In mushroom cultivation the term "contamination" is used to describe any microbial growth outside the species we are intending to grow. This term is used loosely to describe a variety of competing bacteria or fungi. This document is intended to help you identify what is contamination and what is not, and additionally provide you more information about dealing with contamination.
Unlike plants, mushrooms do not thrive in a competitive environment, especially in the early stages. Even the strongest fungus is no match for common mold and bacteria, and it is for this reason, we must start mycelium colonies (young fungus) isolated from all other microorganisms. Any organism besides the target strain we are attempting to grow is considered a "contaminate" of the substrate.
There are many ways to define contamination. There is medical contamination, food contamination, biological contamination the list goes on. Simply put by our team of mycologists; Contamination occurs when bacteria, molds, or other microorganisms come into contact with your agar and uses the available nutrition to grow and multiply. Which is the same thing fungi does, so that puts them in direct competition.
Common Types of Contamination
In the world of mushroom cultivation, ensuring a clean and sterile environment is crucial for successful growth and harvest. However, even with the best practices in place, substrate contamination can still occur. Understanding the common types of substrate contamination can help mushroom growers identify and prevent potential issues. Let's explore some of the most prevalent types of contamination in mushroom cultivation.
Bacterial Contamination
Bacterial contamination is one of the most common types of substrate contamination in mushroom cultivation. Bacteria can enter the substrate through various sources, such as unsterilized equipment, contaminated water, or improper handling. Once inside the substrate, bacteria can multiply rapidly and compete with the mushroom mycelium for nutrients, leading to poor growth and yield. To prevent bacterial contamination, it is essential to maintain strict hygiene practices, including sterilizing equipment, using clean water sources, and practicing proper handling techniques.
Fungal Contamination
Fungal contamination is another prevalent issue in mushroom cultivation. It occurs when unwanted fungi, other than the desired mushroom species, colonize the substrate. Fungal contamination can arise from contaminated spawn, unsterilized substrate materials, or airborne spores. These contaminants can outcompete the desired mushroom mycelium, resulting in stunted growth or complete failure of the crop. To prevent fungal contamination, it is crucial to use high-quality spawn, sterilize substrate materials thoroughly, and maintain a clean growing environment.
Mold Contamination
Mold contamination is a specific type of fungal contamination that deserves special attention. Mold spores are ubiquitous in the environment and can easily find their way into the mushroom cultivation area. Once mold spores land on the substrate, they can quickly colonize and spread, causing significant damage to the crop. Mold contamination is often characterized by fuzzy growth, discoloration, and unpleasant odors. To prevent mold contamination, it is essential to maintain proper ventilation, control humidity levels, and promptly remove any contaminated materials.
Yeasts Contamination
Yeasts are single-celled fungi that can also contaminate mushroom substrates. They are commonly found in the environment and can enter the cultivation area through the air or contaminated materials. Yeast contamination can lead to changes in substrate pH, excessive carbon dioxide production, and altered nutrient availability, negatively impacting mushroom growth. To prevent yeast contamination, it is crucial to maintain proper sanitation practices, including regular cleaning and disinfection of equipment and growing areas.
Viral Contamination
Viral contamination is relatively rare in mushroom cultivation but can still occur under certain circumstances. Viruses can infect mushroom mycelium, leading to abnormal growth, reduced yield, and overall crop decline. Viral contamination can be introduced through infected spawn or contaminated growing environments. To prevent viral contamination, it is essential to source spawn from reputable suppliers and maintain strict hygiene protocols.
By understanding the common types of substrate contamination in mushroom cultivation, growers can take proactive measures to prevent and mitigate these issues. Implementing proper sterilization techniques, maintaining a clean growing environment, and sourcing high-quality materials are key to successful mushroom cultivation.
Five Common Contaminants
1. Trichoderma
Trichoderma is a group of green mold fungi present in all soil. It has the ability to form symbiotic relationships with plants. Trichoderma harzianum is one of the most common forms of contamination seen in mushroom cultivation. This mold produces white mycelium that will rapidly cover substrates before producing green spore-bearing structures. Trichoderma has a fluffy appearance.
2. Orange Bread Mold
Orange bread mold (Neurospora crassa) is a common and extremely fast-growing fungal contaminant. Used in genomics research, this neon orange mold can be a challenging contaminate to handle. It first appears as an orange-white wisp but develops into a bright orange patch. These patches produce spore formations. Once found, contain the source by disposing of it immediately. be careful not to disturb the mold as it will release orange spores into the air which can spread. After disposal, sterilize the affected area.
3. Bacillus spp. (Bacterial contamination)
The most common form of bacterial contamination is known as “sour rot” and can look like a wet spot. It is a colorless or gray slime with a sour-smelling odor that appears wet and mucus-like often forming in uncolonized patches along the bottom of grain containers. Their reproductive structures are called endospores, which are heat resistant, and will survive sterilization. Grains should be soaked for 12 to 24 hours at room temperature, allowing the endospores to germinate and be vulnerable during sterilization. If the contamination is encountered, it is possible to separate it from the rest of the grains (so long as the patch is small and confined to one area) by physically scooping out the patch using an alcohol sanitized or flame sterilized spoon.
4. Cobweb Mold
Cobweb mold (Hypomyces rosellus) is a harmful fungi species often encountered in mushroom cultivation, especially in environments with still air, low oxygen, and high humidity. It can be difficult to detect due to its gray, white, and fluffy appearance which resembles mycelium but its growth pattern is different, appearing to hover above substrate in wispy, white tufts. Additionally, this mold often forms in the last days of incubation, when substrates are fully colonized just prior to fruiting. Cobweb mold spreads fast: a small patch can cover a medium surface quickly. Hypomyces are parasitic fungi, so if left untreated the infection can result in pinning mushrooms aborting their growth and mature mushrooms becoming rotten.
Growers can prevent cobweb mold by lowering the humidity in their mushroom environment, which can be accomplished through careful attention to substrate hydration and improving Fresh Air Exchange.
5. Black Bread Mold
Black Bread Mold (Rhizopus stolonifer) is known as pinhead mold, a mushroom contaminant that is common in soil and the air. A fast growing fungi with a dense mycelium that starts white and becomes gray with black dots at the ends of the structures.
How to Identify Contamination In Mushroom Substrate
As a mushroom grower, it is crucial to be able to identify contamination in your mushroom substrate. Contamination can hinder the growth and development of your mushrooms, leading to poor yields and potential crop loss. In this guide, we will discuss the common signs of contamination and how to prevent its spread.
1. Foul Odor: One of the first signs of contamination is a foul or unpleasant odor coming from your mushroom substrate. If you notice a strong, pungent smell that is different from the earthy aroma of healthy mushrooms, it may indicate the presence of contaminants.
2. Discoloration: Contaminated mushroom substrate often exhibits unusual discoloration. Look for patches of green, blue, orange, or black on the surface of the substrate. These colors are indicative of mold or bacterial growth and should be addressed immediately.
3. Fuzzy Growth: Contamination can manifest as fuzzy or cotton-like growth on the substrate. This fuzzy growth is typically white or off-white and may spread rapidly if left unchecked. It is important to identify and remove contaminated areas promptly to prevent further contamination.
4. Slimy Texture: Healthy mushroom substrate should have a firm and dry texture. If you notice a slimy or wet texture, it may be a sign of contamination. Contaminated substrate can become slimy due to bacterial or fungal overgrowth, which can inhibit mushroom growth.
5. Abnormal Mushroom Growth: Contamination can affect the appearance and development of mushrooms. Look for mushrooms that have unusual shapes, colors, or textures. Mushrooms that appear shriveled, discolored, or have abnormal growth patterns may be a result of contamination.
Preventing Contamination: To prevent contamination in your mushroom substrate, it is essential to maintain a clean and sterile environment. Here are some tips:
- Follow strict sterile practices when inoculating, transferring, or working with culture. Wear latex gloves and a mask while performing procedures. Always work in a laminar flow hood if available.
- Sterilize all equipment, including containers, tools, and surfaces, before and after each use. Use 50%-70% alcohol to sterilize all surfaces and work areas regularly. Do not use a higher concentration of alcohol (like 90%), because it will not work correctly.
- Use high-quality mushroom grow bags with breathing filters and sturdy seals to minimize the risk of contamination. Seals are very important, and a bad seal is often a cause of contamination. Obtain a high quality sealer if you are doing large amounts of bags, it is worth it. Be sure to test your seals while sealing them.
- Store your mushroom substrate in a clean and dry area, away from potential sources of contamination. Monitor the temperature and humidity levels to create an optimal environment for mushroom growth while discouraging the growth of contaminants.
Remedies for Contaminated Substrate
If spotted early, many contaminates be controlled with a 3% hydrogen peroxide solution sprayed on the infected area. Soaking a paper towel in hydrogen peroxide and placing it on the affected area is helpful at controlling small patches of contamination and preventing further spread. You may also try to surgically remove the contaminated area. When performing this type of extraction, be sure to use sterilized equipment in a laminar flow hood. Make cuts well beyond the visible contamination providing 1 cm or more margin. Make slow steady hand movements during the dissection. During removal, avoid carrying the removed contaminated parts over clean substrate. Attempt to position the contaminated portion downwind from uninfected areas and carry the contaminated portion toward you away from the clean area.
The Final Straw
If you have uncontrollable and untreatable contamination in your mushroom substrate, it is best to remove it immediately to prevent further spread. Remember to dispose of contaminated substrate properly in order to avoid contaminating other batches or the overall growing area.
By being vigilant and proactive in identifying and addressing contamination, you can ensure the success of your mushroom cultivation endeavors. If you have any further questions or concerns, feel free to reach out to us at Liquid Fungi, your trusted source for mushroom growing information and supplies.