In order to clarify interspecific relationships and to investigate the intraspecific phylogenetic structure of the genus , 16S to 23S ribosomal DNA (16S-23S) and 23S to 5S ribosomal DNA (23S-5S) internally transcribed spacers (ITSs) were used for sequence analyses. The 16S-23S and 23S-5S ITSs from 22 strains were amplified by PCR and directly sequenced. The average levels of nucleotide similarity of the 16S-23S and 23S-5S ITSs for the four valid species were 87.6% ± 3.9% and 83% ± 2.2%, respectively. For the most part, intraspecific sequence differences were not found in the two ITSs; the only exception was K194, which differed from other strains by 1 bp in the 23S-5S ITS. The strains had a smaller 16S-23S ITS region than the other strains, which may be useful for differentiating these organisms from other species. The characteristics of the two ITS regions make them more useful than 16S rRNA sequences as a tool for defining and identifying strains. However, K161had two types of 23S-5S ITSs; , separated by I digestion, had two additional nucleotides inserted between positions 52 and 55. Most of the 16S-23S and 23S-5S ITS sequences of K161and strains of “” were identical; the only exception was in K161. The lengths and levels of sequence divergence of the two ITSs of sp. strain K180 were different from the lengths and levels of sequence divergence of the ITSs of other species. These findings suggest that a taxonomic revision of the genus is necessary. Two trees based on 16S-23S and 23S-5S ITS sequences revealed distinct interspecific relationships in the genus .


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