In my opinion, the dissolved oxygen level is not the best parameter for control of the optimal oxygen supply in fermentation processes. The optimal oxygen supply you can find, if you measure oxygen uptake rate or CO2 evolution rate by means of O2 or CO2 analysis in outlet gas. Increasing or decreasing agitation rate or aeration rate (it depends on what you use for control of oxygen supply) you can find the point, where there will be any increasing of oxygen uptake rate with increasing agitation or aeration rate. It is the optimal point for agitation or aeration rate . You can see at that moment also DO value, but it is not necessary. Because it depends on liquid viscosity and biomass concentration, which usually change during fermentation process. It means also, that to keep the optimal oxygen supply you should repeat the seeking procedure from time to time during fermentation process.

Hi Mohammed

Usually, the answer depends on a few conditions like cell density, foaming activity of your media and the kind of reaction you perform.

If you have oxidation steps, the consumption and availability might be higher, perhaps you need to have a high turbidity, possibility to regulate the back presssure to increase the partial pressure of dissolved air inside your mix and eventually a possibility you to sparkle pure oxygen, if nothing else works.

Do you have a pO2-measuring and regulation available at your unit?

Think your pO2 should be clearly above zero, perhaps you can fix a minimum at 10% to have a little buffer before your cells really limit; maybe you need to increase the speed of your stirrer or/and the absolute airflow to keep this value.

good luck

Mohamed Sebak : at first I would like to point out that fermentation generally means an anaerobic process. Please see definitions of fermantation on web.

It looks that you are talking about aerobic cultivation of actinobacteria. If the process should be really aerobic, you have to reach dissolved oxygen concentration >1.5 mg.L-1 to avoid starting limitation by oxygen, called anoxic stress. It is the reason why for wastewater treatment using activated sludge process the lowest concentration of dissolved oxygen is 2 mg.L-1.

Best regards

Vit

We are culturing Actinobacteria in 30 liters M2 production medium, inoculated with seeding culture (10% v/v) which is operated under agitation, 200 rpm; aeration, 1.5 vvm; pH, 7.0 ± 1; and temperature, 28 ˚C to isolate and purify crude extract for further investigation. Then, if you found any novel natural product, you may proceed for optimization of culture conditions.

Regards

Hi Mohmed,

You will probably enjoy reading on these recent publications, both by our group:

Article NOVEL EXOPOLYSACCHARIDE PRODUCED BY Acinetobacter bouvetii U...

Where aeration conditions are explicit for the same bacteria genera; and

Article Stable bioemulsifiers are produced by Acinetobacter bouvetii...

In my opinion, the dissolved oxygen level is not the best parameter for control of the optimal oxygen supply in fermentation processes. The optimal oxygen supply you can find, if you measure oxygen uptake rate or CO2 evolution rate by means of O2 or CO2 analysis in outlet gas. Increasing or decreasing agitation rate or aeration rate (it depends on what you use for control of oxygen supply) you can find the point, where there will be any increasing of oxygen uptake rate with increasing agitation or aeration rate. It is the optimal point for agitation or aeration rate . You can see at that moment also DO value, but it is not necessary. Because it depends on liquid viscosity and biomass concentration, which usually change during fermentation process. It means also, that to keep the optimal oxygen supply you should repeat the seeking procedure from time to time during fermentation process.

Thanks for your great answers, really I got great knowledge from the answers and attached papers. Thanks again