Enhancement of astaxanthin production in Schizochytrium limacinum B4D1 under ethanol induction

Schizochytrium limacinum is one of the most extensively studied marine algae for production of docosahexaenoic acid (DHA) which is a type of omega-3 fatty acid important for brain development and human health. This microorganism has shown significant potential for carotenoid production, i.e., astaxanthin. In this study, we have investigated the effects of different ethanol concentrations on the production of astaxanthin in S. limacinum B4D1. We have also characterized a series of physiological and biological properties (i.e., biomass, lipid content, and fatty acid composition) to explore the metabolic mechanisms of astaxanthin production in S. limacinum B4D1 induced by ethanol. Results have shown that high concentration of ethanol (≥3%) promotes the accumulation of astaxanthin and alters the proportion of fatty acids. In order to explore the molecular mechanisms causing these changes, we detected the expression levels of genes involved in astaxanthin synthesis pathway and competitive pathways using quantitative real-time PCR technology. Results showed that ethanol significantly enhanced transcriptional expression of five genes (HMGR, MK, GGPS, crtIBY, and crtZ) responsible for biosynthesis of astaxanthin and decreased expression of two genes (ACACA and FDFT1) involved in competitive pathways. We further evaluated the expression of three genes (SOD, CAT, and APX) inhibiting the production of reactive oxygen species (ROS). Results showed that the transcription levels of these three genes were significantly increased by ethanol with various concentrations. Our study has demonstrated that ethanol is an effective inducer to promote astaxanthin accumulation in S. limacinum B4D1.