This activity explores soil microbes and the work they do for us. Part one explains how to build a habitat for some very colourful microbes. Part two demonstrates some the crucial work these microbes do – by soft-boiling an egg in a compost bin!
Soil Microbe Habitats
Mud from the edge of a stream, wetland or lake
2 hard-boiled eggs, chopped
1 sheet of newspaper ripped into small pieces
2 litre soft drink bottle, glass vase, or large jar
Bacteria and other microbes live in all soils, but this activity works best with gooey black mud from the edge of an open, wet area. These soils have bacteria that grow in aerobic conditions (with oxygen) and anaerobic conditions (lack of oxygen).
The hard boiled eggs provide food for the bacteria that use sulphur. The top of the column does not have as much sulphur so other types of bacteria will grow there.
By changing these conditions, we are creating habitats for different types of soil bacteria. It is impossible to see and individual bacterium without the use of a powerful microscope. But, as bacteria begin to reproduce and grow in these special habitat, we can see colonies of bacteria as colourful patches in the mud.
To make the habitat, remove sticks, stones, and other large pieces of material from the mud. Add water to the mud so its consistency is similar to raw egg whites.
Mix in the newspaper. Newspaper is a food source and speeds up bacterial growth. In nature, the microbes use organic matter in the soil.
Fill 1/3 of the container with mud.
Add the eggs and stir gently.
Top up the container with the mud.
Tap the container on the table a few times to dislodge any air bubbles. We want the bottom of the container to be anaerobic (without oxygen).
Add some water to the container so that it does not dry out.
For best results, shine a light on the container 24 hours a day. Some bacteria grow in light, other bacteria grow in dark conditions.
You’ll know when the bacteria are working. As the use the eggs as food, they produce some pretty smelly gases. If you gently squeeze the bottle, it may burp – or pass gas. This should settle down after a few days. Keep some plastic wrap on the bottle or jar, but don’t seal it.
Within a couple of weeks, you should see colonies begin to grow. The soil habitat in the photo has been sitting in a shed for about 18 months, with sunlight as its only light source. Isn’t it pretty!
Microbes At Work – Soft Boiling An Egg In A Compost Bin
a raw egg
a plastic bag
wheelbarrow of glass clippings OR
Soil microbes – and other soil creatures – are responsible for recycling organic matter over and over again. This activity demonstrates microbes at work. It is best done during the warmer part of the year. You can either do it in a wheelbarrow of fresh grass clippings, or in an active compost pile. (An active pile is one that is regularly turned – and doesn’t have pumpkins growing out of it!)
Place the egg into the plastic bag – the kind you get from the supermarket is ideal. Tie the egg up in the bottom of the bag and use the top of the bag as a ‘tail’ sticking out of the compost or grass clippings. This allows you to more easily find and remove the bag.
If you are using a compost bin, add the grass clippings to the bin. Otherwise leave the grass clippings in the wheelbarrow.
Bury the egg in the clippings, leaving the end of the ‘tail’ exposed.
If the clippings are quite dry, wet them a bit – but don’t make them soggy.
Leave the egg in the clippings for a couple of days. When you dig out the egg, you will likely feel the heat generated by the microbes as they work to break down the grass clippings – similar to how humans produce heat when we work hard. You may also see steam and fungi growing – the fungi helps the compost/clippings break down.
Remove the egg and cut it open. Chances are, some or all of it will be hard-boiled! The egg is not safe to eat, but if you put it in the compost bin, the microbes will get to work and recycle it,
A note of caution:
Take care when digging through the compost to retrieve the egg. Avoid breathing in dust or mist coming from the compost
The mud column is called a Winogradsky column. Growing soil microbes, an activity from the Science Learning Hub, has additional information about the microbes and the gases they produce.