The metabolism of cyclohexanol by Acinetobacter NCIB 9871

Genetic analysis of a gene cluster for cyclohexanol oxidation in Acinetobacter sp. Strain SE19 by in vitro transposition

Biological oxidation of cyclic alcohols normally results in formation of the corresponding dicarboxylic acids, which are further metabolized and enter the central carbon metabolism in the cell. We isolated an Acinetobacter sp. from an industrial wastewater bioreactor that utilized cyclohexanol as a sole carbon source. A cosmid library was constructed from Acinetobacter sp. strain SE19, and oxidation of cyclohexanol to adipic acid was demonstrated in recombinant Escherichia coli carrying a SE19 DNA segment. A region that was essential for cyclohexanol oxidation was localized to a 14-kb fragment on the cosmid DNA. Several putative open reading frames (ORFs) that were expected to encode enzymes catalyzing the conversion of cyclohexanol to adipic acid were identified. Whereas one ORF showed high homology to cyclohexanone monooxygenase from Acinetobacter sp. strain NCIB 9871, most of the ORFs showed only moderate homology to proteins in GenBank. In order to assign functions of the various ORFs, in vitro transposon mutagenesis was performed using the cosmid DNA as a target. A set of transposon mutants with a single insertion in each of the ORFs was screened for cyclohexanol oxidation in E. coli. Several of the transposon mutants accumulated a variety of cyclohexanol oxidation intermediates. The in vitro transposon mutagenesis technique was shown to be a powerful tool for rapidly assigning gene functions to all ORFs in the pathway.

Simultaneous identification of two cyclohexanone oxidation genes from an environmental Brevibacterium isolate using mRNA differential display

The technique of mRNA differential display was used to identify simultaneously two metabolic genes involved in the degradation of cyclohexanone in a new halotolerant Brevibacterium environmental isolate. In a strategy based only on the knowledge that cyclohexanone oxidation was inducible in this strain, the mRNA population of cells exposed to cyclohexanone was compared to that of control cells using reverse transcription-PCR reactions primed with a collection of 81 arbitrary oligonucleotides. Three DNA fragments encoding segments of flavin monooxygenases were isolated with this technique, leading to the identification of the genes of two distinct cyclohexanone monooxygenases, the enzymes responsible for the oxidation of cyclohexanone. Each monooxygenase was expressed in Escherichia coli and characterized. This work validates the application of mRNA differential display for the discovery of new microbial metabolic genes.

3,4-Dihydrocoumarin hydrolase with haloperoxidase activity from Acinetobacter calcoaceticus F46

A novel lactonohydrolase, an enzyme that catalyzes the hydrolysis of 3,4-dihydrocoumarin, was purified 375-fold to apparent homogeneity, with a 22.7% overall recovery, from Acinetobacter calcoaceticus F46, which was isolated as a fluorene-assimilating micro-organism. The molecular mass of the native enzyme, as estimated by high-performance gel-permeation chromatography, is 56 kDa, and the subunit molecular mass is 30 kDa. The enzyme specifically hydrolyzes 3,4-dihydrocoumarin, and the Km and Vmax for 3,4-dihydrocoumarin are 0.806 mM and 4760 U.mg-1, respectively. The N-terminal and internal amino acid sequences of the enzyme show high similarity to those of bacterial non-heme haloperoxidases. The enzyme exhibits brominating activity with monochlorodimedon in the presence of H2O2 and 3, 4-dihydrocoumarin or an organic acid, such as acetate and n-butyrate.

Identification of a transcriptional activator (ChnR) and a 6-oxohexanoate dehydrogenase (ChnE) in the cyclohexanol catabolic pathway in Acinetobacter sp. Strain NCIMB 9871 and localization of the genes that encode them

We identified chnR, a gene encoding an AraC-XylS type of transcriptional activator that regulates the expression of chnB, the structural gene for cyclohexanone monooxygenase (CHMO) in Acinetobacter sp. strain NCIMB 9871. The gene sequence of chnE, which encodes an NADP(+)-linked 6-oxohexanoate dehydrogenase, the enzyme catalyzing the fifth step of cyclohexanol degradation, was also determined. The gene arrangement is chnB-chnE-chnR. The predicted molecular masses of the three polypeptides were verified by radiolabeling by using the T7 expression system. Inducible expression of cloned chnB in Escherichia coli depended upon the presence of chnR. A transcriptional chnB::lacZ fusion experiment revealed that cyclohexanone induces chnB expression in E. coli, in which a 22-fold increase in activity was observed.

Biodegradation of cyclohexylamine by Brevibacterium oxydans IH-35A

A bacterial strain capable of growing on cyclohexylamine (CHAM) was isolated by using enrichment and isolation techniques. The strain isolated, strain IH-35A, was classified as a member of the genus Brevibacterium. The results of growth and enzyme studies are consistent with degradation of CHAM via cyclohexanone (CHnone), 6-hexanolactone, 6-hydroxyhexanoate, and adipate. Cell extracts obtained from this strain grown on CHAM contained CHAM oxidase, and the model for CHAM oxidation by this enzyme was similar to the model for deamino oxidation of amine by amine oxidase.

Utilization of cyclohexanol by bacteria in a tropical estuarine water

The Lagos lagoon is a wide expanse of estuarine water. The range of temperature, pH and conductivity of samples collected from 3 sources were 27-30 degrees C, 7.8-8.3 and 2.34-2.85 mS respectively. Consistent increase and decrease in the population of indigenous bacteria occurred in the test and control experiments respectively. Organisms in samples from Apapa and Iddo utilized cyclohexanol better than those in the sample from the University of Lagos. The cyclohexanol degrading bacteria were identified as species of Pseudomonas. Acinetobacter, Vibrio, Micrococcus and Flavobacterium. Pseudomonas sp. had the highest growth potential on cyclohexanol. These organisms play important roles in reducing the pollutant loads of the Lagos lagoon.

Enzyme reactions involved in anaerobic cyclohexanol metabolism by a denitrifying Pseudomonas species

The enzymes involved in the anaerobic degradation of cyclohexanol were searched for in a denitrifying Pseudomonas species which metabolizes this alicyclic compound to CO2 anaerobically. All postulated enzyme activities were demonstrated in vitro with sufficient specific activities. Cyclohexanol dehydrogenase catalyzes the oxidation of the substrate to cyclohexanone. Cyclohexanone dehydrogenase oxidizes cyclohexanone to 2-cyclohexenone. 2-Cyclohexenone hydratase and 3-hydroxycyclohexanone dehydrogenase convert 2-cyclohexenone via 3-hydroxycyclohexanone into 1,3-cyclohexanedione. Finally, the dione is cleaved by 1,3-cyclohexanedione hydrolase into 5-oxocaproic acid. Some kinetic and regulatory properties of these enzymes were studied.

Camphor revisited: studies of 2,5-diketocamphane 1,2-monooxygenase from Pseudomonas putida ATCC 17453

The oxygenating component of 2,5-diketocamphane 1,2-monooxygenase from Pseudomonas putida ATCC 17453 was purified to homogeneity by a combination of ammonium sulfate fractionation and chromatography on DEAE-cellulose and polyanion SI-17 columns. It had an Mr of 78,000, bound one molecule of nonautooxidizable flavin mononucleotide (FMN), consisted of two subunits of equal molecular weight, and existed in two electrophoretically distinguishable active forms. The oxygenating complex was constructed from equimolecular amounts of an NADH oxidase, which could be purified separately (Mr, 36,000), and the oxygenating component. Most of the NADH oxidase dissociated from the oxygenating component during purification, although traces remained, to give the final preparation of the oxygenating component significant oxygenase activity. FMN did not dissociate significantly from the oxygenating component during purification, but it was not covalently bound and could be removed under a variety of conditions. Binding between the two proteins that made up the active complex was fairly weak and freely reversible. It probably occurred through the FMN which was strongly bound to the oxygenating component and for which the NADH had a weak binding site. Iron was not present at a significant level in the oxygenating component, and in common with other characterized Baeyer Villiger monooxygenases, 2,5-diketocamphane 1,2-monooxygenase was found to be a simple flavoprotein.

The degradation of 1-phenylalkanes by an oil-degrading strain of Acinetobacter lwoffi

An oil-degrading bacterium identified as Acinetobacter lwoffi was isolated by elective culture on North Sea Forties crude oil from an activated sludge sample. It grew on a wide range of n-alkanes (C12-C28) and 1-phenylalkanes, including 1-phenyldodecane, 1-phenyltridecane and 1-phenyltetradecane. The organism degraded 1-phenyldodecane to phenylacetic acid which was further metabolized via homogentisic acid, whilst 1-phenyltridecane was transformed to trans-cinamic and 3-phenylpropionic acid which were not further metabolized. Evidence is presented for a relationship between aromatic amino acid catabolism and 1-phenyldodecane degradation in this organism.

Bacterial formation and metabolism of 6-hydroxyhexanoate: evidence of a potential role for omega-oxidation

Alkane-utilizing strains of Pseudomonas spp. were found to omega-oxidize hexanoate, 6-hydroxyhexanoate, and 6-oxohexanoate to adipic acid in 5, 30, and 90% molar yields, respectively, after induction with n-hexane. 6-Hydroxyhexanoate was identified as the immediate product of hexanoate omega-hydroxylation by whole cells and was further oxidized into adipic acid and an unexpected metabolite identified as 2-tetrahydrofuranacetic acid. This same metabolite, together with adipic acid, was also detected when similarly induced cells were incubated with hexanoate or 1,6-hexanediol, but not with 6-oxohexanoate (adipic semialdehyde). Cells grown on hexanoate and incubated with 6-hydroxyhexanoate were also found to accumulate 2-tetrahydrofuranacetic acid, which was not further degraded. Utilization of 6-hydroxyhexanoate for growth was restricted to those organisms also able to utilize adipate. Similar observations were made with 1,6-hexanediol serving as the carbon source and cells obtained from one organism, Pseudomonas aeruginosa PAO, grown either on 1,6-hexanediol or 6-hydroxyhexanoate, were found to be well induced for both 6-oxohexanoate and adipate oxidation. The results indicate that 6-hydroxyhexanoate and 1,6-hexanediol are susceptible to both beta- and omega-oxidative attack; however, the former pathway appears to be of no physiological significance since it generates 2-tetrahydrofuranacetic acid as a nonmetabolizable intermediate, making omega-oxidation via adipate the exclusive pathway for degradation.

Camphor revisited: involvement of a unique monooxygenase in metabolism of 2-oxo-delta 3-4,5,5-trimethylcyclopentenylacetic acid by Pseudomonas putida

Previously, Pseudomonas putida was shown to degrade (+)-camphor, and cleavage of the first ring of the bicyclic structure involved two monooxygenases (a hydroxylase and a ring oxygen-inserting enzyme), a dehydrogenase, and spontaneous cleavage of an unstable oxygenation product (lactone). Cleavage of the second ring was not demonstrated but was assumed also to occur by ring oxygen insertion, since the predicted oxygenation product was extracted from whole-cell incubation systems. Our investigation established that metabolism of the first ring cleavage intermediate, 2-oxo-delta 3-4,5,5-trimethylcyclopentenylacetic acid, occurred through the sequential action of two inducible enzymes, a coenzyme A ester synthetase and an oxygenase. The oxygenase was purified to homogeneity and had a molecular weight of 106,000. This enzyme carried a single molecule of flavin adenine dinucleotide and consisted of two identical subunits. Iron was not present at a significant level. The oxygenase was specific for NADPH as the electron donor and absolutely specific for the coenzyme A ester of 2-oxo-delta 3-4,5,5-trimethylcyclopentenylacetic acid as the substrate. The reaction stoichiometry was compatible with this enzyme being a monooxygenase, and a mass spectral analysis of the methyl ester of the product confirmed the insertion of a single oxygen atom. The enzyme appeared to be analogous to, although distinct from. 2,5-diketocamphane 1,2-monooxygenase in catalyzing a "biological Baeyer-Villiger" reaction with the formation of a lactone. Structural analogy suggested that this lactone, like the first, was also unstable and susceptible to spontaneous ring opening, although this was not experimentally established.

Metabolism of cyclohexaneacetic acid and cyclohexanebutyric acid by Arthrobacter sp. strain CA1

A strain of Arthrobacter was isolated by enrichment culture with cyclohexaneacetate as the sole source of carbon and grew with a doubling time of 4.2 h. In addition to growing with cyclohexaneacetate, the organism also grew with cyclohexanebutyrate at concentrations not above 0.05%, and with a variety of alicyclic ketones and alcohols. Oxidation of cyclohexaneacetate proceeded through formation of the coenzyme A (CoA) ester followed by initiation of a beta-oxidation cycle. beta-Oxidation was blocked before the second dehydrogenation step due to the formation of a tertiary alcohol, and the side chain was eliminated as acetyl-CoA by the action of (1-hydroxycyclohexan-1-yl)acetyl-CoA lyase. The cyclohexanone thus formed was degraded by a well-described route that involves ring-oxygen insertion by a biological Baeyer-Villiger oxygenase. All enzymes of the proposed metabolic sequence were demonstrated in cell-free extracts. Arthrobacter sp. strain CA1 synthesized constitutive beta-oxidative enzymes, but further induction of enzymes active toward cyclohexaneacetate and its metabolites could occur during growth with the alicyclic acid. Other enzymes of the sequence, (1-hydroxycyclohexan-1-yl)acetyl-CoA lyase and enzymes of cyclohexanone oxidation, were present at negligible levels in succinate-grown cells but induced by growth with cyclohexaneacetate. The oxidation of cyclohexanebutyrate was integrated into the pathway for cyclohexaneacetate oxidation by a single beta-oxidation cycle. Oxidation of the compound could be divided into two phases. Initial oxidation to (1-hydroxycyclohexan-1-yl)acetate could be catalyzed by constitutive enzymes, whereas the further degradation of (1-hydroxycyclohexan-1-yl)acetate was dependent on induced enzyme synthesis which could be inhibited by chloramphenicol with the consequent accumulation of cyclohexaneacetate and (1-hydroxycyclohexan-1-yl)acetate.

Metabolism of cyclohexane carboxylic acid by Alcaligenes strain W1

Thirty-three microorganisms capable of growth with cyclohexane carboxylate as the sole source of carbon were isolated from mud, water, and soil samples from the Aberystwyth area. Preliminary screening and whole-cell oxidation studies suggested that, with one exception, all of the strains metabolized the growth substrate by beta-oxidation of the coenzyme A ester. This single distinctive strain, able to oxidize rapidly trans-4-hydroxycyclohexane carboxylate, 4-ketocyclohexane carboxylate, p-hydroxybenzoate, and protocatechuate when grown with cyclohexane carboxylate, was classified as a strain of Alcaligenes and given the number W1. Enzymes capable of converting cyclohexane carboxylate to p-hydroxybenzoate were induced by growth with the alicyclic acid and included the first unambiguous specimen of a cyclohexane carboxylate hydroxylase. Because it is a very fragile protein, attempts to stabilize the cyclohexane carboxylate hydroxylase so that a purification procedure could be developed have consistently failed. In limited studies with crude cell extracts, we found that hydroxylation occurred at the 4 position, probably yielding the trans isomer of 4-hydroxycyclohexane carboxylate. Simultaneous measurement of oxygen consumption and reduced nicotinamide adenine dinucleotide oxidation, coupled with an assessment of reactant stoichiometry, showed the enzyme to be a mixed-function oxygenase. Mass spectral analysis enabled the conversion of cyclohexane carboxylate to p-hydroxybenzoate by cell extracts to be established unequivocally, and all of our data were consistent with the pathway: cyclohexane carboxylate --> trans-4-hydroxycyclohexane carboxylate --> 4-ketocyclohexane carboxylate --> p-hydroxybenzoate. The further metabolism of p-hydroxybenzoate proceeded by meta fission and by the oxidative branch of the 2-hydroxy-4-carboxymuconic semialde-hyde-cleaving pathway.

The metabolism of trans-cyclohexan-1,2-diol by an Acinetobacter species

1. Acinetobacter TD63 was one of some thirty organisms isolated by elective culture with trans-cyclohexan-1,2-diol as sole source of carbon. The great majority of these isolates displayed the same growth spectrum as Nocardia globerula CL1 and Acinetobacter NCIB 9871 being capable of utilizing trans-cyclohexan-1,2-diol, 2-hydroxycyclohexan-1-one, cyclohexanol, cyclohexanone,1-oxa-2oxocycloheptane and adipate and were assumed to use well described metabolic pathways. 2. Acinetobacter TD63 was distinctive in being incapable of growth with cyclohexanol, cyclohexanone or 1-oxa-2-oxocycloheptane and because of this it was hoped that it would display an alternative pathway for the oxidation of trans-cyclohexan-1,2-diol. 3. Studies with cell extracts have shown the presence of inducible dehydrogenase for the conversion of trans-cyclohexan-1,2-diol to 2-hydroxycyclohexan-1-one and cyclohexan-1,2-dione and of 6-oxohexanoate to adipate. These enzymes are linked into a metabolic sequence by the action of a monooxygenase of broad specificity but efficiently capable of converting 2-hydroxy-cyclohexan-1-one into the lactone 1-oxa-2-oxo-7-hydroxycycloheptane that spontaneously rearranges to yield 6-oxohexanoate. 4. An enzyme capable of attacking cyclohexan-1,2-dione (mono-enol) in the absence of an electron donor or oxygen has also been detected. Evidence has been presented indicating that this enzyme catalyses a keto-enol tautomerization between cyclohexan-1,2-dione (mono-enol) and cyclohexan-1,2-dione (mono-hydrate) and is not involved in the pathway of ring cleavage. 5. The failure of Acinetobacter TD63 to grow with cyclohexanol, cyclohexanone or 1-oxa-2-oxocycloheptane is due not to this organism possessing a distinctive metabolic sequence but to a narrow inducer specificity coupled with an inability to form a lactone hydrolase enabling it to cleave the stable 1-oxa-2-oxocycloheptane which is an intermediate in the established pathway of cyclohexanol and cyclohexanone oxidation.

The purification and properties of cyclohexanone oxygenase from Nocardia globerula CL1 and Acinetobacter NCIB 9871

1. Cyclohexanone oxygenases from Norcardia globerula CL1 and Acinetobacter NCIB 9871 have been purified 12-fold and 35-fold respectively and each gives a single symmetrical sedimentation peak in the ultracentrifuge and a single protein band on 2.25 nm average pore radius polyacrylamide gels. 2. The enzyme from N. globerula has a molecular weight of 53000 while that from Acinetobacter has a molecular weight of about 59000. Each is a single polypeptide chain with one mole of bound FAD per mole of protein that does not dissociate during purification. Acidification of the Acinetobacter enzyme in the presence of (NH4)2SO4 releases the bound FAD and yields native apoenzyme from which the active holoenzyme can be reconstituted. The apparent dissociation constant for the FAD is 40 nM.