Exploring Photosynthetic Microbes in Our Soil: A Hands-On Experiment

The activity below was contributed by Dr. Barry Goldman during our podcast interview.

Beneath our feet lies a hidden universe. Soil is home to a vast array of microorganisms, each playing a crucial role in the health of our planet’s ecosystems. These tiny microbes are too small to see with the naked eye, but they perform essential functions like decomposing leaves and recycling nutrients.

One amazing thing certain microbes (algae and some bacteria) can do is photosynthesize. Just like plants, these photosynthetic microbes can use sunlight, water, and carbon dioxide to make their own food. This process is called photosynthesis.

• Sunlight: Microbes use sunlight as energy to power the chemical reactions of photosynthesis.
• Water: Water is essential for the process of photosynthesis. It’s broken down into hydrogen and oxygen.
• Carbon dioxide: Microbes take in carbon dioxide from the air and use it to make food.

When microbes photosynthesize, they release oxygen into the air, which is important for all living things, including humans. Photosynthesis also helps to keep the Earth’s atmosphere balanced.

By conducting this experiment, you can introduce your students to the fascinating world of soil microbiology and help them understand the vital roles that microbes play in our ecosystems. This activity can also be used to teach important scientific concepts such as photosynthesis, energy transfer, and the carbon cycle.

Materials:

• BG-11 media (available from the University of Texas)
• Sterilized test tubes
• Soil samples from different locations (e.g., garden, park, near a stream)
• LED lamp or sunlight
• Petri dishes
• LB or R2A media (for culturing other microbes)

Instructions:

1. Prepare the Media: Fill the test tubes with BG-11 media.
2. Collect Soil Samples: Gather soil samples from various environments.
3. Inoculate the Media: Add a small amount of each soil sample to separate test tubes.
4. Expose to Light: Place the test tubes in a location with adequate sunlight or under an LED lamp.
5. Observe Growth: Over the next few weeks, monitor the test tubes for signs of microbial growth. The media should begin to turn green, blue, or yellow due to the photosynthetic activity of the microbes.
6. Isolate Other Microbes: Once the photosynthetic microbes have grown, transfer some of the culture to Petri dishes containing LB or R2A media. This will allow you to isolate and observe other microbes that may be present in the original soil samples.
7. Analyze Microbial Diversity: Examine the different types of colonies that grow on the Petri dishes. Observe their colors, shapes, and textures to gain insights into the diversity of microbes in your samples.
8. Identify Microbes (Optional): If you have a microscope, you can try to identify some of the microbes based on their physical characteristics, which may be more easily distinguishable for algae. Use microbial identification guides or online resources to compare the observed features with known microbial species.

By following these steps, you can create a miniature ecosystem that showcases the fascinating world of microbial diversity. This experiment is a great way to learn about the interconnectedness of different microbial species and their essential roles in our environment.