Metabolic mechanism of astaxanthin biosynthesis in Xanthophyllomyces dendrorhous in response to sodium citrate treatment

Abstract

Astaxanthin is an important ketocarotenoid widely used in industries, but the application of astaxanthin is limited due to its low yield. Sodium citrate (Na-citrate), one of the major carbon sources for the microorganism, can promote cell growth and product accumulation. The basidiomycetous red yeast Xanthophyllomyces dendrorhous was chosen to study the effect of Na-citrate on cell growth and astaxanthin synthesis. The highest biomass and astaxanthin yield (6.04 g/L and 22.53 mg/L) were obtained in Shake-flask when adding 3 g/L Na-citrate at 24 h, which were 1.8 and 2.0 times higher than those of the control group, respectively. Furthermore, metabolomics and quantitative real-time polymerase chain reaction (RT-qPCR) analysis were conducted to study the metabolic pathways of X. dendrorhousin response to Na-citrate, which revealed that Na-citrate facilitated glucose consumption, promoted the metabolic flux from glycolysis, and regulated the tricarboxylic acid (TCA) cycle, providing more energy and substrates for the synthesis of astaxanthin. The gene analysis presented that adding Na-citrate significantly upregulated the expression of six key genes (ICL, HMGS, crtE, crtYB, crtI and crtS) involved in pathways related to astaxanthin biosynthesis. These results provided the potential valuable strategy to stimulate astaxanthin production by exogenous Na-citrate in X. dendrorhous.