Resveratrol, an ingredient of traditional Chinese medicine, has beneficial effects on human health and huge potential for application in modern medicine. Polydatin is extracted from plants and then deglycosylated into resveratrol; enzymatic methods are preferred for this reaction. In this study, a β-D-glucosidase from Sphingomonas showed high efficiency in transforming polydatin into resveratrol and was tolerant toward organic solvents. Applying this enzyme in a biphasic transformation system resulted in 95.3% conversion of 20% concentration crude polydatin to resveratrol in 4 h. We thus report a new method for high-efficiency, clean production of resveratrol.

Acetoin is an important platform chemical with a variety of applications in foods, cosmetics, chemical synthesis, and especially in the asymmetric synthesis of optically active pharmaceuticals. It is also a useful breath biomarker for early lung cancer diagnosis. In order to enhance production of optical (S)-acetoin and facilitate this building block for a series of chiral pharmaceuticals derivatives, we have developed a systematic approach using in situ-NADH regeneration systems and promising diacetyl reductase. Under optimal conditions, we have obtained 52.9 g L⁻¹ of (S)-acetoin with an enantiomeric purity of 99.5% and a productivity of 6.2 g (L h)⁻¹. The results reported in this study demonstrated that the production of (S)-acetoin could be effectively improved through the engineering of cofactor regeneration with promising diacetyl reductase. The systematic approach developed in this study could also be applied to synthesize other optically active α-hydroxy ketones, which may provide valuable benefits for the study of drug development.

Steviol glycosides are natural sweeteners extracted from Stevia rebaudiana that have been applied in food for many years. However, the considerable content of stevioside and small amounts of rubusoside, rebaudioside B and rebaudioside C in Stevia extract lead to a significant bitter aftertaste. Rebaudioside A (RA) tastes sweet with no unpleasant aftertaste, so the taste of steviol glycosides can be improved by removing the steviol glycosides other than RA. Traditionally, macroporous resin adsorption, hydrophilic chromatography, and crystallization have been applied to separate RA from Stevia extract, which causes the use of large amounts of organic solvent. In this study, we co-expressed multiple β-glucosidases (SPBGL1, SBGL, SBGL2 and SBGL3) and an α-L-rhamnosidase (SPRHA2) in Escherichia coli and used cell extracts or whole cells, aiming to hydrolyze the components of Stevia extract other than RA. When crude enzyme extract of strain E5 or whole-cell catalysis by strain E5 was used in hydrolysis of Stevia extract, the content of RA increased from 24% to 71.4% and 83.4%, respectively. The final product of hydrolysis, steviol is sparingly soluble in water and can therefore be removed readily by centrifugation. This enzymatic technology allows RA preparation with no consumption of organic solvents, which provides a green way to improve the taste of Stevia extract.

Although β-xylosidases with xylanase activity are preferential for the hydrolysis of xylan and production of xylitol, reports on their use are scarce. In this study, a multifunctional β-xylosidase (XYL4) was identified. In addition to β-xylosidase activity, XYL4 also exhibited xylanase and low α-arabinosidase activity. The enzyme was able to hydrolyze bagasse xylan, oat spelt xylan, birchwood xylan, beechwood xylan, and corncob xylan, and showed the highest hydrolysis activity for corncob xylan. Structural modeling analysis indicated that XYL4 had an additional PA14 domain, which may play a key role in binding xylan substrates. Moreover, XYL4 was used to hydrolyze corncob xylan to produce xylose. When enzymatic hydrolysis and whole-cell catalysis were used to hydrolyze 100 g/L of corncob xylan, the xylose yields were 60.26% and 35.85%, respectively. Then, the Candida tropicalis was inoculated with the above hydrolysates for fermentation to produce xylitol. Using enzymatic hydrolysis and whole-cell catalysis, xylitol yields of 77.56% and 73.67% were obtained by C. tropicalis after the optimization of fermentation, respectively.

A convenient and effective sucrose transport assay for Clostridium strains is needed. Traditional methods, such as ¹⁴C-sucrose isotope labelling, use radioactive materials and are not convenient for many laboratories. Here, a sucrose transporter from potato was introduced into Clostridium, and a fluorescence assay based on esculin was used for the analysis of sucrose transport in Clostridium strains. This showed that the heterologously expressed potato sucrose transporter is functional in Clostridium. Recombinant engineering of high-level sucrose transport would aid sucrose fermentation in Clostridium strains. The assay described herein provides an important technological platform for studying sucrose transporter function following heterologous expression in Clostridium.