High concentration lead acetate (100 ppm) produce visible white color particle when added into LB broth media. What are the possible reasons for this...It could be visible even at 10 ppm level. Is it because lead reaction with Cl in media to form PbCl2?
I am also trapped in this problem. But one thing I can be clear is that the precipitation is not only PbCl2, since I once tried to mix lead(II) nitrate with pure yeast extract solution (main nutrient ingredient of YA broth) and precipitation still exist.
I heard some suggestions of adding chelating reagents like EDTA to handle this problem, but I am not definite about the exact dosage.
Dear Rui,
Thank you for your reply. But we cannot add EDTA because it chelates divalent cations which important in culture media. Do you have any clue about pH change?
Dear Nilmini,
The less solubility of Pb-salts and its property to under go displacement reaction might be the major concern leading to the formation of precipitate when its added to complex-chemical media. As of few literature, the complete solubility of Pb can be achieved by adding strong acids. if microbes are capable of transferring Pb into less toxic species, or pyromorphite, the change in pH of the media from slightly acidic to alkaline is observed. This further depends on the type of fungi/bacteria/yeast used in studies.
As Rui suggested, even few data has suggested the incorporation of EDTA as chelating agent at certain ratio 2(edta):1(Pb), but its bio-availability and acting by microbial enzymes depends on many other factors.
Hi all,
Here are some updates of my previous answer. After weeks of attempts, my advisor lost his patience and I had to using total lead concentration instead of ionic concentration. Of course, the amount of bioavailable lead is different from that of total lead, but we can still find a turning point where higher lead concentration (total) will significantly inhibit bacterial growth. However, since my research field is close to civil engineering and does not need a precise determination of minimum inhibitory concentration (MIC), I am not sure this tactic is suitable for medical or biochemical research.
As Bhavya G. said, if you take a look at pH values after adding lead solution (1-10 mM) to culture media, there will be an increase. There must be some reasons in it, but unfortunately I have not mastered relating chemistry theories yet. Also, with higher total lead concentration (>100 mM), the pH increase cannot last forever and a turning point will occur.
Lead salts specially lead acetate tends to form insoluble salts and complexes with proteins. As any broth culture media contains high quantity of proteins, so it will form whit precipitate upon lead acetate addition.
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