Mushroom cultivation and mycology, the study of mushrooms, are fascinating fields that attract more and more enthusiasts, both amateurs and professionals.
For those who wish to learn about growing mushrooms in the laboratory or at home, the use of Petri dishes is an essential starting point.
This practical guide explains why you should use Petri dishes, how to choose the right culture medium, and presents a simple method for preparing and pouring agar plates for your mycology experiments.
Why use Petri dishes in mycology?
Petri dishes are flat, clear containers, usually made of plastic or glass, used primarily for growing microorganisms on nutrient agar .
In mycology, they create a controlled environment to observe and study the growth of fungi, whether for research, cloning, strain selection or simply learning. Petri dishes offer several advantages:
- Control of cultivation conditions: They allow you to manipulate parameters such as the type of environment, temperature, humidity, and exposure to light.
- Easy observation: The transparent lid facilitates direct observation of the development of the mycelia without opening the box, thus minimizing the risk of contamination.
- Ease of isolation and selection: Petri dishes allow specific strains to be isolated or healthy mycelia to be selected for future cultures.
The different culture media for Petri dishes and their usefulness
The choice of growing medium is crucial in mycology, as it directly affects the growth and health of mushrooms. Growing media come in the form of powders to mix with water and are enriched with various nutrients to encourage the growth of fungi. Here are the main types of growing media and their uses:
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“MPA” medium (Malt, Peptone, Agar-agar): This medium is a classic in mycology. It is ideal for the multiplication of most mycelia. Due to its balanced composition, it promotes rapid and healthy growth of mushrooms, making it an excellent choice for beginners.
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“Sabouraud + Antibiotic” medium: This medium is enriched with antibiotic (chloramphenicol) to limit the development of bacteria and make the culture very selective. It is recommended for more delicate work, such as cloning mushrooms from nature or germinating spores. However, the growth of mycelia on this medium is generally slower than with MPA.
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Pure agar-agar: If you want to experiment or create your own media recipes, pure agar-agar is available separately. It is possible to enrich it with different ingredients such as potato extract, malt, dog kibble, manure extract, sugar, sawdust, etc., depending on the specific needs of the mushrooms you are growing.
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Water Agar Medium: This medium is an agar without enrichment, mainly used for specific laboratory work such as strain purification or selection.
To discover our ranges of culture media for Petri dishes, visit our products here .
You can also purchase our sterile Petri dishes, perfect for these applications, here .
Recipe for preparing MPA or Sabouraud agar
Preparing agar is an essential step for growing mushrooms in Petri dishes. Here is how to easily make an MPA or Sabouraud culture medium:
Necessary ingredients:
- 47 g of MPA or Sabouraud medium powder.
- 1 liter of hot water (preferably distilled or demineralized).
Preparation steps:
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Mixing: Mix 47 g of medium powder in 1 liter of hot water. Mix well to make sure the powder is completely dissolved.
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Sterilization: Sterilize the mixture at 121°C (15 PSI) for 20 to 30 minutes. This can be done using an autoclave or pressure cooker. This step is crucial to eliminate any unwanted microorganisms.
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Cooling: Allow the mixture to cool to around 45-50°C. This cooling is important to prevent the formation of condensation on the lids of the Petri dishes.
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Pouring: In a sterile environment (under a laminar flow hood or near a Bunsen burner), pour the agar into the Petri dishes. Make sure the thickness of the agar is approximately 0.5 to 1 cm.
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Closing: Close the Petri dishes quickly to avoid contamination by ambient air.
Sterility Techniques in Mycology
Sterility is one of the most crucial factors in growing mushrooms, as contaminants, like bacteria and mold, can quickly invade your crops and ruin your work. In mycology, establishing a sterile environment throughout the cultivation process is therefore essential to obtain reliable results. Here are some essential sterility techniques to minimize the risk of contamination.
1. Using a laminar flow hood
A laminar flow hood is equipment designed to provide a sterile environment by filtering air and pushing it in a uniform direction. This helps limit the circulation of contaminated air on work surfaces. If you don't have a fume hood, you can work near a Bunsen burner flame, which creates a sterile air barrier.
2. Wear gloves and a mask
Before handling, it is recommended to wear sterile gloves and a face mask. Disinfect your gloves with 70% isopropyl alcohol before starting each manipulation. This reduces the possibility of transferring contaminants from hands to crops.
3. Sterilization of tools
All tools used, such as scalpels, forceps or needles, must be sterilized. Using a Bunsen burner to heat sterilize these instruments is a common method. It is also possible to sterilize them with 70% isopropyl alcohol followed by a flame to burn off the alcohol residue.
4. Sterilization of culture media
Culture media (agar, liquids) must be sterilized before use. The most common method is to autoclave or pressure cook them at 121°C for 20 to 30 minutes to eliminate any unwanted microorganisms.
5. Disinfection of the work surface
The work surface must be thoroughly cleaned and disinfected before and after each work session. A 70% alcohol spray or diluted bleach solution can be used to disinfect surfaces, boxes and other materials to be handled.
6. Minimal opening of Petri dishes
When working with Petri dishes, it is important to open them as little as possible and keep their opening facing the flow of sterile air or the Bunsen burner to avoid contamination by ambient air.
Typical Example: Collecting a Carpophore from Nature for a Culture
Here is an example detailing the steps to follow to take a carpophore (visible part of the mushroom) from nature, cultivate it on Sabouraud + chloramphenicol agar for cloning, then multiply it on MPA agar and finally perform a liquid culture.
Step 1: Preparation of Culture Media
- Prepare Sabouraud + chloramphenicol agar according to the instructions described in the previous article.
- Also prepare MPA agar which will be used later for mycelium multiplication.
Step 2: Harvesting the Carpophore
- Find a healthy carpophore in nature.
- In a sterile environment, clean the surface of the carpophore with a cotton ball soaked in isopropyl alcohol to remove most external contaminants. Tear the mushroom, avoiding touching the internal parts of the mushroom.
- Using a sterilized scalpel, cut out a small piece of the internal tissue of the mushroom. Work quickly to minimize exposure to air.
Step 3: Inoculation on Sabouraud Agar + Chloramphenicol
- In a Petri dish containing Sabouraud agar enriched with chloramphenicol (to limit bacterial growth), place the sampled piece of tissue.
- Quickly close the Petri dish and place it in an incubator at a suitable temperature (usually around 25-27°C for most mushroom species).
- Monitor the box regularly for mycelium growth, which should appear as white filaments.
Step 4: Multiplication on MPA Agar
- Once the mycelium is well developed on the Sabouraud agar, transfer a piece of this healthy mycelium using a sterile scalpel to a new Petri dish containing MPA agar.
- This transfer accelerates the growth of the mycelium in a more nutritious environment.
Step 5: Preparing a Liquid Culture
- When the mycelium has propagated well on the MPA agar, it is time to move to a liquid culture for greater biomass production.
- Prepare a sterile liquid culture medium, such as malt broth, by sterilizing it in an autoclave.
- In a bioreactor or a sterile flask, inoculate this medium with a piece of mycelium taken from the MPA agar.
- Place the bottle in a dry, dark environment at an appropriate temperature and shake it regularly to ensure good ventilation of the environment.
Conclusion
Making petri dishes with the appropriate culture media is a basic but essential skill for any beginner in mycology. With the right tools and products, such as those available on our site lamycosphere.com, you can easily embark on the fascinating study of mushrooms.
Remember that success in mycology largely depends on following sterilization procedures and choosing the culture medium suited to your project. Happy growing!
