Hi again,
I think you should try to find out how much yeast extract is in the solution that you will use because that concentration is really the important one. You are probably right that the 2% means one-fiftieth of the volume of the mud. So, if you have 32 ounces of mud by volume then you would add about 0.6 oz of yeast extract which would be--if my kitchen measurements are correct--a little more than one tablespoon.
As I said, how much you should add to the mud really depends on how concentrated the yeast extract is. In other words, how much yeast extract was added to what volume of water. In the lab, this would usually be expressed as grams of YE per milliliter, g/mL, so you probably should use metric measurements when doing the calculations.
Remember that YE contains mostly amino acids and peptides and is a nitrogen source. Your mud bacteria still need a carbon source like glucose or sucrose. You can test YE alone, but you should also test YE plus sugar. Here is the recipe for a commonly used medium called Luria broth that is used to grow bacteria such as E coli:
http://cshprotocols.cshlp.org/content/2 ... _only=true
Luria broth contains 5 g of YE per liter which would be 0.5%. But the recipe calls for powdered YE, not a solution. If, for example, you had a 10% solution of YE, how much would you have to add to one liter to be equivalent to 5 g? A 10%, weight to volume solution, has 10 g per 100 mL of water so you would have to add 50 mL of 10% YE to make one liter of Luria broth.
What I am trying to do is make a comparison between how much YE is in a common bacterial growth medium and how much YE you would be adding to the mud if you added 2% of the mud's volume. Once you find out the YE concentration then you can work from that to calculate the amount of YE being added to the mud and see how it compares to the amount in Luria broth.
I hope I haven't confused you with all this math! These are the kinds of calculations scientists have to do every day, so we are used to it. Getting the concentrations of things right is critical and many experiments have failed because someone made a solution wrong or wrote down milligrams when they meant micrograms!
Keep us posted on your progress and don't hesitate to ask any question. We want you to understand why you are doing things a certain way and not just follow a recipe.
Good luck!
Sybee
