FUNGI AS TEST ORGANISMS 219 



before analysis. It is probable that amino acids and other nitrogen 

 sources containing reduced nitrogen would also affect the amount of 

 molybdenum needed. Mulder (1948) investigated the use of Aspergillus 

 niger as a test organism (Table 37). For further discussion and refer- 

 ences to the use of microorganisms in essential-element assay see Vande- 

 caveye (1948). 



SUGARS 



Yeasts and other microorganisms have been used to separate optical 

 isomers and complex mixtures of sugars. Pasteur (18G0) used Pemcillium 

 glaucum to obtain the "unnatural" isomer of tartaric acid from rfZ-tartaric 

 acid. Fischer and Hertz (1892) used brewer's yeast to ferment D-galac- 

 tose, while L-galactose in the same medium was not utilized. Auernheimer 

 el al. (1948) used the specific fermentative powers of Hansenula suaveolens 

 and Candida guilliermondi in the separation of L-arabinose and D-xylose 

 obtained from the hydrolysis of straw and corn cobs. H. suaveolens does 

 not utilize L-arabinose, while C. guilliermondi utilizes both pentoses. 

 Saccharomyces carlshergensis was used to demonstrate the absence of 

 D-glucose in the hydrolysates. These yeasts were used in conjunction 

 with chemical methods of analysis. Appling et al. (1947) found Sac- 

 charomyces carlshergensis var. mandschuricus to ferment D-galactose but 

 not L-galactose. Similarly, H. suaveolens utilized D-xylose but not 

 L-xylose. 



These citations indicate the usefulness of yeasts and other organisms 

 in the solution of problems difficult to solve by other methods. The 

 value of microorganisms in such applications is due to their specificity. 



TESTS FOR CERTAIN METABOLIC PRODUCTS 



Fungi excrete into the media in w^hich they grow various physiologically 

 active substances. In the older literature these are referred to as staling 

 'products. Among the metabolic products are those which may stimulate 

 or inhibit growth and reproduction. The kind and the amount of com- 

 pounds excreted depend upon the particular fungus involved as well as 

 the composition of the medium. The effect of the metabolic products ot 

 one fungus upon another is simply demonstrated when fungi are gro^vn 

 in association. The beneficial effect of one fungus upon another was 

 demonstrated by Kogl and Fries (1937). Neither Nematospora gossypii 

 or Polyporus adustus grew when inoculated alone into a synthetic medium, 

 but when both fungi were inoculated together in the same flask, both 

 began to grow rapidly after about a week. N. gossypii is deficient for 

 biotin but synthesizes thiamine, while P. adustus is deficient for thiamine 

 but synthesizes biotin. Kogl and Fries called this artificial symbiosis. 

 Schopfer and Guilloud (1945) cite other examples in connection with 

 work on strains of Candida guilliermondi involving vitamin deficiencies. 



