Partial recN gene sequences (>1 kb) were obtained from 35 type strains of the genus Amycolatopsis. Phylogenetic trees were constructed to determine the effectiveness of using this gene to predict taxonomic relationships within the genus. The use of recN sequence analysis as an alternative to DNA-DNA hybridization (DDH) for distinguishing closely related species was also assessed. The recN based phylogeny mostly confirmed the conventional 16S rRNA and gyrB gene-based phylogenies and thus provides further support for these phylogenetic groupings. As is the case for the gyrB gene, pairwise recN sequence similarities cannot be used to predict the DNA relatedness between type strains but the recN genetic distance can be used as a means to assess quickly whether an isolate is likely to represent a new species in the genus Amycolatopsis. A recN genetic distance of >0.04 between two Amycolatopsis strains is proposed to provide a good indication that they belong to different species (and that polyphasic taxonomic characterization of the unknown strain is worth undertaking).

To describe three new Amycolatopsis strains and assess the antibiotic biosynthetic potential of the genus. Three strains, designated S1�P3(T) , S3�P6(T) and SE(8)3(T) , belonging to the genus Amycolatopsis were isolated and found to cluster together by 16S rRNA and gyrB gene-based phylogenetic analysis. Genetic distance values, based on the gyrB gene, were calculated between the strains and their closest relatives and were all above the threshold value of 0�P02 that has been proposed to distinguish Amycolatopsis type strains. DNA-DNA hybridization experiments against related type strains confirmed that strain S3�P6(T) represents a unique genomic species. Strain S3�P6(T) was also found to be distinct from strains S1�P3(T) and SE(8)3(T) , the latter two of which were also shown to be distinct from each other. Antibiotic biosynthetic genes were identified from multiple Amycolatopsis strains, and their presence was found to be phylogenetically associated. The data presented in this study indicate that strains S1�P3(T) , SE(8)3(T) and S3�P6(T) belong to three novel species, for which the names Amycolatopsis circi sp. nov. (= DSM 45561(T) = NRRL B-24841(T)), Amycolatopsis equina sp. nov. (= DSM 45563(T) = NRRL B-24842(T)) and Amycolatopsis hippodromi sp. nov. (= DSM 45562(T) = NRRL B-24843(T)) are proposed. Three new species of Amycolatopsis are described, and the knowledge of the antibiotic biosynthetic potential of the genus has been extended.