Nutrient broth with lead acetate

[AlanaC]

Heya,

Stumbled upon an problem. We are trying to create nutrient broth with a range of concentrations of lead acetate in order to grow lead-tolerant bacteria. The problem is, when we add the lead acetate solution to the nutrient broth it immediately precipitates, it then reacts and changes from a white precipitate to a grey/black precipitate when we autoclave it.

Anyone got a solution? We know its been done before, but we don't know how and seem to be missing something...

Thanks

[Iota]

http://www.lenntech.com/periodic/water/lead/lead-and-water.htm

 

Try Lead Carbonate. Can you alter the acidity of the broth without affecting the bacteria too much? If so apparently Lead is more soluble in slightly acidic soft water.

 

Found this, read Solubility of Lead and Lead compounds specifically. The whole page looks potentially helpful with your problem though.

 

Also, does the compound look like Lead Hydroxide, turning into Lead Oxide?

Edited July 17, 2013 by Iota

[AlanaC]

Thankyou!

We did try altering the acidity of the solution we made, which did make the lead dissolve, but then we pipetted some of that into the nutrient broth and the white powder just reappeared. We also tried adding the acid once the lead was in the broth but it had no effect whatsoever!

And it does look like lead hydroxide when we first put it in, and then changes once autoclaved.

Edited July 17, 2013 by AlanaC

[John Cuthber]

How much lead do you think you need to add?

If you are adding so much that it falls out of solution, how could you have that much naturally present?

[AlanaC]

Soil samples contained lead ranging from 7-10%

Edited July 18, 2013 by AlanaC

[Iota]

If that doesn't work let the forums know, there are obviously people far better at chemistry (and Google searches) than me here who can probably help.

 

Welcome to the forums btw!

[AlanaC]

Thankyou!

[John Cuthber]

Soil samples contained lead ranging from 7-10%

How much of that 7% is actually soluble in water?

 

If it's not soluble then it's not available to the bacteria so there's no point trying to "mimic" it in the culture medium.

I think most media contain chlorides and that will precipitate lead so there's no way to get the lead content much higher that the concentration you get from a saturated solution of lead chloride.

[CharonY]

In addition autoclaving is generally a bad idea, as often your pH shifts promoting precipitation or oxidation of metals, for example. Sterile filtration is usually better. However there may be other salts with which the lead could potentially react, depending on what you use as medium. From what I recall (and it has been a long while) Pb-Ac is quite soluble in water (IIRC the stock solutions were maybe around 20-30%). But routine use for certain test media are likely not more than 1%.

[John Cuthber]

Lead acetate is quite soluble, but lots of other lead compounds are not. For example, lead phosphate isn't very soluble.

If the medium has phosphate in it (and it's tricky to see how the bugs will grow without it) then you will get lead phosphate precipitated if the product of the concentrations of phosphate ions and lead ions exceeds the solubility product for lead phosphate (estimates vary but that's of the order of 10^-10 in near neutral solutions and 10^-40 in alkaline solutions.).

 

Autoclaving it may well produce side reactions with (in particular) sulphur containing compounds.

If you can't sterile filter the mixture then autoclave the lead solution and the rest of the material separately then mix them.

 

The important thing is that lead which has fallen out of solution can't affect the bacteria.

 

Another option would be to add something like EDTA to keep the lead in solution- but then that might kill the bugs and, of course, the lead EDTA complex will have a different toxicity.

[AlanaC]

Thankyou very much, we will have a play around with it next week. We're using the same/similar concentrations of lead used by previous papers so it must be possible somehow...