Your First Microbiology Experiment

This experiment does not require sterile media, but keep things as clean as possible.

The first microbiologists did not have culture tubes, fancy equipment, or special supplies. Just like them, we can accomplish much with the same kitchen foods they used. If you have culture tubes, use them, but otherwise you can conduct this experiment using a drinking glass or small bottles or any other useful container. One advantage of culture tubes is that it costs less to fill them, but the materials for this experiment are cheap.

Our first experiment is very inexpensive. We will try to culture (grow) baker's yeast (from the grocery store) on various carbohydrates learn what it needs to grow. Before a microbiologist can do much with a microbe, he must find a way to grow it. As we work with baker's yeast and then other microbes, you will learn what is needed to grow microbes and what containers will be useful. Thus you can begin building up supplies and equipment for your home microbiolgy lab.

Safety Now. Don't begin this experiment until you have read my general safety page and the special safety notes for these experiments at the bottom of this page. Become a student who always works carefully and safely.

Expt 1.   Growing a Baker's Yeast Culture

Growing a yeast culture is simple and easy, yet it introduces many concepts you need to understand if you want to conduct a serious microbiology project. This experiment will demostrate some of the biochemical principles used to identify bacteria and yeast species. You can find everything you need at home or in the grocery store and that is the first reason we are beginning with bakers yeast, Saccharomyces cerevisiae, but another reason is that since we eat yeast, we know it is safe for beginners to work with. This simple experiment can be expanded into many more complex experiments and become an outstanding science project.

The standard steps for growing a microbe are

To search the web for information useful for this project, I would try these keywords: yeast, baker's yeast, baking yeast, "Saccharomyces cerevisiae", culture, yeast culture,culture medium, bread making, agar, microbiology, science project, home science project, science fair, zymology, enzymes, glucose, sucrose, starch, hydrolysis, slime flux, etc.

Preparation of the Medium.

Medium is the name for the food we grow microbes in. The medium must contain everything our yeast needs.

Tube your medium and sterilize it.

Inoculate your culture(s).

Incubate your yeast cultures

Record the results

Examine your tubes for growth at daily or 12 hour intervals. Discard any tubes that get moldy, wash them carefully so you do not inhale any mold spores. If any tube breaks, do not get cut by the contaminanted glass. If you get cut, wash the wound with clean soap and water and flood with alcohol.

If you wish, you could perform the above experiment using a bit of garden soil (or slime flux) as the inoculum instead of bakers yeast. Since garden soil contains dozens of different species of bacteria and fungi, the results will be different and perhaps useless because soil usually contains bacteria capable of growing at most temperatures and on most foods.

Expt 21B. Growth of Bakers Yeast on Other Sugars.

Biochemists have discovered dozens of sugars and other carbohydrates in nature. Various species of bacteria and yeasts differ in their ability to grow on these carbohydrates. The ability of a strain of bacteria or yeast to grow on certain sugars is one of the main methods for indentifying them to Genus and species. Since fungi have huge genomes and the genetic codes to make enzymes to digest most carbohydrates, sugar digestion is not as useful in for identifying fungi.

Testing the ability of bakers yeast to grow on three carbohydrates.

Additional suggestions:

Expt #21C. Using A Complete Medium

Corn syrup water is not a very good medium because it is low in nitrogen. All living things require amino acids to make their proteins. Some proteins make up muscle or other structures; other proteins are called enzymes. Enzymes are catalysts which reduce the energy level required for reactions. Thus, fire at high temperature burns sugar, but using enzymes some bacteria can burn (oxidize) sugar near the freezing point.

While all organisms require nitrogen, very few can use nitrogen directly from the air. Plants can use inorganic salts called nitrates and some can use ammonium salts. Many bacteria can use ammonium, nitrite, or nitrate salts and some can use nitrogren direct from the air. Many microbes and humans can use only amino acids. Humans can eat proteins and digest them down to amino acids. It is hard to find sources of free amino acids around the home, but there are lots of sources of proteins including egg white, milk, meat, and beans (has other things also).

Since some microbes require amino acids, common microbial media contain proteins, peptides, or amino acids. Peptides are partially digested proteins. We could add milk to our corn syrup medium. Milk alone makes a good medium for some bacteria because it contains proteins and lactose, a sugar. The white color of milk makes it difficult to see the growth of the bacteria unless the bacterium has a strong color. Meat broth is a good way to add proteins, peptides, and amino acids to a medium.

Using these ideas you can try to make a more complete medium for bacteria. By February 1998, this site will have a page devoted to home-made media.

For now you can try some experiments on your own, such as adding soil to milk and incubating at 4C, cold room, normal room, or higher temperatures. Expect some very strong odors. If you screw the lids on tight, there is a risk that gas pressures could build so high that the bottle or tube will burst. Don't overlook the use of plastic bags for cultures, but they may leak.

Expt #21D. Selective Medium

Many kinds of food are made using selective medium and bacterial fermentations. Salt or vinegar is often added to prevent the growth of most kinds of bacteria. Try adding varying amounts of salt to tubes of a good medium for yeast add gas collection tube if you have them, does the salt interfere with growth of the yeast. Some yeasts grow at remarkably high salt levels.

Try adding vinegar in varying amounts to your proven yeast medium. In general, yeasts are noted for growing at acidic pH. If you don't have a pH indicator, you might try red cabbage juice. See URL:

Here is a cabbage experiment. Slice some cabbage finely. Pack it tightly into 3 small jars. Add dilute vinegar to jar #1. Add dilute salt water to Jar #2. Add nothing to jar #3. Put the lids on loosely and incubate at room temperature or a little cooler. Jar #3 will rot quite quickly. Jars #1 and #2 will rot but less so. For an interesting project, get a canning book and the help of your mother, grandmother, or any experienced canner and try making fermented pickles or sauerkraut using such selective methods. The food is safe to eat only if you follow the directions carefully--it is safer to have an expert cook with canning experience to help you.

During 1998 this site will have pages dealing with selective enrichment methods. The first such page is Isolation of Vibrio phosphoreum using low temperature and seawater to select luminous bacteria on fresh seafish or squid. Fresh fish from inland markets is seldom fresh enough to have the bacterium.

Suggested Further Experiments (incomplete)

Much of this will be used on other pages .

Most advanced microbial experiments require the use of solid media for isolation of pure cultures and the use of sterile medium. Pasteur accomplished much using selective methods, but he and others began using sterile medium and then rapid advances began.

move page LINK for moremedia and steiliar;ona


Observe examples of microbial growth around you.

Selective growth of an organism. vingegar, salt.

Notice that when microbes multiply gets cludy, corn syrup in water and inoculate.

sterile toothpicks tostart rotten apples

tyddalize milk 3 days in a row save a conrtol

Safety Rules for Microbiology

Be sure to keep your experiments away from small childern

Work with your parents to plan a place to keep your things so that small kids or unsuspecting adults do not drink or eat your experiments because they thought it was food. This means you should not keep your experiments in the refrigerator or on food shelves. You can keep them in suitable boxes with a sign so they are will marked.

Safety Rules.

Safety First. Do not sniff moldy items. There is a chance that the spores could get into your longs and begin to grow. Certain fungi can grow in our lungs and antibiotics do not help much. Death has a good chance of occuring if you get infected by such fungi. I will write about the fungi later. Actually, one cubic centimeter of air in homes commonly has 5,000 or 8,000 particles of dust and some of these are mold spores including the dangerous ones. Each good deep breath contains about 20 million particles.

Rule #1. Don't waste too much time wishing for equipment you don't have. Spend your time thinking about things you can do with what you have.

I love working with bacteria, yeasts, fungi, protozoa, algae, and bacterial viruses at home. The study of these things is called microbiology. The study of all of them uses approximately the same equipment. Therefore, this series of pages B020 => B024 will concentrate on the supplies and equipment for studying bacteria. Later, I will write pages about the equipment to study the other organisms.

You should read these pages in the order listed.

I might be helpful to read the first four pages before you do anything. The begin some simple experiments and you will learn what you need. Later you may want to buy some supplies, but at first see how much you can do with items from your home, farm, and gifts of discarded items.

These experiments still need lots of rewriting, but the facts are correct. If you were able to sterilize your medium. Save a culture of the yeast for your collection, but it is just as well to wait until we can isolate a culture by streaking in a later experiment.

Revision #3 1998 Feb 3
Written by Harold Eddleman, Ph. D., President, Indiana Biolab, 14045 Huff St., Palmyra IN 47164
Please help by sending me an e-message containing your ideas for improvement.

  • If you have a pressure cooker, you can use it to kill all the microbes, including spores of all kinds and viruses.
  • If you have a pressure cooker, put your liquid medium in a glass jar with the lid on loosely and cook (autoclave) at 15 pounds pressure for 15 minutes. Read the manual for the pressure cooker to learn the setting for 15 pounds and read the safety precautions. Get the owner of the cooker to supervise your work. It is possible for a pressure cooker lid to fly off and injure you. Do not forget to p

    In fact, the early humans and all animals and plants are involved with microbes. With each breath, you inhale about 5 million to 20 million dust particles and many of those are microbes.

    Bacteria and other microbes are all around us. I am having trouble getting this page started because there are so many things we can do that I do not know what will interest you the most. I will just begin listing some simple experiments and you can do what ever you like.