Optimizing Monascus pigment production: Insights from mycelial morphology, gene expression, and transcriptomic analysis in simulated seawater fermentation

Monascus pigments (MPs) are secondary metabolites produced by Monascus spp., which can be significantly influenced by the extreme environment. In this work, the regulatory mechanism of MPs in simulated seawater fermentation (SSF) were investigated following mycelial morphology, gene expression, and transcriptomic analysis. Yield of the extracellular yellow pigments (EYPs) was significantly increased by 34.2 % in SSF, compared with the conventional fermentation (CF). The relative proportion of four EYPs (Y1/Y2-Y4) and the relative content of intracellular orange pigments to yellow pigments (O/Y) were also significantly (p < 0.05) changed. Fluorescence inverted microscope (FIM) and field emission scanning electron microscope (FE-SEM) showed the mycelium morphology was regulated in better status to facilitate the metabolism and secretion of MPs in SSF. The pigment biosynthesis gene MpFasA2, MpFasB2, MpPKS5, mppB, mppC, mppD, and mppE were significantly (p < 0.05) up-regulated, whereas the regulatory genes mppR1, mppR2 were significantly (p < 0.05) down-regulated in SSF. Transcriptome further revealed 83 differentially expressed genes (DEGs) between the two groups (CF vs SSF), with 40 up-regulated and 43 down-regulated. Among them, polyketide synthase genes and fatty acid oxidative degradation pathways related to pigment synthesis were significantly up-regulated in SSF, which promoted the metabolism of MPs. The down-regulation of DNA replication pathway indicated a slowdown in cell growth and differentiation, which keeping a favorable state for MPs synthesis. Biometabolism-related pathways of cell wall component and secretion-related pathways were also significantly regulated to accelerate the transmembrane transport of EYPs. This study may provide clues to clarify the response mechanism of high osmotic tolerance of Monascus spp.