A soil bacterium strain, capable of using p-nitrophenol (PNP) as its sole source of carbon and energy, was isolated by enrichment on minimal salt medium (MSM). On the basis of a phylogenetic analysis of 16S rRNA gene sequences the bacterium is a species of Arthrobacter, closely related to Arthrobacter ureafaciens DSM 20126. This strain has an unusually high substrate tolerance for PNP degradation in MSM. Greatest degradation of PNP was observed at 30 degrees C and under slightly alkaline pH (pH 7-9) conditions. Effective degradation rates slowed as the concentration of PNP was increased. Addition of glucose from 0.1% to 0.5% generally enhanced the degradation of PNP at high concentration (400 mg/l) although acidification as a result of glucose metabolism had a negative effect on PNP depletion. Biodegradation of PNP at high concentration was greatly accelerated by beta-cyclodextrin at a concentration of 0.5%, indicating that beta-cyclodextrin could be a promising addictive for effective PNP bioremediation.