PHOSPHORUS 



301 



chemicals and inert container materials come to the attention of the 

 biologist. 



1. PHOSPHORUS 



In culture media a level of potassium phosphate (monobasic or di- 

 basic) of 0.004 M is usually provided; reported optimum concentrations 

 — affected, of course, by the carbon and nitrogen level — are of the 

 order of magnitude of 0.001-0.003 M (75, 100, 187, 241). These 

 levels are, however, too low to provide adequate buffering against ap- 

 preciable organic acid formation. 



Orthophosphate may be replaced, at least for some fungi, by other 

 forms of inorganic phosphate (49), by phytic acid (220), by adenosine 

 phosphates (223), or by casein (22). Aspergillus niger cannot utilize 

 phosphite or hypophosphite (49); phosphites appear to be generally 

 inert in biological systems (203). 



Phosphate deficiencies cause several metabolic disturbances. The 

 most easily observed, as one would expect, is a lowered rate of glucose 

 utilization (33, 123, 130); other metabolic symptoms of deficiency are 

 presumably secondary to this direct effect. 



In the typical culture cycle, phosphorus is absorbed rapidly during 



Time, days 



Figure 1. Growth and phosphorus changes in Aspergillus niger. From data oi 

 Mann (135). Seven-minute phosphorus is organic phosphorus mineralized by acid 

 hydrolysis of 7 minutes duration. 



