282 PHYSIOLOGY OF THE FUNGI 



The fungi which have been tested for itaconic acid production are mainly 

 selected isolates of A. terreus. Relatively few isolates produce sufficient 

 itaconic acid to have commercial possibilities (Calam et al., 1939; Moyer 

 and Coghill, 1945). 



Various attempts have been made to produce mutants of A. terreus 

 by irradiating conidia with ultraviolet light (Raper et al., 1945). Less 

 success attended these efforts than comparable treatment of conidia of 

 Penicillium chrysogenum for obtaining mutants with enhanced penicillin 

 production. 



Among the factors which affect the production of itaconic acid by 

 isolates of .4. terreus are the composition of the medium, hydrogen-ion 

 concentration, temperature, and aeration. Glucose and ammonium 

 nitrate appear to be the best sources of carbon and nitrogen. The pH 

 range in which itaconic acid accumulates is narrow and low, 1.9 to 2.3. 

 The aluminum ion is toxic to A. terreus, but aluminum trays may be used 

 if the concentration of magnesium ion in the medium is high. As much 

 as 4.75 g. of magnesium sulfate heptahydrate per liter of medium may be 

 used. It is probable that this high concentration of magnesium ion also 

 enables the fungus to withstand low pH values (Lockwood and Ward, 

 1945). 



Fumaric acid. This unsaturated, four-carbon, dicarboxylic acid is 

 produced by many fungi, although only a relatively few species synthe- 

 size large amounts. With few exceptions, the fungi which synthesize 

 fumaric acid in significant amounts are Phycomycetes. The formula for 

 fumaric acid is given below: 



HOOC— CH 



II 

 HC— COOH 



Fumaric acid 



The factors which affect the production of fumaric acid by Rhizopus 

 nigricans were studied by Foster and Waksman (1939). The concentra- 

 tion of zinc was found to be especially important. Optimum production 

 of fumaric acid occurred in cultures receiving less zinc than that required 

 for optimum growth. Not all isolates of R. nigricans synthesized fumaric 

 acid in equal amounts or under the same conditions. One isolate studied 

 by Foster and Waksman (1939a) produced fumaric acid anaerobically 

 and aerobically, whereas another produced fumaric acid aerobically only. 



Various proposals have been made to explain the mechanism of fumaric 

 acid formation. Anaerobic synthesis is thought to involve the formation 

 of oxalacetic acid from pyruvic acid and carbon dioxide (Foster and 

 Davis, 1948). The follo^^•ing steps would convert oxalacetic acid to 

 fumaric acid: oxalacetate — ^ malate — > fumarate. It is probable that 

 fumaric acid is produced aerobically from acetic acid as follows: 2 (ace- 



