Engineering a novel biosynthetic pathway in Escherichia coli for the production of caffeine
Caffeine (Cf, 1,3,7-trimethylxanthine), a major secondary metabolite of many higher plants, is widely used in popular non-alcoholic beverages, and in the pharmaceutical and health industries. Currently, this valuable chemical is mainly manufactured by chemical synthesis. In this study, we developed a novel approach for de novo caffeine production in metabolically engineered Escherichia coli. Xanthine-to-caffeine conversion was first achieved by the expression of a plant-derived gene encoding tea caffeine synthase (TCS1). Caffeine accumulation was then increased using two metabolic strategies: higher-level expression of the target enzymes, and enhancement of xanthine and S-adenosyl-L-methionine biosynthesis. The final strain (BL21/pRSF-eCS1-SAM2-vgb-eGUD1) produced up to 21.46 ± 1.03 mg L−1 caffeine from 20 g L−1 of glucose in shake flask culture, yielding caffeine up to 2.96 mg g−1 glucose, which represents the highest titer of caffeine produced by fermentation reported to date. This novel microbial conversion also represents an innovative approach to produce value-added methylxanthine chemicals from cheap carbon sources.