Intrageneric Structure of the Genus Rhodobacter: Transfer of Rhodobacter sulfidophilus and Related Marine Species to the Genus Rhodovulum gen. nov.

Abstract

Phylogenetic relationships among species of the genus Rhodobacter and related taxa were elucidated by studying 16s rRNA sequence information and genomic DNA homology data. The 16s rRNA gene was amplified by the PCR and was sequenced directly by a combined method consisting of cycle sequencing and automated fluorescence detection. Pairwise sequence comparisons and a distance matrix analysis showed that the Rhodobacter species could be divided into two major clusters; one cluster included the freshwater and terrestrial species, and the other cluster contained the marine species. The cluster containing the freshwater Rhodobacter species also included Rhodopseudomonas blustica and was linked more closely to the chemotroph Paracoccus denitr@cans and the aerobic phototroph Roseobacter denitriJicans than to the cluster containing the marine Rhodobacter species. Genomic DNA-DNA hybridization data supported the results of 16s ribosomal DNA sequence comparisons. With few exceptions, the marine Rhodobacter species can be differentiated phenotypically from the freshwater species on the basis of salt requirement for optimal growth, sulfide tolerance, final oxidation product of sulfide, and polar lipid composition. Thus, we propose that all marine Rhodobacter species should be transferred to the genus Rhodovulum gen. nov.; Rhodovulum su&duphilum comb. nov. is the type species of this genus.In 1984 Imhoff et al. (25) described a rearrangement of the genera and species of phototrophic purple nonsulfur bacteria and proposed creation of the new genus Rhodobacter and the new combinations Rhodobacter adriaticus, Rhodobacter capsulatus (type species), Rhodobacter sphaeroides, and Rhodobacter suljidophilus, all of which had been included previously in the genus Rhodopseudomonas. Since then, two new species, Rhodobacter veldkampii (12) and Rhodobacter euryhalinus (31), have been added to this genus. Strains of Rhodobacter species are gram negative and facultatively photoheterotrophic and are characterized by their ovoid to rod-shaped morphology, their formation of vesicular intracytoplasmic membranes together with carotenoids of the spheroidene series, and their ability to grow anaerobically and phototrophically in the presence of sulfide as an electron donor (23). They are also similar in their chemotaxonomic properties, such as quinone compositions (18, 19, 22), fatty acid profiles (24, 28), and lipid A structures (42, 43). Although Rhodobacter species share many common characteristics, as noted above, they can be divided clearly into two groups on the basis of their natural habitats. Freshwater and terrestrial environments are common sources of Rhodobacter capsulatus, Rhodobacter sphaeroides, and Rhodobacter veldkampii, while Rhodobacter adriaticus, Rhodobacter euryhalinus, and Rhodobacter sulfidophilus are found only in marine and hypersaline environments. As suggested by their natural habitats, strains of the latter three species require 0.5 to 7.5% NaCl for optimal growth. There are also differences in polar lipid composition (2...

Parvularcula bermudensis gen. nov., sp. nov., a marine bacterium that forms a deep branch in the α-Proteobacteria

“…S. lacuscaerulensis is a long (9-18 mm), non-motile, catalasepositive, gas vacuole-containing rod that grows optimally at 45 uC (Petursdottir & Kristjansson, 1997). R. sulfidophilum is a facultative anaerobic phototrophic organism that contains bacteriochlorophyll a (Hiraishi & Ueda, 1994). Therefore, strain HTCC2503 T cannot be identified as a member of any of the genera described above.…”

Rhodoplanes gen. nov., a New Genus of Phototrophic Bacteria Including Rhodopseudomonas rosea as Rhodoplanes roseus comb. nov. and Rhodoplanes elegans sp. nov.

“…Comparisons of rRNA, i.e., DNA-rRNA hybridization and 16s rRNA cataloging and sequencing, have demonstrated that these bacteria belong to several different lines of descent within the alpha-2 subclass of the Proteobacteria (2,33,34). Exceptionally, Rhodopseudomonas blastica is a member of the alpha-3 subclass, closely related to Rhodobacter species (14,18), and this situation has led to the proposal for transfer of R. blastica to the genus Rhodobacter (18). The phenotypic and chemotaxonomic heterogeneity in the genus Rhodopseudomonas has been summarized by Imhoff et al (16).…”

Biosynthesis of the 3‐Acetyl and 131‐Oxo Groups of Bacteriochlorophyll a in the Facultative Aerobic Bacterium, Rhodovulum sulfidophilum

“…R. sulfidophilum, formerly known as Rhodobacter sulfidophilus [13], was supplied as R. sulfidophilus (DSM Strain 1374 T ) by the Deutsche Sammlung von Mikroorganismen und Zellkulturen GmbH, Braunschweig, Germany. It was maintained by growing aerobically in the dark in liquid culture with sub-culturing every five days in a modified Erythrobacter medium of Shioi [14] supplemented with glucose (2.0 g/l), malate (6.0 g/l) and nicotinic acid (2.0 mg/l) and biotin (0.02 mg/l): ferric citrate in the original medium was replaced with ferric-ammonium citrate.…”