Effectively Improve the Astaxanthin Production by Combined Additives Regulating Different Metabolic Nodes in Phaffia rhodozyma

Astaxanthin is an important natural resource that is widely found in marine environments. Metabolic regulation is an effective method for improving astaxanthin production in Phaffia rhodozyma. Most studies have focused on single regulators, which have limited effects. In this study, 16 metabolic regulators were screened to improve astaxanthin production in high-yield and wild-type strains. Fluconazol and glutamic acid increased astaxanthin volumetric yield in MVP14 by 25.8 and 30.9%, respectively, while ethanol increased astaxanthin volumetric yield in DSM626, 29.3%. Furthermore, six additives that inhibit the competing pathways and promote the main pathway for astaxanthin synthesis were selected for combination treatment. We found that the optimal combination was penicillin, ethanol, triclosan, and fluconazol, which increased astaxanthin cell yield by 51%. Therefore, we suggest that simultaneously promoting the master pathways (mevalonate) and inhibiting competing pathways (fatty acid synthesis and ergosterol) is the best strategy to improve astaxanthin cell yield. Moreover, regulators of the biomass pathway should be avoided to improve cell yield. This study provides a technical basis for the utilisation of astaxanthin in P. rhodozyma.

Rice Straw Hydrolysis and Cultivation of Xanthophyllomyces dendrorhous for Astaxanthin Production and Antioxidant Properties

Astaxanthin is a natural pigment with strong antioxidant activity and is widely supplied as dietary supplement. The red yeast Xanthophyllomyces dendrorhous is one of the potential sources for astaxanthin production. Rice straw was considered for utilization on cultivation and astaxanthin production. Rice straw was treated by autoclave-assisted alkaline pretreatment. and hydrolyzed by cellulase hydrolysis. X. dendrorhous TISTR5730 was cultured and accumulated as the astaxanthin on rice straw hydrolysate. The highest reducing sugar concentration of rice straw hydrolysate was 89.82±0.39g/L (0.71±0.01g/g) when using rice straw (3.3%) and cellulase loading (3 mL). High cell density X. dendrohous TISTR5730 cultivation on rice straw hydrolysate with 20 and 40 g/L of initial reducing sugar was investigated. 40 g/L was appropriate for biomass production while 20 g/L was suitable for astaxanthin accumulation. The highest astaxanthin content was 417.28±50.89 μg/g cell basis at 192 h. Astaxanthin productivity and yield coefficient were 0.01±0.00 mg/L/h and 0.11±0.01 mg/g sugar consumed. The antioxidant activities of astaxanthin were determined by DPPH and ABTS scavenging and FRAP reducing power. The produced astaxanthin represented the high antioxidant activities with IC50 of 9.30 and 1.67 μg/mL of DPPH and ABTS scavenging respectively and FRAP reducing power of 5.31±0.07 μg TEAC/mL. This research indicated that rice straw hydrolysate could be an alternative medium for astaxanthin production. Antioxidant activity of astaxanthin was proved and was feasible for further applications.

Sequential Continuous Mixotrophic and Phototrophic Cultivation Might Be a Cost-Effective Strategy for Astaxanthin Production From the Microalga Haematococcus lacustris

Although Haematococcus lacustris has been developed for astaxanthin production for decades, the production cost is still high. In order to modify the production processes, we proposed a novel strategy of cultivation, featured by sequential indoor continuous mixotrophic cultivation for the production of green cells followed by outdoor phototrophic induction for astaxanthin accumulation. The continuous mixotrophic cultivation was first optimized indoor, and then the seed culture of mixotrophic cultivation was inoculated into outdoor open raceway ponds for photoinduction. The results showed that mixotrophically grown cultures could efficiently grow without losing their photosynthetic efficiency and yielded higher biomass concentration (0.655 g L−1) and astaxanthin content (2.2% DW), compared to phototrophically grown seed culture controls. This novel strategy might be a promising alternative to the current approaches to advance the production technology of astaxanthin from microalgae.