Towards commercial levels of astaxanthin production in Phaffia rhodozyma

Astaxanthin (AX) is a potent antioxidant with increasing biotechnological and commercial potential as a feed supplement, and gives salmonids and crustaceans their attractive characteristic pink color. The red yeast Phaffia rhodozyma naturally produces AX as its main fermentation product but wild-type strains and those previously generated through classical random mutagenesis produce low yields of AX. Existing strains do not meet commercial economic requirements, fundamentally due to a lack of understanding of the underlying mechanisms and genotype-phenotype associations regarding AX production in P. rhodozyma. In the present study, screening of P. rhodozyma CBS 6938 mutant strains generated through chemical and ultra violet radiation mutagenesis delivered increased AX production yields that were then maximized using culture media optimization and fed-batch culture kinetic modeling. The whole genomes of the wild-type and eight increased production strains were sequenced to identify genomic changes. The selected strains produced 50-fold more AX than the wild-type strain with a total biomass of around 100 gDCW/L and a carotenoid production of 1 g/L. Genomic variant analyses found 368 conserved mutations across the selected strains with important mutations found in protein coding regions associated with regulators and catalysts of AX precursors in the mevalonate pathway, the electron transport chain, oxidative stress mechanisms, and carotenogenesis.