Non-exponential growth curves?

I’ve been having a similar issue in a couple different contexts. My periods of growth in between dilution events are not very exponential. They seem kind of… sigmoidal? (img below)

Any one have ideas/experience/solutions for this?

My hypotheses/experiments to try listed here:

  1. Is it a simple calibration issue? Recalibrate to test.
  2. Is it a true biological effect, where they saturate at relatively low density? The most likely candidate for such a limiting resource is oxygen, so maybe try different stir rate and see if it goes away? (currently stirring at “8”, do people routinely do higher?)
  3. Is it that I’m looking at or thinking about this incorrectly? Perhaps i shouldn’t expect to see a exponential-like curve at these scales. I’m just hoping to get my data looking as best I can for calculating growth rates later on.


You’re thinking about it correctly. I think its most likely a limitation of the OD reading. We might not be able to hit the higher OD readings right now with how your system is currently setup, measuring absorbance instead of scattering. Again, I’m still figuring out details on this. Will keep you posted.