Abstract
Monascus purpureus YY-1 is widely used in food colorant production in China. Our previous study clearly illustrated the whole-genome data for YY-1 and provided useful insight into evolutionary research and industrial applications. However, the presence of citrinin, which has nephrotoxic, hepatotoxic, and carcinogenic activities, has attracted attention to the safety of Monascus products. In an effort to reduce the harmful effects of citrinin in Monascus-related products, a random mutant of M. purpureus YY-1 with low citrinin production (designated as “winter”) was obtained in this study. To analyze the biosynthesis and regulation mechanisms of pigment and citrinin, a transcriptomic analysis of the M. purpureus YY-1 and winter strains was performed. Comparative transcriptomic analysis reveals pksCT, the essential gene for citrinin synthesis, showed a low expression level in M. purpureus YY-1 and winter, which suggested there might be isoenzymes in M. purpureus YY-1 that were responsible for the citrinin synthesis during evolution. In addition, changes in transcription factor expression may also influence the network regulating the citrinin synthesis pathway in M. purpureus. Moreover, the yields of pigments produced by the winter mutant were significantly increased. Repressing the central carbon metabolism and improving the acetyl-CoA pool can contribute to a high pigment yield, and enhanced NADPH regeneration can also lead to the metabolic flux of pigment production in M. purpureus. Investigations into the biosynthesis and regulation of citrinin and pigment production in M. purpureus will enhance our knowledge of the mechanisms behind the biosynthesis of fungal secondary metabolites.
Highlights
The filamentous fungus Monascus has a long history of being used to produce fermented foods in eastern Asia (Shi and Pan, 2011)
The pigment regulatory gene (pigR) deletion strain could no longer produce pigments, but its capacity to produce citrinin was greatly enhanced (Xie et al, 2013). These results suggested a close relationship between the pigment and citrinin biosynthesis pathways
To obtain a non-citrinin-producing mutant, the hygromycin phosphotransferase-encoding gene was introduced into M. purpureus YY-1 using protoplast transformation with pHPH, as described previously (Das et al, 1989)
Summary
The filamentous fungus Monascus has a long history of being used to produce fermented foods in eastern Asia (Shi and Pan, 2011). Deletion of pksCT in Monascus aurantiacus resulted in dramatically decreased citrinin production This mutant exhibited a stronger ability to produce red and yellow pigments (Fu et al, 2007). The overexpression of MpigE had positive effects on pigment formation and led to a decrease in citrinin production (Liu et al, 2014) These researchers identified and characterized a pigment regulatory gene (pigR). The pigR deletion strain could no longer produce pigments, but its capacity to produce citrinin was greatly enhanced (Xie et al, 2013) These results suggested a close relationship between the pigment and citrinin biosynthesis pathways. The scientific elucidation of the complex relationship between pigment biosynthesis and citrinin biosynthesis in Monascus will broaden our knowledge of the mechanisms involved in the biosynthesis of fungal secondary metabolites and will provide important insights into the genetic engineering of industrial strains to increase the production of specific metabolites
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