Reduction of fatty acid flux results in enhancement of astaxanthin synthesis in a mutant strain of Phaffia rhodozyma

Abstract

A moderate-temperature mutant strain of the yeast Phaffia rhodozyma, termed MK19, was selected by 1-methyl-3-nitro-1-nitrosoguanidine (NTG) and Co60 mutagenesis. MK19 displayed fast cell growth and elevated astaxanthin content at 25 degrees C, whereas optimal temperature for growth and astaxanthin synthesis of wild-type P. rhodozyma was 17-21 degrees C. Optimized astaxanthin yield for MK19 after 4 days culture in shaking flask at 25 degrees C, determined by response surface methodology, was 25.8 mg/l, which was 17-fold higher than that of the wild-type. MK19 was tolerant of high initial concentration of glucose (>100 g/l) in optimized medium. Total fatty acid content of MK19 was much lower than that of the wild-type. Acetyl-CoA is a common precursor of fatty acid and terpenoid biosynthesis, and it is possible that decreased fatty acid synthesis results in transfer of acetyl-CoA to the carotenoid biosynthetic pathway. Our results indicate that astaxanthin content is negatively correlated with fatty acid content in P. rhodozyma. Nutrient analysis showed that MK19 cells are enriched in lysine, vitamin E, and other rare nutrients, and have potential application as fish food without nutritional supplementation. This moderate-temperature mutant strain is a promising candidate for economical industrial-scale production.

Study on the relationship between intracellular metabolites and astaxanthin accumulation during Phaffia rhodozyma fermentation

“…Therefore, selecting an amino acid-deficient strain through breeding methods [40] or adopting a metabolic regulation method to inhibit protein synthesis [21,22,24] can be an effective method to improve astaxanthin yield. P. rhodozyma is known as a kind of oleaginous yeast and can accumulate a large quantity of lipids [23]. Thus, as an essential component of the cell membrane, a large number of fatty acids should be accumulated to meet the needs of cell growth.…”

“…The synthesis of protein and fatty acids, which are important cell components, as well as that of astaxanthin requires numerous carbon sources, energy (ATP), NADPH, and acetyl-CoA [18,19,20]. Thus, competition for these factors exists among protein, fatty acids, and astaxanthin synthesis and may thus encourage astaxanthin accumulation in cells, whereas protein and fatty acid synthesis were inhibited to a certain extent [21,22,23]. In the process of glucose catabolism, ethanol will be produced during yeast fermentation if dissolved oxygen is insufficient or if glucose concentration is extremely high.…”

Overexpression of a bifunctional enzyme, CrtS, enhances astaxanthin synthesis through two pathways in Phaffia rhodozyma

“…Mutant P. rhodozyma strain MK19 was generated from wild-type JCM9042 by NTG and Co60 mutagenesis in our previous study [11]. The microbial strains and plasmids used in the present study are listed in Table 2.…”

“…Media, seed culture, and flask fermentation were as described previously [11]. Batch fermentation was performed in a 7.5-L bioreactor (Baoxing; Shanghai, China) containing 5 L medium, with initial glucose concentration 60% (w/v), temperature 25°C, pH 5.0, agitation at 700 rpm, and aeration rate 10 L/min.…”

“…We previously generated a moderate-temperature, astaxanthin-overproducing mutant P. rhodozyma strain, termed MK19, by NTG and Co60 mutagenesis [11]. In comparison with wild-type strain JCM9042, fatty acid content was lower, optimized astaxanthin yield was ~17-fold higher, and carotenoid composition was strikingly altered in MK19.…”