Résumé
Xanthomonas albilineans causes leaf scald disease of sugarcane and exhibits distinctive pathogenic mechanisms, ecology and taxonomy when compared to other species of Xanthomonas. For example, X. albilineans does not possess the xanthan gum biothesis gene cluster and the Hypersensitive response and pathogenicity type 3 secretion system (Hro-T3SS). X. ambilineans also exhibits large intra-species variability as illustrated with occurrence of three serotypes and 10 PFGE genetic groups revealed by serotyping and Pulsed-Field Gel Elecreophoresis (PFGE), respectively. In this study, we performed a multi-locus sequence analysis using 15 strains spanning the PFGE diversity of X. albilineans, three strains of Xanthomonas sacchari and two strains belonging to the tentatively novel species X. pseudoabilineans. Analysis of the lipopolysaccharides (LPS) genes located between the conserved etfA and metB genes revealed three different alellic forms of the LPS locus named LPS1, LPS2 and LPS3, associated to serotype 1, serotype 2 and serotype 3 of X. albilineans, respectively. Locus LPS1 contains five specific genes and shares seven genes with locus LPS3. Locus LPS2 contains 10 specific genes and shares five genes with locus LPS3. The 14 genes of locys LPS3 are conserved in twi strains of X. sacchari. Strains belonging to a given PFGE group belong to the same serotype or exhibit the same LPS allelic form, suggesting that the gene transfer events that resulted to the distribution of the three LPS allelic forms in X. albilineans occurred before the differentiation of the PFGE lineages of this sugarcane pathogen. (Texte intégral)