Essakhi Salwa, Cesbron Sophie, Fischer-Le Saux Marion, Bonneau Sophie, Jacques Marie-Agnès, Manceau Charles
INRA, UMR 1345, Institut de Recherche en Horticulture et Semences, Beaucouzé, France.
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
Appl Environ Microbiol. 2015 Aug 15;81(16):5395-410. doi: 10.1128/AEM.00835-15. Epub 2015 Jun 5.
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.
传统上，栖木黄单胞菌被认为是一类植物致病细菌，包括七个致病型。本研究表明，栖木黄单胞菌还包括在其宿主上不引起明显疾病症状的非致病细菌。本研究的目的是评估与核桃相关的栖木黄单胞菌种群结构，包括非致病菌株，以便更好地了解非致病黄单胞菌在核桃微生物群中的作用。对100株栖木黄单胞菌进行了多位点序列分析（MLSA），其中包括从核桃中分离出的27株非致病菌株。非致病菌株聚集在由致病型定义的簇之外，并形成了单独的遗传谱系。对从核桃中分离出的栖木黄单胞菌菌株进行的多位点可变数目串联重复分析（MLVA）表明，非致病菌株与包含栖木黄单胞菌胡桃致病型菌株的克隆复合体分开聚类。一些栖木黄单胞菌的非致病菌株不包含典型的III型分泌系统（T3SS），仅含有一到三个III型效应子（T3E）基因。在非致病菌株CFBP 7640和CFBP 7653中，未检测到T3SS基因或任何分析的T3E基因。这一发现引发了关于非致病菌株的起源以及栖木黄单胞菌中植物致病性进化的问题。在任何研究的非致病分离物中未检测到的T3E基因是栖木黄单胞菌中负责致病性的极佳候选基因。
