CARBON SOURCES 



125 



Sugar acids. Three types of sugar acids may be produced from aldoses 

 by oxidizing the terminal groups. Oxidation of the aldehyde group 

 yields aldonic acids, such as D-gluconic acid from glucose, while oxidation 

 of the primary alcohol group yields uronic acids, such as D-galacturonic 

 acid from D-galactose. Oxidation of both the aldehyde and primary 

 alcohol groups yields saccharic acids. The uronic acids are widely 

 distributed in natural polysaccharides such as plant gums and mucilages 

 and in pectin. The fungi in nature must frequently come in contact 

 with uronic acids, but data on utilization of these and other sugar acids 

 are rare. Steinberg (1942) cultured Aspergillus niger on media which con- 



Table 25. Milligrams op Mycelium Produced by FrvE Fungi Grown upon 

 Glucose, Mannose, and Galactose and the Corresponding Sugar Alcohols 

 These compounds were used at a rate which supplied 8 g. of carbon per liter. Each 

 125-ml. flask contained 20 ml. of medium. Cultures were incubated at 25°C. (Mar- 

 golin, thesis, West Virginia University, 1942.) 



tained 1 g. of the calcium salts of the following sugar acids per culture 

 (the weight of mycelium in milligrams is given in parentheses) : 2-keto-D- 

 gluconic (201), 5-keto-D-gluconic (25), D-gluconic (32), D-glucuronic (206), 

 and mucic (102). Tamiya (1932) reports that A. oryzae utilizes 

 D-gluconic acid. While such compounds as the sugar acids are little 

 used in making media, they are of interest in attempting to discover the 

 relation between structure and configuration on the one hand and 

 utilization on the other. 



Mixed carbon sources. In nature the fungi usually come in contact 

 with mixed carbon sources rather than a single source of carbon. Certain 

 fungi make more growth when supplied with a mixture of carbon sources. 

 This increased utilization may be expected only if one or both carbon 

 sources are poorly utilized. Horr (1936) investigated the growth of 

 Aspergillus niger upon mixtures of glucose and galactose. Some of these 

 data are given in Table 26. If these two carbon sources were utilized 

 independently, and without one affecting the utilization of the other, the 

 weight of mycelium produced on the combination of 18 g. of galactose 

 and 2 g. of glucose should be 42.4 -\- 145.6, or 188 mg. The actual 

 yield was 577.4 mg. The experiment indicates that A. niger is able to 



