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) 10‘ 5 - 3 M EDTA plug 10' 6 M Cu; B) 10' 6 3 M EDTA plus 10' 3 M Tris; 
C) 10' 5 3 M 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 solid 
phase, presumably in some calcium precipitates (apatite or CaHPC^), 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 Si 02 can form in the medium. 
49 
