Kinetic analysis of red pigment and citrinin production by Monascus ruber as a function of organic acid accumulation

In submerged cultures performed in synthetic medium containing glucose and glutamate, the filamentous fungus Monascus ruber produced a red pigment and a mycotoxin, citrinin. In oxygen-limiting conditions, the production of th ese two metabolites was growth-associated, as was the production of primary metabolites. In oxygen-excess conditions, the profile of citrinin producti on was typical of a secondary metabolite, since it was produced mostly duri ng the stationary phase. In contrast, the production of the pigment decreas ed rapidly throughout the culture, showing a profile characteristic of an i nhibitory mechanism. The organic acids produced during the culture, L-malat e and succinate, were shown to be slightly inhibitory against pigment produ ction, while citrinin production was unaffected. However, this inhibition c ould not account for the observed profile of pigment production in batch cu ltures. Other dicarboxylic acids such as fumarate or tartrate showed a simi lar effect to that provoked by malate and succinate as regards pigment prod uction. It was concluded that the decrease in red pigment production during the culture was due to the inhibitory effect of an unknown product whose a ccumulation was favored in aerobic conditions. (C) 2000 Elsevier Science In c. All rights reserved.