242 



NITROGEN NUTRITION AND METABOLISM 



200 



400 

 Nitrogen, mg per liter 



600 



800 



Figure 1. The relation between growth of Aspergillus niger and nitrogen supply 

 (ammonium nitrate) in media containing sucrose at 50 gm per liter (curve 1) and 

 25 gm per liter (curve 2). Drawn from data of Steinberg and Bowling (496). 



compounds occurs, of course, in the phase of autolysis (Chapter 1). 

 Studies of Scopulariopsis brevicaulis indicate that upon exhaustion 

 of the utilizable nitrogen of the medium, there is a mobilization and 

 reutilization of at least part of the nitrogen from older hyphae to sup- 

 port development of new mycelium (374). 



1. INORGANIC SOURCES OF NITROGEN 



Primary attention must be devoted here to three inorganic forms 

 of nitrogen: ammonium salts, nitrites, and nitrates. Other inorganic 

 nitrogen compounds have been little studied but appear in general to 

 be utilized only if easily or spontaneously converted to one of the 

 types above-named (278, 494). Cyanide as a nutrient and metabolite 

 is considered separately. 



The Utilization of Nitrate Nitrogen. Nitrates are excellent sources 

 of nitrogen for many fungi (30, 221, 326, 459). Inability to utilize 

 nitrate is especially common in some groups, e.g., the higher basidio- 

 mycetes (221, 234, 275, 327, 397, 546), the Saprolegniaceae (55, 434, 

 562), and the Blastocladiales so far as known (90). Nitrate utilization, 

 or at least nitrate reduction, is common in the actinomycetes, although 



