Regulatory Effect of 5 Metal Ions on the Spectrum of Major Secondary Metabolites of Monascus purpureus

Objective: This study was to investigate the regulatory effect of Cu²⁺, Zn²⁺, Mg²⁺, Mn²⁺ and Co²⁺ on the growth and the major secondary metabolite of M. purpureus. Methods: The spores of M. purpureus were inoculated into solid medium with different concentration of metal ions, and investigate the effects of different ions on their growth and pigments synthesis. Meanwhile, different concentrations of metal ions and 8-hydroxyquinoline were added into the liquid medium respectively, and biomass, the main secondary products such as Monascus pigment, monacolin K, γ-aminobutyric acid, citrinin and changes in the metabolite profile in the fermentation broth were measured. Results: The result showed that Cu²⁺ (0.5 mmol/L) leads to a 1.01, 1.07 and 0.73 times increase in the yield of water-soluble red, orange and yellow pigments, respectively, and alcohol-soluble pigments increased by 2.83, 1.74 and 1.95 times, respectively. Monacolin K and citrinin increased by 1.78 and 5.53 times, respectively. The water-soluble and alcohol-soluble pigments under Zn²⁺ (0.5 mmol/L) increased by 93.3%, 78.6%, 57.6%, and 2.9, 1.54, and 0.54 times, respectively, monacolin K and citrinin increased by 0.92 and 6.91 times, respectively. Biomass was no changed under Mg²⁺(0.5 mmol/L) treatment, but the water-soluble and alcohol-soluble pigments were increased by 2.68, 2.25, 2.02-fold and 1.26, 1.23 and 1.82-fold, respectively, monacolin K increased by 51.8%. Whereas, citrinin increased by 1.79 times at the concentration of 0.25 mmol/L Mg²⁺. Mn²⁺ (0.5 mmol/L) led to increase of the yields of water-soluble and alcohol-soluble pigments by 48.3%, 29.9%, 24.8% and 131.1%, 83.6% and 49.2%, respectively, and monacolin K increased by 1.01-fold. Citrinin increased by 92.3% under the stimulation of 1 mmol/L Mn²⁺. Co²⁺ (0.5, 1 mmol/L) led to a 47.9% and 53.7% reduction of biomass, respectively. The alcohol-soluble pigments was improved by 4.07, 5.04, 2.62 times, and 3.07, 3.41, 2.70 times, respectively, citrinin decreased by 90.8% and 93.9%, respectively, with no effect on the Monacolin K synthesis. None of the above ions were detrimental to the synthesis of γ-aminobutyric acid. The metal ion chelator 8-hydroxyquinoline(20 μmol/L) was responsible for a 26.9% decrease in biomass and a 40.6%, 34.3% and 26% decrease in water-soluble pigments, respectively, and monacolin K and citrinin decreased by 56.7% and 90.1%, respectively. The spectrum (200~600 nm) scanning of fermentation broth showed that the metal ions did not change the metabolite types, but only regulated the metabolite content. Conclusion: The results suggested that metal ions not only affect the growth of M. purpureus, but also significantly regulate its main secondary metabolite profile.