INTRAGENERIC STRUCTURE OF THE GENUS RHODOBACTER - TRANSFER OF RHODOBACTER-SULFIDOPHILUS AND RELATED MARINE SPECIES TO THE GENUS RHODOVULUM GEN-NOV

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 blastica and was linked more closely to the chemotroph Paracoccus denitrificans and the aerobic phototroph Roseobacter denitrificans 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 sulfidophilum comb. nov. is the type species of this genus.