 1345, Institut de Recherche en Horticulture et Semences, Beaucouzé, France.
authors.forename: Sophie
authors.initials: S
authors.lastname: Cesbron
authors.affiliation: INRA, UMR 1345, Institut de Recherche en Horticulture et Semences, Beaucouzé, France.
authors.forename: Marion
authors.initials: M
authors.lastname: Fischer-Le Saux
authors.affiliation: INRA, UMR 1345, Institut de Recherche en Horticulture et Semences, Beaucouzé, France.
authors.forename: Sophie
authors.initials: S
authors.lastname: Bonneau
authors.affiliation: INRA, UMR 1345, Institut de Recherche en Horticulture et Semences, Beaucouzé, France.
authors.forename: Marie-Agnès
authors.initials: MA
authors.lastname: Jacques
authors.affiliation: INRA, UMR 1345, Institut de Recherche en Horticulture et Semences, Beaucouzé, France Anses, Laboratoire de la Santé des Végétaux, Unité Expertise-Risques Biologiques, Angers, France charles.manceau@anses.fr.
authors.forename: Charles
authors.identifier: http://orcid.org/0000-0003-3590-6454
authors.initials: C
authors.lastname: Manceau
mesh_terms: D016000:Cluster Analysis; D005838:Genotype; D031324:Juglans / Q000382:microbiology*; D018598:Minisatellite Repeats; D008969:Molecular Sequence Data; D058885:Multilocus Sequence Typing; D010802:Phylogeny; D010935:Plant Diseases / Q000382:microbiology; D017385:Sequence Homology; D000069296:Type III Secretion Systems / Q000235:genetics*; D014974:Xanthomonas / Q000145:classification* / Q000235:genetics* / Q000302:isolation & purification
chemical_list: D000069296:Type III Secretion Systems