I typically don't adjust the pH of my CSM (SC-HIS) or YPD media when growing yeast, and wondered if it had a significant effect on growth? After measuring both, YPD seems fairly neutral however the pH of the CSM is about 4.5-5 which seems fairly low - should I be concerned about this? And if I should, can I just add NaOH to neutralise it?
You can just try growing the strain at different pH and decide based on what you want. From my experience with Candida albicans it doesn't grow well at low pH. However, it all depends on what environment one wants to mimic in vitro: if that of the vagina, the pH should be low. I bet S. cerevisiae also prefers a less acidic pH. And yes, adding NaOH is OK to raise the pH of an acidic medium.
Just to clarify my answer above. What you are asking about is adjusting the pH of CSM mix (which is not the final media used for cultivation). The final (SC) media consists of CSM + glucose (or whatever carbon source you are using) + YNB. Usually the adjustment is done with a buffer either in the final media or YNB. So no you do not need to worry about the pH of the CSM. In addition just to grow your cultures ON (routine cultivation) buffering the YPD is not necessary. Best of luck!
When you grow yeast cells, the pH of the medium gets more acidic over time. If you want to keep the cells growing for a long time it is good -as suggested by Hanna- to include a buffer in the recipe.
The optimum pH for most micro-organisms is near the neutral point (pH 7.0). Moulds and yeasts are usually acid tolerant and are therefore associated with the spoilage of acidic foods. Yeasts can grow in a pH range of 4 to 4.5 and moulds can grow from pH 2 to 8.5, but favour an acid pH
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