clumpy yeast

John Cannon cannon at MEDSCI.MBP.MISSOURI.EDU
Wed Nov 24 16:51:41 EST 1993

  The buffering capacity for yeast nitrogen base is very low. It only
uses phosphate (pK 6.8) to buffer a growth medium at 5.8 . Since
yeast will obviously acidify the medium during fermentive growth, a low
pH may be what is causing the cluminess. Check the pH! I have found
the pH can reach as low as 1.9!! in SD medium. The best way to solve this
is to buffer with succinic acid (pk somewhere about 5.8). Dicarboxylic
acids are not taken up by yeast and the pK of this buffer is good. We
use 10 gm of succinic acid (make sure its the free acid) and 4.5 gm
NaOH added before autoclaving. No pH adjustment necessary, just make
sure everythings dissolved before you autoclave otherwise you will
carmelize the sugar. Good luck,
John Cannon
Department of Molecular Microbiology and Immunology
University of MIssouri
Columbia, Missouri  65212

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