Improving mycelial morphology and adherent growth as well as metabolism of Monascus yellow pigments using nitrate resources.

ABSTRACT

Mycelial adhesion affects cell growth and the production of water-soluble extracellular yellow pigment (EYP) in submerged fermentation with Monascus ruber CGMCC 10910. Two nitrates, NaNO3 and KNO3, were used as nitrogen sources for mitigating mycelial adhesion and improving the production of EYP in this study. The results showed that the adhesion of mycelia in the fermentation broth significantly decreased by adding 5 g/L NaNO3, which prevented mycelia from attaching to the inner wall of the Erlenmeyer flask. It was suggested that NaNO3 reduced the total amount of extracellular polysaccharides, increased extracellular proteins, and decreased the viscosity of the fermentation broth. Scanning electron microscopy (SEM) analysis revealed that the mycelial morphology was shorter and more dispersed and vigorous under NaNO3 conditions than under the control conditions. The biomass increased by 49.2% and 45.4% with 5 g/L NaNO3 and 6 g/L KNO3 treatment, respectively, compared with that of the control, and the maximum production of EYP was 267.1 and 241.8 AU350, which increased by 70.0% and 53.9% compared with that of the control, respectively. Simultaneously, the ratios of intracellular yellow pigment to orange pigment increased significantly with 5 g/L of NaNO3 addition (p < 0.05). Genetic analysis found that the expression levels of the key genes for Monascus pigment biosynthesis were significantly upregulated by NaNO3 addition (p < 0.05 or p < 0.01). This study provides an effective strategy for the production of water-soluble Monascus yellow pigments.Key Points• Nitrate addition decreased mycelial adhesion and improved cell growth in Monascus pigment fermentation.• The biosynthesis genes of water-soluble extracellular yellow pigment (EYP) were upregulated by nitrate addition.• The mycelial morphology was significantly influenced to enhance EYP biosynthesis with nitrate addition.