6. Carbon Metabolism 



Part III 



Organic Acids, Lipids, 



and Other Compounds 



T, 



.he final group of carbon metabolites of the fungi has 

 as its most important members the organic acids and the lipids. Brief 

 consideration must also be given to other carbon compounds of 

 various types. Many of the miscellaneous compounds included here 

 have not been studied from a physiological point of view. Neverthe- 

 less, they are involved in metabolism and therefore in physiology; 

 they will not remain indefinitely as biochemical curiosities. Space 

 does not permit an exhaustive listing of the aromatic and other com- 

 pounds known to be produced by fungi; many more will be found in 

 the reviews cited later. 



1. THE METABOLISM OF ALIPHATIC ORGANIC ACIDS 



The fungi are perhaps best known in microbiology for their toler- 

 ance of acidity — although this is much less general than usually 

 thought — and for the ability of some to accumulate non-volatile 

 organic acids. This section considers the metabolism of the organic 

 acids, exclusive of the higher fatty acids, the keto acids of the respira- 

 tory pathways, and those acids which are basically ring compounds. 



Sugar Acids. Acids derived by direct oxidation of either or both 

 terminal carbon atoms of a sugar may be grouped together as the 

 sugar acids. Of these, the only one to be formed in quantity is 

 gluconic acid. The reaction was discovered by Molliard (379) in 

 Aspergillus niger, and subsequent work has shown that at least small 

 amounts of gluconate are formed by a variety of fungi (Table 1). So 



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