Enhanced Production of Astaxanthin without Decrease of DHA Content in Aurantiochytrium limacinum by Overexpressing Multifunctional Carotenoid Synthase Gene

Aurantiochytrium limacinum produces both docosahexaenoic acid (DHA) and astaxanthin, respectively. Organisms that produce these industrially important materials more efficiently than microalgae are currently needed. In this study, we overexpressed a putative homolog of CarS , which is involved in synthesizing the astaxanthin precursor, β-carotene, in A. limacinum to increase carotenoid synthesis with the goal of obtaining strains that produce large amounts of both DHA and carotenoids. AlCarS transformants #1 and #18 produced significantly increased amounts of astaxanthin as assessed according to culture (up to 5.8-fold) and optical density (up to 9.3-fold). The improved astaxanthin production of these strains did not affect their DHA productivity. Additionally, their CarS expression levels were higher than those of the wild-type strain, suggesting that CarS overexpression enhanced β-carotene production, which in turn improved astaxanthin productivity. Although cell yields were slightly decreased, these features will be valuable in health food, medical care, and animal feed fields.