Microbial upcycling of agricultural cabbage waste into novel dietary carotenoid, phytoene: Advancing circular economy from waste to natural products

Growing concerns over food shortages and climate-related environmental issues have increased interest in technologies that recycle renewable resources and add value to byproducts. Here, we report microbial upcycling of agricultural cabbage waste (ACW) into phytoene, a novel dietary carotenoid through rational metabolic engineering. To make the base strain, the ability to produce phytoene was initially tested in various E. coli strains harboring the crtB and crtE genes that are essential for phytoene synthesis. Next, the mevalonate biosynthetic pathway gene cluster was introduced to further increase carbon flux toward phytoene production. Finally, the gene cluster for poly(3-hydroxybutyrate) [P3HB] biosynthesis was further introduced into the phytoene-producing strain to increase phytoene storage capacity and enhance photostability of phytoene. The final engineered strain PHY4 produced 9.51 mg/L (5.6 mg/g DCW) of phytoene, with a productivity of 0.4 mg/L/h from 1% ACW hydrolysates, resulting in approximately a 22.1-fold increase in phytoene titer compared to the base strain PHY1 (0.43 ± 0.06 mg/L) from 10 g/L of glucose. Moreover, the PHY4 strain exhibited a three-fold improvement in photostability for phytoene. The strategies reported here will be useful for the microbial upcycling of various waste resources into high-valued natural products.