Enhanced Lutein Production in Chlamydomonas reinhardtii by Overexpression of the Lycopene Epsilon Cyclase Gene

Chlamydomonas reinhardtii is a well-established microalgal model species with a shorter doubling time, which is a promising natural source for the efficient production of high-value carotenoids. In the microalgal carotenoid biosynthetic pathway, lycopene is converted either into β-carotene by lycopene β-cyclase or into α-carotene by lycopene ε-cyclase (LCYE) and lycopene β-cyclase. In this study, we overexpressed the LCYE gene in C. reinhardtii to estimate its effect on lycopene metabolism and lutein production. Chlamydomonas transformants (CrLCYE#L1, #L5, and #L6) produced significantly increased amounts of lutein per culture (up to 2.6-fold) without a decrease in cell yields. Likewise, the expression levels of LCYE gene in transformants showed a significant increase compared with that of the wild-type strain. These results suggest that LCYE overexpression enhances the conversion of lycopene to α-carotene, which in turn improves lutein productivity. Interestingly, their β-carotene productivity appeared to increase slightly rather than decrease. Considering that the inhibition of the lycopene cyclization steps often induces higher expression in genes upstream of metabolic branches, this result implies that the redirection from β-carotene to α-carotene by LCYE overexpression might also enhance upstream gene expression, thereby leading to auxiliary β-carotene production.