Integrated Approach for Improving Lutein Production of Chlorella sp. via Adaptive Evolution and Casein Acid Hydrolysate.

Lutein is a high value-added product in microalgae. There are several strategies to improve its production, including isolation and selection of high-lutein producing algal strains; strain improvement by metabolic engineering, synthetic biology, or adaptive evolution; and metabolic regulation. In this study, an integrated approach was developed to improve lutein production by adaptive evolution and metabolic regulation. Firstly, a starting strain with a lutein content of ~5.18 mg/g was selected. Secondly, adaptive evolution was performed using an environmental stress of 300 mg/L phenol. The evolved strain, P30, was obtained after 30 cycles; its lutein content had increased to ~5.91 mg/g. Thirdly, the effects of 5-30 g/L NaCl on the lutein contents of the evolved strain were determined. We found that 10 g/L NaCl increased the lutein content by 11% and slightly inhibited growth. No significant changes were observed after adding 20-80 mg/L gibberellin under 10 g/L NaCl conditions. The addition of 10.5 mM casein acid hydrolysate (CAH) promoted the growth of the P30 strain under 10 g/L NaCl conditions. The lutein concentration of Chlorella sp. P30 was 6.91 mg/L at day 5, which was twice the lutein concentration of the starting strain at the same time. When osmotic pressure was removed, the lutein concentration was 8.42 mg/L. The results indicate that CAH supplementation enhances both microalgal growth and lutein biosynthesis. The results of this study provide a valuable reference for the metabolic regulation of lutein biosynthesis.