I have screened 2 fungal strains isolated from serpentine soil for the Cu tolerance (0 ppm - 2000 ppm). At the very first copper in the 1600ppm and 2000ppm (incooperated into Potato Dextrose Agar) were precipitated during the adjusting of pH of the media. But i continued the culturing of fungi in those concentrations also. After 12 days the results was their growth has decreased with the concentraion increment. But next time i added a same volume of EDTA of concentration 30 ppm to each copper concentration + PDA to avoid the precipitation of copper hydroxide. But after 12days the result was confusing. The growth of the fungi has increased with the increment of copper concentration. Can anyone please help me to solve this confusion.
EDTA does a lot of things. It can be used as a carbon source in some instances. It facilitates the uptake of some micronutrients/essential elements and can prohibit uptake a more toxic elements. Even for some molecules it makes it more soluble. So hard to pinpoint at this moment really. I would try non Cu supplemented media with EDTA and see if that has an effect on growth.
Dr. Norman, Dr. Asemoloye, Dr. Macro thank you very much for your answers. Actually i used a EDTA without copper as a negative control. In that one the fungal strain didn't grow showing the inhibitory effect of EDTA. But my problem is as i used same amount of EDTA in each 400, 800, 1000, 1200 ppm of Cu + PDA medium how the fungal growth increased with the Cu concenttation.
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