YEAST MEDIA: an opinionated primer

If you are trying to compare your work to classical S. cerevisiae genetics literature, deletion collection benchmarks, or older plasmid-selection workflows, you should not assume that a product found on the shelf labeled “SC-Leu,” “CSM-Leu,” or “YNB” is equivalent to the medium used in those papers. It is your responsibility to check the actual formulation from any commercially purchased product you use in your experiments.

For classical yeast genetics and dropout media, my default reference is Fred Sherman’s Table 8 from Getting Started with Yeast / Methods in Yeast Genetics lineage recipes. That recipe tradition was the background culture of many yeast labs for years. 

A crucial point: DROPOUT MEDIA ARE DEFINED MEDIA, BUT THEY ARE NOT MINIMAL MEDIA. Once you add amino acids and nucleobases, you are no longer working with a “true minimal salts medium,” even if glucose is the main sugar in the flask. Amino acids contain carbon, nitrogen, and sometimes sulfur. They alter growth, physiology, auxotrophy behavior, and metabolite pools. Treat them as part of the experimental condition. If your biology depends on nitrogen status, amino acid balance, metabolite pools, cell size, or growth physiology, these distinctions matter. Omission of one supplement does not make the medium “minimal!”


TABLE 8: SYNTHETIC COMPLETE MEDIA (SC) (See F. Sherman, Getting started with yeast, Methods Enzymol. 350, 3-41 (2002).)

Constituent Final Stock per 100 mL Amount of Stock (mL) for 1 Liter
 Concentration
 (mg/L)
 ––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––

Adenine sulfate 20 200 mg b 10

Uracil 20 200 mg b 10

L-Tryptophan 20 1 g 2

L-Histidine-HC1 20 1 g 2

L-Arginine-HC1 20 1 g 2

L-Methionine 20 1 g 2

L-Tyrosine 30 200 mg 15

L-Leucine 60 1 g 6

L-Isoleucine 30 1 g 3

L-Lysine-HC1 30 1 g 3

L-Phenylalanine 50 1 g b 5

L-Glutamic acid 100 1 g b 10

L-Aspartic acid 100 1 g b,c 10

L-Valine 150 3 g 5

L-Threonine 200 4 g b,c 5

L-Serine 400 8 g 5

––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––

a SC contains synthetic minimal medium (SD) with various additions. It is convenient

to prepare sterile stock solutions which can be stored for extensive periods. All stock

solutions can be autoclaved for 15 min at 250°F. The appropriate volume of the

stock solutions (see below) is added to the ingredients of SD medium and sufficient

distilled water is added so that the total volume is one liter. The threonine and

aspartic acid solutions should be added separately after autoclaving. Given above are

the concentrations of the stock solutions (amount per 100 ml). Some stock solutions

should be stored at room temperature in order to prevent precipitation, whereas the

other solutions may be refrigerated. It is best to use HCl salts of amino acids

wherever applicable.

bStore at room temperature.

cAdd after autoclaving the media.

TE note: amino acid powders are fine stored at room temperature in the dark (in a drawer). Once dissolved in water, they are no longer light sensitive, with the exception of tryptophan, which is light sensitive and heat sensitive.  


A note on commercially prepared "Yeast Minimal Media" Formulations

Commercial powders are convenient. They are not neutral. Proceed with skepticism. 

Different vendors sell products with similar names that belong to different formulation families. These can vary in which amino acids are present, whether it contains ammonium sulfate or glucose (dextrose), whether it is closer to classical SC, CSM, or a broader “Hopkins mixture” style product, etc. 

Very important distinction: “SC-Leu” is not the same thing as “CSM-Leu”. This is one of the most common mistakes. A vendor product labeled CSM-Leu is often a supplement mix intended to be added to a defined base such as YNB plus carbon source. It may contain only a subset of amino acids and bases. Again it is YOUR RESPONSIBILITY to confirm the media used in your experiments conform to the convention in the field. 

Finally: DO NOT BE LAZY OR CHEAP OUT WITH YOUR MEDIA.

Use molecular biology grade reagents from a manufacturer with real batch control and act as if your reputation is on the line. It's BD Difco or take a hike.  If you save thirty dollars on media and spend six months generating uninterpretable growth phenotypes using chicken broth you sterile filtered to remove the chopped scallions... I don't want to hear about it. Absolutely no discount vendors promising “equivalent” white mystery dust with three typos in the product description blended by a guy named Kevin in a basement with a dream. And no, technical grade is not the same as molecular biology grade!

If your strains are not growing, growing slowly, or failing to match published physiology, suspect the medium before you invent new biology.


Finally: Common confounding factors checklist



Links: FRED SHERMAN'S 2002 GETTING STARTED WITH YEAST 

http://cdn.fraserlab.com/courses/pubs/2002_sherman.pdf