polyethylene glycol

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lucilius
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polyethylene glycol

Are there any scientists here that use PEG or have worked with it and are able to explain me why a sample with PEG and a fungus becomes very low in pH.
(maybe the fungus has some importance in the proces, but maybe its just the PEG that can make a solution lower in pH at certain circumstances).

At the start the sample had a pH of about 7, after 5 months all of a sudden the sample reaches a pH not even higher then 3.

Also important to tell: I only noticed this drastical decrease in pH with samples stored at +20°C.

It didnt happen with samples stored at 5°C.

ghunter
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from what you have told, it

from what you have told, it is obvious to me that pH change you have observed is growth related. It doesnt have much to do with the presence PEG.

lucilius
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ghunter wrote:from what you

ghunter wrote:

from what you have told, it is obvious to me that pH change you have observed is growth related. It doesnt have much to do with the presence PEG.

how come you are so sure about that?

Then why isnt there a decrease in pH in the samples preserved by 5°C ? Eventough there is growth in those samples too?

Maybe because the growth in the samples preserved by 20°C is bigger?
Maybe, maybe not?

Another remark then: how come the pH decrease is only viewed after 5 months of preservation? Is this because the fungus is not growing fast enough the first 4 monhts?

Maybe , but how can you explain then that the growth of the fungus is almost the same in the samples preserved by 20°C and 5°C the first months.

you can then answer that it is because of the fact that the fungus preserved by 20°C starts to grow faster and more after 4/5 months, but thats a strange answer to me then.

I wonder if the PEG hasnt got anything to do with it.
I should have stored some negative samples too at 20°C , but I forgot that, didnt think it would be needed.

ghunter
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Basic chemistry. There is no

Basic chemistry. There is no charged groups in PEG. You said you have pH around 7 to start with. It could not have been due to PEG.

lucilius
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Could be, I am not a chemist,

Could be, I am not a chemist, thats why I ask it.

Still, I find it strange.

So basically you state the the temperature has no effect what so ever on PEG?

ghunter
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No. PEG is very stable.

No. PEG is very stable.

However, temperature does have an effect on the growth rate.

Acids are generated while bacteria or fungi grow.

lucilius
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Quote:No. PEG is very stable.

Quote:

No. PEG is very stable.

However, temperature does have an effect on the growth rate.

Acids are generated while bacteria or fungi grow.

I agree on the fact that temperature has an effect in the growth rate and that acids are generated while bacteria or fungi grow.

But I wanted to know for sure that PEG has no influence in it what so ever. (on the change of the pH)

anyway, this brings me to the next question: how come I only see this when I use PEG (not when I use sucrose or ...) and when the temperature is 20°C?
This does mean that the temperature has a big influence on the the stability of PEG (in combination with the fungus then?)

The knowledge that PEG is very stable and that normally when you store PEG without micro-organisms you will not see a decrease in pH makes it only harder for me to understand it because it gives me even more questions.

ghunter
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You have to provide more

You have to provide more details on how did you do this study in order for me to comment on it. However, suger, when used at high concentrations acts as a perservative, while I can not to say the same is true for PEG, because its innertness.

lucilius
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Well ghunter, I will try to

Well ghunter, I will try to explain the test.

I have made suspensions with 10% PEG and 90% demineralized water. These suspensions (6 samples for each temperature) were filled with a fungus at a certain concentration.
They were then stored at 20°C ,5°C and one in the freezer.
I opened the samples and checked the viability of the samples each month for 6 months long. And after 5 months I noticed the really low pH of the samples stored at 20°C.

I have done this with some other suspensions too like the negative control one with demineralized only, with sugars (like sucrose) or with another surfactant (tween).

I hope this helps a bit.

It not really a very specialised research or study.

ghunter
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Back to your original

Back to your original question: "(maybe the fungus has some importance in the proces, but maybe its just the PEG that can make a solution lower in pH at certain circumstances)."

PEG itself should not contribute to the pH change at this temp. At higher temperature, strong light and with plenty oxygen, it may turn to first to aldehyde then acid. The reaction rate is not going to be very fast, though. It can be easily overwhlemed by other facts in your system. First, ask yourself, did you washed the fungus real well (at least 3X) with inorganic saline before you innoculate it? Is there any chance that you brought in additional organic substances? That would complicate the interpretation. Ideally, a tube with 10% PEG alone stored at this temp would be needed as a control.

Would the fungus that you put in grow on PEG and use it as the only carbon source and would it be due to the growth of the fungus that led to the pH change? If you are sure that you have done everything right, check if it has been reported or not. It may worth publishing it if you find out something can grow on PEG and capable of degrade it.

Good luck.

lucilius
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ghunter wrote:

ghunter wrote:

PEG itself should not contribute to the pH change at this temp. At higher temperature, strong light and with plenty oxygen, it may turn to first to aldehyde then acid. The reaction rate is not going to be very fast, though. It can be easily overwhlemed by other facts in your system.

Well, the temperature was only 20°C, so that shouldnt be a problem. The oxygen shouldnt be a problem either, because the tubes were airtight expect once when I took a sample out the tube, but that shouldnt do much.
About the light: it was dark, except the few times someone opened the room.

You have any idea about the reaction speed itself? or maybe the reaction istself, some more information?

ghunter wrote:

First, ask yourself, did you washed the fungus real well (at least 3X) with inorganic saline before you innoculate it? Is there any chance that you brought in additional organic substances? That would complicate the interpretation. Ideally, a tube with 10% PEG alone stored at this temp would be needed as a control.

I cant be 100% sure , but I think it should be done proper. THe fungus was indeed washed 3 times, with deminezalized water.
Any additional organic substances? No normally not.

And indeed, I should have stored a 10% PEG tube as a control tube at 20°C , but I never imagined something would happen so I only stored one at 5°C

ghunter wrote:

Would the fungus that you put in grow on PEG and use it as the only carbon source and would it be due to the growth of the fungus that led to the pH change? If you are sure that you have done everything right, check if it has been reported or not. It may worth publishing it if you find out something can grow on PEG and capable of degrade it.

Good luck.

At the moment I cant find any literature about it.
PEG is mostly known as a fusogen or to change the water potential.

Or sometimes the influcnce of celbinding, but that has to do with the the fusogenactivities

snafu2000
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ghunter is exactly correct on

ghunter is exactly correct on this issue.

snafu2000
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ghunter also states fact

ghunter also states fact about sugar concentration changing from growth factor to preservative in higher concentrations. I would recommend taking his/her advice.

lucilius
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well snafu2000 and ghunter,

well snafu2000 and ghunter, it does seem that there are fungi that are able of using peg as a substrate.
Some fungi can indeed break down peg, but this is very rare!
I could only find 1 paper about this behavior.