A Gram-positive bacterium, Rhodococcus wratislaviensis strain 9, was isolated from groundwater contaminated with nitrophenolics and trichloroethene following enrichment culture technique. The cells of strain 9 grown on LB broth (uninduced) degraded 720 mu M p-nitrophenol (PNP) within 12 h, and utilized as a source of carbon and energy. Orthogonal experimental design analysis to determine optimal conditions for biodegradation of PNP showed that pH had a significant positive effect (P <= .05) on bacterial degradation of PNP, while glucose, di- and tri-nitrophenols exhibited significant negative effect. Cell-free extracts obtained from PNP-grown culture that contained 20 mu g mL(-1) protein degraded 90% of 720 mu M PNP within 5 h of incubation. Two-dimensional protein analysis revealed differential expression of the oxygenase component of PNP monooxygenase and an elongation factor Tu in PNP-grown cells, but not in those grown on glucose. The strain 9 remediated laboratory wastewater containing 900 mu M PNP efficiently within 14 h, indicating its great potential in bioremediation of PNP-contaminated waters. (C) 2017 Elsevier B.V. All rights reserved.