138 



PHYSIOLOGY OF THE FUNGI 



succinic acid was increased. It was surmised that this fungus utilizes 

 carbon dioxide, since none was set free. 



The formation of oxalacetic acid by the reaction between pyruvic acid 

 and carbon dioxide suggests that heterotrophic carbon dioxide fixation 

 may play a role in amino-acid synthesis. Support of this hypothesis may 

 be found in the work of Ajl and Werkman (1949), who found the carbon 

 dioxide requirement of Aerohacter aerogenes could be replaced by oxal- 

 acetic, a-ketoglutaric, fumaric, or aspartic acid. For further information 

 on carbon dioxide utilization by fungi see Foster (1949). 



UTILIZATION OF CARBON 



Carbon compounds are utilized by fungi for two general purposes, as a 

 source of energy and as a source of the chief structural element. These 

 two processes may be the same until a number of chemical transforma- 

 tions have taken place but may then diverge after certain intermediate 

 compounds are formed. The over-all use of carbon is quite easily 

 determined, but it is a problem of a different order to trace all the chemical 

 transformations which occur when a compound is utilized. 



Table 29. The Distribution of Carbon from Arabinose among the Products 



OF Metabolism of Fusarium lini 

 (White and Willaman, Biochem. Jour. 22, 1928. Published by permission of 

 Cambridge University Press.) 



Carbon balances. A general idea of the way a carbon source is utilized 

 may be gained by following the amounts of mycelium synthesized, carbon 

 dioxide evolved, and other metabolic products formed. If the initial 

 amount of carbon is known, its distribution can be followed by analysis. 

 From 95 to 99 per cent of the carbon is usually accounted for in such 

 experiments. The accompanying data from White and Willaman (1928) 

 illustrate this distribution of carbon from arabinose by Fusarium lini 

 (Table 29). 



While the analytical difficulties in experiments of this kind are con- 

 siderable, chemical analysis of the mycelium and the other metabolic 

 products reveals how the carbon originally present in the carbon source is 

 distributed. Such analyses are useful in detecting the major metabolic 



