A Dibasal (minimum Salt, Maximum Yield) Solution for Aspergillus Niger; Acidity and Magnesium Optimum.

Two major difficulties exist in the use of Aspergillus niger v. Tiegh for identification and study of the roles of micronutrients, although these are certainly not unique with this fungus. The water, sucrose, and salts employed may be assumed never to be completely free from impurities of micronutrients. Moreover, increases in yield with apparently non-nutritive elements may be due to biological substitutions and other obscure phenomena and not to essentiality. Decision in some instances is difficult or impossible. These points have been considered by the writer at various times in the past. It was noted that better provision of micronutrients were paralleled by decreased macronutrient needs (2). Addition of traces of organic compounds to the nutrient solution gave no increases in yield except when micronutrients were deficient in quantity for maximum yield (3). Deficiencies in potassium or magnesium led to similar increases in yield with sodium and beryllium (5), respectively. Similar results (unpublished) have also been obtained with other apparently non-nutritive elements (Ti, Cb, Pd, etc.) when micronutrients were insufficient for maximum growth. These studies and the present one have been a direct consequence of the effort to obtain sufficient information to serve as a basis for interpretation of such anomalous increases obtained with apparently nonessential elements. The increases were often the results of actual or induced deficiencies in known nutrient elements and not of nutritive functions of the elements under trial. The phenomena under discussion have also led to a quantitative study of the actual minima of the nutrient elements necessary for maximum yield. Further data are herein presented and should be interpreted particularly in the light of PFEFFER'S (1) conclusion with respect to the mineral nutrition of (higher) plants: "All the elements cannot . . . be simultaneously reduced to the lowest possible minima" in the nutrient solution if growth is to be maximum. Briefly stated, the data herein presented comprise a quantitative comparison of the optima obtained for all the macronutrient elements in quantity-yield experiments with those actually needed in the dibasal nutrient solution. Included also are brief but pertinent data on the relation of these results to micronutrient requirements, and the relation of nutrient solution acidity (pH), chloride, and of quantity and source of inoculum to deficiencies, whether actual or induced. Methods Aspergillus niger v. Tiegh was grown at 350 C. for 4 days on 50 ml. of nutrient solution in 200-ml., quartz, Erlenmeyer flasks. The cultures were