Can I grow mushrooms at home? Yes, but eating them might land me in the hospital

Produced by: Science Popularization China

Author: Rao Gu (School of Life Sciences, Nanjing Normal University)

Producer: China Science Expo

As autumn arrives, it is mushroom picking season again. When picking wild mushrooms, we must carefully identify them, pick and eat them with caution, and prevent poisoning accidents caused by eating wild mushrooms.

At present, as the mushroom bag cultivation technology continues to mature, more and more people are beginning to experience the fun of growing mushrooms at home. However, this has also caused public concerns about health. In rare cases, home-grown mushrooms may cause spore infection in the human lungs, and the clinical symptoms are similar to those of mold infection. In particular, people with weak immunity, such as the elderly and children, are more susceptible to mushroom spores.

Indoor cultivation of oyster mushrooms (Pleurotus ostreatus)

(Photo credit: Photo taken by the author)

How do mushrooms grow?

Mushrooms are actually a type of fungus that reproduces through spores. Mushroom spores are very small, usually more than 5 μm in length, and the largest can be more than 10 to 20 microns. They exist in the soil and air like dust.

When the spores find a suitable environment, they begin to grow and germinate something called "hyphae". These hyphae twist together and frantically absorb nutrients from the soil, rotten wood and other substrates for their own growth. When they are full and satisfied, they will emerge from the substrate and grow what we call "mushrooms". Mushrooms have spores, which can spread their offspring farther through media such as wind and insects.

The "king of fruit fungi" that was very popular on the Internet some time ago - Schizophyllum commune, which grows on apples, is a very tenacious fungus that is widely distributed all over the world. Why can mushrooms grow on apples? A reasonable hypothesis is that Schizophyllum commune first infected the apple tree, causing it to carry spores or hyphae of Schizophyllum commune, and then grew on the apple when the environmental conditions were suitable (such as the rainy season).

Apple with mushrooms

(Photo source: Miss Deng's social account from Deqing)

It is worth mentioning that some bacteria will also produce spores under harsh environmental conditions to cope with environmental pressure, but it is not a way of reproduction, so it is completely different from mushroom spores.

Spore inhalation hazard

Some fungi grow as single cells, such as yeast used in brewing; some form the mushrooms we know as edible, medicinal and poisonous fungi; and some form molds, which cause food spoilage. Molds can cause illnesses, such as allergies to mold spores, inflammation caused by the growth of pathogenic molds in the body, and poisoning caused by mycotoxins.

Pink spore powder of Pleurotus djamor

(Photo credit: Photo taken by the author)

There are a lot of mold spores in the air, mainly from dust, which attach to dust particles and mist droplets. It is estimated that humans inhale 1,000 to 10 billion mold conidia every day. The reason why most people are safe and sound is due to the sterilization function of our lung immune system. Once the spores invade the lungs, immune cells called neutrophils will eat them like beans, and then initiate programmed cell death - that is, cell suicide or apoptosis - to eliminate the invading pathogenic spores.

Surprisingly, some mushroom spores have also become important human pathogens, which can cause a variety of clinical manifestations, including allergic diseases and infectious diseases. Among them, the spores with the strongest pathogenicity are Schizophyllum commune, the "fruit mushroom king" that was very popular on the Internet some time ago, followed by Coprinopsis cinerea. Both are mushrooms widely distributed in the wild and have strong diffusion capabilities.

Coprinus comatus in the autumn forest

(Photo source: veer photo gallery)

Schizophyllum is a commercially cultivated species called "white ginseng". In addition, mushrooms such as Ceriporia lacerata, Volvariella volvacea, Irpex lacteus, Bjerkandera adusta and Cyclomyces tabacinus have also been reported to cause disease.

Most cases of these pathogenic mushrooms involve the respiratory tract, including bronchopulmonary disease and sinusitis, and occur in both normal and low-immune populations. This reminds us not to put mushrooms under our noses when collecting and handling them, so as to avoid inhaling too many spores and endangering our health.

How to avoid spore damage when growing mushrooms at home?

From the above introduction, it can be seen that growing mushrooms at home is a safety hazard, and this is indeed the case. Mushrooms release a large number of spores during the maturation process, and long-term and large-scale inhalation of mushroom spores will increase the risk of infection.

Mushroom growers occasionally get an occupational disease called "mushroom lung," which is an allergic disease with respiratory symptoms caused by inhaling a large amount of mushroom spores. Patients need to leave the spore environment, and those with mild symptoms need to leave the mushroom house for 7-10 days, and those with severe symptoms need to leave the mushroom house for 1-2 months before they can recover. However, the disease may relapse if they are exposed to the spore environment again.

Growing Mushrooms at Home

(Photo source: veer photo gallery)

Although the probability of being infected by mushroom spores when growing mushrooms at home is extremely low, sporadic cases can still be found, which reminds us that we need to be vigilant about the potential harm of mushroom spores to human health. When we grow mushrooms indoors, it is best to pick them before they mature, and we should also wear masks when picking them. People with low immunity, such as children and the elderly, should pay more attention to protection. In addition, if the mushroom bag is found to be moldy, it should be discarded in time, because mold spores can also pose a threat to human health.

Other things to know about mushroom spores

There is a saying on the Internet that if you have touched poisonous mushrooms, it is best not to touch anything edible with your hands, and don't touch them with washed hands, as the spores cannot be washed away.

Mushroom spores can be simply compared to plant seeds. They are both reproductive structures of organisms, but there are many differences between the two. The most important point is that seeds are diploid and contain two sets of chromosomes from their parents, while spores are haploid and contain only one set of chromosomes. Haploid spores of mushrooms germinate into primary hyphae in a suitable environment. Only when compatible hyphae combine can diploid hyphae be formed, and then they can differentiate into mushrooms.

Mushrooms are composed of hyphae, while spores are produced by the differentiation or breakage of hyphae, and should contain the components of the hyphae contents, which is indeed the case. The most popular and studied mushroom spores are Ganoderma lucidum spore powder. We are all familiar with Ganoderma lucidum, which is a traditional precious tonic medicine in China. Studies have shown that Ganoderma lucidum spore powder contains all the active ingredients of Ganoderma lucidum, such as ganoderic acid, Ganoderma lucidum polysaccharide, ergosterol, etc. Since the cell wall of the spores affects the digestion and absorption of the human body, all Ganoderma lucidum spores need to be broken. Studies have shown that the human body's utilization rate of Ganoderma lucidum spore powder after the wall is broken is 8 times that of the unbroken wall.

Ganoderma tsugae

(Photo credit: Photo taken by the author)

The same is true for the spores of poisonous mushrooms. If the mushroom itself is poisonous, then the spores it produces also contain relevant toxins. Scientists extracted a hallucinogenic toxin, ibotenic acid, from the fresh cap and spores of Amanita muscaria, a mushroom containing hallucinogenic toxins. They found that the average content of ibotenic acid in spores was 0.0054%, and the average content in fresh caps was 0.017%, which is more than three times the content of ibotenic acid in spores.

Amanita muscaria

(Image source: wikimedia)

The effective dose for an adult to induce hallucination is about 30-60mg of ibotenic acid, which is usually equivalent to the content of one Amanita muscaria. This is equivalent to the weight of more than three mushrooms of poisonous mushroom spores to produce toxicity. According to this calculation, a handful of poisonous mushroom spore powder should not be enough. This also confirms the old saying that "talking about toxicity without considering the dosage is just hooliganism."

Amanita subjunquillea is a highly toxic plant

(Photo credit: Photo taken by the author)

The length of mushroom spores is generally more than 5μm, and the largest ones can be more than 10 to 20 microns, while bacteria are generally only one or two microns, much smaller than mushroom spores. The smaller the object, the harder it is to wash it off with running water. They will hide in the lines on the hands, making it difficult to remove them all.

The correct hand washing method can effectively remove most of the bacteria on your hands, and it is probably also applicable to mushroom spores. The surface of mushroom spores is smooth or has some patterns, and they will not be tightly attached to the surface of objects. Washing your hands repeatedly can effectively reduce the residue of spores on your hands, or even completely remove them.

Note: Latin text should be in italics

References:

1.Li W, Pires SM, Liu Z, Liang J, Wang Y, Chen W, Liu C, Liu J, Han H, Fu P, Guo Y. 2021. Mushroom Poisoning Outbreaks — China, 2010–2020. China CDC Wkly 3:518–522.

2. Wang Meidan, Hu Yang, Song Hui, et al. Research progress on chemical composition and pharmacological effects of Ganoderma lucidum spore powder and prediction analysis of its quality marker (Q-Marker)[J]. Chinese Herbal Medicine, 2023, 54(23): 7918-7933.

3. Yu Yuhan, Song Yisheng, Zhang Lijiang. Research progress on toxicology and safety evaluation of Ganoderma lucidum and Ganoderma lucidum spore powder[J]. Chinese Journal of Modern Applied Pharmacy, 2023, 40(08): 1147-1154. DOI: 10.13748/j.cnki.issn1007-7693.20222542.

4. STOeRMER, FC, JANAK, K., & KOLLER, GE (2004). Ibotenic acid in Amanita muscaria spores and caps. Mycologist, 18(3), 114-117.

5.Shlezinger N, Irmer H, Dhingra S, et al. Sterilizing immunity in the lung relies on targeting fungal apoptosis-like programmed cell death[J]. Science, 2017, 357(6355): 1037-1041.

6.Chowdhary A, Kathuria S, Agarwal K, et al. Recognizing filamentous basidiomycetes as agents of human disease: a review[J]. Medical Mycology, 2014, 52(8): 782-797.

7. Zhang Qinyuan, Guan Xiaoming, Li Baoqin. Investigation and analysis of spore pneumonia among edible mushroom growers[J]. Journal of Preventive Medicine of PLA, 1994(03):210-211.