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.     

Biotransformation of protocatechuic aldehyde and caffeic acid to vanillin and capsaicin in freely suspended and immobilized cell cultures of Capsicum frutescens

Freely suspended cells and immobilized cell cultures of Capsicum frutescens Mill. were treated with phenylpropanoid intermediates--protocatechuic aldehyde and caffeic acid to study their biotransformation ability. It was found that externally fed protocatechuic aldehyde and caffeic acids were biotransformed to vanillin and capsaicin. It was noted that this culture biotransformed externally fed protocatechuic aldehyde to vanillin more than its conversion to capsaicin, whereas, caffeic acid-treated cultures accumulated more capsaicin than vanillin. The maximum accumulation of vanillin (5.63 mg l(-1)) and capsaicin (3.83 mg l(-1)) was recorded on the 6th and 15th day, respectively in immobilized C. frutescens cell cultures treated with protocatechuic aldehyde, which was 1.8 and 1.4 times higher than in protocatechuic aldehyde-treated freely suspended cell cultures. Caffeic acid-treated immobilized C. frutescens cell cultures accumulated maximum vanillin and capsaicin at 2.68 and 3.03 mg l(-1) culture, respectively, on the 9th and 12th day, which was 1.65 and 1.33 times over freely suspended cultures treated with caffeic acid. The addition of S-adenosyl-L-methionine, a methyl donor, to protocatechuic aldehyde-treated immobilized C. frutescens cell cultures, resulted in accumulation of vanillin (14.08 mg l(-1)) on the 4th day, which was 2.5-fold higher than that in cultures treated with protocatechuic aldehyde alone, suggesting the influence of S-adenosyl-L-methionine on O-methylation of protocatechuic aldehyde, resulting in more vanillin accumulation. The increase in vanillin accumulation was well correlated with an increase in specific activity of caffeic acid O-methyltransferase in protocatechuic aldehyde and S-adenosyl-L-methionine-treated immobilized C. frutescens cell cultures. This study also provides an example for an alternative route to formation of vanillin by C. frutescens cell cultures.     

Bioengineering of the Plant Culture of <Emphasis Type="Italic">Capsicum frutescens</Emphasis> with Vanillin Synthase Gene for the Production of Vanillin

Production of vanillin by bioengineering has gained popularity due to consumer demand toward vanillin produced by biological systems. Natural vanillin from vanilla beans is very expensive to produce compared to its synthetic counterpart. Current bioengineering works mainly involve microbial biotechnology. Therefore, alternative means to the current approaches are constantly being explored. This work describes the use of vanillin synthase (VpVAN), to bioconvert ferulic acid to vanillin in a plant system. The VpVAN enzyme had been shown to directly convert ferulic acid and its glucoside into vanillin and its glucoside, respectively. As the ferulic acid precursor and vanillin were found to be the intermediates in the phenylpropanoid biosynthetic pathway of Capsicum species, this work serves as a proof-of-concept for vanillin production using Capsicum frutescens (C. frutescens or hot chili pepper). The cells of C. frutescens were genetically transformed with a codon optimized VpVAN gene via biolistics. Transformed explants were selected and regenerated into callus. Successful integration of the gene cassette into the plant genome was confirmed by polymerase chain reaction. High-performance liquid chromatography was used to quantify the phenolic compounds detected in the callus tissues. The vanillin content of transformed calli was 0.057% compared to 0.0003% in untransformed calli.     

Biotransformation of Digitoxin in Cell Cultures of Capsicum frutescens in the Presence of β-cyclodextrin

Cell suspension cultures of Capsicum frutescens accumulated digoxin, purpureaglycoside A and other unknown derivatives when digitoxin, a cardiac glycoside, was used as a precursor. The feeding of digitoxin complexed with β-cyclodextrin increased the accumulation of digoxin, purpureaglycoside A and other unknown derivatives. Control cultures (without digitoxin) did not produce any of these metabolites. The growth of cells was affected by both digitoxin as well as digitoxin- β-cyclodextrin. The accumulation of purpureaglycoside A and digoxin reached a maximum of 1241 and 374 μg 100 ml -1 culture on the 6th and 2nd day, respectively, which was 3.9 and 4.5 fold higher than cultures treated with digitoxin alone (sampled on the 13th day). The other unknown derivatives formed in digitoxin- β-cyclodextrin fed cultures were 15 times higher than digitoxin alone fed C. frutescens cultures. The addition of glucose to digitoxin- β-cyclodextrin treated cultures increased the accumulation of purpureaglycoside A which reached a maximum of 3589 μg 100 ml -1 culture after 12 h incubation, which was a 2.9 fold increase over cultures treated with digitoxin- β-cyclodextrin alone.     

Microbial transformation of ferulic acid to vanillic acid by <Emphasis Type="Italic">Streptomyces sannanensis</Emphasis> MTCC 6637

Streptomyces sannanensis MTCC 6637 was examined for its potentiality to transform ferulic acid into its corresponding hydroxybenzoate-derivatives. Cultures of S. sannanensis when grown on minimal medium containing ferulic acid as sole carbon source, vanillic acid accumulation was observed in the medium as the major biotransformed product along with transient formation of vanillin. A maximum amount of 400 mg/l vanillic acid accumulation was observed, when cultures were grown on 5 mM ferulic acid at 28°C. This accumulation of vanillic acid was found to be stable in the culture media for a long period of time, thus facilitating its recovery. Purification of vanillic acid was achieved by gel filtration chromatography using Sephadex™ LH-20 matrix. Catabolic route of ferulic acid biotransformation by S. sannanensis has also been demonstrated. The metabolic inhibitor experiment [by supplementation of 3,4 methylenedioxy-cinnamic acid (MDCA), a metabolic inhibitor of phenylpropanoid enzyme 4-hydroxycinnamoyl-CoA ligase (4-CL) along with ferulic acid] suggested that biotransformation of ferulic acid into vanillic acid mainly proceeds via CoA-dependent route. In vitro conversions of ferulic acid to vanillin, vanillic acid and vanillin to vanillic acid were also demonstrated with cell extract of S. sannanensis. Further degradation of vanillic acid to other intermediates such as, protocatechuic acid and guaiacol was not observed, which was also confirmed in vitro with cell extract.     

Biotransformation of Digitoxin in Cell Cultures of Capsicum frutescens in the Presence of β-cyclodextrin

Cell suspension cultures of Capsicum frutescens accumulated digoxin, purpureaglycoside A and other unknown derivatives when digitoxin, a cardiac glycoside, was used as a precursor. The feeding of digitoxin complexed with &#103 -cyclodextrin increased the accumulation of digoxin, purpureaglycoside A and other unknown derivatives. Control cultures (without digitoxin) did not produce any of these metabolites. The growth of cells was affected by both digitoxin as well as digitoxin- &#103 -cyclodextrin. The accumulation of purpureaglycoside A and digoxin reached a maximum of 1241 and 374 &#119 g 100 ml &#109 1 culture on the 6th and 2nd day, respectively, which was 3.9 and 4.5 fold higher than cultures treated with digitoxin alone (sampled on the 13th day). The other unknown derivatives formed in digitoxin- &#103 -cyclodextrin fed cultures were 15 times higher than digitoxin alone fed C. frutescens cultures. The addition of glucose to digitoxin- &#103 -cyclodextrin treated cultures increased the accumulation of purpureaglycoside A which reached a maximum of 3589 &#119 g 100 ml &#109 1 culture after 12 h incubation, which was a 2.9 fold increase over cultures treated with digitoxin- &#103 -cyclodextrin alone.     

Methyl jasmonate modulated biotransformation of phenylpropanoids to vanillin related metabolites using Capsicum frutescens root cultures.

Normal root cultures of Capsicum frutescens biotransform externally fed precursors, like caffeic acid and veratraldehyde, to vanillin and other related metabolites. The bioconversion of caffeic acid to further metabolites--viz. vanillin, vanillylamine, vanillic acid--was shown to be elicited by treating the cultures with 10 microM methyl jasmonate (MJ). Root cultures treated with MJ accumulated (1.93 times) more of vanillin (20.2 microM on day-3) than untreated ones. A concomitant increase in enzymatic activity of caffeic acid O-methyl transferase (CAOMT, EC 2.1.1.68) was obtained in MJ treated cultures, compared to untreated cultures. After 24 h of MJ treatment, a 13.7-fold increase in CAOMT activity was recorded in root cultures of C. frutescens. Cultures treated with veratraldehyde accumulated more vanillin (78 microM) than caffeic acid fed cultures, 6 days after precursor addition. Capsaicin did not accumulate even after addition of precursors. The efficiencies of biotransformation with caffeic acid and veratraldehyde were 2.2% and 9% with respect to vanillin formation, indicating a possible diversion of the phenylpropanoid pathway towards other secondary metabolites.     

Metabolism of cinnamic, p-coumaric, and ferulic acids by Streptomyces setonii

Streptomyces setonii strain 75Vi2 was grown at 45 degrees C in liquid media containing yeast extract and trans-cinnamic acid, p-coumaric acid, ferulic acid, or vanillin. Gas chromatography, thin-layer chromatography, and mass spectrometry showed that cinnamic acid was catabolized via benzaldehyde, benzoic acid, and catechol; p-coumaric acid was catabolized via p-hydroxybenzaldehyde, p-hydroxybenzoic acid, and protocatechuic acid; ferulic acid was catabolized via vanillin, vanillic acid, and protocatechuic acid. When vanillin was used as the initial growth substrate, it was catabolized via vanillic acid, guaiacol, and catechol. The inducible ring-cleavage dioxygenases catechol 1,2-dioxygenase and protocatechuate 3,4-dioxygenase were detected with an oxygen electrode in cell-free extracts of cultures grown in media with aromatic growth substrates and yeast extract.     

Vanillin production using metabolically engineered <Emphasis Type="Italic">Escherichia coli</Emphasis> under non-growing conditions

Background  

Vanillin is one of the most important aromatic flavour compounds used in the food and cosmetic industries. Natural vanillin is extracted from vanilla beans and is relatively expensive. Moreover, the consumer demand for natural vanillin highly exceeds the amount of vanillin extracted by plant sources. This has led to the investigation of other routes to obtain this flavour such as the biotechnological production from ferulic acid. Studies concerning the use of engineered recombinant Escherichia coli cells as biocatalysts for vanillin production are described in the literature, but yield optimization and biotransformation conditions have not been investigated in details.     

Enzymatic oxidation of vanillin, isovanillin and protocatechuic aldehyde with freshly prepared Guinea pig liver slices.

BACKGROUND/AIMS: The oxidation of xenobiotic-derived aromatic aldehydes with freshly prepared liver slices has not been previously reported. The present investigation compares the relative contribution of aldehyde oxidase, xanthine oxidase and aldehyde dehydrogenase activities in the oxidation of vanillin, isovanillin and protocatechuic aldehyde with freshly prepared liver slices. METHODS: Vanillin, isovanillin or protocatechuic aldehyde was incubated with liver slices in the presence/absence of specific inhibitors of each enzyme, followed by HPLC. RESULTS: Vanillin was rapidly converted to vanillic acid. Vanillic acid formation was completely inhibited by isovanillin (aldehyde oxidase inhibitor), whereas disulfiram (aldehyde dehydrogenase inhibitor) inhibited acid formation by 16% and allopurinol (xanthine oxidase inhibitor) had no effect. Isovanillin was rapidly converted to isovanillic acid. The formation of isovanillic acid was not altered by allopurinol, but considerably inhibited by disulfiram. Protocatechuic aldehyde was converted to protocatechuic acid at a lower rate than that of vanillin or isovanillin. Allopurinol only slightly inhibited protocatechuic aldehyde oxidation, isovanillin had little effect, whereas disulfiram inhibited protocatechuic acid formation by 50%. CONCLUSIONS: In freshly prepared liver slices, vanillin is rapidly oxidized by aldehyde oxidase with little contribution from xanthine oxidase or aldehyde dehydrogenase. Isovanillin is not a substrate for aldehyde oxidase and therefore it is metabolized to isovanillic acid predominantly by aldehyde dehydrogenase. All three enzymes contribute to the oxidation of protocatechuic aldehyde to its acid.     

Rapid degradation of ferulic acid via 4-vinylguaiacol and vanillin by a newly isolated strain of Bacillus coagulans

A new strain Bacillus coagulans BK07 was isolated from decomposed wood-bark, based on its ability to grow on ferulic acid as a sole carbon source. This strain rapidly decarboxylated ferulic acid to 4-vinylguaiacol, which was immediately converted to vanillin and then oxidized to vanillic acid. Vanillic acid was further demethylated to protocatechuic acid. Above 95% substrate degradation was obtained within 7 h of growth on ferulic acid medium, which is the shortest period of time reported to date. The major degradation products, was isolated and identified by thin-layer chromatography, high performance liquid chromatography and ¹H-nuclear magnetic resonance spectroscopy were 4-vinylguaiacol, vanillin, vanillic acid and protocatechuic acid.     

Dynamics of phenolic acids and lignin accumulation in metal-treated Matricaria chamomilla roots

Phenylalanine ammonia-lyase (PAL) activity, 11 phenolic acids and lignin accumulation in Matricaria chamomilla roots exposed to low (3 μM) and high (60 and 120 μM) levels of cadmium (Cd) or copper (Cu) for 7 days were investigated. Five derivatives of cinnamic acid (chlorogenic, p-coumaric, caffeic, ferulic and sinapic acids) and six derivatives of benzoic acid (protocatechuic, vanillic, syringic, p-hydroxybenzoic, salicylic acids and protocatechuic aldehyde) were detected. Accumulation of glycoside-bound phenolics (revealed by acid hydrolysis) was enhanced mainly towards the end of the experiment, being more expressive in Cu-treated roots. Interestingly, chlorogenic acid was extremely elevated by the highest Cu dose (21-fold higher than control) suggesting its involvement in antioxidative protection. All compounds, with the exception of chlorogenic acid, were detected in the cell wall bound fraction, but only benzoic acids were found in the ester-bound fraction (revealed by alkaline hydrolysis). Soluble phenolics were present in substantially higher amounts in Cu-treated roots and more Cu was retained there in comparison to Cd. Cu strongly elevated PAL activity (by 5.4- and 12.1-fold in 60 and 120 μM treatment, respectively) and lignin content (by 71 and 148%, respectively) after one day of treatment, indicating formation of a barrier against metal entrance. Cd had slighter effects, supporting its non-redox active properties. Taken together, different forms of phenolic metabolites play an important role in chamomile tolerance to metal excess and participate in active antioxidative protection.     

Dissimilation of ferulic acid byBacillus subtilis

Bacillus subtilis utilized ferulic acid and its intermediates vanillin, vanillic acid, and protocatechuic acid as sole carbon source. The enzymes of the ferulic acid degradative pathway such as deacetylase, vanillin oxidase, vanillate-o-demethylase, and protocatechuate 3,4-dioxygenase were inducible in nature. Concentration of the inducer profoundly influenced the induction of the enzymes involved in ferulic acid dissimilation.     

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     

Rapid degradation of ferulic acid via 4-vinylguaiacol and vanillin by a newly isolated strain of bacillus coagulans

A new strain Bacillus coagulans BK07 was isolated from decomposed wood-bark, based on its ability to grow on ferulic acid as a sole carbon source. This strain rapidly decarboxylated ferulic acid to 4-vinylguaiacol, which was immediately converted to vanillin and then oxidized to vanillic acid. Vanillic acid was further demethylated to protocatechuic acid. Above 95% substrate degradation was obtained within 7 h of growth on ferulic acid medium, which is the shortest period of time reported to date. The major degradation products, was isolated and identified by thin-layer chromatography, high performance liquid chromatography and ¹H-nuclear magnetic resonance spectroscopy were 4-vinylguaiacol, vanillin, vanillic acid and protocatechuic acid.     

A two-step bioconversion process for vanillin production from ferulic acid combining Aspergillus niger and Pycnoporus cinnabarinus

A two-step bioconversion process of ferulic acid to vanillin was elaborated combining two filamentous fungi, Aspergillus niger and Pycnoporus cinnabarinus. In the first step, A. niger transformed ferulic acid to vanillic acid and in the second step vanillic acid was reduced to vanillin by P. cinnabarinus. Ferulic acid metabolism by A. niger occurred essentially via the propenoic chain degradation to lead to vanillic acid, which was subsequently decarboxylated to methoxyhydroquinone. In 3-day-old cultures of P. cinnabarinus supplied with vanillic-acid-enriched culture medium from A. niger as precursor source, vanillin was successfully produced. In order to improve the yields of the process, sequential additions of precursors were performed. Vanillic acid production by A. niger from ferulic acid reached 920 mg l⁻¹ with a molar yield of 88% and vanillin production by P. cinnabarinus from vanillic acid attained 237 mg l ⁻¹ with a molar yield of 22%. However, the vanillic acid oxidative system producing methoxyhydroquinone was predominant in P. cinnabarinus cultures, which explained the relatively low level in vanillin.     

Transportation mechanism for vanillin uptake through fungal plasma membrane

Protoplasts of the basidiomycete, Fomitopsis palustris (formerly Tyromyces palustris), were utilized to study a function of the fungal plasma membrane. Fungal protoplasts exhibited metabolic activities as seen with intact mycelial cells. Furthermore, the uptake of certain compounds into the protoplast cells was quantitatively observed by using non-radioactive compounds. Vanillin was converted to vanillyl alcohol and vanillic acid as major products and to protocatechuic acid and 1,2,4-trihydroxybenzene as trace products by protoplasts prepared from F. palustris. Extracellular culture medium showed no activity responsible for the redox reactions of vanillin. Only vanillic acid was detected in the intracellular fraction of protoplasts. However, the addition of disulfiram, an aldehyde dehydrogenase inhibitor, caused an intracellular accumulation of vanillin, strongly suggesting that vanillin is taken up by the cell, followed by oxidation to vanillic acid. The addition of carbonylcyanide m-chlorophenylhydrazone, which dissipates the pH gradient across the plasma membrane, inhibited the uptake of either vanillin or vanillic acid into the cell. Thus, the fungus seems to possess transporter devices for both vanillin and vanillic acid for their uptake. Since vanillyl alcohol was only observed extracellularly, the reduction of vanillin was thought to be catalyzed by a membrane system.     

Mode of antimicrobial action of vanillin against Escherichia coli, Lactobacillus plantarum and Listeria innocua

AIMS: To investigate the mode of action of vanillin, the principle flavour component of vanilla, with regard to its antimicrobial activity against Escherichia coli, Lactobacillus plantarum and Listeria innocua. METHODS AND RESULTS: In laboratory media, MICs of 15, 75 and 35 mmol l(-1) vanillin were established for E. coli, Lact. plantarum and L. innocua, respectively. The observed inhibition was found to be bacteriostatic. Exposure to 10-40 mmol l(-1) vanillin inhibited respiration of E. coli and L. innocua. Addition of 50-70 mmol l(-1) vanillin to bacterial cell suspensions of the three organisms led to an increase in the uptake of the nucleic acid stain propidium iodide; however a significant proportion of cells still remained unstained indicating their cytoplasmic membranes were largely intact. Exposure to 50 mmol l(-1) vanillin completely dissipated potassium ion gradients in cultures of Lact. plantarum within 40 min, while partial potassium gradients remained in cultures of E. coli and L. innocua. Furthermore, the addition of 100 mmol l(-1) vanillin to cultures of Lact. plantarum resulted in the loss of pH homeostasis. However, intracellular ATP pools were largely unaffected in E. coli and L. innocua cultures upon exposure to 50 mmol l(-1) vanillin, while ATP production was stimulated in Lact. plantarum cultures. In contrast to the more potent activity of carvacrol, a well studied phenolic flavour compound, the extent of membrane damage caused by vanillin is less severe. CONCLUSIONS: Vanillin is primarily a membrane-active compound, resulting in the dissipation of ion gradients and the inhibition of respiration, the extent to which is species-specific. These effects initially do not halt the production of ATP. SIGNIFICANCE AND IMPACT OF THE STUDY: Understanding the mode of action of natural antimicrobials may facilitate their application as natural food preservatives, particularly for their potential use in preservation systems employing multiple hurdles.     

Potential of Rhodococcus strains for biotechnological vanillin production from ferulic acid and eugenol

The potential of two Rhodococcus strains for biotechnological vanillin production from ferulic acid and eugenol was investigated. Genome sequence data of Rhodococcus sp. I24 suggested a coenzyme A-dependent, non-β-oxidative pathway for ferulic acid bioconversion, which involves feruloyl–CoA synthetase (Fcs), enoyl–CoA hydratase/aldolase (Ech), and vanillin dehydrogenase (Vdh). This pathway was proven for Rhodococcus opacus PD630 by physiological characterization of knockout mutants. However, expression and functional characterization of corresponding structural genes from I24 suggested that degradation of ferulic acid in this strain proceeds via a β-oxidative pathway. The vanillin precursor eugenol facilitated growth of I24 but not of PD630. Coniferyl aldehyde was an intermediate of eugenol degradation by I24. Since the genome sequence of I24 is devoid of eugenol hydroxylase homologous genes (ehyAB), eugenol bioconversion is most probably initiated by a new step in this bacterium. To establish eugenol bioconversion in PD630, the vanillyl alcohol oxidase gene (vaoA) from Penicillium simplicissimum CBS 170.90 was expressed in PD630 together with coniferyl alcohol dehydrogenase (calA) and coniferyl aldehyde dehydrogenase (calB) genes from Pseudomonas sp. HR199. The recombinant strain converted eugenol to ferulic acid. The obtained data suggest that genetically engineered strains of I24 and PD630 are suitable candidates for vanillin production from eugenol.     

Effect of bioconversion conditions on vanillin production by Amycolatopsis sp. ATCC 39116 through an analysis of competing by-product formation

This study investigated the effects of transformation conditions such as initial pH, the initial concentration of glucose and yeast extract in the medium, and the separate addition of ferulic acid and vanillic acid, on the production of vanillin through an analysis of competing by-product formation by Amycolatopsis sp. ATCC 39116. The extent and nature of by-product formation and vanillin yield were affected by initial pH and different initial concentrations of glucose and yeast extract in the medium, with a high yield of vanillin and high cell density obtained at pH 8.0, 10 g/l glucose, and 8 g/l yeast extract. High concentrations of ferulic acid were found to negatively affect cell density. Additional supplementation of 100 mg/l vanillic acid, a metabolically linked by-product, was found to result in a high concentration of vanillin and guaiacol, an intermediate of vanillin. Via an analysis of the effect of these transformation conditions on competing by-product formation, high concentrations of ferulic acid were transformed with a molar yield to vanillin of 96.1 and 95.2 %, by Amycolatopsis sp. ATCC 39116 and Streptomyces V1, respectively, together with a minor accumulation of by-products. These are among the highest performance values reported in the literature to date for Streptomyces in batch cultures.