MONOSACCHARIDES AND THEIR DERIVATIVES 63 



some. The toxicity is evidenced by death of the hyphal tips, followed 

 by branching of the mycelium below the killed portion (116). Fungi, 

 e.g., Neurospora crassa, which normally spread widely on an agar 

 plate grow as small colonies in a medium with sorbose (204). The 

 fundamental basis of sorbose toxicity is not yet known; although often 

 more pronounced in a maltose medium, toxicity to some fungi is 

 equally well expressed in glucose media, so that interference with 

 maltose utilization cannot be the explanation. Sorbose inhibition oc- 

 curs only at relatively high concentrations and is strongly affected by 

 temperature (116). A possible line of approach to the problem of its 

 mode of action may be found in the hypothesis that sorbose interferes 

 with a respiratory pathway; organisms dependent on this pathway 

 would then be inhibited completely, fungi which have alternate path- 

 ways would be less or not at all affected. 



Heptoses. The naturally occurring 7-carbon sugars have not been 

 tested as carbon sources for fungi, except for the report (195) that 

 Aspergillus niger does not grow with D-mannoheptulose. 



Pentoses. D-Xylose is the most generally utilizable of the pentoses, 

 and has even been reported to be superior to glucose for some organ- 

 isms (12, 150, 216). Some fungi and actinomycetes grow poorly or 

 not at all with xylose, and species within the same genus may differ 

 markedly (195, 201). It must be remembered that xylose is known 

 to be broken down to furfural during autoclaving, for which reason 

 all reports of its non-utilizability should be regarded with some reserve 

 until confirmed with filter-sterilized xylose. Phymatotrichum omniv- 

 orum makes better growth with alcohol-sterilized than with auto- 

 ciaved xylose (18), but the poor growth of Venturia inaequalis strains 

 on agar with xylose is not improved by filter sterilization of the sugar 

 (113). 



Both isomers of arabinose occur in nature and are commercially 

 available. Probably, in those publications in which the isomer used 

 is not specified the L-isomer, which is more easily available, was used. 

 Penicilliurn urticae utilizes D-arabinose much less well than it does 

 L-arabinose (57). In most studies, L-arabinose is inferior to xylose and 

 glucose as a carbon source (116a). In a medium containing a second 

 carbon source, however, several fungi, e.g., Endoconidiophora adiposa, 

 utilize L-arabinose with a long incubation period, apparently adap- 

 tive!}' (116). 



Relatively few studies on rhamnose, a methyl pentose, have been 

 made, but the indications are that it is used by only a few organisms, 

 including StacJiybotiys atra (99) and Streptomyces coelicolor (39). 



