Three bacterial isolates from soil, capable of degradation or transformation of nitroaromatic compounds and displaying a rod-coccus growth cycle, were studied by a polyphasic approach. On the basis of 16S rRNA sequence analysis and of chemotaxonomic characteristics, such as type A3alpha peptidoglycan with an interpeptide bridge Ala-Thr-Ala, the major menaquinone MK-9(H(2)) and fatty acid composition, the isolates were assigned to the genus Arthrobacter. DNA-DNA hybridization, riboprinting and phenotypic studies revealed that the three strains constitute a single species, distinct from phylogenetically neighbouring Arthrobacter aurescens and Arthrobacter ilicis. A novel species, Arthrobacter nitroguajacolicus sp. nov., with the type strain G2-1(T) (=CCM 4924(T)=DSM 15232(T)) is proposed.