The application of phylogenetic taxonomic procedures led to improvements in the classification of bacteria assigned to the phylum Actinobacteria but even so there remains a need to further clarify relationships within a taxon that encompasses organisms of agricultural, biotechnological, clinical, and ecological importance. Classification of the morphologically diverse bacteria belonging to this large phylum based on a limited number of features has proved to be difficult, not least when taxonomic decisions rested heavily on interpretation of poorly resolved 16S rRNA gene trees. Here, draft genome sequences of a large collection of actinobacterial type strains were used to infer phylogenetic trees from genome-scale data using principles drawn from phylogenetic systematics. The majority of taxa were found to be monophyletic but several orders, families, and genera, as well as many species and a few subspecies were shown to be in need of revision leading to proposals for the recognition of 2 orders, 10 families, and 17 genera, as well as the transfer of over 100 species to other genera. In addition, emended descriptions are given for many species mainly involving the addition of data on genome size and DNA G+C content, the former can be considered to be a valuable taxonomic marker in actinobacterial systematics. Many of the incongruities detected when the results of the present study were compared with existing classifications had been recognized from 16S rRNA gene trees though whole-genome phylogenies proved to be much better resolved. The few significant incongruities found between 16S/23S rRNA and whole genome trees underline the pitfalls inherent in phylogenies based upon single gene sequences. Similarly good congruence was found between the discontinuous distribution of phenotypic properties and taxa delineated in the phylogenetic trees though diverse non-monophyletic taxa appeared to be based on the use of plesiomorphic character states as diagnostic features.

Morphological, cultural and physiological properties of two strains of soil thermophilic actinomycetes were studied. These strains were compared to the actinomycetes of related genera and were found to be close to Micropolyspora and Actinomadura. However, they differed from both genera by the structure of the sporiferous apparatus, from Micropolyspora by the type of the cell wall, and from Actinomadura by the fatty acid composition of lipids of the mycelium. A new genus of actinomycetes, Excellospora Agre a. Guzeva gen. nov., is suggested on the basis of this study. Two species belonging to the genus Micropolyspora are proposed to assign to the new genus as Excellospora viridinigra and Excellospora rubrobrunea. Since these strains differ from the aforementioned species by the traits used for differentiation of the species of actinomycetes, they are described as a new species of the new genus Excellospora Agre a. Guzeva gen. nov. sp. nov.