Agar plates are a crucial tool in mycology for cultivating and identifying fungi. In this blog post, we will explore the history and importance of agar plates in mycology and provide a recipe and step-by-step instructions on how to make and store them.
The use of agar plates in mycology dates back to the early 20th century when scientists began to use agar as a solid medium for cultivating fungi. Before this, mycologists had to rely on liquid culture media, which made it difficult to isolate individual fungal species and study their growth patterns. Agar, a solidifying agent derived from seaweed, proved to be an ideal medium for culturing fungi due to its stability and ability to hold nutrients.
The go-to formulas in mycology are Potato Dextrose Agar (PDA) and Malt Extract Agar (MEA), to which yeast is added as a nutritional supplement. These formulas have been refined over the years to create optimal conditions for fungal growth and are widely used in research and industry.
Agar plates are used for a variety of applications, including:
- Isolation of pure cultures of fungi
- Identification of fungal species
- Testing the effectiveness of antifungal agents
- Study of fungal growth patterns and behavior
- Production of spores and mycelium for further research
Recipe and Step-by-Step Instructions for Making Malt Extract Agar Plates
For Every 1000ml of H2O
- 20g agar powder
- 20g Barley malt extract
- 2g nutritional yeast
- Sterilization equipment (autoclave or pressure cooker)
- Petri dishes
- Mix the agar powder, malt extract, and yeast extract in a large flask with distilled water.
- Sterilize the mixture using an autoclave or pressure cooker for 30min at 15psi. This will kill any bacteria or other microorganisms that might be present in the mixture. Be sure not to fill up the flask completely, only ⅔ or ¾ of the way, and cover the opening with cotton and aluminum foil before inserting in the pressure cooker. Add approximately ½ inch of water at the bottom of the pressure cooker to create steam, and do not let the pressure cooker's temperature exceed 250 F to avoid caramelization of the sugar.
- Allow the pressure cooker to return to 1 psi before opening.
- Mix the media to evenly distribute the ingredients and pour the mixture into sterile Petri dishes. Cover each dish with a lid. To reduce condensation, wait for the mixture to cool down before pouring.
- Allow the agar plates to cool and solidify at room temperature. This should take 30-60 minutes.
- Once the agar plates have solidified, remove the lid and place a strip of parafilm across the top of the plate. Make sure the parafilm is long enough to cover the entire diameter of the plate and hang over the edges slightly.
- Gently stretch the parafilm to create a tight seal over the plate. The parafilm should adhere to the edge of the plate and create a secure, airtight seal.
- Label your plates with the appropriate information, such as the date, type of media, and strain or sample name.
- Store the agar plates in a cool, dry place until ready to use.
Rhizomorphic growth in mycelium refers to the development of branching, root-like structures that allow the fungus to absorb nutrients from its environment efficiently. To promote rhizomorphic growth in mycelium, a few modifications can be made to the standard agar plate recipe.
- 2g calcium carbonate (CaCO3)
- 2g gypsum (calcium sulfate, CaSO4)
- Follow the standard agar plate recipe and just add 2g of calcium carbonate and 2g of gypsum to the agar mixture in Step 1. These minerals help adjust the medium's pH and provide a source of calcium and sulfur, which are important for mycelial growth.
By adjusting the pH and providing a source of calcium and sulfur, these minerals can enhance the fungus's nutrient availability and overall health, leading to more robust growth and efficient nutrient absorption.
Tips for Making and Storing Agar Plates
- Make sure all equipment is properly sterilized before use.
- Keep the agar mixture and Petri dishes covered to prevent contamination.
- Agar plates can be stored in the refrigerator for several weeks or in the freezer for several months.
Before using agar plates, allow them to fully come to room temperature.