Bacterial Terrarium (AKA Winogradsky Column)

The Winogradsky column was invented by Sergei Winogradsky to study microbes in something resembling their natural environment. It differs from typical methods (culturing on a petri dish) because it cultures microbes together instead of separating them out into individual species. This allows for a range of organisms to be grown that don't grow on petri dishes, and is great for showing the diversity of microorganisms that exist in environments.

The bacteria separate out into different layers based on their nutritional requirements. A quick google search will provide a wealth of information at varying levels of complexity if you wish to examine this in more detail. I would suggest building one and then when you have questions go and search out the answers then.

The columns are very useful in understanding what microbes need to survive and how things in the environment are broken down to create nutrients that feed different forms of life. Often microbes are spread out and are hard to see because they are so small. This device allows for them to breed to very large numbers in specific partss so that you can identify them by their colours.

Step 1: Step 1: Materials

You will need:

• A bottle or glass jar
• A bucket
• Something to scoop up pond scum (a shovel works well)
• Calcium Carbonate (garden lime or crushed eggshells work well)
• A source of sulfur. I've used gypsum, but you can also use the yolk of an egg.
• A carbon source. A sheet of shredded paper is good.
• A spoon

A lot of the ingredients can be substituted or even omitted if you can't get them. Play around and see what works.

Step 2: Step 2: Collect Pond Scum

Find a local pond. Stagnant water works really well, and if it smells like a toilet it will be great! The smell is made by bacteria. This bacteria will be what we are culturing.

Walk to the edge of the pond and look for some mud that is silty. Start scooping it up into your bucket, trying to avoid sticks and rocks. If there are lots of leaves, these can just be picked out from the scoop before you put the mud into the bucket. You may want to use gloves if you are touching the mud.

Once you have collected enough mud to fill the jar (and a little bit more) collect some of the water. This water and mud will contain all the bacteria and algae that will grow in your jar.

Step 3: Step 3: Add Nutrients and Fill Jars

Shred your paper and mix it into the slurry in your bucket. Add about a teaspoon of the calcium carbonate and a teaspoon of the sulfur source per jar you want to make. Once everything is mixed in, scoop the solution into the jars. Fill them to about 2/3rds to 3/4ths full and fill the rest with the water. Put the lid on top and your terrarium is ready.

Step 4: Step 4: Observe and Document Changes

Place the terrarium in either direct or indirect sunlight. There are two types of microbes in the jar: ones that make energy from sunlight (autotrophs) and ones that get energy from eating things around them (heterotrophs). The sunlight will allow the microbes to grow and make energy for the system. Once the autotrophs die, they will feed the heterotrophs. The carbon source will also allow the heterotrophs to eat.

The bottom of the jar will contain bacteria performing non-oxygen producing photosynthesis. Can you work out a way to identify the autotrophs from the heterotrophs?

It may take 3-6 weeks to see changes in the environment. Write the date on the side of the bottle so you can track the age of the terrarium and see when changes start to happen. If you keep a book nearby you can record your observations. It can be fun to take photos every day to make into a time lapse movie.

Step 5: Step 5: Extensions and Hacks

You might want to try some of the following hacks:

• Put on jar in the sun and one in darkness and compare them
• Use a syringe to extract isolated and enriched bacteria for other uses such as algal bioreactors
• Use them as a power source (see bottom of the page)
• Insert things like a nail into them against the front to see what microbes grow around it.
• Make terrariums from different places and times of the year. These can help you understand what conditions microbes use to grow.