GENETIC ANALYSES OF THE GENUS NOCARDIOIDES AND RELATED TAXA BASED ON 16S-23S RDNA INTERNALLY TRANSCRIBED SPACER SEQUENCES

The 16S-23S internally transcribed spacer (ITS) sequences were analyse d to clarify inter- and intraspecific relationships among strains of t he genus Nocardioides and the relationship between two Aeromicrobium s pecies. The 16S-23S ITS regions from 33 Nocardioides strains, two Aero microbium species and Terrabacter tumescens were sequenced directly af ter polymerase chain reaction (PCR) amplification and lambda exonuclea se treatment. The genomes of some Nocardioides strains included two ty pes of 16S-23S ITS sequences. The sizes of the 16S-23S ITS sequences o f Nocardioides strains ranged from 328 to 539 bp, The 16S-23S ITS sequ ences of Aeromicrobium erythreum NSP37(T), Aeromicrobium fastidiosum N SP38(T) and T. tumescens NSP39(T) were 349, 355 and 386 bp long, respe ctively. Nucleotide similarity among 16S-23S ITS sequences of Nocardio ides albus strains and of Nocardioides simplex strains was 84.1-100% a nd 97.7-100%, respectively. The 16S-23S ITS sequence of Nocardioides l uteus was identical to that of 'Nocardioides fulvus' NSP32(T) and was only 1 bp different from that of 'Nocardioides flavus' strains. Howeve r, the 16S-23S ITS sequences of 'N. fulvus' NSP33 showed only a low de gree of similarity to 'N. fulvus' NSP32(T) (54.8%). The degree of 16S- 23S ITS similarity between N. luteus NSP20(T) and N. albus strains ran ged from 85 to 93%. The mean nucleotide similarity values between the type strains of validly described Nocardioides species were highly div ergent at 68.1 +/- 16.8%. The two Aeromicrobium species showed a level of 16S-23S ITS similarity of 71.2%. In this study, 16S-23S ITS sequen ces of the members of the genera Nocardioides and Aeromicrobium were u seful for inferring the relationships between closely related strains and species. However, they were not found to be appropriate for elucid ating the phylogenetic relationships between distantly related organis ms at the genus level.