Production of Flavonoid 7-O-glucosides by Bioconversion Using Escherichia coli Expressing a 7-O-glucosyltransferase from Tobacco (Nicotiana tabacum).

Flavonoid 7-O-glucosides exhibit various biological activities; however, some are not abundant in nature. Therefore, a method to produce flavonoid 7-O-glucosides was investigated. Escherichia coli expressing tobacco-derived glucosyltransferase (Ec-NtGT2) converted several flavonoids (apigenin, luteolin, quercetin, kaempferol, and naringenin) to their 7-O-glucosides with conversion rates of 67-98%. In scaled-up production, Ec-NtGT2 yielded 24 mg/L of apigenin 7-O-glucoside, 41 mg/L of luteolin 7-O-glucoside, 118 mg/L of quercetin 7-O-glucoside, 40 mg/L of kaempferol 7-O-glucoside, and 75 mg/L of naringenin 7-O-glucoside through sequential administration of substrates in 4-9 h. The conversion rates of apigenin, luteolin, quercetin, kaempferol, and naringenin were 97%, 72%, 77%, 98%, and 96%, respectively. These results indicated that Ec-NtGT2 is a simple and efficient bioconversion system for the production of flavonoid 7-O-glucosides.

Production of flavonol and flavone 6-C-glucosides by bioconversion in Escherichia coli expressing a C-glucosyltransferase from wasabi (Eutrema japonicum).

OBJECTIVES: To produce flavonol and flavone 6-C-glucosides by bioconversion using recombinant Escherichia coli expressing a C-glucosyltransferase from wasabi (WjGT1). RESULTS: Escherichia coli expressing WjGT1 (Ec-WjGT1) converted flavones (apigenin and luteolin) and flavonols (quercetin and kaempferol) into their 6-C-glucosides in M9 minimal media supplemented with glucose, and released these products into the culture media. Ec-WjGT1 system also converts a flavanone (naringenin) into its C-glucoside at a conversion rate of 60% in 6 h. For scale-up production, apigenin, kaempferol, and quercetin were sequentially fed into the Ec-WjGT1 system at concentrations of 20-50 µM every 15-60 min, and the system was then able to produce isovitexin, kaempferol 6-C-glucoside, and quercetin 6-C-glucoside at an 89-99% conversion rate. CONCLUSIONS: The Ec-WjGT1 system quickly and easily produces flavone and flavonol 6-C-glucosides at high conversion rates when using sequential administration to avoid precipitation of substrates.

The roseoflavin producer Streptomyces davaonensis has a high catalytic capacity and specific genetic adaptations with regard to the biosynthesis of riboflavin.

The bacterium Streptomyces davaonensis synthesizes the antibiotic roseoflavin in the stationary phase of growth. The starting point for roseoflavin biosynthesis is riboflavin (vitamin B2 ) and four enzymes (RibCF, RosB, RosA and RosC) are necessary to convert a vitamin (riboflavin) into a potent, broad-spectrum antibiotic (roseoflavin). In S. davaonensis, seven enzymatic functions are required to synthesize the roseoflavin precursor riboflavin from the central building blocks GTP and ribulose 5-phosphate. When compared with other bacterial and in particular Streptomyces genomes the S. davaonensis genome contains an unusual high number (21) of putative riboflavin biosynthetic genes (rib genes), including a rib gene encoding an additional riboflavin synthase originating from an Archaeon. We show by complementation analyses and enzyme assays that 17 out of these 21 putative rib genes indeed encode for riboflavin biosynthetic enzymes. Biochemical analyses of selected enzymes support this finding. Transcriptome analyses show that all of the rib genes are expressed either in the exponential or in the stationary phase of growth and thus do not represent silent genes. We conclude that the Rib enzymes produced in the stationary phase represent a physiological adaptation to support roseoflavin biosynthesis.