Acinetobacter junii A8 was able to biotransform nitroaromatic compounds like o-nitroaniline, o-nitrotoluene, m-nitrotoluene, 2,4,6-trinitrotoluene and o-nitrophenol under aerobic condition, within 36h of incubation. These compounds, which are normally considered to be toxic to microorganisms, caused the induction of drug metabolizing enzymes such as cytochrome P-450, aminopyrine N-demethylase, acetanilide hydroxylase and glutathione S-transferase. These enzymes constitute the bacterial mixed function oxidase system. Induction of this system implies its involvement in biotransformation of these nitro compounds. The biotransformed metabolites were characterized by IR, H-1 NMR and GC-mass spectroscopy. It was observed that o-nitroaniline and m-nitrotoluene were reduced to their respective amines, whereas o-nitrotoluene was oxidized to acid. However, 2,4,6-trinitrotoluene (TNT) and o-nitrophenol were completely mineralized. The metabolites of TNT biotransformation were characterized as 2,6-dinitro-4-nitrosotoluene, 4-amino-2,6-dinitrotoluene and 4-amino-2,6-dinitrobenzoic acid. The result of this study showed that these nitroaromatics induced the mixed function oxidase system, which resulted in the degradation of these compounds. (c) 2005 Elsevier Inc. All rights reserved.