Genomic and phenotypic characterization of Xanthomonas cynarae sp. nov., a new species that causes bacterial bract spot of artichoke (Cynara scolymus L.).

Abstract

A bacterial disease of artichoke (Cynara scolymus L.) was first observed in 1954 in Brittany and the Loire Valley, France. This disease causes water-soaked spots on bracts and depreciates marketability of the harvest. Ten strains of the pathogen causing bacterial spot of artichoke, previously identified as a member of the genus Xanthomonas, were characterized and compared with type and pathotype strains of the 20 Xanthomonas species using a polyphasic study including both phenotypic and genomic methods. The ten strains presented general morphological, biochemical and physiological traits and GMC content characteristic of the genus Xanthomonas. Sequencing of the 16S rRNA gene confirmed that this bacterium belongs to the genus Xanthomonas, and more precisely to the Xanthomonas campestris core. DNA-DNA hybridization results showed that the strains that cause bacterial spot of artichoke were 92-100 % related to the proposed type strain CFBP 4188 T and constituted a discrete DNA homology group that was distinct from the 20 previously described Xanthomonas species. The results of numerical analysis were in accordance with DNA-DNA hybridization data. Strains causing the bacterial bract spot of artichoke exhibited consistent determinative biochemical characteristics, which distinguished them from the 20 other Xanthomonas species previously described. Furthermore, pathogenicity tests allowed specific identification of this new phytopathogenic bacterium. Thus, it is concluded that this bacterium is a new species belonging to the genus Xanthomonas, for which the name Xanthomonas cynarae is proposed. The type strain, CFBP 4188 T , has been deposited in the Collection Franc: aise des Bacte! ries Phytopathoge ' nes (CFBP).

Assessment of the Genetic Diversity among Strains of Xanthomonas cynarae by Randomly Amplified Polymorphic DNA Analysis and Development of Specific Characterized Amplified Regions for the Rapid Identification of X. cynarae

“…With the 40 selected RAPD primers, we obtained many species-specific markers for X. cynarae, in agreement with the fact that X. cynarae is a genomic species in the genus Xanthomonas (33). Moreover, 112 of 163 RAPD markers were common to all X. cynarae strains.…”

“…Therefore, we did not use the RAPD technique for a phylogenic study in the genus Xanthomonas. More appropriate technical tools (phenotypical and biochemical tests, DNA-DNA hybridization, and 16S ribosomal DNA sequencing) were used to classify X. cynarae in the genus Xanthomonas (33). Before starting the RAPD study within the X. cynarae species, we performed a primer-screening step, in order to select a set of RAPD primers which produces reliable fingerprints.…”

“…It was recently classified at the species level as Xanthomonas cynarae (33). An identification test of X. cynarae was described based on biochemical, physiological, and pathogenicity tests (33). Colonies of X. cynarae are yellow and surrounded with a white halo when grown on a Tween medium (17) and produce the typical symptoms of this disease when inoculated to detached scarified bracts of artichoke.…”

“…The causal agent of this disease was first isolated by Ridé (25) from such bract spots and was identified as a phytopathogenic bacterium belonging to the genus Xanthomonas (25). It was recently classified at the species level as Xanthomonas cynarae (33). An identification test of X. cynarae was described based on biochemical, physiological, and pathogenicity tests (33).…”

Thermomonas haemolytica gen. nov., sp. nov., a gamma-proteobacterium from kaolin slurry.

“…The 16S rDNA sequence determined for strain A50-7-3 T was compared with those of all validly published species of Stenotrophomonas, Xanthomonas and Xylella (Wells et al, 1987 ;Drancourt et al, 1997 ;Hauben et al, 1997 ;Moore et al, 1997 ;Hauben et al, 1999 ;Tre! baol et al, 2000), as well as strains comprising distinct genomic species of Stenotrophomonas but which are not differentiated taxonomically (Hauben et al, 1999) (Table 3).…”