Phycomyces blakesleeanus, thiamine

Many of the micro-organisms proposed, even some that have been extensively used, show a certain lack of specificity their requirement for thiamine as a growth factor can also be met by the pyrimidine and thiazole moieties of the molecule, either singly or in combination. Such is the case for the yeast Saccharomyces cerevisiae and the mould Phycomyces blakesleeanus. 

When it was found that the pyrimidine and thiazole components of thiamin could often replace thiamin, the opportunity was taken to examine the question of the biological specificity of the molecule, since a large number of related pyrimidines and thiazoleshad been prepared by the workers engaged in the synthesis of thiamin. Detailed studies on the specificity of the pyrimidine and thiazole portions of thiamin and of thiamin analogs have been made for Staph, aureus (169) Phycomyces blakesleeanus (38, 305, 306, 333, 334, 348) for various protozoa (236, 237) and for pea-roots (29, 30, 37). [Comparative summaries are given in 159, 211, 309]. 

Direct evidence for the synthesis of thiamin by joining the pyrimidine and thiazole components was shown for Phycomyces blakesleeanus by Bonner and Buchman (38). They further showed that after growth the resting mycelium broke down the thiamin, with destruction of the thiazole and liberation of the free pyrimidine. With Staph, aureus Hills (127) found similarly that the destruction of the thiazole was more rapid than that of the pyrimidine. 

Those organisms e.g., Glaucoma piriformis and Phytophthora cinruimomi) which require the intact thiamin molecule and cannot use the two components, evidently cannot link them together as other protozoa. Staph, aureus, Phycomyces blakesleeanus, and pea-roots can when the substitution in the 5 —CH2-group is suitable. 

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