Microorganisms degrading chlorobenzene via a meta-cleavage pathway harbor highly similar chlorocatechol 2,3-dioxygenase-encoding gene clusters

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 ␤-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.

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“…hapI encodes a ferredoxin that might be involved in reduction of the ironmetal cofactor of extradiol dioxygenases (27,36,37,69,84).…”

Section: Resultsmentioning

confidence: 99%

Elucidation of the 4-Hydroxyacetophenone Catabolic Pathway in Pseudomonas fluorescens ACB

et al. 2008

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“…For catechol 2,3-dioxygenases it was reported that in some degradation pathways, these proteins are needed for the reductive reactivation of the iron cofactor (25,33,34,53,71). A similar in vivo protection of HQDO can be envisioned for HapI.…”

Section: Discussionmentioning

confidence: 96%

Hydroquinone Dioxygenase from Pseudomonas fluorescens ACB: a Novel Member of the Family of Nonheme-Iron(II)-Dependent Dioxygenases

et al. 2008

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Several aerobic microorganisms are capable of utilizing acetophenones for their growth (16,17,(30)(31)(32). However, relatively little is known about the oxidative enzymes involved in acetophenone mineralization (45,47). The catabolism of 4-hydroxyacetophenone in Pseudomonas fluorescens ACB proceeds through the initial formation of 4-hydroxyphenyl acetate and hydroquinone (31,37,47). The latter compound is further degraded via 4-hydroxymuconic semialdehyde and maleylacetate to ␤-ketoadipate (46). We have purified HapA, the enzyme responsible for the Baeyer-Villiger oxidation of 4-hydroxyacetophenone, and expressed its gene in Escherichia coli (37). Moreover, we established that this flavin adenine dinucleotide-containing monooxygenase is useful for the production of phenols and catechols, which are valuable intermediates in the synthesis of pharmaceuticals, agricultural chemicals, and material products (36,38,48).In the accompanying paper (46), we showed that the genes encoding 4-hydroxyacetophenone monooxygenase (hapA), 4-hydroxyphenylacetate esterase (hapB), 4-hydroxymuconic semialdehyde dehydrogenase (hapE), and maleylacetate reductase (hapF) belong to a gene cluster (hapCDEFGHIBA) involved in 4-hydroxyacetophenone utilization. Based on biochemical data and sequence analysis, we proposed that the function of the hapC and hapD genes is linked to the conversion of hydroquinone to 4-hydroxymuconic semialdehyde.Several ring cleavage enzymes acting on substituted hydroquinones have been described. These include intradiol dioxygenases acting on hydroxyhydroquinone (4,20,22,35,39,42,55,66) and extradiol dioxygenases that are active with (homo-)gentisate (3, 28) or chlorohydroquinone (10,44,51). However, enzymes that use hydroquinone as the physiological ring cleavage substrate have not been characterized. Here we report on the purification and properties of hydroquinone dioxygenase (HQDO) from P. fluorescens ACB. It is shown that the heterotetrameric enzyme, encoded by the hapC and hapD genes, is a novel member of the family of nonheme-iron(II)-dependent dioxygenases. The present results confirm that the hapG gene, encoding an intradiol dioxygenase (46), is not involved in 4-hydroxyacetophenone degradation. This finding has important implications for the function of related genes involved in the catabolism of other aromatic compounds.

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“…A chemically stable acylation product of meta pyrocatechase consistently could not be shown. While inactivation-Bresistant^meta-pyrocatechases have been found among 3-chlorocatechol cleaving enzymes (Göbel et al 2004), no such type was found for 3-fluorocatechol (Mars et al 1997;and own unpublished results). The fact that this resistance in essence has been an improved tolerance against inactivation only indicated that no actual mechanismdependent resistance has been newly evolved.…”

Section: Halogenated Catechol Derivatives: 3-fluorocatecholmentioning

confidence: 94%

The biodegradation vs. biotransformation of fluorosubstituted aromatics

Kiel

Engesser

2015

Appl Microbiol Biotechnol

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Fluoroaromatics are widely and--in recent years--increasingly used as agrochemicals, starting materials for chemical syntheses and especially pharmaceuticals. This originates from the special properties the carbon-fluorine bond is imposing on organic molecules. Hence, fluoro-substituted compounds more and more are considered to be important potential environmental contaminants. On the other hand, the microbial potentials for their transformation and mineralization have received less attention in comparison to other haloaromatics. Due to the high electronegativity of the fluorine atom, its small size, and the extraordinary strength of the C-F bond, enzymes and mechanisms known to facilitate the degradation of chloro- or bromoarenes are not necessarily equally active with fluoroaromatics. Here, we review the literature on the microbial degradation of ring and side-chain fluorinated aromatic compounds under aerobic and anaerobic conditions, with particular emphasis being placed on the mechanisms of defluorination reactions.

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Microorganisms degrading chlorobenzene via a meta-cleavage pathway harbor highly similar chlorocatechol 2,3-dioxygenase-encoding gene clusters

Cited by 28 publications

References 32 publications

Elucidation of the 4-Hydroxyacetophenone Catabolic Pathway in Pseudomonas fluorescens ACB

Elucidation of the 4-Hydroxyacetophenone Catabolic Pathway in Pseudomonas fluorescens ACB

Hydroquinone Dioxygenase from Pseudomonas fluorescens ACB: a Novel Member of the Family of Nonheme-Iron(II)-Dependent Dioxygenases

The biodegradation vs. biotransformation of fluorosubstituted aromatics

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