200 PHYSIOLOGY OF THE FUNGI 



of yeast tested. However, the omission of both pyridoxine and thiamine 

 caused a decrease in the growth of two of these strains. Apparently 

 these two yeasts were capable of synthesizing either thiamine or pyri- 

 doxine, provided that the other vitamin w^as present. This is a common 

 effect among fungi partially deficient for two or more vitamins. The 

 presence of one vitamin for which a fungus is partially deficient may 

 enable the fungus to synthesize other vitamins with greater ease. 



Among the filamentous fungi, deficiency for pyridoxine seems to be 

 characteristic of certain species of Ceratostomella and a few other fungi 

 (Robbins and Ma, 1942o, 19426). Some species reported to be deficient 

 for pyridoxine, with other deficiencies given in parentheses, are Cerato- 

 stomella ulmi, C. ips (thiamine, biotin), C. pseudotsugae (thiamine), C. 

 piceaperda 240 (biotin), C. pini (thiamine, biotin), C montium (thiamine, 

 biotin), C. pilifera, C. multiannulata (thiamine), C. pluriannulata (thia- 

 mine), C. microspora (thiamine, biotin), Ophiostoma catonianum (thia- 

 mine), Trichophyton discoides (thiamine, inositol). 



Specificity. One of the important uses of vitamin-deficient organisms 

 is for the purpose of vitamin assay. Certain vitamin-deficient fungi 

 and bacteria are used to determine the vitamin content of foodstuffs and 

 other natural products. For such tests to be of any value, it is necessary 

 to know if the organism used responds to substances other than the 

 vitamin itself. Snell et at. (1942) found that Streptococcus faecalis gave 

 much greater apparent yields of pyridoxine when used for assay than did 

 yeast. It was then discovered (Snell, 1942) that autoclaving pyridoxine 

 with the basal medium for 20 min. increased the activity of pyridoxine 

 forty-one times, and that this change in activity for certain organisms 

 was correlated with oxidation and heating with certain amino acids. 



Snell (1944) then postulated that vitamers of pyridoxine were formed 

 by these treatments. When this problem was under investigation, these 

 vitamers of unknown structure were called "pseudopyridoxine," which 

 was later found to consist of either one or both of the following compounds : 



HO- 

 CH3 



^^— CHoOH HO— r^^— CH2OH 



Pyridoxal Pyridoxamine 



These two compounds were synthesized by Harris et al. (1944) and tested 

 by Snell. 



It was concluded that this vitamin consists of three or more closely 

 related compounds. Saccharomyces carlsbergensis responds about equally 

 to the three compounds, while the reaction of certain bacteria is much 

 greater to pyridoxal and pyridoxamine than to pyridoxine, Ceratosto- 



