Re: [DIYbio] Re: Transformation questions

Although in practise, you can get away with sugars/aminos for straightforward growth media. You'll get caramelisation but the bugs won't care.

Cory Tobin <cory.tobin@gmail.com> wrote:

>> A professor I met told me you can't autoclave CaCl2 ...??
>>
>> Sounds strange to me because it's a salt... Does it dissociate??
>> Anyone heard of this? Maybe it's common knowledge which I didn't have
>yet...
>>
>> She told me that you just filter the cacl2 (and showed me where the
>filters
>> are in case I want to use 'em) and bactreria are filthered out by
>this
>> filters.
>
>The dissolution of CaCl2 in water is highly exothermic, so it's
>possible to precipitate CaCl2 by heating. But in practice I have
>never had any problem with autoclaving CaCl2 by itself. I do it all
>the time for making competent cells. But I think if the concentration
>is high enough you can get precipitation.
>
>Although, if you are mixing CaCl2 with growth media, you definitely
>have to mix the CaCl2 into the media *after* autoclaving. I just
>autoclave the two separately, then mix the two solutions in sterile
>conditions after the solutions have cooled. For some reason stuff
>precipitates in media/CaCl2 mixtures when heated, I'm not sure what it
>is though.
>
>Some other things you should not autoclave:
>- Detergents
>- Sugars (Sometimes this works OK, sucrose is usually fine, but I
>filter sterilize just to be safe)
>- Sugars with amino acids (Maillard reaction)
>- Phosphates with metals
>
>-cory
>
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