Isolation of High Carotenoid-producing Aurantiochytrium sp. Mutants and Improvement of Astaxanthin Productivity Using Metabolic Information.

The marine eukaryotic microheterotroph thraustochytrid genus Aurantiochytrium is a known producer of polyunsaturated fatty acids, carotenoids, and squalene. We previously constructed a lipid fermentation system for Aurantiochytrium sp. strains using underutilized biomass, such as canned syrup and brown macroalgae. To improve the productivity, in this study, Aurantiochytrium sp. RH-7A and RH-7A-7 that produced high levels of carotenoids, such as astaxanthin and canthaxanthin, were isolated through chemical mutagenesis. Moreover, metabolomic analysis of the strain RH-7A revealed that oxidative stress impacts carotenoid accumulation. Accordingly, the addition of ferrous ion (Fe), as an oxidative stress compound, to the culture medium significantly enhanced the production of astaxanthin by the mutants. These approaches improved the productivity of astaxanthin up to 9.5 mg/L/day at the flask scale using not only glucose but also fructose which is the main carbon source in fermentation systems with syrup and brown algae as the raw materials.