Aerobic Formation of Fumaric Acid in the Mold Rhizopus Nigricans

Recent studies' have demonstrated that fumaric acid formation from glucose by Rhizopus nigricans No. 45 involves at least two mechanisms, one of which is aerobic, the other anaerobic.The latter involves a bulk fixation of CO2 via oxalacetate, in confirmation of the reaction qualitatively demonstrated in this mold eight years ago with radioactive carbon dioxide (C"102) .2The aerobic mechanism is the subject of the present work.Methods of cultivation and handling of the mold, submerged mycelium and analytical procedures are those given in detail by Foster and Davis" 3 and additional details will be given where necessary. Experiments and Results.-Relation of C2 Compounds to Fumarate Forma-tion from Glucose: Using washed submerged mycelium the essential surface culture results of Butkewitsch and Federoff4 5 and Foster and Waksman6 were confirmed, namely: aerobically ethanol accumulates in the early stages of the carbohydrate utilization, and gradually disappears, with a concomitant increase in fumarate, implying that alcohol is an inter- mediate between glucose and fumarate.Also confirmed was the formation of fumarate from alcohol as the sole carbon source, as well as from acetate, first noted by Takahasbi and Asai in 1927.7 A systematic study of fuma- rate formation from C2 compounds (an aerobic process) was, therefore, undertaken.Conversion of Alcohol to Fumarate: Extensive experimentation indicates the following conditions are essential for high efficiency of this conversion: (a) good aeration conditions, such as agitating thin layers on a reciprocal- * Supported in part by grants to J.