Science Buddies: "Ask an Expert"

I'd like to be able to measure the amount of sugar in a liquid solution that is processed by bacteria.
I was going to use different types of sugars in different tests and maybe different amounts.
I wanted to use two different bacteria: e coli and Saccharomyces cerevisiae (yeast).

What is the proper procedure for growing bacteria and would the same procedure be OK for these two different types of bacteria?
Can I just use distilled water as the medium? Would a 5 or 10 percent solution sugar/water be good?
I'm not sure what kind of nutrients to include in the mixture -- various minerals, but I'm not sure what is best.
Is there a premade mix that I could buy inexpensively?

I wanted to use disposable culture tubes.
How much solution should I put into the tubes and how much culture should be added?

Do I need to have an incubator or is room temperature OK -- are there easy ways to improvise an incubator?
I wanted the experiment to last until the bacteria stopped processing the sugars.
Is there a way to tell when that is complete? How long should that take?
[I thought it might be nice to measure how much bacteria has grown -- I've read something about using a photospectrometer to do that, but didn't quite get it. Is that a good way to do it or are there other ways?]

Then I wanted to measure the unprocessed sugar in the solution.
I'm not sure how to do that at all. I think I want to separate out the bacteria and nutrients from the remaining sugar solution and then somehow estimate the remaining sugar.
Would I need a centrifuge to do that or some kind of membrane or filter? I don't have a centrifuge but might be able to get one.
Could I then evaporate the water to estimate the remaining sugar, or maybe there is a better way to measure the sugar -- maybe I could measure the remaining solution concentration, but I'm not sure how?

Hi and welcome to scibuddies! You have asked a lot of questions so let me try to answer them one by one. But first let me correct one serious error in your post. Yeast are NOT bacteria. They are in the Fungi kingdom (http://en.wikipedia.org/wiki/Fungus) while bacteria are in the Eubacteria kingdom (http://www.ric.edu/faculty/ptiskus/six_kingdoms/). Fungi have a different type of cell wall from bacteria and their genes are organized into chromosomes enclosed within a nucleus while bacteria do not have a nucleus.

Growth procedure – E coli and S cerevisiae are both single-celled and can be grown in liquid medium with sugar, a nitrogen source and some simple salts—but definitely not distilled water alone.

E coli medium – The E coli K12 strain (safe to work with) and liquid culture medium can be purchased from Carolina Biologicals (http://www.carolina.com)

S cerevisiae medium – If you do a google search for this you will find many sites. Here is one: http://www.google.com/url?sa=t&rct=j&q= ... 4037,d.eXY

Growth conditions – You can buy disposable culture tubes from Carolina Bio. The amount of liquid medium to use depends on the size of the tube but is typically about 3 mL. E coli grow best at 37C but will grow ok at 24C. The yeast prefers about 40C but can be grown at 24C.

Cells per tube – You said you want to compare the ability of E coli and yeast to digest sugars so you need to standardize the number of cells you add to each culture tube. This can easily be done in a microbiology lab by using one of several different methods for counting cells (http://en.wikipedia.org/wiki/Cell_counting). It would be very helpful if you could do these experiments in a lab.

Measuring sugar metabolism – If you use glucose as the sugar you can buy glucose test strips and measure the amount remaining in the culture medium after one day, two days, three days, etc until the sugar is used up. Measuring concentration of other sugars such as sucrose and fructose is more difficult without being able to work in a chemistry lab.

This should help you in answering most of your questions but I’m sure you will have more. This is an advanced project and will take time for learning, gathering the materials and working out the procedures. Keep posting to Scibuddies and we will guide you through the planning and execution.

Good luck!

Sybee