Systematics of actinobacteria

─Past, present, and future─

Abstract

Actinobacteria are Gram-stain-positive bacteria with a variety of morphologies. They produce various secondary metabolites and are therefore treated as distinct from other bacteria. Until the early 1970s actinobacteria were classified mainly on the basis of their morphological features, but they are currently classified by a combination of their chemotaxonomic characteristics and phylogenetic relationships based on 16S rRNA gene sequences. However, this classification is problematic, because the phenotypic diversity of actinobacteria has led to excessive division of genera and species. Recent taxonomic studies using whole-genome sequences have resulted in more reliable phylogenetic relationships than those based on 16S rRNA gene sequences and should therefore facilitate the reclassification of known species. Furthermore, recent increases in the sophistication of analytical instruments are enabling more detailed chemotaxonomic characterization and could lead to the discovery of new taxonomic indicators. Therefore, more appropriate classification systems will likely be built through a combination of detailed chemotaxonomic characterization and phylogenetic analysis based on whole-genome sequences.