Fig.3-8 Mycelium and spore morphology of C100, ΔMareA and OE-MareA in media with different nitrogen sources
3.3 Solid-state fermentation of C100, ΔMareA and OE-MareA
3.3.1 Yield of red yeast rice by solid state fermentation
Monascus consumes nutrients in rice to meet its own growth and development needs during solid-state fermentation. Different strains of bacteria utilize rice to varying degrees, so the dry weight of red yeast rice can reflect the growth and metabolism of different Monascus strains in the solid-state fermentation process. In the rice fermentation medium without adding any nitrogen source, the knockout strain ΔMareA weighed the heaviest at 10.48g, indicating slower growth in the rice medium, while the overexpression strain OE-MareA weighed the lightest at 9.67g, suggesting better utilization of nutrients in rice. When comparing the dry weights of red yeast rice with different nitrogen sources added, it was observed that OE-MareA had the lightest weight after fermentation, followed by C100, and ΔMareA had the heaviest weight. The addition of Gln resulted in a consistent lighter weight for red yeast rice around 9.10 g, indicating that Gln addition was most favorable for Monascus ’ fermentation of rice and was not affected by AreA gene. The weight of Monascus was the heaviest compared to other nitrogen sources, reaching more than 15g, as it could not effectively utilize (NH4)2SO4. However, when NaNO3 was added, ΔMareA showed poor utilization resulting in heavier red yeast rice. On the other hand, OE-MareA red yeast rice was lighter in weight. When Urea was added to the fermentation medium, both ΔMareA and OE-MareA fermented red yeast rice weighed less compared to NaNO3. In conclusion, the addition of Gln had no effect on red yeast fermentation regardless of deletion or overexpression of the AreA gene, whereas NaNO3 best demonstrated the impact of this gene on red yeast fermentation. As shown in Figure 3-9.