Enzyme and Microbial Technology 37 (2005) 527–533 Biotransformation of nitroaromatics and their effects on mixed function oxidase system I. Soojhawon, P.D. Lokhande, K.M. Kodam, K.R. Gawai ∗ Department of Chemistry, University of Pune, Pune 411 007, India Received 5 October 2004; accepted 31 March 2005 Abstract 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 36 h 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, 1 H 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. © 2005 Elsevier Inc. All rights reserved. Keywords: Mixed function oxidase system; Biotransformation; Acinetobacter junii A8; Nitroaromatics; Cytochrome P-450 1. Introduction Nitroaromatics are important priority pollutants entering the environment primarily through anthropogenic activities associated with the industrial production of dyes, explosives, pesticides and pharmaceuticals [1,2]. Discharge of these compounds into the environment poses serious health haz- ards as they are mutagenic and bioaccumulate in the food chain [3–5]. Most of the nitroaromatics are potent uncou- plers of oxidative and photosynthetic phosphorylation [6]. The toxicity of these compounds and their recalcitrant na- ture can prove to be problematic for their effective biological treatment [7]. Moreover, aromatic compounds with multiple nitro substituents are known to be resistant to electrophilic attack by oxygenases [8]. These compounds are readily re- duced by anaerobic consortia to their respective amines [9]. However, very often, the amines are not metabolized further ∗ Corresponding author. Tel.: +91 20 25691728; fax: +91 20 25691728. E-mail address: iswarduth8@yahoo.co.uk (K.R. Gawai). under anaerobic conditions [7]. Thus, a sequential anaerobic and aerobic condition is proposed for the degradation of ni- tro aromatic compounds [10]. The biotransformation of these chemicals is carried by a group of enzymes, which is termed as mixed function oxidase system. Cytochrome P-450 is the main component of the mixed function oxidase system, which is of great catalytic versatil- ity, found in animals, plants and microorganisms. It plays an important role in the biotransformation of a wide va- riety of xenobiotics [11]. Several strains of microorgan- isms such as Streptomyces carbophilus, Rhodotorula minuta, Bacillus megaterium, Pseudomonas putida, Candida mal- tosa, etc. are known to contain cytochrome P-450 proteins [12–14]. Cytochrome P-450 typically catalyzes the monoxy- genation reaction of non-polar substrates in the presence of oxygen and two reducing equivalents [15]. Microbial cy- tochrome P-450 plays a key role in the biodegradation of a wide variety of contaminants, such as pesticides, polycyclic aromatic hydrocarbons, nitroaromatics, etc. [16–18]. Be- sides cytochrome P-450 proteins, enzymes like demethylase, 0141-0229/$ – see front matter © 2005 Elsevier Inc. All rights reserved. doi:10.1016/j.enzmictec.2005.03.011