Highly efficient biotransformation of eugenol to ferulic acid and further conversion to vanillin in recombinant strains of Escherichia coli

The vaoA gene from Penicillium simplicissimum CBS 170.90, encoding vanillyl alcohol oxidase, which also catalyzes the conversion of eugenol to coniferyl alcohol, was expressed in Escherichia coli XL1-Blue under the control of the lac promoter, together with the genes calA and calB, encoding coniferyl alcohol dehydrogenase and coniferyl aldehyde dehydrogenase of Pseudomonas sp. strain HR199, respectively. Resting cells of the corresponding recombinant strain E. coli XL1-Blue(pSKvaomPcalAmcalB) converted eugenol to ferulic acid with a molar yield of 91% within 15 h on a 50-ml scale, reaching a ferulic acid concentration of 8.6 g liter(-1). This biotransformation was scaled up to a 30-liter fermentation volume. The maximum production rate for ferulic acid at that scale was 14.4 mmol per h per liter of culture. The maximum concentration of ferulic acid obtained was 14.7 g liter(-1) after a total fermentation time of 30 h, which corresponded to a molar yield of 93.3% with respect to the added amount of eugenol. In a two-step biotransformation, E. coli XL1-Blue(pSKvaomPcalAmcalB) was used to produce ferulic acid from eugenol and, subsequently, E. coli(pSKechE/Hfcs) was used to convert ferulic acid to vanillin (J. Overhage, H. Priefert, and A. Steinbüchel, Appl. Environ. Microbiol. 65:4837-4847, 1999). This process led to 0.3 g of vanillin liter(-1), besides 0.1 g of vanillyl alcohol and 4.6 g of ferulic acid liter(-1). The genes ehyAB, encoding eugenol hydroxylase of Pseudomonas sp. strain HR199, and azu, encoding the potential physiological electron acceptor of this enzyme, were shown to be unsuitable for establishing eugenol bioconversion in E. coli XL1-Blue.     

Biotransformation of eugenol to vanillin by a mutant of Pseudomonas sp. strain HR199 constructed by disruption of the vanillin dehydrogenase (vdh) gene

The catabolism of eugenol in Pseudomonas sp. strain HR199 (DSM7063) proceeds via coniferyl alcohol, coniferyl aldehyde, ferulic acid, vanillin, vanillate and protocatechuate, which is further degraded by the ortho-cleavage pathway. The vanillin dehydrogenase of Pseudomonas sp. strain HR199, which catalyses the NAD⁺-dependent oxidation of vanillin to vanillate, was inactivated by the insertion of omega elements into the vdh gene, which was characterized recently. Omega elements conferring resistance against kanamycin (ΩKm) or gentamycin (ΩGm) were constructed by polymerase chain reaction amplification of the aminoglycoside 3′-O-phosphotransferase gene and the gentamycin- 3-acetyltransferase gene, using the plasmids pSUP5011 and pBBR1MCS-5 respectively as template DNA. A 211-bp BssHII fragment of the vdh gene was substituted by ΩKm or ΩGm, and the functional vdh gene was replaced by vdhΩKm or vdhΩGm in Pseudomonas sp. strain HR199 by homologous recombination. Cells of the mutant Pseudomonas sp. strain HRvdhΩKm, pregrown on gluconate, accumulated up to 2.9 mM vanillin during incubation in mineral medium with 6.5 mM eugenol. As a result of another vanillin dehydrogenase activity (VDH-II), the accumulated vanillin was further degraded, when coniferyl aldehyde was exhausted from the medium. Characterization of the purified VDH-II revealed the identity of this enzyme with the recently characterized coniferyl-aldehyde dehydrogenase. Received: 19 March 1999 / Received revision: 31 June 1999 / Accepted: 5 July 1999     

Highly Efficient Biotransformation of Eugenol to Ferulic Acid and Further Conversion to Vanillin in Recombinant Strains of Escherichia coli

The vaoA gene from Penicillium simplicissimum CBS 170.90, encoding vanillyl alcohol oxidase, which also catalyzes the conversion of eugenol to coniferyl alcohol, was expressed in Escherichia coli XL1-Blue under the control of the lac promoter, together with the genes calA and calB, encoding coniferyl alcohol dehydrogenase and coniferyl aldehyde dehydrogenase of Pseudomonas sp. strain HR199, respectively. Resting cells of the corresponding recombinant strain E. coli XL1-Blue(pSKvaomPcalAmcalB) converted eugenol to ferulic acid with a molar yield of 91% within 15 h on a 50-ml scale, reaching a ferulic acid concentration of 8.6 g liter⁻¹. This biotransformation was scaled up to a 30-liter fermentation volume. The maximum production rate for ferulic acid at that scale was 14.4 mmol per h per liter of culture. The maximum concentration of ferulic acid obtained was 14.7 g liter⁻¹ after a total fermentation time of 30 h, which corresponded to a molar yield of 93.3% with respect to the added amount of eugenol. In a two-step biotransformation, E. coli XL1-Blue(pSKvaomPcalAmcalB) was used to produce ferulic acid from eugenol and, subsequently, E. coli(pSKechE/Hfcs) was used to convert ferulic acid to vanillin (J. Overhage, H. Priefert, and A. Steinbüchel, Appl. Environ. Microbiol. 65:4837-4847, 1999). This process led to 0.3 g of vanillin liter⁻¹, besides 0.1 g of vanillyl alcohol and 4.6 g of ferulic acid liter⁻¹. The genes ehyAB, encoding eugenol hydroxylase of Pseudomonas sp. strain HR199, and azu, encoding the potential physiological electron acceptor of this enzyme, were shown to be unsuitable for establishing eugenol bioconversion in E. coli XL1-Blue.     

Biotransformation of Eugenol to Ferulic Acid by a Recombinant Strain of Ralstonia eutropha H16

The gene loci ehyAB, calA, and calB, encoding eugenol hydroxylase, coniferyl alcohol dehydrogenase, and coniferyl aldehyde dehydrogenase, respectively, which are involved in the first steps of eugenol catabolism in Pseudomonas sp. strain HR199, were amplified by PCR and combined to construct a catabolic gene cassette. This gene cassette was cloned in the newly designed broad-host-range vector pBBR1-JO2 (pBBR1-JO2ehyABcalAcalB) and transferred to Ralstonia eutropha H16. A recombinant strain of R. eutropha H16 harboring this plasmid expressed functionally active eugenol hydroxylase, coniferyl alcohol dehydrogenase, and coniferyl aldehyde dehydrogenase. Cells of R. eutropha H16(pBBR1-JO2ehyABcalAcalB) from the late-exponential growth phase were used as biocatalysts for the biotransformation of eugenol to ferulic acid. A maximum conversion rate of 2.9 mmol of eugenol per h per liter of culture was achieved with a yield of 93.8 mol% of ferulic acid from eugenol within 20 h, without further optimization.     

Biotransformation of eugenol to ferulic acid by a recombinant strain of Ralstonia eutropha H16

The gene loci ehyAB, calA, and calB, encoding eugenol hydroxylase, coniferyl alcohol dehydrogenase, and coniferyl aldehyde dehydrogenase, respectively, which are involved in the first steps of eugenol catabolism in Pseudomonas sp. strain HR199, were amplified by PCR and combined to construct a catabolic gene cassette. This gene cassette was cloned in the newly designed broad-host-range vector pBBR1-JO2 (pBBR1-JO2ehyABcalAcalB) and transferred to Ralstonia eutropha H16. A recombinant strain of R. eutropha H16 harboring this plasmid expressed functionally active eugenol hydroxylase, coniferyl alcohol dehydrogenase, and coniferyl aldehyde dehydrogenase. Cells of R. eutropha H16(pBBR1-JO2ehyABcalAcalB) from the late-exponential growth phase were used as biocatalysts for the biotransformation of eugenol to ferulic acid. A maximum conversion rate of 2.9 mmol of eugenol per h per liter of culture was achieved with a yield of 93.8 mol% of ferulic acid from eugenol within 20 h, without further optimization.     

Harnessing eugenol as a substrate for production of aromatic compounds with recombinant strains of Amycolatopsis sp. HR167

To harness eugenol as cheap substrate for the biotechnological production of aromatic compounds, the vanillyl alcohol oxidase gene (vaoA) from Penicillium simplicissimum CBS 170.90 was cloned in an expression vector suitable for Gram-positive bacteria and expressed in the vanillin-tolerant Gram-positive strain Amycolatopsis sp. HR167. Recombinant strains harboring hybrid plasmid pRLE6SKvaom exhibited a specific vanillyl alcohol oxidase activity of 1.1U/g protein. Moreover, this strain had gained the ability to grow on eugenol as sole carbon source. The intermediates coniferyl alcohol, coniferyl aldehyde, ferulic acid, guajacol, and vanillic acid were detected as excreted compounds during growth on eugenol, whereas vanillin could only be detected in trace amounts. Resting cells of Amycolatopsis sp. HR167 (pRLE6SKvaom) produced coniferyl alcohol from eugenol with a maximum conversion rate of about 2.3 mmol/h/l of culture, and a maximum coniferyl alcohol concentration of 4.7 g/1 was obtained after 16 h biotransformation without further optimization. Beside coniferyl alcohol, traces of coniferyl aldehyde and ferulic acid were also detected.     

Enhanced vanillin production from ferulic acid using adsorbent resin

High vanillin productivity was achieved in the batch biotransformation of ferulic acid by Streptomyces sp. strain V-1. Due to the toxicity of vanillin and the product inhibition, fed-batch biotransformation with high concentration of ferulic acid was unsuccessful. To solve this problem and improve the vanillin yield, a biotransformation strategy using adsorbent resin was investigated. Several macroporous adsorbent resins were chosen to adsorb vanillin in situ during the bioconversion. Resin DM11 was found to be the best, which adsorbed the most vanillin and the least ferulic acid. When 8% resin DM11 (wet w/v) was added to the biotransformation system, 45 g l⁻¹ ferulic acid could be added continually and 19.2 g l⁻¹ vanillin was obtained within 55 h, which was the highest vanillin yield by bioconversion until now. This yield was remarkable for exceeding the crystallization concentration of vanillin and therefore had far-reaching consequence in its downstream processing.     

Isolation and characterization of indene bioconversion genes from Rhodococcus strain I24

Rhodococcus strain I24 is able to convert indene into indandiol via the actions of at least two dioxygenase systems and a putative monooxygenase system. We have identified a cosmid clone from I24 genomic DNA that is able to confer the ability to convert indene to indandiol upon Rhodococcus erythropolis SQ1, a strain that normally can not convert or metabolize indene. HPLC analysis reveals that the transformed SQ1 strain produces cis-(1R,2S)-indandiol, suggesting that the cosmid clone encodes a naphthalene-type dioxygenase. DNA sequence analysis of a portion of this clone confirmed the presence of genes for the dioxygenase as well as genes encoding a dehydrogenase and putative aldolase. These genes will be useful for manipulating indene bioconversion in Rhodococcus strain I24. Received: 8 December 1998 / Received revision: 26 January 1999 / Accepted: 5 February 1999     

Towards a high-yield bioconversion of ferulic acid to vanillin

Natural vanillin is of high interest in the flavor market. Microbial routes to vanillin have so far not been economical as the medium concentrations achieved have been well below 1 g l⁻¹. We have now screened microbial isolates from nature and known strains for their ability to convert eugenol or ferulic acid into vanillin. Ferulic acid, in contrast to the rather toxic eugenol, was found to be an excellent precursor for the conversion to vanillin, as doses of several g l⁻¹ could be fed. One of the isolated microbes, later identified as Pseudomonas putida, very efficiently converted ferulic acid to vanillic acid. As vanillin was oxidized faster than ferulic acid, accumulation of vanillin as an intermediate was not observed. A completely different metabolic flux was observed with Streptomyces setonii. During the metabolism of ferulic acid, this strain accumulated vanillic acid only to a level of around 200 mg l⁻¹ and then started to accumulate vanillin as the principal metabolic overflow product. In shake-flask experiments, vanillin concentrations of up to 6.4 g l⁻¹ were achieved with a molar yield of 68%. This high level now forms the basis for an economical microbial production of vanillin that can be used for flavoring purposes. Received: 15 October 1998 / Received revision: 13 January 1999 / Accepted: 18 January 1999     

Pseudomonas resinovorans SPR1, a newly isolated strain with potential of transforming eugenol to vanillin and vanillic acid

In this study a novel strain was isolated with the capability to grow on eugenol as a source of carbon and energy. This strain was identified as Pseudomonas resinovorans (GenBank accession no. HQ198585) based on phenotypic characterization and phylogenetic analysis of 16S rDNA gene. The intermediates coniferyl alcohol, coniferyl aldehyde, ferulic acid, vanillin and vanillic acid were detected in the culture supernatant during eugenol biotransformation with this strain. The products were confirmed by thin layer chromatography (TLC), high performance liquid chromatography (HPLC) and spectral data achieved from UV-vis, FTIR and mass spectroscopy. Using eugenol as substrate and resting cells of P. resinovorans SPR1, which were harvested at the end of the exponential growth phase, without further optimization 0.24 g/L vanillin (molar yield of 10%) and 1.1g/L vanillic acid (molar yield of 44%) were produced after 30 h and 60 h biotransformation, respectively. The current work gives the first evidence for the eugenol biotransformation by P. resinovorans.     

Vanilla Flavour Production Through Biotransformation Using Capsicum frutescens Root Cultures

Normal roots of Capsicum frutescens were excised from tissue-cultured plants into half strength Murashige and Skoog's medium with 2.23 μM naphthalene acetic acid. Maximum growth of cultured roots was 6.5 g fresh weight 40 ml^-1, as recorded on day 20. Even though normal roots were unable to accumulate capsaicin, they contained other phenylpropanoid intermediates and vanillylamine, as detected by HPLC analysis. Normal roots of Capsicum frutescens were treated with ferulic acid and protocatechuic aldehyde in order to study their biotransformation ability. Ferulic acid, which is the nearest precursor to vanillin, when fed at concentrations of 1 and 2 mM led to the accumulation of vanilla flavour metabolites, vanillin being the major one. In cultures treated with 1 and 2 mM ferulic acid, maximum vanillin accumulation of 12.3 and 16.4 μM was observed, on day 6 after precursor addition, respectively. Feeding of ferulic acid and β-cyclodextrin complex (2 mM each) enhanced the accumulation of biotransformed products. Moreover, vanillin accumulation was recorded as 24.7 μM on day 6 after precursor addition, which was 1.5 times higher than in cultures fed with ferulic acid (2 mM) alone. When ferulic acid was fed along with β-cyclodextrin (1 mM each) to cultures growing in a three-litre bubble column bioreactor, the maximum vanillin production of 10.7 μM was obtained; other vanilla flavour metabolites were also formed after 9 days of precursor addition. Root cultures could also biotransform protocatechuic aldehyde wherein a maximum vanillin production of 7.9 μM was recorded on day 6 after precursor addition. The bioconversion efficiency was observed to be 5–7% in case of ferulic acid fed cultures and 3.2% in case of protocatechuic aldehyde fed cultures suggesting the possible channelling of precursors to alternate biosynthetic pathways such as lignin.     

二穗短柄草(Brachypodium distachyon)BdAD1基因的克隆、表达及功能分析

本研究利用生物信息学结合RT-PCR技术从二穗短柄草(Brachypodium distachyon)中克隆出BdAD1的c DNA基因,该基因编码一个包含500个氨基酸残基的乙醛脱氢酶家族蛋白。系统进化关系分析表明,该BdAD1蛋白序列与小麦(Triticum aestivum)、羊草(Leymus chinensis)和大麦(Hordeum vulgare)的同源蛋白具有较近的亲缘关系。BdAD1基因在植物细胞的细胞核和细胞质中均有表达,而且BdAD1蛋白兼具松柏醛脱氢酶和芥子醛脱氢酶的活性(CALDH/SALDH),可将松柏醛与芥子醛分别酶解生成阿魏酸和芥子酸,但它对松柏醛的催化效率显著高于芥子醛,因此推测BdAD1可能在苯丙烷代谢途径中对阿魏酸的合成具有重要的调控作用。     

Production of methoxyphenol-type natural aroma chemicals by biotransformation of eugenol with a new Pseudomonas sp.

In our screening program for microorganisms that are able to metabolize eugenol, the main component of the essential oil of the clove tree Syzigium aromaticum (sy. Eugenia cariophyllus), we found a new Pseudomonas sp. that produces several substituted methoxyphenols when eugenol is fed to the culture. A taxonomic characterization of this new organism has been performed. Examples of the biotransformation products, produced in high amounts, were vanillic acid with 3.25 g/l within 99 h, ferulic acid with 5.8 g/l within 75 h and coniferyl alcohol with 3.22 g/l within 47.5 h. By changing the culture conditions the ratio of the different metabolites could be varied. Based on these results a scheme for the degradation of eugenol by this strain has been established. Received: 1 April 1996 / Received revision: 24 June 1996 / Accepted: 1 July 1996     

O-4-Linked coniferyl and sinapyl aldehydes in lignifying cell walls are the main targets of the Wiesner (phloroglucinol-HCl) reaction

Summary.  The nature and specificity of the Wiesner test (phloroglucinol-HCl reagent) for the aromatic aldehyde fraction contained in lignins is studied. Phloroglucinol reacted in ethanol-hydrochloric acid with coniferyl aldehyde, sinapyl aldehyde, vanillin, and syringaldehyde to yield either pink pigments (in the case of hydroxycinnamyl aldehydes) or red-brown pigments (in the case of hydroxybenzaldehydes). However, coniferyl alcohol, sinapyl alcohol, and highly condensed dehydrogenation polymers derived from these cinnamyl alcohols and aldehydes did not react with phloroglucinol in ethanol-hydrochloric acid. The differences in the reactivity of phloroglucinol with hydroxycinnamyl aldehydes and their dehydrogenation polymers may be explained by the fact that, in the latter, the unsubstituted (α,β-unsaturated) cinnamaldehyde functional group, which is responsible for the dye reaction, is lost due to lateral chain cross-linking reactions involving the β carbon. Fourier transform infrared spectroscopy and thioacidolysis analyses of phloroglucinol-positive lignifying plant cell walls belonging to the plant species Zinnia elegans L., Capsicum annuum var. annuum, Populus alba L., and Pinus halepensis L. demonstrated the presence of 4-O-linked hydroxycinnamyl aldehyde end groups and 4-O-linked 4-hydroxy-3-methoxy-benzaldehyde (vanillin) end groups in lignins. However, given the relatively low abundance of 4-O-linked vanillin in lignifying cell walls and the low extinction coefficient of its red-brown phloroglucinol adduct, it is unlikely that vanillin contributes to a great extent to the phloroglucinol-positive stain reaction. These results suggest that the phloroglucinol-HCl pink stain of lignifying xylem cell walls actually reveals the 4-O-linked hydroxycinnamyl aldehyde structures contained in lignins. Histochemical studies showed that these aldehyde structures are assembled, as in the case of coniferyl aldehyde, during the early stages of xylem cell wall lignification. Received April 17, 2002; accepted May 21, 2002; published online October 31, 2002 RID="*" ID="*" Correspondence and reprints: Department of Plant Biology, University of Murcia, 30100 Murcia, Spain. Abbreviations: DHP dehydrogenation polymers; FT-IR spectroscopy Fourier transform infrared spectroscopy.     

Biochemical and Genetic Analyses of Ferulic Acid Catabolism in Pseudomonas sp. Strain HR199

The gene loci fcs, encoding feruloyl coenzyme A (feruloyl-CoA) synthetase, ech, encoding enoyl-CoA hydratase/aldolase, and aat, encoding β-ketothiolase, which are involved in the catabolism of ferulic acid and eugenol in Pseudomonas sp. strain HR199 (DSM7063), were localized on a DNA region covered by two EcoRI fragments (E230 and E94), which were recently cloned from a Pseudomonas sp. strain HR199 genomic library in the cosmid pVK100. The nucleotide sequences of parts of fragments E230 and E94 were determined, revealing the arrangement of the aforementioned genes. To confirm the function of the structural genes fcs and ech, they were cloned and expressed in Escherichia coli. Recombinant strains harboring both genes were able to transform ferulic acid to vanillin. The feruloyl-CoA synthetase and enoyl-CoA hydratase/aldolase activities of the fcs and ech gene products, respectively, were confirmed by photometric assays and by high-pressure liquid chromatography analysis. To prove the essential involvement of the fcs, ech, and aat genes in the catabolism of ferulic acid and eugenol in Pseudomonas sp. strain HR199, these genes were inactivated separately by the insertion of omega elements. The corresponding mutants Pseudomonas sp. strain HRfcsΩGm and Pseudomonas sp. strain HRechΩKm were not able to grow on ferulic acid or on eugenol, whereas the mutant Pseudomonas sp. strain HRaatΩKm exhibited a ferulic acid- and eugenol-positive phenotype like the wild type. In conclusion, the degradation pathway of eugenol via ferulic acid and the necessity of the activation of ferulic acid to the corresponding CoA ester was confirmed. The aat gene product was shown not to be involved in this catabolism, thus excluding a β-oxidation analogous degradation pathway for ferulic acid. Moreover, the function of the ech gene product as an enoyl-CoA hydratase/aldolase suggests that ferulic acid degradation in Pseudomonas sp. strain HR199 proceeds via a similar pathway to that recently described for Pseudomonas fluorescens AN103.     

Analysis of Hydroxycinnamic Acid Degradation in Agrobacterium fabrum Reveals a Coenzyme A-Dependent,Beta-Oxidative Deacetylation Pathway

The soil- and rhizosphere-inhabiting bacterium Agrobacterium fabrum (genomospecies G8 of the Agrobacterium tumefaciens species complex) is known to have species-specific genes involved in ferulic acid degradation. Here, we characterized, by genetic and analytical means, intermediates of degradation as feruloyl coenzyme A (feruloyl-CoA), 4-hydroxy-3-methoxyphenyl-β-hydroxypropionyl–CoA, 4-hydroxy-3-methoxyphenyl-β-ketopropionyl–CoA, vanillic acid, and protocatechuic acid. The genes atu1416, atu1417, and atu1420 have been experimentally shown to be necessary for the degradation of ferulic acid. Moreover, the genes atu1415 and atu1421 have been experimentally demonstrated to be essential for this degradation and are proposed to encode a phenylhydroxypropionyl-CoA dehydrogenase and a 4-hydroxy-3-methoxyphenyl-β-ketopropionic acid (HMPKP)–CoA β-keto-thiolase, respectively. We thus demonstrated that the A. fabrum hydroxycinnamic degradation pathway is an original coenzyme A-dependent β-oxidative deacetylation that could also transform p-coumaric and caffeic acids. Finally, we showed that this pathway enables the metabolism of toxic compounds from plants and their use for growth, likely providing the species an ecological advantage in hydroxycinnamic-rich environments, such as plant roots or decaying plant materials.     

Biochemical and genetic analyses of ferulic acid catabolism in Pseudomonas sp. Strain HR199.

The gene loci fcs, encoding feruloyl coenzyme A (feruloyl-CoA) synthetase, ech, encoding enoyl-CoA hydratase/aldolase, and aat, encoding beta-ketothiolase, which are involved in the catabolism of ferulic acid and eugenol in Pseudomonas sp. strain HR199 (DSM7063), were localized on a DNA region covered by two EcoRI fragments (E230 and E94), which were recently cloned from a Pseudomonas sp. strain HR199 genomic library in the cosmid pVK100. The nucleotide sequences of parts of fragments E230 and E94 were determined, revealing the arrangement of the aforementioned genes. To confirm the function of the structural genes fcs and ech, they were cloned and expressed in Escherichia coli. Recombinant strains harboring both genes were able to transform ferulic acid to vanillin. The feruloyl-CoA synthetase and enoyl-CoA hydratase/aldolase activities of the fcs and ech gene products, respectively, were confirmed by photometric assays and by high-pressure liquid chromatography analysis. To prove the essential involvement of the fcs, ech, and aat genes in the catabolism of ferulic acid and eugenol in Pseudomonas sp. strain HR199, these genes were inactivated separately by the insertion of omega elements. The corresponding mutants Pseudomonas sp. strain HRfcsOmegaGm and Pseudomonas sp. strain HRechOmegaKm were not able to grow on ferulic acid or on eugenol, whereas the mutant Pseudomonas sp. strain HRaatOmegaKm exhibited a ferulic acid- and eugenol-positive phenotype like the wild type. In conclusion, the degradation pathway of eugenol via ferulic acid and the necessity of the activation of ferulic acid to the corresponding CoA ester was confirmed. The aat gene product was shown not to be involved in this catabolism, thus excluding a beta-oxidation analogous degradation pathway for ferulic acid. Moreover, the function of the ech gene product as an enoyl-CoA hydratase/aldolase suggests that ferulic acid degradation in Pseudomonas sp. strain HR199 proceeds via a similar pathway to that recently described for Pseudomonas fluorescens AN103.     

Purification and Characterization of the Coniferyl Aldehyde Dehydrogenase from Pseudomonas sp. Strain HR199 and Molecular Characterization of the Gene

The coniferyl aldehyde dehydrogenase (CALDH) of Pseudomonas sp. strain HR199 (DSM7063), which catalyzes the NAD⁺-dependent oxidation of coniferyl aldehyde to ferulic acid and which is induced during growth with eugenol as the carbon source, was purified and characterized. The native protein exhibited an apparent molecular mass of 86,000 ± 5,000 Da, and the subunit mass was 49.5 ± 2.5 kDa, indicating an α₂ structure of the native enzyme. The optimal oxidation of coniferyl aldehyde to ferulic acid was obtained at a pH of 8.8 and a temperature of 26°C. The K_m values for coniferyl aldehyde and NAD⁺ were about 7 to 12 μM and 334 μM, respectively. The enzyme also accepted other aromatic aldehydes as substrates, whereas aliphatic aldehydes were not accepted. The NH₂-terminal amino acid sequence of CALDH was determined in order to clone the encoding gene (calB). The corresponding nucleotide sequence was localized on a 9.4-kbp EcoRI fragment (E94), which was subcloned from a Pseudomonas sp. strain HR199 genomic library in the cosmid pVK100. The partial sequencing of this fragment revealed an open reading frame of 1,446 bp encoding a protein with a relative molecular weight of 51,822. The deduced amino acid sequence, which is reported for the first time for a structural gene of a CALDH, exhibited up to 38.5% amino acid identity (60% similarity) to NAD⁺-dependent aldehyde dehydrogenases from different sources.     

Metabolic engineering of Pediococcus acidilactici BD16 for production of vanillin through ferulic acid catabolic pathway and process optimization using response surface methodology

Occurrence of feruloyl-CoA synthetase (fcs) and enoyl-CoA hydratase (ech) genes responsible for the bioconversion of ferulic acid to vanillin have been reported and characterized from Amycolatopsis sp., Streptomyces sp., and Pseudomonas sp. Attempts have been made to express these genes in Escherichia coli DH5α, E. coli JM109, and Pseudomonas fluorescens. However, none of the lactic acid bacteria strain having GRAS status was previously proposed for heterologous expression of fcs and ech genes for production of vanillin through biotechnological process. Present study reports heterologous expression of vanillin synthetic gene cassette bearing fcs and ech genes in a dairy isolate Pediococcus acidilactici BD16. After metabolic engineering, statistical optimization of process parameters that influence ferulic acid to vanillin biotransformation in the recombinant strain was carried out using central composite design of response surface methodology. After scale-up of the process, 3.14 mM vanillin was recovered from 1.08 mM ferulic acid per milligram of recombinant cell biomass within 20 min of biotransformation. From LCMS-ESI spectral analysis, a metabolic pathway of phenolic biotransformations was predicted in the recombinant P. acidilactici BD16 (fcs ⁺/ech ⁺).     

Metabolic engineering of Pseudomonas fluorescens for the production of vanillin from ferulic acid

Vanillin is one of the most important flavors in the food industry and there is great interest in its production through biotechnological processes starting from natural substrates such as ferulic acid. Among bacteria, recombinant Escherichia coli strains are the most efficient vanillin producers, whereas Pseudomonas spp. strains, although possessing a broader metabolic versatility, rapidly metabolize various phenolic compounds including vanillin. In order to develop a robust Pseudomonas strain that can produce vanillin in high yields and at high productivity, the vanillin dehydrogenase (vdh)-encoding gene of Pseudomonas fluorescens BF13 strain was inactivated via targeted mutagenesis. The results demonstrated that engineered derivatives of strain BF13 accumulate vanillin if inactivation of vdh is associated with concurrent expression of structural genes for feruloyl-CoA synthetase (fcs) and hydratase/aldolase (ech) from a low-copy plasmid. The conversion of ferulic acid to vanillin was enhanced by optimization of growth conditions, growth phase and parameters of the bioconversion process. The developed strain produced up to 8.41 mM vanillin, which is the highest final titer of vanillin produced by a Pseudomonas strain to date and opens new perspectives in the use of bacterial biocatalysts for biotechnological production of vanillin from agro-industrial wastes which contain ferulic acid.