16S RIBOSOMAL DNA-SEQUENCE ANALYSIS CONFIRMS THE CLOSE RELATIONSHIP BETWEEN THE GENERA XANTHOBACTER, AZORHIZOBIUM, AND AQUABACTER AND REVEALS A LACK OF PHYLOGENETIC COHERENCE AMONG XANTHOBACTER SPECIES

A comparative 16S ribosomal DNA (rDNA) sequence analysis was used to i nvestigate the phylogenetic position of members of the genus Xanthobac ter. We determined 16S rDNA sequence data for the type strains of the three Xanthobacter species and five additional Xanthobacter strains. T he close relationship between the genera Xanthobacter, Azorhizobium, a nd Aquabacter previously demonstrated by DNA-rRNA hybridization studie s was confirmed. The results of our phylogenetic analysis indicate tha t members of the genera Xanthobacter , Azorhizobium, and Aquabacter ar e intermixed and that there is no clear generic cluster consisting of the Xanthobacter species. A comparison of the Xanthobacter sequences w ith the 16S rDNA sequences available from environmental clone studies indicated that members of this genus have not been detected by noncult uring approaches.