Screening of astaxanthin-overproducing Xanthophyllomyces dendrorhous strains via iterative ARTP mutagenesis and cell sorting by flow cytometry

AIMS

The astaxanthin-producing yeast Xanthophyllomyces dendrorhous is widely used in aquaculture. Due to the production of carotenoid, this yeast shows visible color; however, high-throughput approaches for identification of astaxanthin-overproducing strains remain rare.

METHODS AND RESULTS

This study verified an effective approach to identify astaxanthin-overproducing mutants of X. dendrorhous by flow cytometry (FCM) and cell sorting. First, the mutant libraries were generated by atmospheric and room-temperature plasma (ARTP) mutagenesis. Second, a highly direct correlation between the concentrations of intracellular astaxanthin and the levels of emitting fluorescence was constructed by testing a variety of astaxanthin-contained populations via FCM and cell sorting. Third, iterative cell sorting efficiently improves the identification of astaxanthin-overproducing strains. Finally, two mutants producing 4.96 mg astaxanthin g-1 DCW (dry cell weight) and 5.30 mg astaxanthin g-1 DCW were obtained, which were 25.3% and 33.8% higher than that of the original strain, respectively.

CONCLUSIONS

This study demonstrated that iterative ARTP mutagenesis along with cell sorting by FCM is effective for identifying astaxanthin-overproduction strains.

Enhancement of astaxanthin production from food waste by Phaffia rhodozyma screened by flow cytometry and feed application potential

Astaxanthin is widely used in food, aquaculture, cosmetics, and pharmaceuticals due to its strong antioxidant activity and coloring ability, but its production from Phaffia rhodozyma remains the main challenge due to the high fermentation cost and low content of carotenoid. In this study, the production of carotenoids from food waste (FW) by a P. rhodozyma mutant was investigated. P. rhodozyma mutant screened by UV mutagenesis and flow cytometry could stably produce high carotenoids at 25°C, with carotenoid production (32.9 mg/L) and content (6.7 mg/g), respectively, increasing by 31.6% and 32.3% compared with 25 mg/L and 5.1 mg/g of wild strain. Interestingly, the carotenoid production reached 192.6 mg/L by feeding wet FW, which was 21% higher than batch culture. The 373 g vacuum freeze-dried products were obtained from the fermentation of 1 kg FW by P. rhodozyma, which contained 784 mg carotenoids and 111 mg astaxanthin. The protein, total amino acids, and essential amino acids content of the fermentation products were 36.6%, 40.5%, and 18.2% (w/w), respectively, and lysine-added fermentation products had the potential of high-quality protein feed source. This study provides insights for the high-throughput screening of mutants, astaxanthin production, and the development of the feed potential of FW.

Microbial astaxanthin: from bioprocessing to the market recognition

The attractive biological properties and health benefits of natural astaxanthin (AXT), including its antioxidant and anti-carcinogenic properties, have garnered significant attention from academia and industry seeking natural alternatives to synthetic products. AXT, a red ketocarotenoid, is mainly produced by yeast, microalgae, wild or genetically engineered bacteria. Unfortunately, the large fraction of AXT available in the global market is still obtained using non-environmentally friendly petrochemical-based products. Due to the consumers concerns about synthetic AXT, the market of microbial-AXT is expected to grow exponentially in succeeding years. This review provides a detailed discussion of AXT's bioprocessing technologies and applications as a natural alternative to synthetic counterparts. Additionally, we present, for the first time, a very comprehensive segmentation of the global AXT market and suggest research directions to improve microbial production using sustainable and environmentally friendly practices. KEY POINTS: • Unlock the power of microorganisms for high value AXT production. • Discover the secrets to cost-effective microbial AXT processing. • Uncover the future opportunities in the AXT market.

Metabolic engineering for high yield synthesis of astaxanthin in Xanthophyllomyces dendrorhous

Astaxanthin is a carotenoid with a number of assets useful for the food, cosmetic and pharmaceutical industries. Nowadays, it is mainly produced by chemical synthesis. However, the process leads to an enantiomeric mixture where the biologically assimilable forms (3R, 3'R or 3S, 3'S) are a minority. Microbial production of (3R, 3'R) astaxanthin by Xanthophyllomyces dendrorhous is an appealing alternative due to its fast growth rate and easy large-scale production. In order to increase X. dendrorhous astaxanthin yields, random mutant strains able to produce from 6 to 10 mg/g dry mass have been generated; nevertheless, they often are unstable. On the other hand, site-directed mutant strains have also been obtained, but they increase only the yield of non-astaxanthin carotenoids. In this review, we insightfully analyze the metabolic carbon flow converging in astaxanthin biosynthesis and, by integrating the biological features of X. dendrorhous with available metabolic, genomic, transcriptomic, and proteomic data, as well as the knowledge gained with random and site-directed mutants that lead to increased carotenoids yield, we propose new metabolic engineering targets to increase astaxanthin biosynthesis.

Enhancing Astaxanthin Biosynthesis by Rhodosporidium toruloides Mutants and Optimization of Medium Compositions Using Response Surface Methodology

Astaxanthin is a valuable carotenoid, which has been approved as a food coloring by the US Food and Drug Administration and is considered as a food dye by the European Union (European Commission). This work aimed to attain Rhodosporidium toruloides mutants for enhanced astaxanthin accumulation using ultraviolet (UV) and gamma irradiation mutagenesis. Gamma irradiation was shown to be more efficient than UV for producing astaxanthin-overproducer. Among the screened mutants, G17, a gamma-induced mutant, exhibited the highest astaxanthin production, which was significantly higher than that of the wild strain. Response surface methodology was then applied to optimize the medium compositions for maximizing astaxanthin production by the mutant G17. The optimal medium compositions for the cultivation of G17 were determined as a peptone concentration of 19.75 g/L, malt extract concentration of 13.56 g/L, and glucose concentration of 19.92 g/L, with the maximum astaxanthin yield of 3021.34 µg/L ± 16.49 µg/L. This study suggests that the R. toruloides mutant (G17) is a potential candidate for astaxanthin production.