Phylogenetic Analysis of Xanthomonas Strains Based on the Nucleotide Sequences of 16S-23S rRNA Spacer Region, 23S rRNA and gyrB Genes

Abstract

The genus Xanthomonas consists of six species of plant pathogenic bacteria attacking a variety of important crops. To date, however, most of Xanthomonas strains have been classified as pathovars of X campestris mainly based on host specificity, and most of them are not distinguishable phenotypically. Accordingly, X. campestris contained more than 140 pathovars. Attempts have been made to reclassify this genus using established molecular biological methods such as DNA reassociation (4), which is generally used, for species delineation. Until recently, 16SrDNA sequence (1) and DNA fingerprinting such as rep-PCR and AFLP (3) were employed for comparative analyses within Xanthomonas strains. Although 16S rDNA sequence analysis revealed only limited discrimination within strains, the DNA fingerprinting methods appeared to be more discriminatory and, hence, can be used as rapid means for determining taxonomic diversity and phylogenetic relationships. In line with the continued search of other discriminating methods, we conducted phylogenetic analyses based on sequences of other ribosomal genes such as 23S rRNA, 16S-23S rRNA intergenic spacer region (ITS), as well as that of gyrB (DNA gyraseßsubunit gene) as a first step.