Effects of glycerol on pigments and monacolin K production by the high-monacolin K-producing but citrinin-free strain, Monascus pilosus MS-1

Glycerol is the principal by-product of bio-diesel production which can be utilized by fungi for beneficial metabolites production. In this study, effects of glycerol on main metabolites production and gene expression of pigment and monacolin K (MK) synthesis-related genes of Monascus pilosus MS-1, a high-MK-producing but citrinin-free strain, were investigated. The results indicated that addition of glycerol could increase the dry cell weight but decrease the fermentation broth pH value. Pigments production could be enhanced significantly after adding 2 g/L glycerol and the maximum pigments yield (13.78 U/mL) of fermentation broth was obtained when the glycerol content was up to 40 g/L (p < 0.05). Effect of glycerol on MK production was different from that of Monascus pigment. MK yield of fermentation broth was decreased significantly when the glycerol addition was up to 10 g/L while that of mycelia could be improved as glycerol addition increased (p < 0.05). Results of real-time PCR revealed that when the glycerol additions were up to 40 and 300 g/L, respectively, the gene expressions of regulatory gene (ctnR) for pigment synthesis were 17.31- and 22.22-folds of ctnR in the control; the gene expressions of structural gene (PKS5) for pigment synthesis were 33.27- and 60.07-folds of PKS5 in the control; respectively. However, the gene expressions of regulatory (mkH) and structural (mkA) genes of MS-1 for MK production were decreased after adding glycerol. All this suggesting that glycerol can be used for improving production of citrinin-free Monascus pigments and MK.