pH problem

Jeffrey A. Radding JARADDING at
Sat Jan 15 17:10:23 EST 1994

Tien-Hsien Chang <tchang at> writes:
>     We are studying a particular drug resistance/sensitivity of the budding 
>yeast.  We noticed that the pH of the yeast culture in minimal medium 
>supplemented with required amino acids drops substantially to nearly 3.  This 
>created a problem for us, as the drug may get inactivated or converted to other
>chemical forms at such a low pH.
>     Is there any well-established protocol to buffer the SD (synthetic 
>dextrose) medium, both liquid and solid, allowing pH to be maintained at 7.0 in
>the culture ?  Any other relevant information or references will be greatly 
CCLS recommends a MOPS buffered RPMI
medium.  We have tried this with SD meedia for yeast in dilution microbroth
assays and have measured the pH with an electrode before and after growth of
the cultures at pH's ranging from 5.0 to 7.0.   At pH 7.0 the culture pH
after growth for 48 hrs dropped only 0.2  pH units, so it seems to buffer well
in SD media.  We have not tried it in solid media, but you might give it a
shot.MOPS is 0.1 M and titration to the pH with NaOH.  There is an NCCLS
on the recommended susceptibility test system, but I don't have the reference
immediately accessible.  Hope this helps.
Jeff Radding
Eli Lilly and Co.
"Opinions expressed are my own and do not in any way represent the views or
opinions of Eli Lilly and Co."

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