PHYLOGENETIC ANALYSIS OF THE PURPLE PHOTOSYNTHETIC BACTERIA

Seven species of purple photosynthetic bacteria have been characerized by oligonucleotide cataloging of their 16S ribosomal RNAs. The relationships so revealed among them do not agree well with their classical taxonomic classification. However, they are in agreement with those derived from comparative analysis of cytochrome c sequences. Since the two macromolecules, rRNA and cytochrome c, are functionally unrelated, the agreement between the two methods virtually rules out lateral gene transfer as the cause of either result. The patterns seen reflect the true genealogies of the organisms. The purple photosynthetic bacteria constitute a major phylogenetic unit-apparently as extensive as the Gram-positive bacteria-but a unit that is not phylogenetically isolated. Intermixed genealogically with these photosynthetic species are many classically recognized nonphotosynthetic Gram-negative organisms. A number of the latter have specific relatives within the photosynthetic cluster. © 1979 Springer-Verlag New York Inc.