PHYLOGENETIC STUDIES OF THE RIBOSOMAL-RNA GROUP-II PSEUDOMONADS BASED ON 16S RIBOSOMAL-RNA GENE-SEQUENCES

Nearly complete sequences of 16S rRNA genes were determined for eight bacterial strains representing five species of the rRNA homology group II pseudomonads that are members of the beta subclass of the class Proteobacteria. Comparative analysis with published sequence data indicated that Pseudomonas andropogonis, Ps. caryophylli, Ps. gladioli pv. gladioli and Ps. cepacia aggregate in one coherent cluster at 94.2% sequence similarity; Ps. solanacearum and Ps. pickettii shared 95.3% and 92.8% similarity with Alcaligenes eutrophus in another cluster. Both clusters joined at 87.8% similarity, which is similar to that for genera in this subclass of Proteobacteria. Based on this study and on comparison with other works we suggest that these species are separated from authentic pseudomonads and constitute a new genus or possibly two related genera accommodating Ps. andropogonis, Ps. caryophylli, Ps. gladioli, Ps. cepacia, and Ps. solanacearum, Ps. pickettii and A. eutrophus, respectively. Four strains of Ps. solanacearum representing Biovars 1, 2, 3 and 4 were subdivided into two clusters at 99.1% sequence similarity, in agreement with other published phenotypic and genotypic studies. The two clusters may be potentially regarded as subspecies.