66 CARBON NUTRITION 



ceae (17); in general it may be expected that the ability of an organism 

 to use a given /^-glycoside will depend on its ability to use the sugar 

 which is split off from it. The cyanogenetic glycosides, however, may 

 not be utilizable by reason of the toxicity of the cyanide liberated on 

 hydrolysis (174). 



3. OLIGOSACCHARIDES 



Chemically, the oligosaccharides are glycosides composed of two or 

 more monosaccharides and are characterized by the nature of the com- 

 ponent sugars, the number ol units, and the type of glycosidic bond. 

 Those which are important in the nutrition of fungi include five 

 disaccharides — maltose, cellobiose, trehalose, sucrose, and lactose — and 

 one trisaccharide, raffinose, which is made up of galactose, glucose, and 

 fructose units. In addition to data on specific sugars, two general 

 problems are relevant at this point: (1) the enzymatic basis of disac- 

 charide utilization, and (2) adaptive growth with oligosaccharides. 



Maltose occurs in nature as a product of starch hydrolysis and is 

 utilized by virtually all fungi which have been tested, even those which 

 have a limited substrate range. A few fungi are known, on the basis 

 of quantitative studies, to grow poorly or not at all with maltose: 

 Chytridium sp. (45), Polychytrium aggregation (2), Entomophthora 

 (Empusa) sp. (242), and Penicillium digitatum (65, 244). Surprisingly, 

 the two chytrids mentioned make at least some growth with starch; 

 the other fungi use neither starch nor maltose. Maltose is more 

 easily hydrolyzed by autoclaving than are sucrose or lactose (136), but 

 even with this possible source of error it seems that it is very generally 

 available to fungi. 



Cellobiose, like maltose, is composed of two glucose residues but the 

 linkage is of the /^-configuration. The data are more limited than 

 those for maltose, but indicate that it is almost as widely utilizable as 

 maltose. Indeed, two of the fungi mentioned above which do not 

 grow with maltose do with cellobiose. Tricholoma flavobrunneiim is 

 among the small group of tested fungi which fail to utilize cellobiose, 

 but other species of the same genus grow well with it as sole carbon 

 source (142). The utilizability of cellobiose reflects the general oc- 

 currence of /3-glucosidases in fungi (Chapter 5). 



Trehalose, a glucose-containing disaccharide produced by fungi and 

 a few higher plants (Chapter 5), appears from the few studies which 

 have been made to be generally available, even to rather fastidious 

 fungi (40, 99, 201, 242). 



Sucrose, the characteristic sugar of higher plants, is generally a good 



