16S rDNA studies on members of Arthrobacter and Micrococcus: An aid for their future taxonomic restructing

16S rDNA sequence data was obtained for 11 species of Arthrobacter and 4 species of Micrococcus and compared with that from other members of the arthrobacterial lineage within the order Actinomycetales. The intermixing of members of these two genera and the placement of Renibacterium salmoninarum within the radiation of these two genera, as previously suggested by 16S rRNA cataloguing, is confirmed. The branching pattern reveals several closely related organisms that cluster around the type species of Arthrobacter and Micrococcus; these species are considered ‘core organisms’. A few species, however, branch outside the radiation of core organisms; these include Micrococcus kristinae, Micrococcus halophilus, and, as previously indicated, Micrococcus sedentarius and M. nishinomiyaensis. As phenotypic data that would support the exclusion of these four species from the genus Micrococcus are still lacking taxonomic conclusions should await more thorough comparative studies.