Making a home for microbes

  1. Make a field trip to the nearest river or stream and bring all the necessary materials and equipment to collect samples of mud and muddy water from it. The mud is full of microbes. If you collect more samples, you should take with you enough buckets and bottles to carry different samples of mud and water. (Make sure that you do not collect samples of mud from polluted sources, to avoid exposure to dangerous microorganisms)
  2. Explain to the students that they will build a home for microbes with only some cups of mud and some other ingredients (food for microbes). They will create an entire ecosystem for microbes called a “Winogradsky column” from each of the samples. (The experiment is named after Sergei Winogradsky, a Russian microbiologist.) Each system will be sealed. Microbes will reuse and recycle nutrients continuously. Over time, different species will separate into visible layers depending on how they use (or do not use) oxygen, light, and nutrients such as carbon or sulfur. Each microbial species will find its habitat according to its needs. Some microbes use oxygen to breathe; others use sulfur as a source of energy.
  3. Preparing the ingredients for our Winogradsky column:
    • Cut off the curved tops of plastic bottles.
    • Put enough mud to be able to fill three quarters of the bottle into a mixing bowl and remove all the stones and other hard particles. Mix it with water until you get a smooth consistency.
    • Put a handful of shredded paper (source of carbon) and an egg yolk (source of sulfur) into another mixing bowl and add one third of the mud from the first mixing bowl and mix everything well together.
  4. Putting the Winogradsky column together:
    • First, fill one quarter of the bottle with mud mixed with shredded paper and an egg Let the mud settle at the bottom.
    • Then take the mud from the first mixing bowl and fill the column with clear mud up to three quarters of the bottle. Let the mud settle.
    • Fill the rest of the bottle with water from the river, leaving about 2.5 cm at the top for air.
    • Take a piece of plastic wrap and rubber bands and close the opening.
  5. In such a way, you can create one or more columns with the same mud or with mud from different samples. Make sure to write the origin of your samples on the bottle.
  6. Put the samples under different light conditions and observe them periodically for at least three weeks (eight to ten weeks for better results). Make notes of what is happening in the columns and photos for later comparison.
  7. After that period, you may change the light conditions and observe your microbes for another period. Make notes and photos for comparison.
  8. Expected results: Over time, different species will separate into visible layers depending on how they use (or do not use) oxygen, light, and nutrients, such as carbon or sulfur.
    • What have you learned from the adaptation of microbes to different living conditions?
    • You can use the Worksheet Identifying Common Microbes to help you to identify some of them.
  9. Discussion: From this activity, you may observe that for all the different niches, with various life conditions, there are microorganisms that found a hospitable environment where they can thrive, grow, and reproduce, by using available resources. The same situation can be observed in rivers. In all the parts of a river, ecosystem microorganisms are present, and they are considered one of the most valuable members of the river community.
  10. Almost any nutrient in a river can be used by micro-organisms as a source of food. In this way, microorganisms directly participate in the decomposition of complex compounds by creating simple molecules that autotrophs can use to create organic molecules in the process of photosynthesis. One problem for microorganisms and rivers may be the presence of newly synthesized contaminants that cannot be used and degraded by microorganisms. This leads to another possibility of using the Winogradsky columns.
    • Try to put some chemicals (bleach) into your column and see what will happen.


The idea for the experiment is taken from: