I am growing e.coli in fermenter with glucose in minimal media at pH 7.4 (50mM SPB). Technically, first D.O. should decrease (to nearly zero) due to cell growth, and then it should increase, due to optimum growth. But, in my case, D.O. is decreasing up to 6-7% and remaining unchanged till end. Although growth and other vital parameters are normal, pH is decreasing and O.D. at 600 is increasing properly. I can't understand what is happening?
You mentioned growing e.coli in fermentor but did not describe how you operated the fermentor system while growing this e.coli.
Did you just run the fermentor at constant airflow and agitation?.
Did you notice a change in these two parameters toward the end of the run?.
Did you have a chance to check the function of your D.O electrode to see if the electrode is still responding properly to air/O2?.
Other than that, unless the culture pH dropped to growth inhibitory point, as you mentioned; cell OD still going up, this indicated the culture is still in a O2 demanding mode and not in a stationary or late stationary stage of growth where you will see oxygen level goes back up due to the supply oxygen not being consumed by the culture.
@ Loc Trinh, Thank you.
airflow (1 vvm) and agitation (300rpm) were constant all through. D.O. electrode is perfectly working. we had to maintain the pH constant all through as it had decreased by time. so the pH of media made remain constant at 7.0. but interestingly, D.O. didn't increased from 8% even after it reached to stationary phase.
secondly, I couldn't understand your question"Did you notice a change in these two parameters toward the end of the run?".......both of the parameters (airflow and agitation) are manually controlled. the answer is NO, I didn't see any change. rather I have seen little increase in pressure (~0.01 bar) at the mid time of the cycle. Could you answer me something more?
To clarify my question earlier regarding the change in airflow/agitation is that if you have had the fermentor system on automatic control of DO then the airflow or agitation would change (this depend on your controller) to accommodate to the change in DO level. Anyway, since you ran these 2 parameter constantly (1vvm/300rpm) then nothing is to discuss of that.
My other thoughts are as follow:
-Your observation of increase in vessel pressure only resulting in increasing the dsssolvability of oxygen but contrary in this case.
-Since your culture was still producing acetic acid (from consuming glucose) to change the pH of the media, I would assume the culture was not actually in a stationary stage therefore you would not have seen the spike in DO level (there may have been something in the media made this time that prolongs the growth stage of the culture??).
-~10% DO is not oxygen starvation level, if all nutrient and carbon source are not exhausted, then cells are still in a growing stage.
-Can you provide more info. on media composition/amount and OD of the growth? hopefully we can come up with a better picture of what was going on.
Yah sure, find attached herewith the growth curve (O.D. vs Time). the composition of media is glucose 1% (w/v), trypton 1% (w/v), cacl2= .015g/l, Mgso4=0.246g/l and kanamycin
0.2mM IPTG was induced after O.D. reached 0.6 (in this case after 5.5 hrs). I doubt caramelization of glucose may have some effect.
Hi Mohammad Saif,
If the case is the DO started decreasing after feeding was carried out, it may be due to the active utilization of the substrates fed by the microbes. I hope I get your question right.
You may want to check also this related RG discussion: https://www.researchgate.net/post/Can-oxygen-uptake-rate-OUR-be-greater-than-oxygen-transfer-rate-OTR
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