Anaerobic Formation of Fumaric Acid by the Mold Rhizopus nigricans

Fumaric acid: fermentative production, applications and future perspectives

The rising prices of petroleum-based chemicals and the growing apprehension about food safety and dairy supplements have reignited interest in fermentation process to produce fumaric acid. This article reviews the main issues associated with industrial production of fumaric acid. Different approaches such as strain modulation, morphological control, selection of substrate and fermentative separation have been addressed and discussed followed by their potential towards production of fumaric acid at industrial scale is highlighted. The employment of biodegradable wastes as substrates for the microorganisms involved in fumaric acid synthesis has opened an economic and green route for production of the later on a commercial scale. Additionally, the commercial potential and technological approaches to the augmented fumaric acid derivatives have been discussed. Conclusion of the current review reveals future possibilities for microbial fumaric acid synthesis.

Mechanism of fumaric acid accumulation in Rhizopus nigricans

It is doubtful that the glyoxylate bypass plays a significant role in the accumulation of fumaric acid by fungi, as has been postulated. In high glucose media, which favor fumarate production, isocitrate lyase (threo-D(s) isocitrate glyoxylate lyase), which is the key enzyme of the glyoxylate bypass, is strongly repressed. The specific activity of this enzyme remains low as long as glucose is present in the medium, even though fumarate formation proceeds at a high level. In addition, the activity of isocitrate lyase is inhibited by phosphoenolpyruvate, which would be formed from glucose. Alternatively, evidence is presented that bulk accumulation of fumaric acid under aerobic conditions in high glucose media takes place through a C(3) plus C(1) carbon dioxide fixation. CO(2) fixation was measured by the direct incorporation of NaHC(14)O(3) into fumaric acid, and by demonstrating that the specific radioactivity of fumaric acid formed from uniformly labeled C(14)-glucose was decreased in the presence of nonradioactive carbonate. The extent of decrease in specific radioactivity is in accord with a C(3) plus C(1) CO(2) fixation mechanism.