Phylogenetic relationships among species of the genus 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 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 species also included and was linked more closely to the chemotroph and the aerobic phototroph than to the cluster containing the marine species. Genomic DNA-DNA hybridization data supported the results of 16S ribosomal DNA sequence comparisons. With few exceptions, the marine 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 species should be transferred to the genus gen. nov.; comb. nov. is the type species of this genus.


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