Effects of Methanol on Carotenoids as Well as Biomass and Fatty Acid Biosynthesis in Schizochytrium limacinum B4D1

Schizochytrium is a promising source for the production of docosa-hexaenoic acid and astaxanthin. The effects of different methanol concentrations on astaxanthin, biomass, and production of the lipids, squalene, and total sterol in Schizochytrium limacinum B4D1 were investigated. Astaxanthin began to accumulate when the methanol concentration reached 3.2% and peaked at 5.6% methanol, with a 2,000-fold increase over that in the control. However, under cultivation with 5.6% methanol, the biomass, lipids, squalene, and total sterol decreased to various degrees. Transcriptomic analysis was performed to explore the effects of different methanol concentrations (0%, 3.2%, and 5.6%) on the expression profile of B4D1. Three key signaling pathways were found to play important roles in regulating cell growth and metabolism under cultivation with methanol. Five central carbon metabolism-associated genes were significantly downregulated in response to 5.6% methanol and thus were expected to result in less ATP and NADPH being available for cell growth and synthesis. High methanol conditions significantly downregulated three genes involved in fatty acid and squalene/sterol precursor biosynthesis but significantly upregulated geranylgeranyl diphosphate synthase, lycopene beta-cyclase, and beta-carotene 3-hydroxylase, which are involved in astaxanthin synthesis, thus resulting in an increase in the levels of precursors and the final production of astaxanthin. Additionally, the transcriptional levels of three stress response genes were upregulated. This study investigates gene expression profiles in the astaxanthin producer Schizochytrium when grown under various methanol concentrations. These results broaden current knowledge regarding genetic expression and provide important information for promoting astaxanthin biosynthesis in Schizochytrium. IMPORTANCE Schizochytrium strains are usually studied as oil-producing strains, but they can also synthesize other secondary metabolites, such as astaxanthin. In this study, methanol was used as an inducer, and we explored its effects on the production of astaxanthin, a highly valuable substance in Schizochytrium. Methanol induced Schizochytrium to synthesize large amounts of astaxanthin. Transcriptomic analysis was used to investigate the regulation of signaling and metabolic pathways (mainly relative gene expression) in Schizochytrium grown in the presence of various concentrations of methanol. These results contribute to the understanding of the underlying molecular mechanisms and may aid in the future optimization of Schizochytrium for astaxanthin biosynthesis.