The role of the citric acid cycle in fungal organic acid fermentations.

Filamentous fungi are well known for their potential to accumulate organic acids in the medium when supplied with large amounts of sugar. Commercial applications of this are the production of citric and itaconic acids. The present review attempts to present the current state of knowledge on the biochemical basis of organic acid accumulation by filamentous fungi (citric, itaconic, fumaric and oxalic acids), particularly with respect to the role of citric acid cycle reactions. The explanations offered are based on recent advances in understanding the compartmentation of the fungal cell, and regulation of some key enzymes. The general conclusion is that fungi accumulate organic acids by mechanisms which avoid the channeling of substrates into the citric acid cycle under conditions of strongly active glycolysis.