The role of MpMag in the magnetic field regulation of biosynthesis of Monascus pigments and citrinin in Monascus purpureus.

We constructed MpMag overexpression (MpMag+) and knockout (ΔMpMag) strains to investigate the role of MpMag in regulating the synthesis of Monascus pigment (MPs) and citrinin (CIT) in Monascus purpureus. After 9 days of cultivation, notable differences in the colony phenotype and the number of cleistothecia on PDA medium were observed between the wild-type (WT), MpMag+ and ΔMpMag strains. The MpMag+ strain exhibited a significantly higher production of MPs and notably lower levels of CIT compared to the WT. In contrast, the ΔMpMag strain exhibited an opposite pattern. Exposure to both 0.9 mT and 1.6 mT low-frequency magnetic fields (LF-MF) significantly promoted the production of MPs in the WT and MpMag+ strains, while also reducing CIT production in the WT. Only the 0.9 mT LF-MF exposure decreased CIT levels in the MpMag+ strain. The intracellular iron content in the MpMag+ strain was significantly lower than in the WT. Exposure to 1.6 mT LF-MF significantly reduced the intracellular iron content in both the WT and MpMag+ strains on the 6th day of fermentation. Furthermore, the LF-MF exposure and the differential expression of the MpMag gene collaboratively regulate the expression levels of genes involved in iron-sulfur cluster assembly, iron homeostasis, regulation of MPs and CIT synthesis. These results imply that the MpMag as a magnetic field-responsive protein regulates the uptake and utilization of iron ions, thereby altering intracellular iron content and influencing the expression of genes related to the synthesis of MPs and CIT in M. purpureus.