Mushroom cultivation and mycology, the study of fungi, are fascinating fields that attract more and more enthusiasts, both amateurs and professionals.
For those who wish to get started with mushroom cultivation in a laboratory or at home, the use of Petri dishes is an essential starting point.
This practical guide explains why to use Petri dishes, how to choose the right culture medium, and presents a simple method to prepare and pour agar plates for your mycology experiments.
Why use Petri dishes in mycology?
Petri dishes are flat, transparent containers, usually made of plastic or glass, primarily used to culture microorganisms on a nutrient agar.
In mycology, they allow for the creation of 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 culture conditions: They allow manipulation of parameters such as the type of medium, temperature, humidity, and light exposure.
- Easy observation: The transparent lid facilitates direct observation of mycelium development without opening the box, thus minimizing the risk of contamination.
- Ease of isolation and selection: Petri dishes allow for isolating specific strains or selecting healthy mycelia for future cultures.
The different culture media for Petri dishes and their uses
The choice of culture medium is crucial in mycology, as it directly affects the growth and health of mushrooms. Culture media come in the form of powders to be mixed with water and are enriched with various nutrients to promote mushroom growth. Here are the main types of culture media and their uses:
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Medium "MEA+" (Malt Extract Agar + Peptone)
Rich nutrient medium, suitable for the cultivation of most mycelia. It also promotes the development of bacteria, making it a good choice for testing the purity of air or samples (contamination tests).
Environment "Sabouraud + Antibiotic"
Enriched with an antibiotic (usually chloramphenicol), this medium limits bacterial growth and becomes highly selective. It is ideal for sensitive manipulations such as cloning wild fungi or spore germination, especially under non-sterile conditions. However, mycelial growth may be somewhat slower than with a medium like MEA+.
Medium "Water Agar" (WA)
If without added nutrients. Used for:
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the strain purification from contaminated tissues,
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natural selection (only the mushrooms survive),
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specific observations (morphology, slow growth tests). It is a neutral medium, useful as a transitional step.
Medium "PDA" (Potato Dextrose Agar)
Prepared from potato extract and glucose, it is a classic and universal medium in mycology. It stimulates mycelium growth and allows for good observation.
Used for:-
the general culture of the mycelium,
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the strain preservation,
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biomass production.
However, it is sensitive to contamination due to its high sugar content.
Medium "MYA" (Malt Yeast Agar)
Contains malt extract and yeast. It is particularly suitable for:
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the germination of spores,
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the demanding species (such as Hericium erinaceus or certain forest species),
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the conditions where vigorous growth is sought.
It can be enriched with peptone to become a very complete medium (MYPA).
Medium "GYEA" (Glucose Yeast Extract Agar)
A simple but nutritious medium, composed of glucose, yeast extract, and agar.
Benefits :-
rapid growth,
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easy to adapt formulation,
but less used in routine culture than MEA or PDA.
Medium "Corn Meal Agar" (CMA)
Less rich, often used to observe the morphology of reproductive structures (such as spores or specialized hyphae).
Rarely used in production, but useful in laboratory or taxonomic identification. -
You can also get our sterile Petri dishes, perfect for these applications, here.
Preparation recipe for MEA or Sabouraud agar
The preparation of an agar plate is an essential step for culturing mushrooms in Petri dishes. Here is how to easily prepare an MEA or Sabouraud culture medium:
Necessary ingredients:
- 47 g of MEA or Sabouraud medium powder.
- 1 litre of hot water (preferably distilled or demineralized).
Preparation steps:
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Mix: Dissolve 47 g of medium powder in 1 liter of hot water. Mix well to ensure 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 a pressure cooker. This step is crucial to eliminate any unwanted microorganisms.
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Cooling: Let the mixture cool down to about 45-50°C. This cooling is important to prevent condensation from forming 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. Ensure that the thickness of the agar is about 0.5 to 1 cm.
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Closure: Quickly close the Petri dishes to avoid any contamination from the ambient air.
Sterility Techniques in Mycology
Sterility is one of the most crucial factors in mushroom cultivation, as contaminants such as bacteria and molds can quickly invade your crops and ruin your work. In mycology, establishing a sterile environment throughout the cultivation process is therefore essential to achieve reliable results. Here are some essential sterility techniques to minimize the risk of contamination.
1. Use of a laminar flow hood
A laminar flow hood is a piece of equipment designed to provide a sterile environment by filtering the air and pushing it in a uniform direction. This helps limit the circulation of contaminated air over work surfaces. If you do not have a hood, you can work near a Bunsen burner flame, which creates a sterile air barrier.
2. Wear gloves and a mask
Before any handling, it is recommended to wear sterile gloves and a face mask. Disinfect your gloves with 70% isopropyl alcohol before starting each handling. This reduces the possibility of transferring contaminants from the hands to the cultures.
3. Sterilization of tools
All tools used, such as scalpels, forceps, or needles, must be sterilized. Using a Bunsen burner to sterilize these instruments by heat is a common method. It is also possible to sterilize them with 70% isopropyl alcohol followed by a flame to burn off the alcohol residues.
4. Sterilization of culture media
Culture media (agar, liquids) must be sterilized before use. The most common method is to autoclave them or use a pressure cooker at 121°C for 20 to 30 minutes to eliminate all unwanted microorganisms.
5. Disinfection of the work surface
The work surface must be carefully cleaned and disinfected before and after each work session. A 70% alcohol spray or a 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 to keep their opening facing the sterile airflow or the Bunsen burner to avoid contamination from ambient air.
Typical Example: Collecting a Mushroom from Nature for Cultivation
Here is an example detailing the steps to follow to collect a fruiting body (visible part of the mushroom) from nature, cultivate it on Sabouraud agar + chloramphenicol for cloning, then multiply it on MEA agar, and finally perform a liquid culture.
Step 1: Preparation of Culture Media
- Prepare a Sabouraud agar + chloramphenicol according to the instructions described in the previous article.
- Also prepare an MEA agar that will be used later for the multiplication of the mycelium.
Step 2: Sampling the Carpophore
- Find a healthy fruiting body in nature.
- In a sterile environment, clean the surface of the fruiting body with a cotton swab soaked in isopropyl alcohol to remove most external contaminants. Tear the mushroom while avoiding touching the internal parts of the mushroom.
- Using a sterilized scalpel, cut a small piece of the mushroom's internal tissue. 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 piece of collected tissue.
- Quickly close the Petri dish and place it in an incubator at an appropriate temperature (usually around 25-27°C for most mushroom species).
- Regularly monitor the box to observe the growth of the mycelium, which should appear as white filaments.
Step 4: Multiplication on MEA Agar
- Once the mycelium is well developed on Sabouraud agar, transfer a piece of this healthy mycelium using a sterile scalpel to a new Petri dish containing MEA agar.
- This transfer allows accelerating the growth of the mycelium in a more nutritious medium.
Step 5: Preparation of a Liquid Culture
- When the mycelium has spread well on the MEA agar, it is time to move to a liquid culture for a larger 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 MEA agar.
- Place the bottle in a dry and dark environment at an appropriate temperature and shake it regularly to ensure good aeration of the medium.
