Sequences of the RNase P RNA gene were investigated for the phylogenetic analysis of the genus Saccharomonospora. Aligned nucleotide sequences, determined from the PCR-amplified RNase P RNA gene of representative strains of the genus Saccharomonospora, displayed 94.22103 O/ O interspecif ic variances. The intraspecific similarity value was 99.7-100 O/ O in all species tested. Saccharornonospora azurea K161 and 'Saccharomonospora caesia ' K76T displayed identical RNase P RNA gene sequences in the region that was determined and Saccharornonospora sp. K180 showed sequences distinct from validly described species with a similarity value of 946*1*0%. The phylogenetic trees constructed by aligning the sequences either within the genus Saccharomonospora or with other Gram-positive bacteria were similar to the ones derived using sequences of the 165 rDNA gene. Advantageous features of this gene for application as a molecular phyletic marker are discussed.

Saccharomonospora species were subjected to DNA-DNA relatedness determination to investigate their genetic relationships based on genomic DNA. The levels of DNA-DNA relatedness among the type strains of the four validly described Saccharomonospora species ranged from 18 to 46 %. Saccharomonospora wiridis KCTC 91 56, which was described as 'Saccharomonospora internatus' but later reclassified as a member of 5. wiridis, showed a similarity level of 90% to S. wiridis KCTC 9115T. Sacchammonospora sp. strain K180 exhibited levels of DNA-DNA relatedness that are indicative of a new species. Saccharomonospora azurea exhibited levels of DNA-DNA homology of 84-95 O/ O to 'Saccharomonospora caesia' strains including the type strain. Therefore, on the basis of DNA-DNA relatedness data and taxonomic data described previously, it is proposed that '5. caesia' should be considered as a synonym of 5. azurea.Keywords : Saccharomonospora species, DNA-DNA relatedness, taxonomic revisionThe genus Saccharomonospora was proposed by Nonomura & Ohara (1971) for monosporic actinomycetes which contain meso-diaminopimelic acid, arabinose and galactose in the cell-wall peptidoglycan [wall chemotype IV sensu Lechevalier & Lechevalier (1 970)]. The additional phenotypic characteristics and phylogenetic analysis of this genus have been described elsewhere (Kim et al., 1995;Yoon et al., 1996Yoon et al., , 1997. There are currently four validly described Saccharomonospora species, namely, Saccharomonospora azurea (Runmao, 1987), Saccharomonospora cyanea (Runmao et al., 1988), Saccharomonospora glauca (Greiner-Mai et al., 1988) and Saccharomonospora viridis (Nonomura & Ohara, 1971), the type species of the genus. ' Saccharomonospora caesia ' was previously classified as Micropolyspora caesia (Kalakoutskii, 1964). However, Kurup (1981) considered M . caesia to be a member of the genus Saccharomonospora, and this was confirmed by Greiner-Mai et al. (1987). The name of ' S . caesia' was not included on the Approved Lists of Bacterial Names (Skerman et al., 1980) for a strain previously classified as Micropolyspora internatus (Agre et al., 1974), but this strain was regarded as a synonym of S. viridis (Greiner-Mai et al., 1988). Another invalidly described Saccharomonospora strain, ' S. yunnanensis ' was reported by Chenglin & Lihua, 1985) but was not available for our study.From 16s rDNA sequence analysis, the four validly described Saccharomonospora species exhibited high levels of 16s rDNA similarity (Kim et al., 1995). The 16s rDNA sequences of most Saccharomonospora species were more than 98 YO similar; the only exception was S. viridis whose 16s rDNA showed levels similar to other Saccharomonospora species. In particular, S. azurea and ' S. caesia' strains had identical 16s rDNA sequences (Kim et al., 1995). S. azurea has also been shown to be closely related to ' S . caesia' strains from several other taxonomic studies. S. azurea and ' S . caesia' have identical sequences in 5s rRNA (unpublished), in 16s-23s rDNA ITS (internally transcribe...

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