Isolation of Arthrobacter strains on the basis of their cystite formation.

positive, catalase-positive and pleomorphic rods, and belong to the order Actinimycetales (Stackebrandt et al., 1997). According to a list of bacterial names with standing in nomenclature (URL: http://www.bacterio. cict.fr/) (Euzéby, 1997), the number of species accounted for in this genus is 30, eliminating the species reidentified as other taxa than the genus Arthrobacter. The species of the genus Arthrobacter are separated into two major groups, the Arthrobacter globiformis/A. citreus group and the Arthrobacter nicotianae group by their chemotaxonomic features (Jones and Keddie, 1992; Keddie et al., 1986). The peptidoglycan type of the A. globiformis/A. citreus group is A3a, whereas that of the A. nicotianae group is A4a. In addition, their menaquinone systems and cell-wall polymers differ from each other. The species of the A. globiformis/A. citreus group have MK-9(H2) and neutral polysaccharides, whereas those of the A. nicotianae group have MK-8 and/or MK-9 and teichoic acid. As an exception, A. crystallopoietes in the A. globiformis/A. citreus group has teichoic acid. Recently, the phylogenetic relationship of the genus Arthrobacter was studied, and it was found that each of the species of the A. globiformis/A. citreus group and the A. nicotianae group is placed in several clusters by the 16S rRNA gene sequence (Tanaka et al., 2001). Additionally, the genus Arthrobacter is closely related to other genera, particularly to the genus Micrococcus (Koch et al., 1994). Approximately 250 Arthrobacter strains are available from culture collections around the world. These strains were isolated by the use of various media from environments, especially soils for the screening of useful substance-producing bacteria (Brim et al., 1999; Nakajima-Kambe et al., 1995; Stevenson, 1967; Westerberg et al., 2000) and for research into microbiological diversity (Balkwill and Ghiorse, 1985; Crocker et al., 2000; Eppard et al., 1996; Gardener and Bruijn, 1998), and from clinical specimens (Funke et al., 1996; Hou et al., 1998; Wauters et al., 2000). A considerable number of Arthrobacter strains have been identified, but the others have been remained unidentified at the species level. Additionally, some Arthrobacter species consist of only one strain. Probably, the media used for the above isolations were not focused on the isolation of a variety of Arthrobacter strains, and the strains were isolated by chance. Therefore, Arthrobacter strains available from culture collections are rather limited to certain species, and a considerable number of the strains come from the same origins. New Arthrobacter strains are needed for the further taxonomic study of the genus Arthrobacter. As part of the study, media for the isolation of Arthrobacter strains should be designed in consideration of their characterIsolation of Arthrobacter strains on the basis of their cystite formation