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How to adjust the pH of a bacterial culture medium using a buffer?


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#1 Ellen Sepanian

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Posted 08 December 2016 - 01:58 PM

Hi 

I am trying to adjust the pH of a bacterial culture medium containing Peptone, 10g, Beef extract, 10 g, NaCl, 5g, pH 7.3 ± 0.1  in order to test the pH range my bacterial isolates can tolerate. I am going to use sodium acetate/acetic acid, Tris/HCl and  glycine/sodium hydroxide buffers to adjust the pH of the medium to below 6, 6-9, above 9, respectively. Could anyone help me with the whole procedure. which buffering capacity for each buffer I should go with? Should I add the buffer after autoclaving or before? 

Thank you



#2 bob1

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Posted 09 December 2016 - 07:34 AM

Does it need to be buffered? Currently your system is not buffered (assuming those components are the only ones). Generally you can adjust the pH of non-buffered systems using HCl or NaOH. Acetate would work too for low pH, but you should consider the bio-availability of the free acetate and the role this might play in metabolism - simple molecules can have big differences on bacteria.



#3 Ellen Sepanian

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Posted 10 December 2016 - 07:44 AM

I decided to buffer the system because the pH of the medium would drop after autoclaving. Maybe I should have adjusted the pH after autoclaving. for that matter, is it neccessary to sterilize NaOH or HCl (by autoclaving or filter sterilizing)?


Edited by Ellen Sepanian, 10 December 2016 - 07:56 AM.


#4 El Crazy Xabi

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Posted 12 December 2016 - 03:15 PM

The pH change after autoclaving is normal and most pre-made complex media indicate this in the SDS/label/manufacturer's website. If you need such an strict pH try to account for the pH change and adjust the pH to a slightly higher value before autoclaving. That;s the safest bet.

 

Adjusting pH in sterile conditions is a pain and introducing a buffer will change the culturing conditions... and introducing different buffers for different pH values may create very different conditions. e.g. you are adding potential C and/or N sources (acetate and glycine)






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