I am doing Acetone-Butanol-Ethanol fermentation with C.acetobutylicum and C.beijerinckii. I often experince that cells don't switch to solventogenesis and don't produce solvents.
I experienced it even when I had pH Control. Some literature suggests that butyric acid might be inhibiting, thus preventing the metabolic switch. However, I couldn't see a direct correlation between the butyric acid concentration and the switch.
I also looked at the relationship with the cell growth rate and the switch, but didn't obtain anything there either.
The problem was not the medium as I checked it to make sure that is not limiting.
Hi Cansu,
Do you use both strains together, in the same culture (batch, continuous,?)
I wrote a small paper about ABE production in bacterial consortia.
It deals fairly well with the questions you are asking yourself. See :
Thierie J. & Penninckx M. (2004a)
Possible occurrence of a Crabtree effect in the production of lactic and butyric acids by a floc forming bacterial consortium.
Current Microbiology 48 (3): 224-229 (March 2004)
Hope it can help you!
Hi Jacques,
Thank you for Your answer. You paper indeed has some useful Insights which can help me to understand what is going on.
I use only one strain at a time, so it is not mixed culture Experiment. I did only batch and fed-batch fermentation so far.
I had similar thoughts in fact: sugar concentration might have an impact on the metabolic pathway, so I changed the initial sugar concentrations and repeated the Experiments but I again couldn't find any Association.
Dear Cansu
Have you tried to add the small amount of acetic acid (1-3g/L) at the beginning of fermentation? (do not forget to adjust pH back). It was working in my case to do a metabolic switch relatively quickly.
Dear Igor,
Thank you for your answer.
According to my HPLC results, there is already some acetic acid in the begining of the fermentation (1-2 g/l) coming from the inoculum, I think. I shall try what you suggest as well, but my concern is the acid toxicity. Literature suggests that if total amount of acids reaches 5 g/l, cell growth is inhibited. Have you experienced inhibition due to acetic acid addition when working with Clostridia?
Dear Cansu
What type of bottles/reactors are you using for your experiment. Though it is not always compared and much mentioned but the type of reactor and the fermentation process do have profound impact of partial pressure of hydrogen produce during acidogenesis, which inturn effects tranfer to sovetogenesis phase.
I used serum bottle sealed with rubber stoper during butanol production from lignocellulosic waste. Because of variation in rubber stoppers sometime gas produce during acidogenesis got leaked which inturn effected sovent production. More H2 partial pressure, more solvent and more butanol production. Once H2 pressure exceeds, it inhibit further h2 production which than inhibits acidogenesis and tranformation to soletogenesis.
So depending on your reactor do you get high gas/H2 pressure?
Dear Mustafa,
Thank you for Your answer. I did the fermentations using microreactors, serum flasks as you did and 1 L fermenters. Switching to solventogenesis was always a problems in some of them, so I couldn't conclude anything based on the scale of Application.
I would think that whatever is present in the system would have an effect on the metabolic pathway. I can imagine that Dissolved or headspace gases would have an impact, but I was more worried about the CO2 other than H2. I have only measured the CO2 in the outlet gas stream from the fermenter, so I don't know about H2 gas particularly.
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