I had previously made a series of (modified SFM) agars at high alkaline pH 8----->13.6. I did not measure the pH of the resulting solidified agar because it just seemed a bit awkward and I was just trying to ascertain a maximumpH tolerance. Now I am writing the paper connected to this experiment and I am trying to have a idea of the change in pH of agar once it is sterilized. I have noted in my writing that this is indeed just pre-sterilization figures. However,iIn a letter to IJSEM, 2005, DY Sorokin stated that life was not possible above pH 10 !!!! He cited the poor quality of the studies because many did not mention the final pH (guilty !) and media not properly buffered (also guilty). However, we observed growth on the agar at pH 13 (measurement of pre-sterile agar solution). Are there any good articles on change in pH of agar or on organisms that they have definitively proved to have gone beyong pH 10 ?
Thanks Muhanna . Any literature references to this or is it just from experience ?
By experimentation we found that the pH of our agar (IPS 2 agar and modified SFM agar) would change after sterilisation. If the initial agar pH was adjusted to pH 13.0 with NaOH before autoclave, it might be as low as pH 11.0 after autoclave and then steadily decrease upon daily measurements. This could be modified by the addition of sterilised buffer after autoclaving. The decrease in pH has been attributed to gradual absorbtion of CO2 by thre media by some researchers. Some of our pH measurements of an alkaliphile are available here Research A Novel Alkaliphilic Streptomyces Inhibits ESKAPE Pathogens
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