In this paper, the taxonomy of the genus Arthrobacter is discussed, from its first description in 1947 to the present state. Emphasis is given to intrageneric phylogeny and chemotaxonomic characteristics, concentrating on quinone systems, peptidoglycan compositions and polar lipid profiles. Internal groups within the genus Arthrobacter indicated from homogeneous chemotaxonomic traits and corresponding to phylogenetic grouping and/or high 16S rRNA gene sequence similarities are highlighted. Furthermore, polar lipid profiles and quinone systems of selected species are shown, filling some gaps concerning these chemotaxonomic traits. Based on phylogenetic groupings, 16S rRNA gene sequence similarities and homogeneity in peptidoglycan types, quinone systems and polar lipid profiles, a description of the genus Arthrobacter sensu lato and an emended description of Arthrobacter roseus are provided. Furthermore, reclassifications of selected species of the genus Arthrobacter into novel genera are proposed, namely Glutamicibacter gen. nov. (nine species), Paeniglutamicibacter gen. nov. (six species), Pseudoglutamicibacter gen. nov. (two species), Paenarthrobacter gen. nov. (six species) and Pseudarthrobacter gen. nov. (ten species).

Brevibacterium liquefaciens ATCC 14929(T) was reclassified as Corynebacterium liquefaciens by Lan?elle et al. (1980). A further study by Stackebrandt et al. (1983) described the same strain, indicating high genomic and chemotaxonomic relatedness to Arthrobacter nicotianae; however, reclassification was not formally proposed. Because of the discrepancies between their previous work and the data of Collins & Kroppenstedt (1983), Lan?elle and colleagues re-examined B. liquefaciens and withdrew their recommendation for the assignment of B. liquefaciens to the genus Corynebacterium (Lan?elle et al., 1984). Formal reclassification of B. liquefaciens as A. nicotianae is now proposed.