Thread: How do you count yeast cells?

I'm planning to do a project on the effects of various chemicals on the growth of yeast, but I've got a problem. I have everything figured out apart from how I could get quantitative results of the actual growth rate. I work with very small quantities, so drying them won't do any good. No matter how hard I thought about this I couldn't come up with anything solid, only a vague idea of finding the average "population density". Does anybody have any ideas?

P.S In case you're wondering, this is not part of any class work.

Individually. :P Joking.

Can't you count the number of colonies formed?

All the best,

Tridimity

Perhaps you could use the fact that the more yeast cells you have, the more light the solution will absorb. I guess you could measure this with a spectro photo meter (I don't know if that's the proper term).

like thyristor said your best idea would be some form of calibration technique where you find a property that depends on the number of yeast cells present.

then take a sample of a known number of yeast cells and measure this property,

produce a calibration curve of yeast cells vs property.

then whenever you need to know the number of cells just measure this property and look it up on the curve

Originally Posted by Escherichia

. Does anybody have any ideas?

None at all, but this site seemed interesting and there might be something relevant in the references.

Is it not possible to just use a haemocytometer for this?

Originally Posted by TheBiologista

Is it not possible to just use a haemocytometer for this?

Labour intensive and tedious, but ya that's probably your best bet.

Flow cytometer then. Bigger sample set, less error prone, more information.

I have a feeling someone in Zambia might not have access to a flow cytometer, they can be pretty expensive. Your recommendation of the hemocytometer is probably the simplest way.

Edit: The spectrophotometer recommendation is a good one too, although you would need some sort of control to know what kind of absorptions to expect for a given cell density in your growth medium. (It's also not very sensitive)

Thank you for your suggestions guys, but I see now that I should have put more detail into the original question. First of all, I use a liquid medium (a sucrose solution to be precise). And concerning equipment, this is the scenario: The best laboratory that I would have available is the only lab in a 5-year-old mission school in the middle of Africa. This obviously doesn't give me the best of equipment, so it might be that I won't be able to do this at all. However, if despite these limiting factors, you have any ideas, they are very welcome.

If you can't get a hold of hemocytometers you can still do serial dilutions of your medium and do a manual count under the microscope. Make sure you always put the same volume on the slide, you'll need a micropipette.

It's not going to be very accurate with regular slides, but you can probably get a rough idea of how many you have. I hope you have micropipettes and microscopes, or I'm out of ideas.

Thanks, I'll try that. Short question though, what do you mean by a micropipette? And why do I need that? At school we have pipettes with which I could measure 1/2 ml (maybe even 1/4). Would that be alright?

Originally Posted by Escherichia

Thanks, I'll try that. Short question though, what do you mean by a micropipette? And why do I need that? At school we have pipettes with which I could measure 1/2 ml (maybe even 1/4). Would that be alright?

Not at all, unfortunately- these are quite remarkably inaccurate on the scale that we're concerned with. Micropipettes typically work with accuracy over a range from less than 1 ul (that is one microlitre or 1/1000th of a ml) up to 1 ml. But typically used in the range from 50-200 ul for your purposes. Eppendorf and Gilson make good ones- but a decent set of them with various volume ranges will probably cost you at least $700. Plus you have to buy disposable plastic tips for them.

Could you give us a rough run-down of the lab equipment that is available to you. Installed equipment and consumables?

TheBiologista wrote

Could you give us a rough run-down of the lab equipment that is available to you.

This is all I can think of that would be applicable to this topic:
Microscopes (magnification 1200x), pipettes (accurate to 1/2ml), standard microscope slides & covers, test tubes, vials (5ml holding capacity), standard lab equipment (bunsen burners, spatulas, etc.).
I'd have to check if there are any others in case you need them.

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