Evaluating the effects of microparticle addition on mycelial morphology, natural yellow pigments productivity, and key genes regulation in submerged fermentation of Monascus purpureus.

Morphology plays an important role in fungal fermentation and secondary metabolites biosynthesis. One novel technique, microparticle-enhanced cultivation was successfully utilized to control the morphology of Monascus purpureus precisely and enhance the yield of yellow pigments. The production of yellow pigments increased to 554.2 U/ml when 4 g/L 5000 mesh talc added at 24 h. Field emission scanning electron microscope observation indicated that the actual effect depends on the properties of microparticle. Sharp-edged microparticles showed better stimulatory effects than smooth, round-shaped ones. Particle size analysis, scanning electron microscope, and cell integrity evaluation proved obvious morphological changes were induced by talc addition, including smaller mycelial size, rougher hyphae, and decreased cell integrity. Furthermore, the expression levels of MrpigG, MrpigD, MrpigE, and MrpigH were significantly upregulated by the addition of talc. It indicated that the microparticle could not only affect the mycelial morphology, but also influence the expression levels of key genes in biosynthetic pathway of Monascus yellow pigments.