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Applied and Environmental Microbiology, August 2006, p. 5670-5672, Vol. 72, No. 8
0099-2240/06/$08.00+0 doi:10.1128/AEM.00609-06
Copyright © 2006, American Society for Microbiology. All Rights Reserved.
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Plant Research International, P.O. Box 16, 6700 AA Wageningen, The Netherlands
Received 15 March 2006/ Accepted 16 June 2006
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In plants, resveratrol is produced as a branch from the phenylpropanoid pathway (9). It is derived from p-coumaric acid, which is an intermediate in lignin production. By the action of 4-coumarate:coenzyme A (CoA) ligase (4CL) (EC 6.2.1.12), it is converted into coumaroyl-CoA. Coumaroyl-CoA and three units of malonyl-CoA are condensed into resveratrol by the action of stilbene synthase (STS) (EC 2.3.1.95) (Fig. 1).
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FIG. 1. Biosynthetic pathway of resveratrol. The biosynthesis of resveratrol starts by the coupling of p-coumaric acid to CoA by the 4CL enzyme. Subsequently, coumaroyl-CoA is converted into resveratrol by sequential addition of three malonyl-CoA units with the release of carbon dioxide.
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max of 305 nm and elution at 28.9 min in the culture medium (Fig. 2). Both absorption spectrum and retention time of this compound corresponded to those of a standard of resveratrol (Sigma). Further identification using mass spectrometry revealed that this compound had an m/z value of 227.07 [M-H], thus confirming the identity of the product as resveratrol (Fig. 2). The formation of resveratrol was followed by HPLC analysis of 5-ml samples during the growth of the culture (Fig. 3A). During logarithmic cell growth (up to 24 h), the amount of resveratrol increased to 12 to 20 mg/liter, while the p-coumaric acid concentration dropped to 0.2 mM after 20 h. During the subsequent stationary phase, both the concentration of resveratrol and that of p-coumaric acid decreased to undetectable levels.
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FIG. 2. HPLC analysis of resveratrol produced by E. coli at 307 nm. The upper chromatogram (A) was derived from an extract of a culture of E. coli BL21 plus pAC-4CL-STS grown with p-coumaric acid for 20 h. Culture medium was separated by an HPLC setup as described in reference 2, and absorbance was recorded at 307 nm. The lower chromatogram (B) shows the same for control E. coli BL21 plus pACYC-DUET1. The peak at 17 min represents p-coumaric acid, and the peak at 28.9 min represents resveratrol. The absorption spectrum of the peak at 28.9 min is shown in the "PDA" inset, while the mass spectrum, recorded with a QTOF ULTIMA mass spectrometer (negative electrospray ionization mode) is shown in the "MS" inset.
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FIG. 3. Production of resveratrol in E. coli (A) and S. cerevisiae (B) over time. Each graph displays the concentration of resveratrol in mg/liter in the culture medium as measured after extraction, the concentration of p-coumaric acid (p-CA) in g/liter, and the density of the culture (no absolute values indicated). The values shown are averages of two measurements of individual cultures.
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max = 273 nm) was found to occur during the later phases of growth. This compound was identified as hydroxyphenyl-propionic acid (Fig. 1) by comparison with reference standards and mass spectrometry ([M-H] = 165.0559 m/z). The concentration of this compound increased up to 3 mM. Its synthesis appeared to depend on the presence of the 4CL-STS expression construct, since this peak was absent in untransformed yeast cultures when incubated with p-coumaric acid.
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FIG. 4. Cassette for integration of STS and 4CL into the yeast genome. LEU21-546, LEU2 gene from nucleotides 1 to 546 of the coding region; Pi, promoter of the ILV2 gene; ILV2-SMR, sulfometuron methyl resistance gene; Ti, terminator of the ILV2 gene; Tc, terminator of the CYC gene; STS, coding region of the grape STS gene; PGAL1, promoter of the GAL1 gene; PGAL10, promoter of the GAL10 gene; 4CL, coding region of the 4CL2 gene from tobacco; Ta, terminator of the ADH1 gene; LEU2547-1060, LEU2 gene from nucleotides 547 to 1060 of the coding region; PacI, unique PacI restriction site.
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In the past few years, a number of results have been published on the production in microorganisms of plant-specific polyphenols, mainly naringenin, to different levels (0.45 mg/liter [3], 7 mg/liter [4], and 20 mg/liter [10]). During review of the manuscript, a report on the production of resveratrol in E. coli by use of a peanut STS gene appeared (11). Our data indicate that the recombinant yeast expression platform, using the same biosynthetic genes, is not much less efficient than E. coli. Thus, yeast is capable of producing high levels of resveratrol from inexpensive plant-derived precursors, contrary to previously published data (1). The advantage of yeast over E. coli is its food-grade status, which should, in principle, allow for applications in human nutrition. Interestingly, in both systems the desired product accumulated naturally in the medium rather than in the cells. This is particularly advantageous considering the envisaged commercial production system and its commercial viability. We conclude that economic resveratrol production is viable in a food-grade yeast.
The CEN.PK yeast strain was courtesy of Paul van Heusden, and the ILV2-SMR gene was courtesy of Brigitte Rønnow.
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