64 CARBON NUTRITION 



Although Penicillium urticae grows with D-ribose as carbon source 

 (57), it and the other naturally occurring pentoses and methyl pentoses 

 have not been investigated thoroughly. Early studies, not all satis- 

 factory in their methods, on pentose utilization by fungi are reviewed 

 by Hawkins (80) and by Peterson et al. (155). 



It seems, in conclusion, that xylose is often a good source of carbon 

 for fungi and that contrary findings should be examined closely. The 

 pathway of utilization of xylose is not known; it seems likely that it 

 enters the phosphogluconate oxidation pathway (Chapter 7) as pen- 

 tose phosphate. L-Arabinose is used by several fungi, probably not by 

 most. The other pentoses and methyl pentoses have been investigated 

 rather infrequently, but they appear in general to be poor sources of 

 carbon or not utilizable at all. 



Other Monosaccharides. A single study of a 4-carbon sugar (195) 

 indicates that D-threose is not utilized by Aspergillus niger. 



The L-isomers of the naturally occurring aldohexoses and of xylose 

 do not support growth of fungi, nor do those monosaccharides which 

 do not occur in nature (99, 195, 201). Acetylation or methylation of 

 the ring carbons of glucose yields derivatives which are not utilized 

 by representative fungi (187), although Aspergillus niger has been 

 reported to make a limited growth, after adaptation, with pentaacetyl- 

 glucose (8). Aspergillus niger also grows with 2-deoxyglucose as car- 

 bon source (8). 



Polyhydric Alcohols. Reduction of the sugars yields sugar alcohols, 

 e.g., D-sorbitol arises by reduction of D-glucose, D-mannitol by reduction 

 of D-fructose or D-mannose. In addition to the hexitols, derived from 

 the hexose sugars, tetritols, pentitols, and heptitols, related respec- 

 tively to 4-, 5-, and 7-carbon sugars, occur in nature. Glycerol may be 

 considered as a reduction product of a 3-carbon sugar. 



Mannitol is the most generally utilizable of the hexitols, and is 

 equivalent to glucose for many fungi and actinomycetes (39, 100, 144, 

 180). However, many fungi with generally wide substrate ranges 

 grow only poorly or not at all with mannitol as sole carbon source (65, 

 129, 152). In the lower phycomycetes, a few forms grow poorly with 

 mannitol (17, 32); most do not utilize it at all. 



Sorbitol and dulcitol are unavailable to most fungi and actinomy- 

 cetes. From the limited data, it appears that sorbitol, the reduction 

 product of glucose, is more generally used than is dulcitol, which is 

 related chemically to galactose. It may be significant that many or- 

 ganisms able to utilize dulcitol are also able to grow more or less well 



