Abstract
Background4-Hydroxymandelic acid (4-HMA) is a valuable aromatic fine chemical and widely used for production of pharmaceuticals and food additives. 4-HMA is conventionally synthesized by chemical condensation of glyoxylic acid with excessive phenol, and the process is environmentally unfriendly. Microbial cell factory would be an attractive approach for 4-HMA production from renewable and sustainable resources.ResultsIn this study, a biosynthetic pathway for 4-HMA production was constructed by heterologously expressing the fully synthetic 4-hydroxymandelic acid synthase (shmaS) in our l-tyrosine-overproducing Escherichia coli BKT5. The expression level of shmaS was optimized to improve 4-HMA production by fine tuning of four promoters of different strength combined with three plasmids of different copy number. Furthermore, two genes aspC and tyrB in the competitive pathway were deleted to block the formation of byproduct to enhance 4-HMA biosynthesis. The final engineered E. coli strain HMA15 utilized glucose and xylose simultaneously and produced 15.8 g/L of 4-HMA by fed-batch fermentation in 60 h.ConclusionsMetabolically engineered E. coli strain for 4-HMA production was designed and constructed, and efficiently co-fermented glucose and xylose, the major components in the hydrolysate mixture of agricultural biomass. Our research provided a promising biomanufacturing route to produce 4-HMA from lignocellulosic biomass.Electronic supplementary materialThe online version of this article (doi:10.1186/s12934-016-0489-4) contains supplementary material, which is available to authorized users.
Highlights
hydroxymandelate synthase (HmaS) can catalyze the conversion of 4-HPP and phenylpyruvate to 4-Hydroxymandelic acid (4-HMA) and mandelate, respectively, and the biosynthetic pathways for production of D-/L-phenylglycine, and S-/R-mandelic acid from phenylpyruvate were constructed in E. coli [18,19,20]
Native hmaS sequence of A. orientalis is characterized with high GC content and not suitable to express in E. coli
Biosynthesis of 4-HMA was achieved through heterologous expression of fully synthetic synthetic 4-hydroxymandelic acid synthase (shmaS) gene in E. coli
Summary
A biosynthetic pathway for 4-HMA production was constructed by heterologously expressing the fully synthetic 4-hydroxymandelic acid synthase (shmaS) in our l-tyrosine-overproducing Escherichia coli BKT5. The expression level of shmaS was optimized to improve 4-HMA production by fine tuning of four promoters of differ‐ ent strength combined with three plasmids of different copy number. Two genes aspC and tyrB in the competitive pathway were deleted to block the formation of byproduct to enhance 4-HMA biosynthesis. The final engineered E. coli strain HMA15 utilized glucose and xylose simultaneously and produced 15.8 g/L of 4-HMA by fedbatch fermentation in 60 h
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