Summary auto-generated
This study used numerical phenetic analysis to classify 475 strains representing 15 actinomycete genera, including 394 type cultures of Streptomyces. Researchers examined 139 morphological, biochemical, and physiological characters and applied cluster analysis using similarity coefficients and the UPGMA algorithm. The analysis revealed that Streptomyces type cultures fell into one large cluster-group containing 19 major and 40 minor clusters plus 18 single-member clusters at the 77.5% similarity level. Based on phenetic data combined with previous studies, the authors recommended reducing six genera (Actinopycnidium, Actinosporangium, Chainia, Elytrosporangium, Kitasatoa, and Microellobosporia) to synonyms of Streptomyces, while maintaining Intrasporangium, Nocardioides, and Streptoverticillium as distinct genera. The study demonstrated that previous classification schemes relying on limited subjective characters had created artificial taxa, and the results provide a basis for reducing the number of recognized Streptomyces species from approximately 3000 to a more manageable number reflecting natural groupings.
Key findings
- Six morphologically distinct genera should be reduced to synonyms of Streptomyces based on overall phenetic similarity
- Streptomyces type cultures form one large cluster subdivided into 19 major, 40 minor, and 18 single-member clusters at 77.5% similarity level
- Test reproducibility was acceptable with 3.36% average error rate and 93.1% mean similarity between duplicate cultures
- Numerical phenetic analysis reveals extensive overclassification in Streptomyces taxonomy caused by using limited subjectively chosen morphological characters
- Intrasporangium, Nocardioides, and Streptoverticillium remain phenetically distinct from Streptomyces and should retain genus status
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Abstract
SUMMARY: Four hundred and seventy-five strains, which included 394 type cultures of Streptomyces and representatives of 14 other actinomycete genera, were studied. Overall similarities of these strains for 139 unit characters were determined by the SSM and SJ coefficients and clustering by the UPGMA algorithm. Test error and overlap between the phena defined were within acceptable limits. Cluster-groups were defined by the SSM coefficient at the 70.1% similarity (S) level and by the SJ coefficient at the 50% S-level. Clusters were distinguished at the 77.5% SSM and 63% SJ S-levels. Groupings obtained with the two coefficients were generally similar, but there were some changes in the definition and membership of cluster-groups and clusters.
The phenetic data obtained, together with those from previous diverse studies, indicated that the genera Actinopycnidium, Actinosporangium, Chainia, Elytrosporangium, Kitasatoa and Micro-ellobosporia should be reduced to synonyms of Streptomyces, while Intrasporangium, Nocardioides and Streptoverticillium remained as distinct genera in the family Streptomycetaceae. Nocardiopsis dassonvillei also showed strong phenetic affinity to Streptomyces, despite its chemotaxonomic differences. Actinomadura sensu stricto was phenetically distinguishable from Streptomyces and ‘Nocardid’ mediterranea was recognized as a taxon distinct from both these genera and from Nocardia sensu stricto.
Most of the Streptomyces type cultures fell into one large cluster-group. At the 77.5% SSM S-level, they were recovered in 19 major and 40 minor clusters, with 18 strains recovered as single member clusters. The status of the latter as species was therefore confirmed. Most of the minor clusters, consisting of two to five strains, can also be regarded as species. The major clusters varied in size (from 6 to 71 strains) and in their homogeneity. Therefore, it is suggested that they be regarded as species-groups until further information is available. The results provide a basis for the reduction of the large number of Streptomyces species which have been described. They also demonstrate that the previous use of a limited number of subjectively chosen characters to define species-groups or species has resulted in artificial classifications.