Three novel enzyme cascades were engineered for the rapid biosynthesis of phenolic glycosides and their derivatives from biomass-derived p-coumaric acid and ferulic acid.

4-Hydroxyphenylacetic, homovanillic, and 3,4-dihydroxyphenylacetic acids are phenolic acids with various attractive bioactivities, such as antioxidative, anti-inflammatory, and antiobesity effects. However, powerful strategies for the efficient and sustainable synthesis of hydroxyphenylacetic acids are lacking. In this work, to promote the synthesis of hydroxyphenylacetic acids, we first engineered an Escherichia coli BL21 (DE3)-reduced aromatic aldehyde reduction strain to accumulate their aromatic aldehyde precursors. Then, we developed a one-pot bioconversion strategy using lignin-related p-coumaric and ferulic acids as starting materials for the abovementioned synthesis. The bioconversions comprise two artificial routes: decarboxylation-epoxidationisomerization-oxidation for the synthesis of 4-hydroxyphenylacetic and homovanillic acids and decarboxylation-epoxidationisomerization-oxidation-hydroxylation for the synthesis of 3,4-dihydroxyphenylacetic acid. This enabled efficient biosynthesis of 4hydroxyphenylacetic acid (13.7 mM, 91.3% yield, 1041 mg/L/h productivity), homovanillic acid (3.8 mM, 76.2% yield, 115.6 mg/ L/h productivity), and 3,4-dihydroxyphenylacetic acid (13.5 mM, 90% yield, 907 mg/L/h productivity). Moreover, we made an example to investigate the synthesis of hydroxyphenylacetic acids from the lignocellulosic biomass hydrolysate, in which 5.2 mM 4hydroxyphenylacetic acid in 57.8% conversion and 2.2 mM 3,4-dihydroxyphenylacetic acid in 55% conversion were produced from 9 and 4 mM p-coumaric acid, respectively. This study provides not only a new strategy to enable the efficient and sustainable synthesis of hydroxyphenylacetic acids but also new insights into the utilization of lignocellulosic biomass in the synthesis of high-value compounds.

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The present study has been conducted towards isolation of bacteria capable of producing heliotropin via microbial conversion. Strain ZMT-1 capable of synthesizing heliotropin efficiently was obtained by enrichment culture of soil samples and a high-throughput screening method, and identified as Serratia liquefaciens. Heliotropin was identified by gas chromatography and gas chromatography-mass spectrometry analysis. In addition, the culture medium was optimized to improve heliotropin yield by experimental designs. The application of a Plackett-Burman design found that NHNO and KHPO•3HO have significant effects on heliotropin production. Central composite design experiments were further used to predict the optimal concentrations of NHNO and KHPO•3HO, which were 1.0 and 0.5 g/l, respectively. After the optimization of cultural medium, heliotropin yield was increased by 4.52-fold when compared with the unoptimized minimal medium. This study is the first to report the biosynthesis of heliotropin by S. liquefaciens. S. liquefaciens ZMT-1 can produce heliotropin efficiently, indicating its potential as one heliotropin-producing strain.

Benzylisoquinoline alkaloids (BIAs) are an important family of plant-derived metabolites with diverse biological activities. Owing to their structural complexity and high stereoselectivity, the efficient synthesis of BIAs is challenging. The...