I am growing cyanobacteria (PCC7942 and 6803) in BG-11 either with or without bicarbonate+HEPES, and seeing a very high pH (9-10) after a few days of growth regardless of the conditions. Any ideas on what could be causing this, and how to deal with it?
Edit: I am using 50 mM NaHCO3 and 25 mM HEPES in Sigma BG-11 media, where the initial pH is ~7.5. I am growing them in 24 well plates (1.5mL culture volume) and 100mL flasks (10mL culture volume), at 30C with a light intensity of 70 umol m-2 s-1. Minimal (orbital) shaking.
You've specified no initial pH; are you providing any buffering capacity to this media? Assuming the bicarb/HEPES are the buffers you also said "plus and minus bicarbonate + HEPES" so some of the cultures have no buffering components? They do have a salt base correct? Again a complete makeup of the media will be essential for anyone to help!
Have you tried different carbon sources? Have you done a growth curve and some plate counts along with the pH monitoring?
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