PHYLOGENETIC EVIDENCE FOR SPHINGOMONAS AND RHIZOMONAS AS NONPHOTOSYNTHETIC MEMBERS OF THE ALPHA-4 SUBCLASS OF THE PROTEOBACTERIA

To clarify the taxonomic relationships of the genera Rhizomonas and Sphingomonas, the 16S rRNA sequence of Rhizomonas suberifaciens IFO 15211(T) (T = type strain) was determined. A phylogenetic analysis of aligned 165 rRNA gene sequences revealed that eight species of the genus Sphingomonas and R. suberifaciens are closely relate to Erythrobacter longus and Porphyrobacter neustonensis and, therefore, belong in the alpha-4 subclass of the Proteobacteria. Within this subclass, Sphingomonas species and R. suberifaciens are phylogenetically interrelated and comprise several subgroups. Our findings show that the genus and species definitions of these organisms are in need of revision.