Reactions Involved in the Lower Pathway for Degradation of 4-Nitrotoluene by Mycobacterium Strain HL 4-NT-1

Abstract

In spite of the variety of initial reactions, the aerobic biodegradation of aromatic compounds generally yields dihydroxy intermediates for ring cleavage. Recent investigation of the degradation of nitroaromatic compounds revealed that some nitroaromatic compounds are initially converted to 2-aminophenol rather than dihydroxy intermediates by a number of microorganisms. The complete pathway for the metabolism of 2-aminophenol during the degradation of nitrobenzene by Pseudomonas pseudoalcaligenes JS45 has been elucidated previously. The pathway is parallel to the catechol extradiol ring cleavage pathway, except that 2-aminophenol is the ring cleavage substrate. Here we report the elucidation of the pathway of 2-amino-4-methylphenol (6-amino-mcresol) metabolism during the degradation of 4-nitrotoluene by Mycobacterium strain HL 4-NT-1 and the comparison of the substrate specificities of the relevant enzymes in strains JS45 and HL 4-NT-1. The results indicate that the 2-aminophenol ring cleavage pathway in strain JS45 is not unique but is representative of the pathways of metabolism of other o-aminophenolic compounds.Nitroaromatic compounds are important industrial feedstocks due to the versatile chemistry of the nitro group (22). Many nitroaromatic compounds are harmful, and their release into the environment has caused concern. The microbial degradation of nitroaromatic compounds is usually initiated by an enzymatic attack on the nitro group (22). One of the strategies involves partial reduction of the nitro group to a hydroxylamino group. The hydroxylamino intermediates can be transformed to catechols which enter the ring cleavage pathways of aerobic degradation of aromatic compounds, as observed during degradation of 4-nitrobenzoate (6, 33), 3-nitrophenol (19), and 4-nitrotoluene (7, 26). Alternatively, the hydroxylamino intermediates can be rearranged, by an intramolecular transfer of the hydroxyl group (10; L. J. Nadeau, Z. He, and J. C. Spain, unpublished data), to ortho-aminophenols, as observed during biodegradation of nitrobenzene (21, 24), 3-or 4-chloronitrobenzene (2, 16, 24), 3-nitrophenol (28), 2-chloro-5-nitrophenol (29), 4-nitrotoluene (30), and 2,4,6-trinitrotoluene (15) by various microorganisms. The initial steps of each of the degradation pathways have been elucidated; however, the lower pathway has been determined only for the metabolism of 2-aminophenol during the degradation of nitrobenzene by Pseudomonas pseudoalcaligenes JS45 (11,14). The pathway is parallel to the catechol extradiol ring cleavage pathway, except that 2-aminophenol is the ring cleavage substrate.Mycobacterium strain HL 4-NT-1 is able to grow on 4-nitrotoluene as the sole source of nitrogen, carbon, and energy (30). 4-Nitrotoluene is converted to 2-amino-4-methylphenol (6-amino-m-cresol) via 4-hydroxylaminotoluene in reactions catalyzed by a nitroreductase and an aminohydroxymutase. In reactions analogous to those used by strain JS45, extracts from induced cells of strain HL 4-NT-1 catalyzed the conversion of 2-amino-4-meth...

Nitroaromatic Compounds, from Synthesis to Biodegradation

“…Similar to the case in the nitrobenzene degradation pathway in P. pseudoalcaligenes JS45 (Fig. 13A and B), the amino group is removed after meta ring cleavage (72). In contrast, degradation of 4NT in Pseudomonas sp.…”

Novel organization of catechol meta pathway genes in the nitrobenzene degrader Comamonas sp. JS765 and its evolutionary implication

“…The catechol meta cleavage pathway ( Fig. 1) is the archetypal extradiol ring cleavage pathway and it is involved in the degradation of a variety of aromatic compounds including benzene, toluene, naphthalene, biphenyl, nitroaromatic and chloroaromatic compounds [5,11,21,25,26,28,29]. Williams and Sayers [28] proposed that two diVerent classes of evidence can be used to piece together the evolutionary history of degradation pathways: (a) comparison of the nucleotide and amino acid sequences of the genes, and, (b) the study of the organization of the genes of a pathway.…”

Federal Integrated Biotreatment Research Consortium (FIBRC): Flask to Field Initiative

“…Only traces of 3-nitrotoluene, 2,3-dinitrotoluene and 3,4-dinitrotoluene were generated during the manufacture of TNT, and such compounds are rare at contaminated sites. Bacteria able to utilize 2-NT Haigler et al, 1994b), 4-NT (Haigler andHe and Spain, 2000b;, 2,4-DNT Haigler et al, 1994a;Spanggord et al, 1991), and 2,6-DNT as sole carbon and nitrogen sources have been isolated and the degradative pathways determined. Multiple pathways for 4-NT degradation, all involving an initial reduction, have been identified (Haigler and Spain, 1993;Rhys-Williams et al, 1993; in three different bacteria (Fig.…”

“…Degradative pathways were worked out using standard techniques including oxygen uptake assays in resting cells, assays with crude cell extracts, and purification and identification of pathway intermediates (Haigier et al, 1994a;Haigier et al, 1994b;He and Spain, 1997;He and Spain, 2000b;Jain et al, 1994;Vorbeck et al, 1998). Individual enzymes were purified and characterized with regard to size, sequence, structure, substrate range, inhibitors, cofactors, and possible reaction mechanisms Haigier et al, 1999;Haigier et al, 1996;Kadiyala and Spain, 1998;Lendenmann and Spain, 1996;.…”