Oxidative Transformation of Aminodinitrotoluene Isomers by Multicomponent Dioxygenases

Abstract

The electron-withdrawing nitro substituents of 2,4,6-trinitrotoluene (TNT) make the aromatic ring highly resistant to oxidative transformation. The typical biological transformation of TNT involves reduction of one or more of the nitro groups of the ring to produce the corresponding amine. Reduction of a single nitro substituent of TNT to an amino substituent increases the electron density of the aromatic nucleus considerably. The comparatively electron-dense nuclei of the aminodinitrotoluene (ADNT) isomers would be expected to be more susceptible to oxygenase attack than TNT. The hypothesis was tested by evaluating three nitroarene dioxygenases for the ability to hydroxylate the ADNT isomers. The predominant reaction was dioxygenation of the ring to yield nitrite and the corresponding aminomethylnitrocatechol. A secondary reaction was benzylic monooxygenation to form aminodinitrobenzyl alcohol. The substrate preferences and catalytic specificities of the three enzymes differed considerably. The discovery that the ADNT isomers are substrates for the nitroarene dioxygenases reveals the potential for extensive bacterial transformation of TNT under aerobic conditions.

Expression of the Nitroarene Dioxygenase Genes inComamonassp. Strain JS765 andAcidovoraxsp. Strain JS42 Is Induced by Multiple Aromatic Compounds

“…Even compounds that do not serve as growth substrates for these strains induced expression, including 2,4-DNT, 2,6-DNT, 2ADNT, 4ADNT, salicylate, and anthranilate. It is also important to note that NBDO is able to release nitrite from all of the nitroaromatic compounds tested except for 2ADNT (18,22). 2NTDO can oxidize nitrobenzene, 2NT, 3NT, and 4NT but not 2,4-DNT (30).…”

Protein Engineering of the Archetypal Nitroarene Dioxygenase of Ralstonia sp. Strain U2 for Activity on Aminonitrotoluenes and Dinitrotoluenes through Alpha-Subunit Residues Leucine 225, Phenylalanine 350, and Glycine 407

“…1); wild-type NDO had no activity on this substrate (Table 2). Variant F350T generated 2A46DNBA at 20% of the rate of wild-type DDO of B. cepacia R34 (13).…”

“…strain DNT (DNT DDO) oxidize 2A46DNT at the 3,4 position, releasing nitrite to form 3-amino-4-methyl-5-nitrocatechol (3A4M5NC), and hydroxylation of the methyl group forms 2-amino-4,6-dinitrobenzyl alcohol (2A46DNBA) ( Fig. 1) (13). The recombinant nitrobenzene dioxygenase from Comamonas sp.…”

“…The recombinant nitrobenzene dioxygenase from Comamonas sp. strain JS765 has been shown to oxidize 4A26DNT at the 2,3 position, releasing nitrite and to generate 3A6M5NC (13). The wild-type naphthalene dioxygenase (NDO) from Ralstonia sp.…”

Biodegradation, Biotransformation, and Biocatalysis (B3)

“…Substituted o-aminophenols can be used to produce polybenzoxazole polymers and starting materials for the production of compounds with electronic, medical, and pharmaceutical applications. Other enzymes from nitroarenedegrading pathways can convert aminodinitrotoluenes to aminonitrocatechols (51). Enzymes of the toluene and nitrobenzene degradation pathways catalyze biotransformations that result in the production of picolinic acids, compounds that can be used as starting materials for the production of pharmaceuticals, herbicides, dyes, and polymers (41).…”