An enhanced electron transport chain improved astaxanthin production in Phaffia rhodozyma

Astaxanthin (AX) is a carotenoid pigment with antioxidant properties widely used as a feed supplement. Wild-type strains of Phaffia rhodozyma naturally produce low AX yields, but we increased AX yields 50-fold in previous research using random mutagenesis of P. rhodozyma CBS6938 and fermentation optimization. On that study, genome changes were linked with phenotype, but relevant metabolic changes were not resolved. In this study, the wild-type and the superior P. rhodozyma mutant strains were grown in chemically defined media and instrumented fermenters. Differential kinetic, metabolomics, and transcriptomics data were collected. Our results suggest that carotenoid production was mainly associated with cell growth and had a positive regulation of central carbon metabolism metabolites, amino acids, and fatty acids. In the stationary phase, amino acids associated with the TCA cycle increased, but most of the fatty acids and central carbon metabolism metabolites decreased. TCA cycle metabolites were in abundance and media supplementation of citrate, malate, α-ketoglutarate, succinate, or fumarate increased AX production in the mutant strain. Transcriptomic data correlated with the metabolic and genomic data and found a positive regulation of genes associated with the electron transport chain suggesting this to be the main driver for improved AX production in the mutant strain.