Co-Culture of Monascus purpureus and Aspergillus niger Isolated from Wuyi Hongqu to Enhance Monascus Pigments Production While Inhibiting Citrinin Production

Wuyi Hongqu (WYH), also called black-skin-red-koji, which has been utilizing as a fermentation starter for more than one thousand years in China, is a symbiotic combination of <i>Monascus</i> spp. and <i>Aspergillus niger</i> formed through long-term application and domestication. In this study, the strains of <i>Monascus purpureus</i> and <i>A. niger</i> isolated from WYH samples were used to investigate their mutual influence, especially the effects on three main secondary metabolites from <i>M. purpureus</i>, <i>Monascus</i> pigments (MPs), monacolin K (MK), and citrinin (CIT), using a double-sided Petri dish (DSPD). The results showed that co-cultivation of <i>M. purpureus</i> and <i>A. niger</i> strains was favorable to increase the MPs production while inhibiting the CIT production by <i>M. purpureus</i>, especially when <i>M. purpureus</i> strains (M_1-1 or M₉) were co-cultivated with certain <i>A. niger</i> strains (An_1-2 or An₉), respectively, and both <i>Monascus</i> strains hardly produced detectable CIT. The expression levels of CIT-related genes in <i>M. purpureus</i> M_1-1 or M₉ were greatly restricted when co-cultivated with <i>A. niger</i> An_1-2 or An₉ confirmed by RT-qPCR. This study provides important insights into the selection of WYH production strains and the effects of fungal interactions.