Molecular characterization of DNA encoding 16S–23S rRNA intergenic spacer regions and 16S rRNA of pectolyticErwiniaspecies

Abstract

Sequences of 16S rDNAs and the intergenic spacer (IGS) regions between the 16S and 23S rDNA of bacterial strains from genus Erwinia were determined. Comparison of 16S rDNA sequences from different species and subspecies clearly revealed intraspecies–subspecies homology and interspecies heterogeneity. Phylogenetic analyses of 16S rDNA sequence data revealed that Erwinia spp. formed a discrete monophyletic clade with moderate to high bootstrap values. PCR amplification of the 16S–23S rDNA regions using primers complementary to the 3' end of 16S and 5' end of 23S rRNA genes generated two DNA fragments. The small 16S–23S rDNA IGS regions of Erwinia spp. examined in this study varied considerably in size and nucleotide sequence. Multiple sequence alignment and phylogenetic analysis of small IGS sequence data showed a consistent relationship among the test strains that was roughly in agreement with the 16S rDNA data that reflected the accepted species and subspecies structure of the taxon. Sequence data derived from the large IGS resolved the strains into coherent groups; however, the sequence information would not allow any phylogenetic conclusion, because it failed to reflect the accepted species structure of the test strains.Key words: Erwinia spp., 16S rDNA, intergenic spacer region, tRNA genes, phylogeny.