Intrageneric relationships of the actinomycete genus Micromonospora

The intrageneric structure of the genus Micromonospora was determined by analyzing the 16S ribosomal DNAs of the type strains of all but one of the 15 validly described species and four subspecies and 19 other Micromonospora strains, most of which represented invalidly described species. One of the 19 other Micromonospora strains grouped outside a phylogenetically tight genus Micromonospora, which appeared to be closely related to other genera belonging to the family Micromonosporaceae. The level of sequence similarity for the 16S ribosomal DNAs of most of the type strains was 98%. Values in the same range were also found when the sequences of the type strains and most of the other Micromonospora strains were compared. Whether the invalidly described species actually represent taxa that are worthy of species status should be investigated by performing DNA reassociation studies and thoroughly comparing physiological and chemotaxonomic properties.