188 PHYSIOLOGY OF THE FUNGI 



These moieties are referred to in the Hterature as the thiamine pyrimidine 

 and thiamine thiazole, respectively. 



Thiamine is somewhat unstable when exposed to alkali and heat, but 

 at pH 3.5 it is unaffected by autoclaving. Sulfur dioxide and sulfites 

 are destructive at pH 5 to 6. These factors must be taken into considera- 

 tion, and it is sometimes desirable to sterilize thiamine separately, either 

 by filtration or by autoclaving in an acidified solution. For most investi- 

 gations, however, it is permissible to autoclave thiamine with the medium. 

 For most fungi 100 fxg of thiamine per liter of medium is near optimum 

 for growth and sporulation. However, the optimum varies with the 

 amount of sugar in the medium and with other conditions. 



Soon after pure thiamine became available, it was discovered that 

 certain treatments destroyed its activity for animals but did not greatly 

 affect the potency when certain fungi were used as test organisms. The 

 solution to this problem was reached when it became known that thia- 

 mine, when autoclaved in the presence of alkali, was broken down into 

 thiamine pyrimidine and thiamine thiazole. 



Thiamine-deficient fungi differ in their ability to utilize or synthesize 

 the moieties of thiamine. These fungi may be classified into four groups 

 on this basis: (1) The intact molecule of thiamine is required by some 

 fungi which are unable to synthesize either moiety or to complete the 

 synthesis of thiamine, even when both moieties are supplied. Examples 

 of the group are species of Phytophthora. (2) Some other fungi, such as 

 Phycomyces hlakesleeanus, are capable of utilizing thiamine, or of syn- 

 thesizing thiamine when furnished with a mixture of the two thiamine 

 moieties. (3) The addition of thiamine or thiamine pyrimidine satisfies 

 the need of those fungi which are able to synthesize the thiazole moiety 

 and combine it with the pyrimidine moiety to make thiamine. Examples 

 are Parasitella simplex and Rhodotorula rubra. (4) Other fungi are able 

 to synthesize only the thiamine pyrimidine and complete the synthesis 

 of thiamine when furnished with the thiazole moiety. Mucor raman- 

 nianus and Stereum frustulosum are examples. 



In the above discussion it was assumed that in every case the intact 

 molecule was the active product and that neither moiety nor the presence 

 of the two had any activity until thiamine was synthesized. Leonian 

 and Lilly (1940) found this hypothesis to be correct. The following fungi 

 Avere grown in a basal medium to which had been added the minimal 

 growth factor: Fusarium niveum (none), Pythiomorpha gonapodyoides 

 (pyrimidine), Mucor ramannianus (thiazole), Phycomyces hlakesleeanus 

 (both moieties of thiamine), and Phytophthora erythroseptica (thiamine). 

 After growth, the mycelium and the medium were tested for thiamine 

 and its moieties by growing fungi of known thiamine or thiamine-moiety 

 requirements upon media containing the mycelium extract and the 

 medium. Some of these data are collected in Table 33. 



