Metabolic engineering of Escherichia coli for production of 2

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Biotechnology and Biological Transformations

Metabolic engineering of Escherichia coli for production of 2-phenylethanol and 2-phenylethylacetate from glucose Daoyi Guo, Lihua Zhang, Sijia Kong, Zhijie Liu, Xun Li, and Hong Pan J. Agric. Food Chem., Just Accepted Manuscript • DOI: 10.1021/acs.jafc.8b01594 • Publication Date (Web): 29 May 2018 Downloaded from http://pubs.acs.org on May 29, 2018

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Metabolic engineering of Escherichia coli for production of 2-phenylethanol and

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2-phenylethylacetate from glucose

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Daoyi Guo*§, Lihua Zhang§, Sijia Kong§, Zhijie Liu #, Xun Li§, Hong Pan*§

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Corresponding author: Tel: +86-797-8393536; E-mail address: [email protected]

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and [email protected]

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§

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Normal University, Ganzhou 341000, China

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#

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Laboratory of Industrial Microbiology, Hubei Collaborative Innovation Center for

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Key Laboratory of Organo-Pharmaceutical Chemistry, Jiangxi Province, Gannan

Key Laboratory of Fermentation Engineering (Ministry of Education), Hubei Key

Industrial Fermentation, Hubei University of Technology, Wuhan 430068, China

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ABSTRACT

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The rose-like odor 2-phenylethanol (2-PE) and its more fruit-like ester

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2-phenylethylacetate (2-PEAc) are two important aromatic compounds and have wide

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applications. In the past, 2-PE and 2-PEAc were mainly produced from

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L-phenylalanine. In this study, the Escherichia coli was engineered to de novo

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biosynthesis of 2-PE and 2-PEAc from glucose. Firstly, overexpression of deregulated

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3-deoxy-D-arabinoheptulosonate-7-phosphate

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mutase/prephenate dehydratase pheAfbr for increasing phenylpyruvate production in E.

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coli. Subsequently, heterologous expression of decarboxylase kdc and overexpression

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of reductase yjgB for the conversion of phenylpyruvate to 2-PE. The engineered strain

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DG01 produced 578 mg/L of 2-PE. Finally, heterologous expression of an

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aminotransferase aro8 to redirect the metabolic flux to phenylpyruvate. 1016 mg/L of

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2-PE was accumulated in the engineered strain DG02. Alcohol acetyltransferase ATF1

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from S. cerevisiae can esterify a wide variety of alcohols including 2-PE. We have

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further demonstrated the biosynthesis of 2-PEAc from glucose by overexpressing atf1

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for the subsequent conversion of 2-PE to 2-PEAc. The engineered strain DG03

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produced 687 mg/L 2-PEAc.

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Keywords:

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2-phenylethylacetate.

metabolic

engineering;

synthase

Escherichia

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aroGfbr

coli;

and

chorismate

2-phenylethanol;

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INTRODUCTION

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The rose-like odor 2-phenylethanol (2-PE) and its more fruit-like ester

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2-phenylethylacetate (2-PEAc) are high-value flavor and fragrance compounds, and

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have a wide range of applications in the cosmetics, perfumery, and food industries.

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Although the production of 2-PE and 2-PEAc by chemical synthesis has advantages in

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cost, consumers prefer more natural or bio products in the area of flavor 1. However,

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such natural extracts of aroma compounds obtained from plant sources by physical

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processes are costly on account of low extraction yields 2, 3. In the past decades, great

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efforts have been made in the biosynthesis of 2-PE and 2-PEAc from L-phenylalanine

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4-6

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maximum titer of 2-PE and/or 2-PEAc. However, in order to achieve economic

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production of 2-PE and/or 2-PEAc, cheaper carbon substrate other than

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L-phenylalanine should be used. In recent years, construction of microbial cell

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factories that are able to produce value-added products directly from renewable

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carbon sources has made significant progress 7-10. Thus, the engineering of the diverse

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microbial pathways to biogenerate large quantities of aroma compounds presents an

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attractive alternative to extractions from plant sources.

. In those studies, L-phenylalanine is used as a starting substrate to reach the

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In this study, two de novo biosynthetic pathways for the production of 2-PE and

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2-PEAc were constructed in Escherichia coli (Figure 1). This study described here

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shows the way for the development of an economical process for biosynthesis of 2-PE

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and 2-PEAc directly from glucose.

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MATERIALS AND METHODS

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Enzymes, chemicals, and strains

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Benzyl alcohol and phenethyl propionate were purchased from Sigma-Aldrich

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(Steinheim, Germany). Restriction endonucleases and DNA polymerases were

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purchased from NEB (New England Biolabs). T4 DNA ligase, plasmid extraction kits,

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PCR purification kits and DNA extraction kits were purchased from Fermentas

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(Burlington, Canada). E. coli DH5α and E. coli BL21 (DE3) were purchased from

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TaKaRa (Dalian, China). The E. coli DH-5α was used for plasmid construction and

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screening. E. coli BL21 (DE3) was used as a host for fermentation to synthesize 2-PE

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and 2-PEAc. All other chemical reagents were analytically pure and purchased from

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Sinopharm Chemical Reagent Co., Ltd ( Shanghai, China).

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Plasmid construction

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All the primers used in this study are listed in Table 1. The strains and plasmids

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used in this study are listed in Table 2. AroGfbr (D146N, GenBank WP_001109196.1)

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was synthesized by Genewiz Biotech Co. Ltd and amplified by PCR using primers

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aroGfbr-XbaI and aroGfbr-SpeI-BamHI, and ligated into pET28a(+) via XbaI and

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BamHI to yield plasmid pDG11. PheAfbr (a truncated pheA, lacking the R-domain

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sequence for feedback inhibition by L-phenylalanine, GenBank NP_311489.1) was

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amplified by PCR from E. coli MG1655 genomic DNA using primers pheAfbr-XbaI

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and pheAfbr-SpeI-SalI, and ligated into pET28a(+) via XbaI and SalI to give pDG12.

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The XbaI-SalI fragments of pheAfbr from pDG12 was inserted into SpeI and SalI sites

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of pDG11 to give pDG13. The XbaI-SalI fragments of aroGfbr and pheAfbr from

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pDG13 was inserted into XbaI- and XhoI sites of pBBRMCS1 to give pDG14.

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Plasmid pPG34, which co-expression of decarboxylase kdc from Saccharomyces

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cerevisiae YPH499 and reductase yjgB from E. coli, was constructed in our previous

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study11. Aro8 gene from S. cerevisiae was amplified by PCR using the primer pair

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aro8-XbaI and aro8-NheI-BamHI, and ligated into pPG34 via NheI and XhoI to yield

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plasmid pDG15. Plasmid pPG37, which co-expression of kdc, yjgB, aro8 and atf1 was

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constructed in our previous study11.

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Shake flask cultures

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Overnight cultures (1 mL) of recombinant E. coli strains were transferred to 100

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mL modified M9 medium with 20 g/L glucose as previously described by Guo12 and

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shaken at 30°C. 36 mg/L chloromycetin and 50 mg/L kanamycin were added to the

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medium, when needed. When the OD600 reached about 0.6-0.8, IPTG was added to

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the medium for induction of gene expression at a final concentration of 0.1 mM.

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Samples were taken at regular intervals after induction and analyzed by GC/MS.

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Analytical methods

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Extraction and GC/MS analysis of 2-PE and 2-PEAc was carried out as previously

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described by Guo12. Glass beads were added to 10 mL culture broth for breaking the

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cells by vigorous shaking. 2-PE and 2-PEAc were extracted using ethyl acetate (15

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mL). After the centrifuge stratification, the upper ethyl acetate phase was withdrawn,

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evaporated to near dryness, and redissolved in 0.6 mL ethyl acetate. A 1 µL portion of

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the ethyl acetate phase was analysed after a split 10:1 injection on an Agilent 7890A

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GC equipped with an Agilent 5975 MS detector and an Agilent HP–5MS capillary

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column. The following temperature program was applied: 80°C for 1 min, an increase

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of 20°C/min to 250°C, and 250°C for 2 min. Benzyl alcohol and phenethyl propionate

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were used as internal standards for quantitative 2-PE and 2-PEAc, respectively.

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Results

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Developing a fermentation protocol for 2-PE production from glucose

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Phenylpyruvate is the precursor substrate for the biosynthesis of 2-PE. Recently,

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microbial 2-PE biosynthesis from L-phenylalanine was developed based on

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transamination of L-phenylalanine to phenylpyruvate by aminotransferase

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However, L-phenylalanine is an expensive precursor compared to glucose. To obtain

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2-PE from glucose, strains needs to have a strong capacity for phenylpyruvate

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synthesis. In this study, a biosynthetic pathway for 2-PE was established from glucose

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in E. coli. The overall pathway includes the upstream pathway from glucose to

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phenylpyruvate and the downstream pathway from phenylpyruvate to 2-PE.

13

.

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The phenylpyruvate can be de novo biosynthesized from glucose via

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L-phenylalanine pathway. However the efficiency is quite low because of feedback

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inhibition in L-phenylalanine pathway 14. Overexpression of feedback resistant mutant

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of

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bifunctional enzyme chorismate mutase/prephenate dehydratase (pheAfbr) is an

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essential strategy to overproduce phenylpyruvate. In this study, an artificial pathway

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was constructed for 2-PE biosynthesis in E. coli. This pathway comprised four gene

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products: feedback-resistant mutants of aroGfbr and pheAfbr for the efficient

3-deoxy-D-arabinoheptulosonate-7-phosphate

synthase

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(aroGfbr)

and

the

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overproduction of phenylpyruvate, 2-keto acid decarboxylase kdc for the conversion

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of phenylpyruvate to phenylacetaldehyde and aldehyde reductase yjgB for the

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conversion of phenylacetaldehyde to 2-PE. The resulting E. coli strain DG01 was

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cultured in a modified M9 medium in shake flasks and produced up to 578 ± 15.1

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mg/L 2-PE within 30 h (Table 3). 2-PE yield and productivity were calculated to be

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28.9 mg/g glycerol and 19.3 mg/L/h, respectively (Table 4). This proved that the

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synthetic pathway was functionally expressed in E. coli. Therefore, this strain could

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be used as a starting strain for further improvement of the production of 2-PE.

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Overexpression of aro8 gene to increase 2-PE production

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To further improve the production of 2-PE, inactivation of competing pathways

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or redirection of the byproducts to the desired intermediates is an effective strategy.

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Phenylpyruvate is precursor substrate for the biosynthesis of 2-PE. Therefore, we

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assumed that increasing phenylpyruvate availability would improve 2-PE production.

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Because phenylpyruvate can be converted to L-phenylalanine by aminotransferase

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tyrB catalysis, the knockout of tyrB gene may be able to promote 2-PE biosynthesis.

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However, a latest report showed that the knockout of tyrB gene caused the poor cell

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growth and eventually leaded to a dramatically decrease in 2-PE production. In this

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study, the heterologous overexpression of an aminotransferase aro8 that redirect

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phenylalanine to phenylpyruvate was used to improve the production of 2-PE. The

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resulting E. coli strain DG02 produced up to 1016 ± 52.9 mg/L 2-PE within 30 h

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(Table 3). 2-PE yield and productivity were calculated to be 50.8 mg/g glucose and

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33.9 mg/L/h, respectively (Table 4). This proves that overexpression of aro8 can

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effectively improve 2-PE production.

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Besides 2-PE, the significant formation of 2-PEAc, 4-hydroxyphenethyl alcohol,

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4-hydroxyphenethylacetate, 3-indolylethanol and 3-indolylacetate were also observed

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with this recombinant E. coli, as revealed by GC/MS analysis (Figure 2). We

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hypothesize that the precursor substrates for 4-hydroxyphenethyl alcohol and

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3-indolylethanol

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4-Hydroxyphenylpyruvic acid and tryptophan pathway intermediate indole-3-pyrucic

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acid, respectively. 4-Hydroxyphenylpyruvic acid and indole-3-pyrucic acid can be

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converted to 4-hydroxyphenylacetaldehyde and indole-3-acetaldehyde by 2-keto acid

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decarboxylase kdc. Then 4-hydroxyphenylacetaldehyde and indole-3-acetaldehyde

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were converted to 4-hydroxyphenethyl alcohol and 3-indolylethanol alcohol by

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aldehyde reductase yjgB. Finally, 4-hydroxyphenethyl alcohol and 3-indolylethanol

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alcohol were converted to 4-hydroxyphenethylacetate and 3-indolylacetate by an

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intrinsic alcohol acetyltransferase-like enzyme of E. coli15.

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Developing a fermentation protocol for 2-PEAc production from glucose

alcohol

are

from

tyrosine

pathway

intermediate

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Compared with 2-PE, 2-PEAc is a more fruit-like odor which is also widely used

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in fields of foods and cosmetics. In theory, 2-PEAc can be obtained from

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esterification of 2-PE in a 2-PE -producing microbe under catalysis of alcohol

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acyltransferase. Although our study shows that an alcohol acyltransferase-like enzyme

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exists in E. coli, the enzyme gene sequence has not been reported yet. Several studies

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showed that alcohol acetyltransferase ATF1 from S. cerevisiae can esterify a wide

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variety of alcohols including 2-PE

16, 17

. In this study, a fermentative route for

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biosynthesis of 2-PEAc was created by further heterologous expression of atf1 for the

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conversion of 2-PE to 2-PEAc in the 2-PE-producing strain. The resulting E. coli

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strain DG03 produced up to 687 ± 62.7 mg/L 2-PEAc within 30 h (Table 3). 2-PEAc

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yield and productivity were calculated to be 34.36 mg/g glucose and 22.9 mg/L/h,

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respectively (Table 4). This proves that ATF1 has a high catalytic activity.

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DISCUSSION

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The rose-like odor 2-PE and its more fruit-like ester 2-PEAc are two important

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perfumery compounds. Great efforts have been made on engineered E. coli or yeast

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for the biosynthesis of 2-PE and 2-PEAc from L-phenylalanine

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engineered S. cerevisiae for the production of 2-PE from L-phenylalanine and 4.8 g/L

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2-PE was produced in a medium containing 10 g/L L-phenylalanine after 195 h 4.

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Hwang et al. engineered E. coli for the whole-cell bioconversion of L-phenylalanine

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and 4.7 g/L 2-PE was produced in a medium containing 100 mM L-phenylalanine 22.

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A cofactor self-sufficient system was developed for enhanced production of 2-PE in E.

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coli 23. 2.2 g/L 2-PE and 1.3 g/L 2-PEAc was produced from 9 g/L L-phenylalanine in

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Kluyveromyces marxianus CBS 600 by the use of in situ product removal (ISPR)

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technique

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used to reduce the cost of production of 2-PE and 2-PEAc. A pathway was

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constructed for the biosynthesis of 2-PE from glucose in E. coli. This pathway

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comprised four gene products: a tyrosine-sensitive DAHP synthase aroF and pheAfbr

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from E. coli, phenylpyruvate decarboxylase kdc from Pichia pastoris GS115 and

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alcohol dehydrogenase adh1 from S. cerevisiae S288c25. However, the titer and yield

18-21

. Kim et al.

24

. However, compared with L-phenylalanine, cheaper substrate should be

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of 2-PE (0.285 g/L and 14.3 mg/g) produced from 20 g/L glucose by this engineered

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E. coli is low. Thus, screening of more active candidate enzymes (such as high

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activity phenylpyruvate decarboxylase) and replacement of wild-type aroF to a

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feedback resistant mutant of DAHP synthase in the future is a promising strategy for

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enhancing 2-PE production. A engineered Kluyveromyces marxianus strain produced

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up to 1.3 g/L of 2-PE from 20 g/L glucose after 72 h cultivation by overexpressing a

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feedback resistant DAHP synthase aroGfbr from Klebsiella pneumonia 26. Because this

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strain requires a long fermentation process for production of 2-PE, the productivity

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(18.1 mg/L/h) is relatively low.

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Compared with yeast, E. coli has a faster growth rate. Here, we attempted to

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engineer E. coli for biosynthesis of 2-PE from glucose. The overall pathway includes

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the upstream pathway from glucose to phenylpyruvate and the downstream pathway

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from phenylpyruvate to 2-PE. The precursor substrate phenylpyruvate can be de novo

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synthesized from glucose via L-phenylalanine pathway. Among the L-phenylalanine

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pathway, the enzyme DAHP synthase and the bifunctional enzyme chorismate

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mutase/prephenate dehydratase PheA are the two key rate-limiting steps toward the

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synthesis of phenylpyruvate27-29. E. coli has three DAHP synthase isoenzymes which

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are encoded by aroF, aroG and aroH. Because AroG contributes most of the overall

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DAHPS activity (about 80%), it is often used as the major candidate enzyme for

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biosynthesis of aromatic amino acids

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variants aroGfbr and pheAfbr have been identified, most of them are thermally unstable

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30, 32-34

30, 31

. Although many feedback resistant (fbr)

. The fermentation performances of six aroGfbr mutants were compared and it is

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found that aroGfbr (D146N) with a good thermostability is the best mutant for

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L-phenylalanine accumulation35. A truncated PheA (lacking the R-domain sequence

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for feedback inhibition by L-phenylalanine) could retain the native catalytic activities

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and thermostability, but release the L-phenylalanine feedback inhibition

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study, the aroGfbr (D146N) and the truncated pheA mentioned above were chosen and

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overexpressed to increase the formation of phenylpyruvate from glucose. Our group

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has reported that the 2-keto acid decarboxylase KDC from S. cerevisiae and aldehyde

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reductase YjgB from E. coli can efficiently convert phenylpyruvate to 2-PE (>82%)11.

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So, the two enzymes mentioned above were chosen to make up the downstream

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pathway from phenylpyruvate to 2-PE. The resulting E. coli strain DG01 produced up

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to 578 ± 15.1 mg/L 2-PE.

35, 36

. In this

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The phenylpyruvate availability is limited due to the endogenous conversion of

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phenylpyruvate to L-phenylalanine by aminotransferase TyrB in E. coli. A previous

234

study showed that knockout of the tyrB gene will cause cell growth to be inhibited

235

and eventually leads to a dramatically decrease in 2-PE production

236

we

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aminotransferase aro8. The resulting E. coli strain DG02 produced up to 1016 ± 52.9

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mg/L 2-PE which is the highest titer reported for the de novo biosynthesis of 2-PE by

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metabolically engineered E. coli so far. Recently, Koma et al reported the biosynthesis

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of 2-PE from glucose through co-expression of aroGfbr, pheAfbr, ipdC and aldehyde

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reductase gen (adhC, yqhD, yjgB or yahK) 37. The titer of 2-PE is about 5.7-6.5 mM

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(695-793 mg/L). Finally, we have further demonstrated the biosynthesis of 2-PEAc

redirect

L-phenylalanine

to

phenylpyruvate

by

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25

. In this study,

overexpression

of

an

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from glucose by overexpressing atf1 for the subsequent conversion 2-PE to 2-PEAc.

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To our knowledge, this is the first report on the biosynthesis of 2-PEAc directly from

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a renewable carbon source. The resulting E. coli strain DG03 produced up to 687 ±

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62.7 mg/L 2-PEAc. Our group has reported that the biosynthesis of 2-PEAc from

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L-phenylalanine by engineered E. coli. We found that a large amount of 2-PE failed to

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be effectively converted to 2-PEAc. We hypothesize that the reason for the low

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conversion is the imbalance of the two precursor substrates, 2-PE and acetyl-CoA.

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2-PE is rapidly synthesized and secreted to the outside of the cell in a synthetic

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system using L-phenylalanine as a precursor substrate and thus could not be esterified

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in time to 2-PEAc.

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The aim of this research was to create a functional synthetic pathway in E. coli

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and develop the completely fermentative route for producing 2-PE and 2-PEAc from

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glucose. It has been demonstrated that 2-PE and 2-PEAc has inhibitory effects on cell

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growth of E. coli when their concentrations are higher than 1.0 g/L

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improvement of the yield of 2-PE and 2-PEAc by synthetic biology technology may

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be hindered by product toxicity. Several studies showed that in situ product removal

259

(ISPR) technique (such as two-phase culture system) can effectively overcome the

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limitation by product toxicity, which resulted in significant improvement of their yield

261

38-40

262

optimization (For example, removal of the product, optimization of culture medium,

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fermentation temperature and pH) will be needed to improve the production of 2-PE

264

and 2-PEAc.

25

. Further

. Thus, future efforts to further strain improvement and fermentative process

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Funding information

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This work was supported by National Natural Science Foundation of China

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(81460312).

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Compliance with ethical standards

269

Conflict of interest The authors declare that they have no competing interests.

270

Ethics approval

271

or animals performed by any of the authors.

272

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13. Etschmann, M. M. W.; Sell, D.; Schrader, J., Screening of yeasts for the production of the aroma compound 2-phenylethanol in a molasses-based medium. Biotechnology Letters 2003, 25, 531-536. 14. Gallardo, E.; De, D. S.; Zamora, R.; Derdelinckx, G.; Delvaux, F. R.; Hidalgo, F. J., Influence of lipids in the generation of phenylacetaldehyde in wort-related model systems. Journal of Agricultural & Food Chemistry 2008, 56, 3155-9. 15. Liu, W.; Xu, X.; Zhang, R.; Cheng, T.; Cao, Y.; Li, X.; Guo, J.; Liu, H.; Xian, M., EngineeringEscherichia colifor high-yield geraniol production with biotransformation of geranyl acetate to geraniol under fed-batch culture. Biotechnology for Biofuels 2016, 9, 58. 16. Guo, D. Y.; Pan, H.; Li, X., Metabolic engineering of Escherichia coli for production of biodiesel from fatty alcohols and acetyl-CoA. Applied Microbiology & Biotechnology 2015, 99, 7805-7812. 17. Rodriguez, G. M.; Tashiro, Y.; Atsumi, S., Expanding ester biosynthesis in Escherichia coli. Nature Chemical Biology 2014, 10, 259. 18. Hazelwood, L. A.; Daran, J. M.; van Maris, A. J.; Pronk, J. T.; Dickinson, J. R., The Ehrlich pathway for fusel alcohol production: a century of research on Saccharomyces cerevisiae metabolism. Applied & Environmental Microbiology 2008, 74, 2259-2266. 19. Eshkol, N.; Sendovski, M.; Bahalul, M.; Katzezov, T.; Kashi, Y.; Fishman, A., Production of 2-phenylethanol from L-phenylalanine by a stress tolerant Saccharomyces cerevisiae strain. Journal of Applied Microbiology 2009, 106, 534-42. 20. Morrissey, J. P.; Etschmann, M. M. W.; Schrader, J.; Billerbeck, G. M., Cell factory applications of the yeast Kluyveromyces marxianus for the biotechnological production of natural flavour and fragrance molecules. Yeast 2015, 32, 3-16. 21. Stark, D.; Münch, T.; Sonnleitner, B.; Marison, I. W.; Stockar, U. V., Extractive Bioconversion of 2-Phenylethanol from l -Phenylalanine by Saccharomyces cerevisiae. Biotechnol Prog 2002, 18, 514-523. 22. Hwang, J. Y.; Park, J.; Seo, J. H.; Cha, M.; Cho, B. K.; Kim, J.; Kim, B. G., Simultaneous synthesis of 2-phenylethanol and L-homophenylalanine using aromatic transaminase with yeast Ehrlich pathway. Biotechnology & Bioengineering 2009, 102, 1323-9. 23. Wang, P.; Yang, X.; Lin, B.; Huang, J.; Tao, Y., Cofactor self-sufficient whole-cell biocatalysts for the production of 2-phenylethanol. Metabolic Engineering 2017, 44, 143. 24. Etschmann, M. M.; Sell, D.; Schrader, J., Production of 2-phenylethanol and 2-phenylethylacetate from L-phenylalanine by coupling whole-cell biocatalysis with organophilic pervaporation. Biotechnology & Bioengineering 2005, 92, 624-34. 25. Kang, Z.; Zhang, C.; Du, G.; Chen, J., Metabolic Engineering of Escherichia coli for Production of 2-phenylethanol from Renewable Glucose. Applied Biochemistry & Biotechnology 2014, 172, 2012-21. 26. Kim, T. Y.; Lee, S. W.; Oh, M. K., Biosynthesis of 2-phenylethanol from glucose with genetically engineered Kluyveromyces marxianus. Enzyme & Microbial Technology 2014, 61-62, 44. 27. Báezviveros, J. L.; Osuna, J.; Hernándezchávez, G.; Soberón, X.; Bolívar, F.; Gosset, G., Metabolic engineering and protein directed evolution increase the yield of L-phenylalanine synthesized from glucose in Escherichia coli. Biotechnology & Bioengineering 2004, 87, 516-524. 28. Doroshenko, V. G.; Tsyrenzhapova, I. S.; Krylov, A. A.; Kiseleva, E. M.; Ermishev, V. Y.; Kazakova, S. M.; Biryukova, I. V.; Mashko, S. V., Pho regulon promoter-mediated transcription of the key pathway gene aroGFbr improves the performance of an L-phenylalanine-producing Escherichia coli strain. Applied Microbiology & Biotechnology 2010, 88, 1287. 29. Kikuchi, Y.; Tsujimoto, K.; Kurahashi, O., Mutational analysis of the feedback sites of

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phenylalanine-sensitive 3-deoxy-D-arabino-heptulosonate-7-phosphate synthase of Escherichia coli. Appl Environ Microbiol 1997, 63, 761-762. 30. Sprenger, G. A., From scratch to value: engineering Escherichia coli wild type cells to the production of l -phenylalanine and other fine chemicals derived from chorismate. Applied Microbiology & Biotechnology 2007, 75, 739-49. 31. Rodriguez, A.; Martínez, J. A.; Flores, N.; Escalante, A.; Gosset, G.; Bolivar, F., Engineering Escherichia coli to overproduce aromatic amino acids and derived compounds. Microbial Cell Factories 2014, 13, 126. 32. Chandran, S. S.; Yi, J.; Draths, K. M.; Von, D. R.; Weber, W.; Frost, J. W., Phosphoenolpyruvate availability and the biosynthesis of shikimic acid. Biotechnology Progress 2003, 19, 808. 33. Flores, N.; Xiao, J.; Berry, A.; Bolivar, F.; Valle, F., Pathway engineering for the production of aromatic compounds in Escherichia coli. Nature Biotechnology 1996, 14, 620. 34. Gerigk, M.; Bujnicki, R.; Ganpo‐Nkwenkwa, E.; Bongaerts, J.; Sprenger, G.; Takors, R., Process control for enhanced L-phenylalanine production using different recombinant Escherichia coli strains. Biotechnology & Bioengineering 2002, 80, 746. 35. Liu, S. P.; Xiao, M. R.; Zhang, L.; Xu, J.; Ding, Z. Y.; Gu, Z. H.; Shi, G. Y., Production of l -phenylalanine from glucose by metabolic engineering of wild type Escherichia coli W3110. Process Biochemistry 2013, 48, 413-419. 36. Zhang, S.; Pohnert, G.; Kongsaeree, P.; Wilson, D. B.; Clardy, J.; Ganem, B., Chorismate mutase-prephenate dehydratase from Escherichia coli. Study of catalytic and regulatory domains using genetically engineered proteins. Febs Journal 1998, 273, 6248. 37. Koma, D.; Yamanaka, H.; Moriyoshi, K.; Ohmoto, T.; Sakai, K., Production of aromatic compounds by metabolically engineered Escherichia coli with an expanded shikimate pathway. Applied & Environmental Microbiology 2012, 78, 6203-16. 38. Etschmann, M. M. W.; Schrader, J., An aqueous–organic two-phase bioprocess for efficient production of the natural aroma chemicals 2-phenylethanol and 2-phenylethylacetate with yeast. Applied Microbiology & Biotechnology 2006, 71, 440. 39. Gao, F.; Daugulis, A. J., Bioproduction of the aroma compound 2-phenylethanol in a solid-liquid two-phase partitioning bioreactor system by Kluyveromyces marxianus. Biotechnology & Bioengineering 2009, 104, 332-9. 40. Mei, J.; Min, H.; Lü, Z., Enhanced biotransformation of l -phenylalanine to 2-phenylethanol using an in situ product adsorption technique. Process Biochemistry 2009, 44, 886-890.

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Table 1. Primers used in this study

386

Primer name aroGfbr-XbaI

Sequence (5’-3’) GTATCTAGAAAGAGGAGATATAATGAATTATCAGAA CGACGATTTACGC

aroGfbr-SpeI-BamHI

TATGGATCCACTAGTTTACCCGCGACGCGCTTTTA

pheAfbr-XbaI

GTATCTAGAAAGAGGAGATATAATGACATCGGAAAA CCCGTTACTG

pheAfbr-SpeI-SalI

ATATGTCGACACTAGTTCACAACGTGGTTTTCGCCGG A

aro8-XbaI

AACTCTAGATTTAAGAAGGAGATATAATGATGACTT TACCTGAATCAAAAGACTTTTC

aro8-NheI-BamHI

ACAGGATCCGCTAGCCTATTTGGAAATACCAAATTCT TCGTATAA

387 388 389 390 391 392 393

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Table 2. Plasmids and strains used in this study

398

Plasmids/strains

Properties

Source/reference

pDG11

pET28a; pT7: aroGfbr

This study

pDG12

pET28a; pT7: pheAfbr

This study

pDG13

pET28a; pT7: aroGfbr and pheAfbr

This study

pDG14

pBBRMCS1; pT7: aroGfbr and pheAfbr

This study

pPG34

pET28a; pT7: kdc and yjgB

11

pDG15

pET28a; pT7: kdc, yjgB and aro8

This study

pPG37

pET28a; pT7: kdc, yjgB, aro8 and atf1

11

DG01

BL21/ pDG14/ pPG34

This study

DG02

BL21/ pDG14/ pDG15

This study

DG03

BL21/ pDG14/ pPG37

This study

Plasmids

Strains

399 400 401 402

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Table 3. 2-PE and 2-PEAc production in engineered E. coli strains. Data are the

407

mean values of three independent experiments ± SD. Strains

2-PE (mg/L)

2-PEAc (mg/L)

DG01

578 ± 15.1

188 ± 12.2

DG02

1016 ± 52.9

246 ± 47.8

DG03

46 ± 10.7

687 ± 62.7

408 409 410 411 412 413 414 415 416 417 418 419 420 421

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Table 4. The yield and productivity calculations in engineered E. coli strains in shake

427

flasks for 30 h. Yield calculated by milligrams 2-PE or 2-PEAc produced divided by

428

grams glucose consumed. Productivity calculated by concentration of 2-PE or 2-PEAc

429

produced per hour. Data are the mean values of three independent experiments ± SD. Strains

Yield (mg/g)

Productivity (mg/L/h)

DG01

28.9 ± 0.75

19.3 ± 0.50

DG02

50.8 ± 2.64

33.9 ± 1.76

DG03

34.36 ± 3.14

22.9 ± 2.09

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Figure legends:

444

Figure.1. Engineered pathways for production of 2-PE and 2-PEAc from glucose.

445

Figure.2. GC/MS analyses of 2-PE and 2-PEAc from engineered E. coli strains.

446

Identified substances: 1, benzyl alcohol (internal standard); 2, 2-PE; 3, 2-PEAc; 4,

447

phenethyl propionate (internal standard); 5, 4-hydroxyphenethyl alcohol; 6,

448

4-hydroxyphenethylacetate; 7, 3-indolylethanol; 8, 3-indolylacetate.

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466 467

Figure.1. Engineered pathways for production of 2-PE and 2-PEAc from glucose.

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478 479

Figure.2. GC/MS analyses of 2-PE and 2-PEAc from engineered E. coli strains.

480

Identified substances: 1, benzyl alcohol (internal standard); 2, 2-PE; 3, 2-PEAc; 4,

481

phenethyl propionate (internal standard); 5, 4-hydroxyphenethyl alcohol; 6,

482

4-hydroxyphenethylacetate; 7, 3-indolylethanol; 8, 3-indolylacetate.

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TOC graphic 224x186mm (300 x 300 DPI)

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