Effects of L-cysteine on the synthesis and secretion of extracellular pigments in submerged fermentation of Monascus purpureus S109

Extracellular Monascus pigments (eMPs), as a crucial component of Monascus pigments (MPs) with functional activities, have been widely utilized. In this study, the effect of L-cysteine on the eMPs production capacity of S109 were investigated, along with the physiological and molecular response of S109 under L-cysteine. The results indicated that increasing the concentration of L-cysteine could promote the growth of S109 and improve the cell membrane permeability and fluidity. However, high concentration of L-cysteine did not constantly promote the yield of eMPs. The optimal condition was achieved with the addition of 2 g/L L-cysteine, under which the production of eMPs increased from 80.42 ± 0.37 to 329.20 ± 2.69 U/mL. Under this condition, all genes involved in the MPs synthesis and secretion pathway were approximately up-regulated. This study proposed a simple and effective method to improve the eMPs, which laid the foundation for the substantial improvement of Monascus fermentation industry.