120 



PHYSIOLOGY OF THE FUNGI 



The configuration of glucose, mannose, and fructose is the same for 

 carbons 3 to 6. In the presence of dilute alkali these sugars undergo 

 enolization to produce the same enol form. 



D-Glucose 

 CHO 



H— C— OH 



R 



D-Mannose 

 CHO 



HO— C— H 



I 

 R 



it 

 CHOH 



II 

 COH 



D-Fructose 

 CH,OH 



C=0 



I 

 R 



R ±: 



Common enol form 



Other effects of alkali and heat on sugars were noted in Chap. 2. 



Many fungi will utilize these three sugars if configuration is important 

 in determining availability. However, these sugars are not equivalent 

 for all fungi. The fact that galactose is not utilized by all fungi which 

 utilize the three closely related sugars is illustrated by the data in Table 

 22. 



Glucose is utilized by more fungi than any other sugar and is nearly a 

 universal carbon source. In attempting to culture fungi of unknown 

 nutritional requirements on synthetic or semisynthetic media, glucose 

 should be the first carbon source used. However, there are a few fungi 

 which are unable to utilize glucose, or any sugar, as a carbon source. 

 Leptomitus lacteus (Schade, 1940; Scliade and Thimann, 1940) is unable to 

 utilize glucose, fructose, galactose, or sucrose. Skoog and Lindegren 

 (1947) have reported the behavior of 12 strains of Saccharomyces cere- 

 visiae which did not utilize glucose when first isolated. These strains 

 became adapted to glucose on sufficiently long exposure to this sugar. 

 Cheo (1949) found certain isolates of Ustilago striiformis to be unable to 

 grow on glucose when freshly transferred from a sucrose medium. After 

 2 to 4 weeks these isolates began to grow. This behavior suggests the 

 formation of an adaptive enzyme which was not formed when these 

 isolates were cultured on sucrose medium. Some fungi, such as L. lacteus, 

 apparently lack the ability to form adaptive enzymes for glucose utili- 

 zation and must be classed as absolutely incapable of glucose utilization, 

 while the yeasts of Skoog and Lindegren and the isolates of U. striiformis 

 are facultatively able to utilize glucose. The differences among these 

 fungi probably lie in the ability to form adaptive enzymes. 



No carbon source can be utilized if the medium is lacking in any 

 essential element or compound. Kinsel (1937) and Stevens and Larsh 

 (1939) reported that Diplodia macrospora would grow only on disacchar- 

 ides and not on media containing glucose or other monosaccharides. 



