Enhancement of beta-carotene content in Chlamydomonas reinhardtii by expressing bacterium-driven lycopene beta-cyclase

beta-Carotene is one of the economically important carotenoids, having functions as the antioxidant to remove harmful free radicals and as the precursor for vitamin A and other high-valued xanthophyll such as zeaxanthin and astaxanthin. Lycopene cyclase plays an important role in the branching of beta-carotene and alpha-carotene. Aiming to develop the microalgae with enhanced beta-carotene productivity, the CrtY gene from bacterium Pantoea agglomerans was integrated into Chlamydomonas reinhardtii. The lycopene-producing E. coli harboring CrtY gene produced 1.59 times of beta-carotene than that harboring DsLcyb1 from Dunaliella salina (a microalga with abundant beta-carotene), confirming the superior activity of CrtY on beta-carotene biosynthesis. According to the pigment analysis by HPLC, in microalgal transformants that were confirmed by molecular analysis, the expression of CrtY significantly increased beta-carotene content from 12.48 mg/g to 30.65 mg/g (dry weight), which is about 2.45-fold changes. It is noted that three out of five transformants have statistically significant higher amount of lutein, even though the increment was 20% in maximum. Besides, no growth defect was observed in the transformants. This is the first report of functional expression of prokaryotic gene in eukaryotic microalgae, which will widen the gene pool targeting carotenoids biosynthesis using microalgae as the factory and thereby provide more opportunity for high-valued products engineering in microalgae.