Biotransformation of Hydroxylaminobenzene and Aminophenol by Pseudomonas putida 2NP8 Cells Grown in the Presence of 3-Nitrophenol

Abstract

Biotransformation products of hydroxylaminobenzene and aminophenol produced by 3-nitrophenol-grown cells of Pseudomonas putida 2NP8, a strain grown on 2-and 3-nitrophenol, were characterized. Ammonia, 2-aminophenol, 4-aminophenol, 4-benzoquinone, N-acetyl-4-aminophenol, N-acetyl-2-aminophenol, 2-aminophenoxazine-3-one, 4-hydroquinone, and catechol were produced from hydroxylaminobenzene. Ammonia, N-acetyl-2-aminophenol, and 2-aminophenoxazine-3-one were produced from 2-aminophenol. All of these metabolites were also found in the nitrobenzene transformation medium, and this demonstrated that they were metabolites of nitrobenzene transformation via hydroxylaminobenzene. Production of 2-aminophenoxazine-3-one indicated that oxidation of 2-aminophenol via imine occurred. Rapid release of ammonia from 2-aminophenol transformation indicated that hydrolysis of the imine intermediate was the dominant reaction. The low level of 2-aminophenoxazine-3-one indicated that formation of this compound was probably due to a spontaneous reaction accompanying oxidation of 2-aminophenol via imine. 4-Hydroquinone and catechol were reduction products of 2-and 4-benzoquinones. Based on these transformation products, we propose a new ammonia release pathway via oxidation of aminophenol to benzoquinone monoimine and subsequent hydrolysis for transformation of nitroaromatic compounds by 3-nitrophenol-grown cells of P. putida 2NP8. We propose a parallel mechanism for 3-nitrophenol degradation in P. putida 2NP8, in which all of the possible intermediates are postulated.Toxic nitroaromatic compounds tend to be reduced by biological systems in the environment due to electron deficiencies on the nitrogen atom or the benzene ring (6,24,37,45). Arylhydroxylamine is one of the common intermediate products during nitro group reduction. Hydroxylamines are both reductants and oxidants that attack biomolecules and have highly toxic, carcinogenic, and mutagenic effects on biological systems and human tissues (12, 22).The previously described routes for metabolism of arylhydroxylamines, which are involved in nitroreductase-initiated degradation of nitroaromatic compounds, include (i) a twoelectron reduction process that produces dead end amines, (ii) the Bamberger rearrangement-like reaction which leads to production of 2-aminophenol (2-AP) or 4-AP (31, 36, 41), and (iii) conversion into a 1,2-dihydroxyl aromatic product by hydroxylaminolyase (19,20,25,38).Only ammonia release from nitroaromatic compounds avoids production of potentially toxic amines in the environment. The following two ammonia release processes during nitroreductase-initiated aerobic degradation of nitroaromatic compounds have been described: (i) ammonia release via ring fission of AP and (ii) ammonia release before ring fission (conversion of arylhydroxylamine into 1,2-dihydroxyl aromatic compounds by proposed hydrolytic hydroxylaminolyases). Nishino and Spain (31) observed the first process in the nitrobenzene (NB) degradation pathway of Pseudomonas pseudoalcaligenes, and Groeneweg...

Paracetamol in the environment and its degradation by microorganisms

“…a Proposed pathway of 4-aminophenol metabolism; b metabolic pathways of aniline and aniline derivatives in P. putida 2NP8; c proposed reaction pathways during photocatalytic degradation of paracetamol (Fig. 5b) (Zhao et al 2000;Hughes et al 2002). The initial reaction in the degradation of anilines is catalyzed by a dioxygenase and yields the corresponding 1-amino-2-hydrodiols as the first metabolites.…”

Substrate Selectivity of a 3-Nitrophenol-Induced Metabolic System in Pseudomonas putida 2NP8 Transforming Nitroaromatic Compounds into Ammonia under Aerobic Conditions

“…1A; RϭH). We postulated that this strain converted the growth substrate 3-NP into hydroxylquinol via oxidation of aminohydroquinone into imine, hydrolysis of the imine into quinone, and reduction of the quinone (13). Many reports describe hydroxylquinol as an intermediate in bacterial metabolism of a wide range of aromatic compounds (4,8,10).…”

“…The 3-nitrophenol (NP)-induced enzyme pathway in Pseudomonas putida 2NP8 is a nitroreductase-initiated metabolic system (12,13). This system converted nitrobenzene (NB), a cometabolic substrate, into aminophenol, with subsequent hydrolysis into ammonia and benzoquinone ( Fig.…”

“…We used a previously reported procedure (11)(12)(13) to test transformation of 30 nitroaromatic compounds (NAs) by 3-NP-grown cells of P. putida 2NP8. Initial transformation rates (Table 1) of most of the NAs were close to the transformation rates of 3-NP and NB.…”

Bacterial Conversion of Hydroxylamino Aromatic Compounds by both Lyase and Mutase Enzymes Involves Intramolecular Transfer of Hydroxyl Groups

“…The rate-limiting step would be the enzymatic conversion of the substrate to the imine intermediate, which would spontaneously hydrolyze to protocatechuate. Hydrolysis of the imine as the mechanism of ammonia release was proposed as a step during the degradation of 3-nitrophenol by P. putida 2NP8, but no experimental evidence was provided (36). Alternatively, the hydroxylamino compound might first be converted to the corresponding AP and the AP group could then be hydrolyzed to produce the dihydroxy compound.…”