238 A MANUAL OF THE ASPERGILLI 



Gluconic Acid: Selected strains of A. niger are used industrially for the 

 production of gluconic acid. This process, like the citric fermentation, 

 has been investigated by many workers. Outstanding contributions have 

 been made by Molliard, Bernhauer, and the U. S. Department of Agri- 

 culture group, including Herrick, May, Wells, Moyer, Gastrock, Porges, 

 and others (see pp. 295-297). 



Oxalic Acid: Under certain conditions some strains of A. niger produce 

 appreciable quantities of oxalic acid. While it is usually avoided rather 

 than encouraged, this fermentation has been investigated by Wehmer (1891 

 and 1892), Raistrick and Clark (1919), Jacquot (1938), and others (see 

 pp. 298-299). 



The production of these various acids in quantities sufficient to have 

 economic importance represents to an appreciable degree specific strain 

 characteristics, and the greatest possible care must be exercised in main- 

 taining these strains in a state of high productivity. It has been found, 

 however, that in certain cases the same strains can be made to produce 

 substantial yields of two or more of these acids by varying the composition 

 of the nutrient solution and certain environmental factors. The reader is 

 referred to the extensive literature on this subject. 



Enzymes: While they are not commonly cultivated for the production 

 of enzymes as such, as are members of the A. flavus-oryzae group, the black 

 aspergilli produce a number of enzymes in appreciable quantities. Be- 

 ginning with Fernbach in Germany (1890) and Bourquolet (1893) in 

 France, various authors have devoted considerable study to their formation. 

 A number of papers relative to enzyme production by members of the group 

 are cited in the "Topical Bibliography" under the subtitle "Enzymes of 

 Aspergillus niger" (pp. 294-295). 



Fat Production: The mycelium of A. niger contains appreciable fatty 

 materials (Pontillon, 1932; Bernhauer and Patzelt, 1935; Schmidt, 1935; 

 and others). The waste mycelium from the citric acid fermentation is 

 reported to provide a satisfactory source of sterols for irradiation in the 

 production of Vitamin D. 



Soil Testing: A. niger has been successfully employed as an assay 

 organism for determining mineral deficiency of soils, particularly de- 

 ficiencies in phosphorus and potassium. Papers on the so-called A. niger 

 method of soil testing were first published by Kiessling and Schmidt and 

 by Schlots, Smith, and Brown in the same year (1932), to be followed by 

 more elaborate studies by Stock (1933), Niklas and associates (1933), and 

 others. Additional references to this method are presented in the "Topical 

 Bibliography" (pp. 313-314). The strain employed by Niklas is main- 

 tained in the culture collection of the Northern Regional Research Lab- 

 oratory as No. 323. 



