A high level of accumulation of 2-hydroxymuconic 6-semialdehyde from aniline by the transpositional mutant Y-2 of Pseudomonas species AW-2

Gene cloning and characterization of a deaminase from the 4-amino-3-hydroxybenzoate-assimilating Bordetella sp. strain 10d

The 4-amino-3-hydroxybenzoate-assimilating Bordetella sp. strain 10d produces a deaminase that catalyzes the deamination of 2-amino-5-carboxymuconic 6-semialdehyde. A gene encoding the deaminase, ahdB, was cloned and expressed in Escherichia coli; ahdB is located downstream from the previously reported genes encoding 4-amino-3-hydroxybenzoate 2,3-dioxygenase (ahdA) and a LysR-type regulator. The deduced amino acid sequence of ahdB shows 30-33% identity to those of previously reported 2-aminomuconate deaminases. We identified a region (RAGDFLXVSG) conserved in AhdB and three other deaminases. The recombinant enzyme AhdB was purified to homogeneity. After a coupled enzyme assay with purified AhdA, AhdB, and the substrate 4-amino-3-hydroxybenzoate, the final product, formed by the action of AhdA, AhdB, and by nonenzymatic decarboxylation, was identified by HPLC, MS, and (1)H-nuclear magnetic resonance analyses as 2-hydroxymuconic 6-semialdehyde.

Metabolism of 4-amino-3-hydroxybenzoic acid by Bordetella sp. strain 10d: A different modified meta-cleavage pathway for 2-aminophenols

Bordetella sp. strain 10d metabolizes 4-amino-3-hydroxybenzoic acid via 2-hydroxymuconic 6-semialdehyde. Cell extracts from 4-amino-3-hydroxybenzoate-grown cells showed high NAD(+)-dependent 2-hydroxymuconic 6-semialdehyde dehydrogenase, 4-oxalocrotonate tautomerase, 4-oxalocrotonate decarboxylase, and 2-oxopent-4-enoate hydratase activities, but no 2-hydroxymuconic 6-semialdehyde hydrolase activity. These enzymes involved in 4-amino-3-hydroxybenzoate metabolism were purified and characterized. When 2-hydroxymuconic 6-semialdehyde was used as substrate in a reaction mixture containing NAD(+) and cell extracts from 4-amino-3-hydroxybenzoate-grown cells, 4-oxalocrotonic acid, 2-oxopent-4-enoic acid, and 4-hydroxy-2-oxovaleric acid were identified as intermediates, and pyruvic acid was identified as the final product. A complete pathway for the metabolism of 4-amino-3-hydroxybenzoic acid in strain 10d is proposed. Strain 10d metabolized 2-hydroxymuconic 6-semialdehyde derived from 4-amino-3-hydroxybenzoic acid via a dehydrogenative route, not via a hydrolytic route. This proposed metabolic pathway differs considerably from the modified meta-cleavage pathway of 2-aminophenol and those previously reported for methyl- and chloro-derivatives.

Chromosome-encoded gene cluster for the metabolic pathway that converts aniline to TCA-cycle intermediates in Delftia tsuruhatensis AD9

Delftia tsuruhatensis AD9 was isolated as an aniline-degrading bacterium from the soil surrounding a textile dyeing plant. The gene cluster involved in aniline degradation was cloned from the total DNA of strain AD9 into Escherichia coli JM109. After shotgun cloning, two recombinant E. coli strains showing aniline oxidation activity or catechol meta-cleavage activity were obtained by simple plate assays. These strains contained 9.3 kb and 15.4 kb DNA fragments, respectively. Sequence analysis of the total 24.7 kb region revealed that this region contains a gene cluster (consisting of at least 17 genes, named tadQTA1A2BRD1C1D2C2EFGIJKL) responsible for the complete metabolism of aniline to TCA-cycle intermediates. In the gene cluster, the first five genes (tadQTA1A2B) and the subsequent gene (tadR) were predicted to encode a multi-component aniline dioxygenase and a LysR-type regulator, respectively, while the others (tadD1C1D2C2EFGIJKL) were expected to encode meta-cleavage pathway enzymes for catechol degradation. In addition, it was found that the gene cluster is surrounded by two IS1071 sequences, indicating that it has a class I transposon-like structure. PFGE and Southern hybridization analyses confirmed that the tad gene cluster is encoded on the chromosome of strain AD9 in a single copy. These results suggest that, in strain AD9, aniline is degraded via catechol through a meta-cleavage pathway by the chromosome-encoded tad gene cluster. The tad gene cluster showed significant similarity in nucleotide sequence and genetic organization to the plasmid-encoded aniline degradation gene cluster of Pseudomonas putida UCC22.

A novel coupled enzyme assay reveals an enzyme responsible for the deamination of a chemically unstable intermediate in the metabolic pathway of 4-amino-3-hydroxybenzoic acid in Bordetella sp. strain 10d

2-amino-5-carboxymuconic 6-semialdehyde is an unstable intermediate in the meta-cleavage pathway of 4-amino-3-hydroxybenzoic acid in Bordetella sp. strain 10d. In vitro, this compound is nonenzymatically converted to 2,5-pyridinedicarboxylic acid. Crude extracts of strain 10d grown on 4-amino-3-hydroxybenzoic acid converted 2-amino-5-carboxymuconic 6-semialdehyde formed from 4-amino-3-hydroxybenzoic acid by the first enzyme in the pathway, 4-amino-3-hydroxybenzoate 2,3-dioxygenase, to a yellow compound (epsilonmax = 375 nm). The enzyme in the crude extract carrying out the next step was purified to homogeneity. The yellow compound formed from 4-amino-3-hydroxybenzoic acid by this purified enzyme and purified 4-amino-3-hydroxybenzoate 2,3-dioxygenase in a coupled assay was identified as 2-hydroxymuconic 6-semialdehyde by GC-MS analysis. A mechanism for the formation of 2-hydroxymuconic 6-semialdehyde via enzymatic deamination and nonenzymatic decarboxylation is proposed based on results of spectrophotometric analyses. The purified enzyme, designated 2-amino-5-carboxymuconic 6-semialdehyde deaminase, is a new type of deaminase that differs from the 2-aminomuconate deaminases reported previously in that it primarily and specifically attacks 2-amino-5-carboxymuconic 6-semialdehyde. The deamination step in the proposed pathway differs from that in the pathways for 2-aminophenol and its derivatives.

Cloning and sequence analysis of two catechol-degrading gene clusters from the aniline-assimilating bacterium Frateuria species ANA-18

The aniline-assimilating bacterium Frateuria species ANA-18 produced two catechol 1,2-dioxygenases, CD I and CD II, and two muconate cycloisomerases, MC I and MC II. The catA genes catA1 and catA2 encoding CD I and CD II, respectively, were cloned from a gene library of this bacterium. The catA1 gene was clustered with catB1 encoding MC I, catC1 encoding muconolactone isomerase (MI), catD encoding beta-ketoadipate enol-lactone hydrolase (ELH), and ORFR1 encoding a putative LysR-type regulator. The organization of these genes was ORFR1catB1C1D. The catA2 gene also constructed a gene cluster involving catB2 encoding MC II, catC2 encoding MI, and ORFR2 encoding a putative LysR-type regulator with the alignment of ORFR2catB2A2C2. The intergenic regions of ORFR1-catB1 and ORFR2-catB2 contained homologous sequences with the catR-catB intergenic region containing a repression binding site and activation binding site of CatR in Pseudomonas putida. These findings suggest that the two cat clusters were regulated independently in their expression. When a product of cloned catD was added to a reaction mixture containing beta-ketoadipate enol-lactone, beta-ketoadipate was produced. This observation showed that the cloned catD encoded ELH and was expressed in Escherichia coli. We found that Frateuria sp. ANA-18 had a large plasmid with a molecular size more than 100kb. Polymerase chain reaction amplifying partial catA genes and Southern hybridization analyses with probes containing catA genes were conducted, to examine the localization of the two catA genes. We concluded that the catA1 and catA2 genes were located on the chromosomal and large plasmid DNAs, respectively, in Frateuria sp. ANA-18.