Biological Degradation of 2,4,6-Trinitrotoluene

Abstract

Nitroaromatic compounds are xenobiotics that have found multiple applications in the synthesis of foams, pharmaceuticals, pesticides, and explosives. These compounds are toxic and recalcitrant and are degraded relatively slowly in the environment by microorganisms. 2,4,6-Trinitrotoluene (TNT) is the most widely used nitroaromatic compound. Certain strains of Pseudomonas and fungi can use TNT as a nitrogen source through the removal of nitrogen as nitrite from TNT under aerobic conditions and the further reduction of the released nitrite to ammonium, which is incorporated into carbon skeletons. Phanerochaete chrysosporium and other fungi mineralize TNT under ligninolytic conditions by converting it into reduced TNT intermediates, which are excreted to the external milieu, where they are substrates for ligninolytic enzymes. Most if not all aerobic microorganisms reduce TNT to the corresponding amino derivatives via the formation of nitroso and hydroxylamine intermediates. Condensation of the latter compounds yields highly recalcitrant azoxytetranitrotoluenes. Anaerobic microorganisms can also degrade TNT through different pathways. One pathway, found in Desulfovibrio and Clostridium, involves reduction of TNT to triaminotoluene; subsequent steps are still not known. Some Clostridium species may reduce TNT to hydroxylaminodinitrotoluenes, which are then further metabolized. Another pathway has been described in Pseudomonas sp. strain JLR11 and involves nitrite release and further reduction to ammonium, with almost 85% of the N-TNT incorporated as organic N in the cells. It was recently reported that in this strain TNT can serve as a final electron acceptor in respiratory chains and that the reduction of TNT is coupled to ATP synthesis. In this review we also discuss a number of biotechnological applications of bacteria and fungi, including slurry reactors, composting, and land farming, to remove TNT from polluted soils. These treatments have been designed to achieve mineralization or reduction of TNT and immobilization of its amino derivatives on humic material. These approaches are highly efficient in removing TNT, and increasing amounts of research into the potential usefulness of phytoremediation, rhizophytoremediation, and transgenic plants with bacterial genes for TNT removal are being done

Novel organization of aromatic degradation pathway genes in a microbial community as revealed by metagenomic analysis

“…The ability to use various aromatic compounds to serve as sources of carbon and energy is widespread in bacteria, and in the natural environment these bacteria contribute greatly to the breakdown of aromatic compounds and to the global carbon cycle (Wittich, 1998;Esteve-Nú ñ ez et al, 2001;Furukawa et al, 2004). The majority of reported bacterial aromatic degradation processes are aerobic (Gibson and Harwood, 2002) and comprise series of enzymes that are usually categorized as either 'upper'-or 'lower'-pathway enzymes (Williams and Sayers, 1994).…”

Study of the role played by NfsA, NfsB nitroreductase and NemA flavin reductase from Escherichia coli in the conversion of ethyl 2-(2′-nitrophenoxy)acetate to 4-hydroxy-(2H)-1,4-benzoxazin-3(4H)-one (D-DIBOA), a benzohydroxamic acid with interesting biological properties

“…These three enzymes, NfsA, NfsB and NemA, which contain the flavin mononucleotide as prostetic group, can reduce up to two nitro groups (-NO 2 − ) from different nitroaromatics compounds as TNT (Esteve-Nuñez et al 2001;Yin et al 2005) to the corresponding amines (-NH 2 ) via hydroxylamino (-NHOH) intermediates. The reduction is catalysed through the addition of one or two electrons from the cofactors NADH and/or NADPH (Roldán et al 2008).…”

Expression of haloacid dehalogenase gene and its molecular protein characterization from Klebsiella pneumoniae ITB1

“…These chemically synthesized organic compounds are not readily degraded in the environment, and many are accumulate in soil water, groundwater, lake, and river (Esteve-Núñez et al 2001;Pervova et al 2002). Besides local and regional contamination, organohalogen continues to be a global issue pollutants, partly because its transport through water and air helps these compounds to spread across the Earth (Iwata et al 1993).…”