Expression of Synthetic Phytoene Synthase Gene to Enhance β-Carotene Production in Scenedesmus sp. CPC2.

β-carotene is a valuable pigment abundant in some microalgal species but the low β-carotene productivity of microalgae has become the major obstacles against its commercialization. This work aims to improve the productivity of algae-based β-carotene via genetic engineering approaches. First, a synthetic psy gene construct (891 bp) encoding 297 amino acids is expressed in Scenedesmus sp. CPC2 host to enhance the β-carotene production. The synthetic psy gene is designed by considering the highest consensus of amino acids (i.e., 62% identity) from Chlamydomonas reinhardtii, Dunaliella salina, and Mariella zofingiensis. The original β-carotene content in wild-type Scenedesmus sp. CPC2 is 10.8 mg g-1 -cell when grown on BG11 medium under 2% CO2 aeration, 150 μmol m-2  s-1 light intensity and 25°C. After transformation of the psy gene into the microalgal host, the β-carotene content of the best recombinant strain (i.e., transformant CPC2-4) significantly increased to over 30 mg g-1 -cell. The optimal production of β-carotene with the CPC2-4 recombinant strain was achieved when the strain is grown on BG11 medium amended with 0.075 g of MgSO4 , giving approximately 3-fold higher β-carotene content than that of the wild-type strain. The best cellular β-carotene content obtained (i.e., 31.8 mg g-1 ) is superior to most algae-based β-carotene production performance reported in the literature.