Enhancing heterotrophic lutein production in Chlorella protothecoides through combined phytohormone and nitrogen strategies

Abstract

Large-scale production of microalgal lutein faces challenges due to limited biomass and lutein content. In this work, we developed an exponential fed-batch model to achieve heterotrophic high-density growth of Chlorella protothecoides CS-41. Then, indole-3-acetic acid (IAA) and high nitrogen were combined to promote lutein accumulation in situ. Fed-batch culture enhanced the TCA cycle of C. protothecoides CS-41 to benefit cell growth while increasing carotenoid flux to facilitate lutein accumulation through redirecting carbon flux towards lutein biosynthesis, improved by IAA. Also, high nitrogen increased lutein content through modulation of CMS (carotenoid methyltransferase synthase), CRTISO (carotenoid isomerase), LCYB (lycopene β-cyclase), ZEP (zeaxanthin epoxidase), and VDE (violaxanthin de-epoxidase). Finally, under heterotrophic conditions, combining 200 mM IAA with 3.6 g/L urea improved pyruvate and 3-phosphoglyceric acid and then boosted lutein content and productivity to 3.27 mg/g and 20.38 mg/L/d, respectively, by increases of 58 % and 56.7 %. Addressing issues including density dilution, container transfer, and in-situ lutein accumulation under heterotrophic high-density conditions offers a cost-effective solution.