CARBON SOURCES 127 



The form in which an organic acid exists (free acid or salt) is a function 

 of the pH of the medium or cells. The free acid is the predominant form 

 at low pH values. The terms for an acid and its salt {e.g., fumaric acid, 

 fumarate) are used in the literature somewhat loosely. The effect of a 

 free acid and its anion may be different (Chap. 8). 



Leptomitus ladeus, w^hich does not utilize sugars, grows on various 

 fatty acids — acetic, butyric to capric — but not on formic or propionic 

 acids (Schade, 1940). Apodachlya hrachynema utilizes the same fatty 

 acids as L. ladeus and also, fumarate, succinate and malate. Aspergillus 

 niger, according to Steinberg (1942), makes some growth on acetate, 

 lactate, tartrate, malate, and fumarate. Growth was very poor com- 

 pared with that on sucrose. Dulaney (1949) reported that little strepto- 

 mycin was produced when organic acids were used by Streptomyces 

 griseus. Yeasts use acetate to synthesize fat (White and Werkman, 

 1947). Tamiya (1932) investigated the utilization of many organic acids 

 by Aspergillus oryzae. Growth w^as poor on most of these compounds 

 except quinic acid. While an organic acid may serve as the sole source 

 of carbon for fungi, in general acids do not allow as much or as rapid 

 growth as carbohydrates. 



An amino acid may serve as a source of both nitrogen and carbon. 

 Peptone may serve as a source of carbon and nitrogen for many fungi. 

 Aspergillus niger, when grown on peptone as the sole source of carbon, 

 deaminates the peptides and amino acids and releases ammonia in 

 quantities greater than the fungus can use. The utilization of amino 

 acids as carbon sources by A. niger w^as investigated by Steinberg (1942a), 

 who found certain combinations of "primary" amino acids to be utilized 

 about three-fourths as efficiently as sucrose. 



The utilization of individual amino acids by Penicillium roqueforti and 

 Fusarium oxysporum var. lycopersici was studied by Gottlieb (1946). 

 Not all the naturally occurring amino acids were utilized as carbon sources 

 by these fungi. The six-carbon straight-chain amino acids norleucine and 

 lysine and the sulfur-containing amino acids cysteine and methionine 

 were not utilized as carbon sources. Glycine and valine were poor 

 carbon sources for P. roqueforti, while F. oxysporum var. lycopersici grew 

 well on these amino acids. Alternaria solani, Helminthosporium sativum, 

 Rhizoctonia solani, Fusarium moniliforme, Chaetomium globosum, and 

 Aspergillus niger were unable to utilize the naturally occurring sulfur- 

 containing amino acids as a source of carbon. 



Yeasts differ in ability to utilize different amino acids as the sole 

 source of carbon (Schultz et al., 1949). Glutamic acid and proline were 

 available to more species than other amino acids. It is characteristic of 

 fungi cultivated on amino-acid media as the sole source of carbon that 

 the medium becomes alkaline. This is probably due to accumulation of 



