STEAM: DIY Microbial Zoo

Bacteria, microscopic fungi, and other single-celled organisms (collectively called “microbes”) are everywhere. While a small number of them can make us sick, most are harmless to us, and some we can’t live without.

In this experiment, we will study soil microbes from your local environment by building a miniature soil ecosystem called a Winogradsky Column, named after Russian microbiologist Sergi Winogradsky, who learned how soil microbes live among each other in nature.

Materials

• Bucket
• Shovel
• Gloves
• Soap
• Two large bowls for stirring
• Two spoons for stirring
• Black marker
• Plastic bottle (1 or 2 liters, but 1 liter will be easier. Clear is best!)
• Scissors
• Water
• Plastic wrap and/or aluminum foil
• Rubber band
• Light source (window or lamp)

Optional:

• A quarter page of newspaper, shredded
• One egg yolk

Instructions

1. Gather your supplies and head to a pond, stream, riverbed, or rain puddle to dig up some mud.
   • Use the shovel and bucket, and wear your rubber gloves.
2. Wash your hands thoroughly with soap and water, and rinse them off completely before moving on to the next steps.
3. Remove all stones, twigs, and other solid objects large enough to see easily from the mud in your bucket.
4. Carefully cut the neck off of the plastic bottle with scissors to form an open-top cylinder.
5. Draw two lines on the plastic bottle with the black marker.
   • The first line should be about a quarter of the way up from the bottom of the bottle.
   • The second line should be about three quarters of the way up from the bottom of the bottle.
6. Put enough mud in the first mixing bowl to fill the bottle up to the second line.
7. Slowly add water to the mud in mixing bowl 1 while stirring until the mud has the consistency of a milkshake.
8. Optional: if you don’t have (or don’t want to use) shredded newspaper and egg yolk, skip to step 13.
9. Move a quarter of the mud from mixing bowl 1 to mixing bowl 2.
10. Add the shredded newspaper and egg yolk to mixing bowl 2 while stirring. Stir until evenly distributed.
11. Now pour the mud from mixing bowl 2 into the bottle, up to the first line but not over. Remove air bubbles by gently lifting the bottle and tapping it on the table a few times.
12. Add the mud shake from mixing bowl 1 to the plastic bottle, up to the top line. Remove air bubbles by gently lifting the bottle and tapping it on the table a few times.
13. Pour water gently on top of the mud in the bottle, leaving about 2.5 cm (about 1 inch) of air at the very top.
14. Cover the open top of the bottle with plastic wrap and aluminum foil, and use the rubber band to hold it tightly in place.
15. Place the bottle in a spot where it can get plenty of light, and let it develop for 6-8 weeks.

Look at the column every few days and keep track of the changes. You can also take photographs from the same angle once a week (or more often) to see how it has changed.

Questions to Consider

While you are watching and comparing, consider the following questions:

• Which parts of the column changed the most over eight weeks?
• Which parts changed the least?
• Oxygen plays a vital role in the miniature ecosystem—what area do you think holds the most oxygen?
• Where do you think there is the least oxygen?
• Keeping track of which colors appear in the different layers can help you determine what kinds of microbes might be living there. You can check out books about microbes from the library or search the Gale in Context: Science database for clues.