8 6 4 



-log (Y)^ 



Figure 4-5. The effect of different molar concentrations of 



copper specific metabolite (Y) on the activity of the cupric ion 



for three variations of Aquil medium. 



Note: A) IQ-^-^M EDTA plus IQ-^M Cu; B) 10-6% ^dTA plus IQ-^M Tris; 

 C) 10-5-3m EDTA. 



media. This is especially true following autoclaving, which brings about a large 

 pH increase by eliminating carbon dioxide from the system. This problem has 

 been studied by researchers involved in the design of culturing media (32, 8, 

 12, 18, 26). The increase in temperature and pH during autoclaving decreases 

 the solubility of calcium carbonate, and results in the precipitation of a 

 magnesium rich solid (this suggests the solid to be magnesium calcite, although 

 aragonite has been identified in such precipitates). Hydrous oxides of iron and 

 manganese can also precipitate under such conditions, depending on the 

 chelating agent concentration and the pH reached during autoclaving. When 

 such precipitates occur, phosphate becomes largely associated with the soHd 

 phase, presumably in some calcium precipitates (apatite or CaHP04), or as an 

 adsorbate on the various solids. Depending on the initial concentration of 

 silicic acid and on the nature of the container, which can increase the silicate 

 concentration of the solution by dissolution, some amorphous or crystalline 

 form of Si02 can form in tlie medium. 



49 



