MONOSACCHARIDES AND THEIR DERIVATIVES 65 



with galactose (17, 180, 201). Erythritol is apparently only rarely 

 utilizable, although the data again are extremely limited. 



Glycerol is often the best carbon source of all for actinomycetes (40, 

 43, 221). In the fungi the ability to utilize glycerol appears to be 

 specific; thus, among fairly omnivorous saprophytes, Aspergillus oryzae 

 and A. niger make only poor growth (195, 201), but Memnoniella echi- 

 nata grows well with glycerol as sole carbon source (150). 



Although the data are insufficient for generalization, it may tenta- 

 tively be concluded that the only polyhydric alcohols available to 

 many fungi are glycerol and mannitol. These may be expected on 

 oxidation to yield, respectively, fructose and glyceraldehyde or di- 

 hydroxyacetone, all of which can after phosphorylation enter known 

 respiratory pathways. 



Sugar Acids. Oxidation of the aldehyde carbon of an aldohexose 

 yields an acid; D-gluconic acid, from D-glucose, is the only one to have 

 been investigated as a source of carbon for fungi. As might be ex- 

 pected from the fact that many strains of Aspergillus niger form and 

 then consume gluconic acid during sugar metabolism (Chapter 6), 

 it is a good source of carbon for A. niger (46) and A. oryzae (201), al- 

 though the strain of A. niger studied by Steinberg (195) could not 

 grow with gluconate as sole carbon source. Several other organisms 

 grow on gluconate (40, 99, 121), but others, e.g., Chalara quercina, do 

 not utilize it (12). Growth with gluconate is probably often limited 

 by an unfavorably high pH resulting from utilization of the neutralized 

 acid. 



Utilization of 2-ketogluconic acid by fungi is, like that of gluconic 

 acid, highly specific (50) and is probably a function of the respiratory 

 systems available. 



A single report (87) indicates, without quantitative data, that Asper- 

 gillus niger grows with D-glucuronic or D-galacturonic acids as sole car- 

 bon source. 



D-Saccharic acid, the dibasic acid resulting from the oxidation of 

 carbon atoms 1 and 6 of D-glucose, has been reported a good source 

 of carbon for Aspergillus niger (46), but a relatively poor source for 

 A. oryzae (201). 



Glycosides. Limited studies of the methylglucosides indicate, as 

 would be expected from the relative ubiquity of /3-glucosidases (Chap- 

 ter 5), that /?-methylglucoside is much more easily utilizable than the 

 ^-isomer (54, 180). Amygdalin, which is hydrolyzed to gentiobiose 

 and rnandelonitrile, is utilized by several members of the Saprolegnia- 



