122 CARBON METABOLISM II 



including cordycepin of Cordyceps militaris (20) and many of the 

 actinomycete antibiotics (22, 56). Whether they are related to toxicity 

 is uncertain, but the possibility is at least suggested by the number of 

 instances uncovered. 



6. THE METABOLISM OF POLYHYDRIC ALCOHOLS 



The compounds of this class that have been studied in connection 

 with the carbon metabolism of fungi include the sugar alcohols, 

 glycerol, and a few glycols. Mannitol and glycerol are the most im- 

 portant. 



Sugar Alcohols. Mannitol was first discovered in fungi by Bracon- 

 not (44, 45), and subsequent work during the nineteenth century 

 revealed its general occurrence in the sporophores of basidiomycetes 

 and ascomycetes (36, 59, 264). Other analyses of cellular material 

 show that mannitol occurs in mycelium, e.g., of Aspergillus elegans 

 (91) and Rhizopus japonicus (130), in sclerotia (70), and in spores 

 (223, 242, 265). Mannitol may also appear in the medium, and very 

 high yields — from 20 to 50 per cent of the glucose consumed — are 

 found in the culture medium of Aspergillus sp. (23) and Byssochlamys 

 fulva (186). 



Mannitol appears to function physiologically as a reserve food (164, 

 165); its general utilizability as a carbon source (Chapter 3) is con- 

 sistent with this function. It is formed in culture from pentoses, 

 hexoses, and glycerol (57, 260). The biosynthesis has not been studied, 

 but it is a reasonable hypothesis that mannitol is formed by the reduc- 

 tion of fructose or a fructose phosphate. Extracts of Stachybotrys atra 

 carry out the reversible reaction (54): 



Fructose + DPNH + H+ ±=; Mannitol + DPN+ (10) 



Provided that a hydrogen donor is available, this reaction could 

 synthesize mannitol. Consistent with a reductive origin of mannitol, 

 mannitol formation is increased by restriction of the oxygen supply 

 (23). 



D-Sorbitol has been reported formed by Boletus bovinus (132), and 

 preformed mats of several basidiomycetes dehydrogenate sorbitol to 

 L-sorbose (239). Other sugar alcohols which are formed by fungi 

 include: D-volemitol (35), D-arabitol (77, 182a, 259), z'-erythritol (168, 

 220, 262, 265). Some of the sugar alcohols account for an appreciable 

 fraction of the carbon metabolized; thus, D-threitol (/-erythritol) con- 

 stitutes 13 per cent of the dry weight of the mycelium of Armillaria 



