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A rearrangement of the species of the "purple nonsulfur bacteria" (Rhodospirillaceae) is proposed. The species with vesicular intracytoplasmic membranes are removed from the genus Rhodopseudornonas and are placed in the new genera Rhodobacter and Rhodopila as Rhodobacter capsulatus (type species), Rhodobacter sphaeroides, Rhodobacter sulfidophilus, Rhodobacter adriaticus, and Rhodopila globiformis (type species). Rhodopseudomonas gelatinosa and Rhodospirillum tenue are united with Rhodocyclirs purpureus (type species) in the genus Rhodocyclus as Rhodocyclus gelatinosus and Rhodocyclus tenuis. The decisions for this rearrangement were based mainly upon morphological and physiological properties; supporting arguments were based on structural similarities of macromolecular cell constituents. Until now, primarily morphological properties have been used to differentiate among the four genera of the Rhodospir- illaceae Pfennig and Truper 1971. Spiral-shaped bacteria have been placed in the genus Rhodospirillum Molisch 1907, and spherical, ovoid, or rod-shaped bacteria have been placed in the genus Rhodopseudomonas Kluyver and van Niel in Czurda and Maresch 1937. The genus Rhodomicro- bium Duchow and Douglas 1949 was placed in the Rhodo- spirillaceas in Bergey 's Manual of Determinative Bacteriol- ogy, 8th ed. (22), on the basis of its phototrophic style of life and its characteristic peritrichously flagellated, stalk-form- ing cells. A fourth genus, Rhodocyclus Pfennig 1978, with spiral-shaped, nonmotile cells, was described later. Much new information has become available during the last few years on the existing species (23), and a number of new species have been described, including Rhodopseudomonas sulfidophila Hansen and Veldkamp 1973, Rhodopseudo- monas globiformis Pfennig 1974, Rhodopseudomonas sulfo- viridis Keppen and Gorlenko 1975, Rhodocyclus purpureus Pfennig 1978, Rhodopseudomonas blastica Eckersley and Dow 1981 (10, 19), Rhodospirillum salexigens Drews 1982 (9, 20), Rhodopseudomonas rutila Akiba et al. 1983 (2), Rhodopseudomonas marina Imhoff 1983 (16), and Rhodo- pseudomonas adriatica Neutzling et al. 1984 (21a). Morphological, cytological, and physiological properties, as well as recently accumulated data on the similarities of macromolecular structures show that the existing genera comprise groups of species with widely differing properties, which do not warrant classification within the same genus. On the other hand, there are high degrees of similarity between species of the phototrophic "purple nonsulfur bac- teria" and certain nonphototrophic species of gram-negative procaryotes on the basis of the amino acid sequences of cytochrome c molecules (3), deoxyribonucleic acid (DNA)- ribosomal ribonucleic acid (rRNA) hybridization studies (7, 8), and 16s rRNA oligonucleotide catalogs (11, 12, 24). Therefore, we believe that a rearrangement of the species and genera of the purple nonsulfur bacteria is urgently needed to reach a better agreement between the taxonomic units and the established similarities of the species. Howev- er, within a determinative taxonomic system the phototro- phic bacteria should be treated separately from their non-

Rearrangement of the Species and Genera of the Phototrophic "Purple Nonsulfur Bacteria"