The growth and lutein accumulation in heterotrophic Chlorella protothecoides provoked by waste Monascus fermentation broth feeding

Although the potential of heterotrophic microalgae served as a sustainable source for lutein, it was still crucial to formulate a suitable medium to offset the cost involved in algal biomass cultivation while improve inherent lutein productivity. The objective of this study was to investigate the feasibilities of waste Monascus fermentation broth medium (MFBM) toward heterotrophic Chlorella protothecoides-enriched lutein. The results indicated that C. protothecoides subjected to MFBM batch feeding achieved 7.1 g/L biomass and 7.27 mg/g lutein. The resulting lutein productivity (7.34 mg/L/day) represented 1.54-fold more than that of frequently used Basal medium. Concurrently, the effective metabolism and absorption of carbon, nitrogen, and phosphorus in MFBM by C. subellipsoidea cultivation make it easily complied with the permissible dischargeable limits for fermentation broth. When response to fed-batch culture mode, the biomass and lutein productivity peaked 20.4 g/L and 9.11 mg/L/day with concentrated MFBM feeding. Transcriptomics data hinted that MFBM feeding manipulated lutein biosynthesis key checkpoints (e.g., lycopene β-cyclase and lycopene ε-cyclase) while accelerated energy pathways (e.g., glycolysis and TCA cycle) to contribute such high lutein productivity in C. protothecoides. These encouraging findings not only provided indications in applying nutrient-rich fermentation broth for affordable microalgae cultivation but also presented possibilities in linking algal high value-added products like lutein with high-efficient biological nutrition removal from industrial fermentation processing.