FVNGI AS TEST ORGANISMS 215 



when different test organisms are used. The review of Snell (1948) 

 represents the critical judgment of an active investigator in this field. 



While the filamentous fungi are frequently passed over in favor of 

 bacteria and yeasts, they offer certain advantages when only simple 

 apparatus is available, or where occasional assays are to be made. The 

 test organisms for the specific vitamins listed below are in part those 

 recommended by Snell (1948). 



Thiamine. Phycomyces hlakesleeanus. This fungus responds to the 

 two moities of thiamine. Schopfer (1935, 1945) used a glucose-asparagine 

 medium and used dry weight of mycelium to measure growth. This is 

 an excellent organism to use in gaining experience with a microbiological 

 assay. Schultz et al. (1942) used Saccharomyces cerevisiae (Fleischmann's 

 baker's yeast) and measured the evolution of carbon dioxide, which was 

 proportional to the thiamine content of the sample. 



Pyridoxine. Saccharomyces carlsbergensis. Snell (1945a) found that 

 this yeast responds about equally to pyridoxine, pyridoxal, and pyridoxa- 

 mine. Growth may be measured turbidimetrically or by weighing the 

 cells. Differential assays for these three vitamers have been devised. 



p-Aminobenzoic acid. Neurospora crassa mutant. Various labora- 

 tories have used this organism (Tatum et al, 1946). For the effect of 

 pH on utilization of this vitamin see Wyss et al. (1944). 



Pantothenic acid. Saccharomyces carlsbergensis. Most, if not all, 

 yeasts respond to the )3-alanine moiety of pantothenic acid. Atkin et al. 

 (1944) noted that the incorporation of Z-asparagine in the basal medium 

 reduced interference due to /3-alanine. 



Nicotinic acid. Lactobacillus arabinosus. This organism responds 

 equally to nicotinic acid and nicotinamide. Growth may be measured 

 either by titrating the acid produced, or turbidimetrically (Krehl et al., 

 1943). Zygosaccharomyces marxianus was used by Leonian and Lilly 

 (1945). 



Inositol. Neurospora crassa mutant. This mutant was first used by 

 Beadle (1944) to assay inositol. It is an easy organism to handle, and 

 since this mutant forms few conidia, it is not a great source of contamina- 

 tion to a laboratoiy. Snell (1948) recommends the use of Saccharomyces 

 carlsbergensis for inositol assay. 



Biotin. Saccharomyces cerevisiae. Various strains have been used. 

 Many, if not all, strains respond also to desthiobiotin (Lilly and Leonian, 

 1944). The existence of many biotin vitamers makes the choice of a test 

 organism difficult. Neurospora crassa and N. sitophila may also be used. 

 It is probable that some of the divergence of assay values obtained when 

 different test organisms are used is due to biotin complexes. Such a 

 complex, biocytin, has been isolated by Wright et al. (1950). The 

 analytical results were unchanged by acid hydrolysis when Lactobacillus 



