Background; Glucosylation is a well-known approach to improve the solubility, pharmacological and biological properties of flavonoids. In recent years, efforts such as enzymatic synthesis have been developed to enhance the production of flavonoid glucosides. However, the low yield of products coupled with the requirement of expensive UDP-sugars limits the application of these systems for large-scale synthesis for human needs. C. glutamicum is a Gram-positive and generally regarded as safe (GRAS) bacteria frequently employed for the large-scale production of amino acids and bio-fuels. Due to the versatility of its cell factory system and its non-endotoxin producing properties, it has become an attractive system for the industrial-scale biosynthesis of alternate products. Here, we explored the cell factory of C. glutamicum for efficient glucosylation of flavonoids using apigenin as a model flavonoid. Results; For the production of apigenin glucosides, a promiscuous glycosyltransferase, YdhE from Bacillus licheniformis was successfully expressed in C. glutamicum. Additionally, the endogenous C. glutamicum genes galU1 encoding UDP-glucose pyrophosphorylase and pgm encoding phosphoglucomutase genes involved in the synthesis of UDP-glucose were overexpressed to create a C. glutamicum cell factory system capable of efficiently glucosylating apigenin with a high yield of glucosides in a comparatively short time. Consequently, the production of various apigenin glucosides was controlled under different temperatures yielding almost 4.2 mM of APG1(apigenin 4’-O-β-glucoside), 0.6 mM of APG2 (apigenin-7-O-β-glucoside), 1.7 mM of APG3 (apigenin 4’,7-O-β-diglucoside) and 2.1 mM of APG4 (apigenin 4’,5-O-β-diglucoside) after 40 h of incubation with the supplementation of 5 mM of apigenin. Conclusion; The developed C. glutamicum cell factory system highly glucosylated apigenin with higher efficiency and the high substrate susceptibility of C. glutamicum makes it the best alternative for large-scale biosynthesis of flavonoid glucosides. The developed system could be used to modify a wide range of plant secondary metabolites with increased pharmacokinetic activities on a large scale without the use of expensive UDP-sugars, thus making a cost-effective system.

Corynebacterium glutamicum has been regarded as a food-grade microorganism. In recent years, the research to improve the activities of beneficial therapeutics and pharmaceutical substances has resulted in the engineering of the therapeutically favorable cell factory system of C. glutamicum. In this study, we successfully glucosylated isoeugenol and other monoterpene derivatives in C. glutamicum using a promiscuous YdhE, which is a glycosyltransferase from Bacillus lichenformis. For efficient glucosylation, cultivation conditions such as the production time, substrate concentration, carbon source, and culture medium were optimized. Our system successfully converted about 93% of the isoeugenol to glucosylated compounds in the culture. The glucoside compounds were then purified, analyzed, and identified as isoeugenol-1-O-β-d-glucoside and isoeugenol-1-O-β-d-(2″-acetyl)-glucoside.