Initial Reductive Reactions in Aerobic Microbial Metabolism of 2,4,6-Trinitrotoluene

Abstract

Because of its high electron deficiency, initial microbial transformations of 2,4,6-trinitrotoluene (TNT) are characterized by reductive rather than oxidation reactions. The reduction of the nitro groups seems to be the dominating mechanism, whereas hydrogenation of the aromatic ring, as described for picric acid, appears to be of minor importance. Thus, two bacterial strains enriched with TNT as a sole source of nitrogen under aerobic conditions, a gram-negative strain called TNT-8 and a gram-positive strain called TNT-32, carried out nitro-group reduction. In contrast, both a picric acid-utilizingRhodococcus erythropolis strain, HL PM-1, and a 4-nitrotoluene-utilizing Mycobacterium sp. strain, HL 4-NT-1, possessed reductive enzyme systems, which catalyze ring hydrogenation, i.e., the addition of a hydride ion to the aromatic ring of TNT. The hydride-Meisenheimer complex thus formed (H−-TNT) was further converted to a yellow metabolite, which by electrospray mass and nuclear magnetic resonance spectral analyses was established as the protonated dihydride-Meisenheimer complex of TNT (2H−-TNT). Formation of hydride complexes could not be identified with the TNT-enriched strains TNT-8 and TNT-32, or with Pseudomonas sp. clone A (2NT−), for which such a mechanism has been proposed. Correspondingly, reductive denitration of TNT did not occur.

Models of 2,4,6-trinitrotoluene (TNT) initial conversion by yeasts

“…Conversely, the respiratory type of glucose catabolism by the representatives of the genus Candida could mediate the ring hydrogenation, giving rise to H-TNT. The combination of alternative modes of TNT initial reduction was observed earlier in Rhodococcus erythropolis HL PM-1 [13] and Enterobacter cloacae PB2 [19]. This transformation mechanism is the most similar to that performed by Candida sp.…”

“…The most important aspect of the environmental pollution with TNT and its metabolites is obviously the exposure of wildlife, food animals and humans to the toxic e¡ects of these compounds. Because of the relatively unstable nature of both HADNT [20] and H-TNT [13], we have chosen the P. caudatum toxicity test, which allows one to perform the test within a reasonably short period of time. Our preliminary experiments revealed that the concentrations of both HADNT and H-TNT were basically unchanged during 1 h incubation with P. caudatum cells, the time frame usually recommended for this test.…”

“…Chemical synthesis of HADNTs and ADNTs was performed as described earlier [13]. Chemical standard of hydride complex of TNT was kindly provided by Prof. H.-J.…”

Function of Coenzyme F 420 in Aerobic Catabolism of 2,4,6-Trinitrophenol and 2,4-Dinitrophenol by Nocardioides simplex FJ2-1A

“…Due to the presence of electron-withdrawing nitro groups as substituents, dinitroaromatic compounds and particular trinitroaromatic compounds like 2,4,6-trinitrotoluene (TNT) and 2,4,6-trinitrophenol (picric acid) are readily susceptible to initial reductive rather than oxidative attack (23,27). Consequently, initial oxidations by microbial mono-or dioxygenases of aerobic microorganisms are unknown for this class of xenobiotic compounds.…”

“…Besides specific and unspecific reductions of the nitro groups (26), unusual hydrogenations of the aromatic ring system have been observed for picrate and TNT. Thus, hydride and dihydride complexes have been identified as initial metabolites (23,27). In addition, the identification of 2,4dinitrophenol (2,4-DNP) and 4,6-dinitrohexanoate (4,6-DNH) (13,14,23,22) as metabolites of picrate indicates that extensive hydrogenation of the aromatic system (6 H per mol of picrate and 4 H per mol of 2,4-DNP) gives rise to a nonoxygenolytic ring cleavage.…”