Hi Itay Katz ,

I'm no expert on the strain you mention in particular but I do have quite a bit of experience with obligate anaerobes and fermenters.

If you want to mimic a high fiber diet, I would suggest feeding them some cellulose and potentially growing a biofilm on a solid matrix if possible as this would be more representative of this strain is likely to exist in its natural habitat.

If you are growing them fermentatively right off the bat you should not need to wait very long as the cells will want to access any type of energy they can. That being said, if you're shifting the conditions drastically, say from aerobic growth on oxygen down to fermentation, you may find there is a lag phase. This would really depend on how nutrient rich your medium is but in my work with Clostridia that can ferment cellulose among other plant-based materials it was not uncommon to have a lag phase of a 3 to 7 days before seeing explosive growth.

One thing you could potentially do is prime their fermentative metabolism with pyruvate, which is a simple sugar that can easily be mixed into defined medium. In terms of testing whether electron acceptors are present, my recommendation is don't make the medium with electron acceptors. If this strain has no genomic evidence of any anaerobic respiratory enzymes such as nitrate or sulfate reductase then it should not be an issue. Either way, even if there are trace electron acceptors they would be rapidly consumed once you inoculate your medium. If you are growing them in medium where there were electron acceptors present to ensure you have a healthy inoculum, centrifuging and washing three time with buffer is a well-accepted step for inoculating cells into the desired growth conditions with minimal carry over from the previous medium.

Really the key here for your piece of mind is use a medium where there are no electron acceptors available. You would need to supply them at mM amounts to have robust growth via respiration. Make sure the atmosphere in your container is N2 or N2/CO2 mix. In my papers I've used argon as well for the headspace in crimp bottles to avoid the metabolization of N2, which many fermenters can convert to reduced nitrogen for growth:

Article Heliobacteria Reveal Fermentation As a Key Pathway for Mercu...

I hope this helps, please let me know if you would like to discuss things further in this thread.

Daniel