The 16S–23S internally transcribed spacer (ITS) sequences were analysed to clarify inter- and intraspecific relationships among strains of the genus and the relationship between two species. The 16S–23S ITS regions from 33 strains, two species and were sequenced directly after polymerase chain reaction (PCR) amplification and λ exonuclease treatment. The genomes of some strains included two types of 16S–23S ITS sequences. The sizes of the 16S–23S ITS sequences of strains ranged from 328 to 539 bp. The 16S–23S ITS sequences of NSP37, NSP38and NSP39were 349, 355 and 386 bp long, respectively. Nucleotide similarity among 16S–23S ITS sequences of strains and of strains was 84·1-100% and 97·7-100%, respectively. The 16S–23S ITS sequence of was identical to that of ‘’ NSP32and was only 1 bp different from that of ‘’ strains. However, the 16S–23S ITS sequences of ‘’ NSP32showed only a low degree of similarity to ‘’ NSP32(54·8%). The degree of 16S–23S ITS similarity between NSP20and strains ranged from 85 to 93%. The mean nucleotide similarity values between the type strains of validly described species were highly divergent at 68·1±16·8%. The two species showed a level of 16S–23S ITS similarity of 71·2%. In this study, 16S–23S ITS sequences of the members of the genera and were useful for inferring the relationships between closely related strains and species. However, they were not found to be appropriate for elucidating the phylogenetic relationships between distantly related organisms at the genus level.


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