Multi-fold enhancement in vitamin E (alpha-tocopherol) production via integration of bioprocess optimisation and metabolic engineering in cell suspension of sunflower

Abstract

Alpha-tocopherol, a highly active form of the antioxidant vitamin E in humans, effectively scavenges free radicals and protects the cell membranes. The aim of our study was to enhance alpha-tocopherol production in sunflower cell suspension using elicitation, precursor addition and culture condition optimization. Among various elicitors and precursors studied, sodium chloride (50 mg/L) added as elicitor and phytol (50 mg/L) added as the precursor to an untransformed sunflower cell suspension, resulted in maximum productivity enhancement of alpha-tocopherol up to 2.3- and 1.9-fold, respectively compared to a control untransformed sunflower cell suspension (0.02 mg/L/d). In separate experiments, the volumetric productivity of alpha-tocopherol in the untransformed suspension was enhanced up to 2.1- fold (0.09 mg/L/d) under optimized conditions of light intensity (3500 lx), temperature (30 °C), initial pH (6.5) and inoculum size (6 g/L). We then extrapolated these strategies (elicitor and precursor addition, culture condition optimization) for implementation on a high alpha-tocopherol yielding metabolically engineered cell suspension overexpressing 4-hydroxyphenylpyruvate dioxygenase (TS4), which resulted in enhancement (1.9-, 1.45- and 2.72-fold respectively) in the volumetric productivity of alpha-tocopherol compared to the transformed cell suspension grown under control conditions (0.18 mg/L/d). Thus, integration of bioprocess optimization and metabolic engineering resulted in a multi-fold (up to 12-fold) enhancement in alpha-tocopherol productivity in comparison to the untransformed cells. Therefore, our study demonstrates that productivity enhancement strategies like bioprocess optimisation and metabolic engineering (developed separately in parallel) for a given system can be combined to achieve maximum productivity in lesser time and cost than a relay system of optimization in long-duration plant cell cultivations.