Studies on molecular systematics of genus saccharomonospora, and genus nocardioides and related taxa

Abstract

Taxonomic studies based on classical phenotypic data have been eclipsed by developments in molecular systematic studies. Actually, numerous microbial taxa, especially prokaryotic organisms, have been taxonomically revised by molecular systematic studies. Recent chemotaxonomic and molecular systematic approaches toward microbial systematics have played a significant role in establishing the systematics of actinomycetes. In this study, two actinomycete taxa, namely the genera Saccharomonospora and Nocardioides, were studied in detail by molecular systematic techniques, together with phenotypic analysis if necessary. The 16S ribosomal DNA (rDNA) sequence analysis showed that the genus Saccharomonospora is a distinct phyletic group within the evolutionary radiation of the family Pseudonocardiaceae. The 16S rDNA sequences of the four validly described Saccharomonospora species exhibited relatively high levels of nucleotide similarity. The 16S rDNAs of most Saccharomonospora species were more than 98% similar; the only exception was S. viridis. S. azurea and "S. caesia" strains had identical 16S rDNA sequence. Intraspecific sequence variation were not found in S. viridis and "S. caesia", and the 16S rDNA sequence of the type strain of S. glauca differed by only one nucleotide from those of other S. glauca strains. Saccharomonospora sp. strain K180 had a sequence that was different from the sequences of the four validly described Saccharomonospora species. The ribotype patterns of the four validly described Saccharomonospora species allowed these taxa to be distinguished. Each ribotype patterns are species-specific. The additional strains produced patterns identical to those of the corresponding representative species. By 16S rDNA sequences analysis and ribotype patterns, some strains previously identified as S. viridis were reclassified as members of other Saccharomonospora species, and unidentified Saccharomonospora strains were identified. The 16S-23S and 23S-5S I...