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Novel Metabolic Pathway for N-Methylpyrrolidone Degradation in Alicycliphilus sp. Strain BQ1.

ABSTRACT: The molecular mechanisms underlying the biodegradation of N-methylpyrrolidone (NMP), a widely used industrial solvent that produces skin irritation in humans and is teratogenic in rats, are unknown. Alicycliphilus sp. strain BQ1 degrades NMP. By studying a transposon-tagged mutant unable to degrade NMP, we identified a six-gene cluster (nmpABCDEF) that is transcribed as a polycistronic mRNA and encodes enzymes involved in NMP biodegradation. nmpA and the transposon-affected gene nmpB encode an N-methylhydantoin amidohydrolase that transforms NMP to ?-N-methylaminobutyric acid; this is metabolized by an amino acid oxidase (NMPC), either by demethylation to produce ?-aminobutyric acid (GABA) or by deamination to produce succinate semialdehyde (SSA). If GABA is produced, the activity of a GABA aminotransferase (GABA-AT), not encoded in the nmp gene cluster, is needed to generate SSA. SSA is transformed by a succinate semialdehyde dehydrogenase (SSDH) (NMPF) to succinate, which enters the Krebs cycle. The abilities to consume NMP and to utilize it for growth were complemented in the transposon-tagged mutant by use of the nmpABCD genes. Similarly, Escherichia coli MG1655, which has two SSDHs but is unable to grow in NMP, acquired these abilities after functional complementation with these genes. In wild-type (wt) BQ1 cells growing in NMP, GABA was not detected, but SSA was present at double the amount found in cells growing in Luria-Bertani medium (LB), suggesting that GABA is not an intermediate in this pathway. Moreover, E. coli GABA-AT deletion mutants complemented with nmpABCD genes retained the ability to grow in NMP, supporting the possibility that ?-N-methylaminobutyric acid is deaminated to SSA instead of being demethylated to GABA.IMPORTANCEN-Methylpyrrolidone is a cyclic amide reported to be biodegradable. However, the metabolic pathway and enzymatic activities for degrading NMP are unknown. By developing molecular biology techniques for Alicycliphilus sp. strain BQ1, an environmental bacterium able to grow in NMP, we identified a six-gene cluster encoding enzymatic activities involved in NMP degradation. These findings set the basis for the study of new enzymatic activities and for the development of biotechnological processes with potential applications in bioremediation.

SUBMITTER: Solis-Gonzalez CJ

PROVIDER: S-EPMC5734037 | biostudies-literature | 2018 Jan

REPOSITORIES: biostudies-literature

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Novel Metabolic Pathway for N-Methylpyrrolidone Degradation in Alicycliphilus sp. Strain BQ1.

Solís-González Claudia Julieta CJ Domínguez-Malfavón Lilianha L Vargas-Suárez Martín M Gaytán Itzel I Cevallos Miguel Ángel MÁ Lozano Luis L Cruz-Gómez M Javier MJ Loza-Tavera Herminia H

Applied and environmental microbiology 20171215 1

The molecular mechanisms underlying the biodegradation of N-methylpyrrolidone (NMP), a widely used industrial solvent that produces skin irritation in humans and is teratogenic in rats, are unknown. Alicycliphilus sp. strain BQ1 degrades NMP. By studying a transposon-tagged mutant unable to degrade NMP, we identified a six-gene cluster (nmpABCDEF) that is transcribed as a polycistronic mRNA and encodes enzymes involved in NMP biodegradation. nmpA and the transposon-af ...[more]

PMID: 29030443

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Project description:Pyridine and its derivatives constitute the majority of heterocyclic aromatic compounds that occur largely as a result of human activities and contribute to environmental pollution. It is known that they can be degraded by various bacteria in the environment; however, the degradation of unsubstituted pyridine has not yet been completely resolved. In this study, we present data on the pyridine catabolic pathway in Arthrobacter sp. strain 68b at the level of genes, enzymes, and metabolites. The pyr gene cluster, responsible for the degradation of pyridine, was identified in a catabolic plasmid, p2MP. The pathway of pyridine metabolism consisted of four enzymatic steps and ended by the formation of succinic acid. The first step in the degradation of pyridine proceeds through a direct ring cleavage catalyzed by a two-component flavin-dependent monooxygenase system, encoded by pyrA (pyridine monooxygenase) and pyrE genes. The genes pyrB, pyrC, and pyrD were found to encode (Z)-N-(4-oxobut-1-enyl)formamide dehydrogenase, amidohydrolase, and succinate semialdehyde dehydrogenase, respectively. These enzymes participate in the subsequent steps of pyridine degradation. The metabolites of these enzymatic reactions were identified, and this allowed us to reconstruct the entire pyridine catabolism pathway in Arthrobacter sp. 68b.IMPORTANCE The biodegradation pathway of pyridine, a notorious toxicant, is relatively unexplored, as no genetic data related to this process have ever been presented. In this paper, we describe the plasmid-borne pyr gene cluster, which includes the complete set of genes responsible for the degradation of pyridine. A key enzyme, the monooxygenase PyrA, which is responsible for the first step of the catabolic pathway, performs an oxidative cleavage of the pyridine ring without typical activation steps such as reduction or hydroxylation of the heterocycle. This work provides new insights into the metabolism of N-heterocyclic compounds in nature.

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Novel Metabolic Pathway for N-Methylpyrrolidone Degradation in Alicycliphilus sp. Strain BQ1.

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Novel Metabolic Pathway for <i>N</i>-Methylpyrrolidone Degradation in Alicycliphilus sp. Strain BQ1.

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