INTRODUCTION

Many xenobiotic chemicals introduced into the environment for agricultural and industrial use are nitro-substituted aromatics. Nitro groups in the aromatic ring are often implicated as the cause of the persistence and toxicity of such compounds. Nitroaromatic compounds enter soil, water, and food by several routes, such as use of pesticides, plastics, pharmaceuticals, landfill dumping of industrial wastes, and the military use of explosives. The nitroaromatic compound, trinitrotoluene (TNT) is introduced into soil and water ecosystems mainly by military activities such as the manufacture, loading, and disposal of explosives and propellants. This contamination problem may increase in future because of the demilitarization and disposal of unwanted weapons systems.

Biotransformation of TNT and other nitroaromatics by aerobic bacteria in the laboratory has been reported frequently (Boopathy et al., 1994a; 1994b; Dickel and Knackmuss, 1991; Duque et al., 1993; Funk et al., 1993; McCormick et al., 1976; 1981; Nishino and Spain, 1993; Spain and Gibson, 1991; Zeyer and Kearney, 1984). Biodegradation of 2,4-dinitrotoluene by a Pseudomonas sp. has been reported to occur via 4-methyl-5-nitrocatechol in a dioxygenase-mediated reaction (Spanggord et al., 1991). Duque et al. (1993) successfully constructed a Pseudomonas hybrid strain that mineralized TNT. White rot fungus has been shown to mineralize radiolabelled TNT (Fernando et al., 1990). The work of Spiker et al. (1992) showed that Phanerochaete chrysosporium is not a good candidate for bioremediation of TNT contaminated sites containing high concentration of explosives because of its high sensitivity to contaminants.