I would like to calculate the pH of a certain bacteria species before after an experiment. I was reading about the pH cell of bacteria and I found out about Bacterial Intracellular pH which I different than the pH level outside the cell. I plan to measure the pH Outside of the cell as a method to represent the pH of the bacteria.

My experiment:

I am soaking a piece of paper into a bacteria solution (bacteria + media). After that, I am exposing the piece of paper to different parameters. I would like to measure the slight change in pH if any, due to the exposure. In sum, I would like to measure the pH level of the bacteria on paper before and after exposing it to different parameters to compare the change.

My idea:

For before and after exposure, I will submerge the paper in a neutral liquid suck as DI water or a new sample of the bacteria media for an hour and measure the pH of the solution. Is that a valid method to measure the pH change or do I have to use a dye to see the color of the cell to quantify the pH?

  • $\begingroup$ I think that the only way you'll find this out for this system is to try it. Why not measure the pH directly in the solution rather than putting the bacteria on paper? It may be very hard to get reproducible amounts of bacteria by soaking the paper. $\endgroup$
    – bob1
    Sep 8, 2021 at 2:13
  • $\begingroup$ @bob1 Aren't nutrient solutions for bacteria usually pH buffered? $\endgroup$
    – Roland
    Sep 8, 2021 at 11:16
  • $\begingroup$ @bob1 I do not know how to take the measurement for the Bacterial Intracellular pH. Therefore, I can not validate my measurement if I took it for the solution or the paper. I was wondering if someone has done both and notice any ddifference. $\endgroup$ Sep 8, 2021 at 13:44
  • 1
    $\begingroup$ @AnwarElhadad I don't think this is a great way to measure external pH (just pH the media), and I don't think any measurement of external pH would be a reliable proxy for cytoplasmic pH unless it was first validated in that specific organism. Different bacteria can have dramatically different pH homeostasis mechanisms. For example, E. coli can maintain its cytoplasmic pH within a range of pH 7.4–7.8 over an external pH range of 5.0–9.0. This review discusses some of the measurements and homeostatic mechanisms. sciencedirect.com/science/article/pii/S0065291109055015 $\endgroup$
    – MikeyC
    Sep 8, 2021 at 19:00
  • $\begingroup$ @MikeyC I was thinking of having a very high-density bacteria solution to come close to the PH of the outer layer of the cell $\endgroup$ Sep 9, 2021 at 1:50

1 Answer 1


The pH level of the Bacterial Intracellular structure is different from the pH level on the eternal side of the cell. Moreover, there are no studies that suggest that a change in the external pH of the cell will have a linear impact on the Intracellular pH. Therefore, the best methods to measure the Intracellular pH of the bacteria cell are:

  • microelectrodes ( Escherichia coli intracellular pH, membrane potential, and cell growth. J Bacteriol 158:246–252)

  • radiolabeled membrane-permeant probes (Escherichia coli intracellular pH, membrane potential, and cell growth. J Bacteriol 158:246–252)

  • pH-sensitive fluorescent probes (Noninvasive measurement of bacterial intracellular pH on a single-cell level with green fluorescent protein and fluorescence ratio imaging microscopy)


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