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Elucidation of the 4-hydroxyacetophenone catabolic pathway in Pseudomonas fluorescens ACB.

ABSTRACT: The catabolism of 4-hydroxyacetophenone in Pseudomonas fluorescens ACB is known to proceed through the intermediate formation of hydroquinone. Here, we provide evidence that hydroquinone is further degraded through 4-hydroxymuconic semialdehyde and maleylacetate to beta-ketoadipate. The P. fluorescens ACB genes involved in 4-hydroxyacetophenone utilization were cloned and characterized. Sequence analysis of a 15-kb DNA fragment showed the presence of 14 open reading frames containing a gene cluster (hapCDEFGHIBA) of which at least four encoded enzymes are involved in 4-hydroxyacetophenone degradation: 4-hydroxyacetophenone monooxygenase (hapA), 4-hydroxyphenyl acetate hydrolase (hapB), 4-hydroxymuconic semialdehyde dehydrogenase (hapE), and maleylacetate reductase (hapF). In between hapF and hapB, three genes encoding a putative intradiol dioxygenase (hapG), a protein of the Yci1 family (hapH), and a [2Fe-2S] ferredoxin (hapI) were found. Downstream of the hap genes, five open reading frames are situated encoding three putative regulatory proteins (orf10, orf12, and orf13) and two proteins possibly involved in a membrane efflux pump (orf11 and orf14). Upstream of hapE, two genes (hapC and hapD) were present that showed weak similarity with several iron(II)-dependent extradiol dioxygenases. Based on these findings and additional biochemical evidence, it is proposed that the hapC and hapD gene products are involved in the ring cleavage of hydroquinone.

SUBMITTER: Moonen MJ

PROVIDER: S-EPMC2493259 | biostudies-literature | 2008 Aug

REPOSITORIES: biostudies-literature

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Elucidation of the 4-hydroxyacetophenone catabolic pathway in Pseudomonas fluorescens ACB.

Moonen Mariëlle J H MJ Kamerbeek Nanne M NM Westphal Adrie H AH Boeren Sjef A SA Janssen Dick B DB Fraaije Marco W MW van Berkel Willem J H WJ

Journal of bacteriology 20080523 15

The catabolism of 4-hydroxyacetophenone in Pseudomonas fluorescens ACB is known to proceed through the intermediate formation of hydroquinone. Here, we provide evidence that hydroquinone is further degraded through 4-hydroxymuconic semialdehyde and maleylacetate to beta-ketoadipate. The P. fluorescens ACB genes involved in 4-hydroxyacetophenone utilization were cloned and characterized. Sequence analysis of a 15-kb DNA fragment showed the presence of 14 open reading frames containing a gene clus ...[more]

PMID: 18502868

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Project description:Pinoresinol is a dimer of two β-β'-linked coniferyl alcohol molecules. It is both a plant defense molecule synthesized through the shikimic acid pathway and a representative of several β-β-linked dimers produced during the microbial degradation of lignin in dead plant material. Until now, little has been known about the bacterial catabolism of such dimers. Here we report the isolation of the efficient (+)-pinoresinol-mineralizing Pseudomonas sp. strain SG-MS2 and its catabolic pathway. Degradation of pinoresinol in this strain is inducible and proceeds via a novel oxidative route, which is in contrast to the previously reported reductive transformation by other bacteria. Based on enzyme assays and bacterial growth, cell suspension, and resting cell studies, we provide conclusive evidence that pinoresinol degradation in strain SG-MS2 is initiated by benzylic hydroxylation, generating a hemiketal via a quinone methide intermediate, which is then hydrated at the benzylic carbon by water. The hemiketal, which stays in equilibrium with the corresponding keto alcohol, undergoes an aryl-alkyl cleavage to generate a lactone and 2-methoxyhydroquinone. While the fate of 2-methoxyhydroquinone is not investigated further, it is assumed to be assimilated by ring cleavage. The lactone is further metabolized via two routes, namely, lactone ring cleavage and benzylic hydroxylation via a quinone methide intermediate, as described above. The resulting hemiketal again exists in equilibrium with a keto alcohol. Our evidence suggests that both routes of lactone metabolism lead to vanillin and vanillic acid, which we show can then be mineralized by strain SG-MS2.IMPORTANCE The oxidative catabolism of (+)-pinoresinol degradation elucidated here is fundamentally different from the reductive cometabolism reported for two previously characterized bacteria. Our findings open up new opportunities to use lignin for the biosynthesis of vanillin, a key flavoring agent in foods, beverages, and pharmaceuticals, as well as various new lactones. Our work also has implications for the study of new pinoresinol metabolites in human health. The enterodiol and enterolactone produced through reductive transformation of pinoresinol by gut microbes have already been associated with decreased risks of cancer and cardiovascular diseases. The metabolites from oxidative metabolism we find here also deserve attention in this respect.

Project description:The antagonistic interaction between a potential fish probiont, Pseudomonas fluorescens strain AH2, and its target organism, Vibrio anguillarum, was investigated by studying the genetic response of the target organism when it was exposed to the antagonist. We compared the differential display of arbitrarily PCR-amplified gene transcripts in V. anguillarum serotype O1 when it was exposed to AH2 supernatant with the display of transcripts in nonexposed control cultures. Growth of V. anguillarum was immediately arrested when the organism was exposed to 50% (vol/vol) AH2 supernatant. A total of 10 potentially differentially expressed transcripts were identified. Among these we identified a gene homologous to rpoS that was induced in a dose-dependent manner when V. anguillarum was cultured in media supplemented with sterile filtered supernatant from AH2. rpoS was also induced when growth was arrested with the iron chelator 2,2-dipyridyl. A chromosomal transcript homologous to vibE that participates in vibriobactin synthesis in Vibrio cholerae was also upregulated during AH2 exposure. This transcript could represent a functionally active gene in V. anguillarum involved in biosynthesis of anguibactin or another V. anguillarum siderophore. On the pJM1 plasmid of V. anguillarum serotype O1, a pseudogene designated open reading frame E (ORF E) that contains a frameshift mutation was previously identified. The gene homologous to vibE identified in this study, interestingly, also has significant homology to ORF E on the amino acid level and does not possess the frameshift mutation. Thus, the chromosomally encoded vibE homologue could fulfil the role of the inactive plasmid-encoded ORF E pseudogene. Addition of Fe(3+) to the system eliminated the growth arrest, and the genes homologous to rpoS and vibE were not induced. To our knowledge, this is the first study linking rpoS induction to iron starvation. Taken together, the results of this study suggest that a major part of the antagonistic property exhibited by strain AH2 is caused by the ability of siderophores in the supernatant to efficiently chelate iron, which results in instant iron deprivation of the pathogen V. anguillarum and complete growth arrest.

Dataset Information

Elucidation of the 4-hydroxyacetophenone catabolic pathway in Pseudomonas fluorescens ACB.

Publications

Elucidation of the 4-hydroxyacetophenone catabolic pathway in Pseudomonas fluorescens ACB.

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