An efficient preparation and biocatalytic synthesis of novel C-glycosylflavonols kaempferol 8-C-glucoside and quercetin 8-C-glucoside by metabolic engineering of Escherichia coli

Abstract

Abstract BackgroundC-glycosylated flavonoids are a main type of structural modification and can endow flavonoids with greater stability, bioactivity, and bioavailability. Although some C-glycosylated flavonoids such as the C-glycosylflavones (vitexin, orientin, isovitexin, and isoorientin), the C-glycosyldihydrochalcone (nothofagin), and the C-glycosylchromone (aloesin) have been biosynthesized in vivo or vitro, only a few C-glycosylflavonols have been prepared by these methods.ResultsIn this study, several UDP-glucose biosynthesis pathways and Escherichia coli hosts were screened to reconstruct recombinant strains for producing the novel C-glycosylflavonols kaempferol 8-C-glucoside and quercetin 8-C-glucoside. To increase C-glycosylflavonol production, the timing of flavonol addition was adjusted, and glycerol was added to avoid degradation of C-glycosylflavonols. By using resting cell bioconversion, the highest kaempferol 8-C-glucoside and quercetin 8-C-glucoside production reached 16.6 g/L and 12.5 g/L, respectively. Then, ultrasound-assisted adsorption/desorption was used to prepare C-glycosylflavonols by using macroporous resins. Through screening macroporous resins and optimizing the adsorption/desorption conditions, the highest adsorption capacity and desorption capacity for kaempferol 8-C-glucoside on HPD100 reached 28.56 mg/g and 24.15 mg/g, respectively. Finally, kaempferol 8-C-glucoside (15.4 g) with a yield of 93% and quercetin 8-C-glucoside (11.3 g) with a yield of 91% were obtained from 1 L of fermentation broth.ConclusionsKaempferol 8-C-glucoside and quercetin 8-C-glucoside are novel C-glycosylflavonols, which have not been extracted from plants. This study provides an efficient method for the preparation and biocatalytic synthesis of kaempferol 8-C-glucoside and quercetin 8-C-glucoside by metabolic engineering of Escherichia coli.