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Sabine Vreeburg: How do you cultivate world’s biggest mushroom? | WURcast

September 6, 2019


I will tell you something about mushrooms: how they are cultivated and how the biggest mushroom in this world is cultivated. I would like to start with the all-round mushroom that everybody knows from the blue boxes in the supermarket, you all know them. A lot of people, however, do not know what a mushroom really is. I don’t think I have to tell here, as I sometimes have to tell at a birthday party, that it really is not a vegetable, but a fungus. And then I often get the response: “Ew! A fungus!” However, when I start telling about the mushrooms; that you can eat them and that they are delicious, then the reactions immediately change. All in all, there is a certain ambiguity against mushrooms: are they fungi or vegetables, and are they delicious? I know that they are also seen as a source of protein. I will come back to the question if mushrooms are a suitable replacement of meat. But first I would like to tell more about what a mushrooms exactly is. This is the life cycle of a mushroom. A mushroom starts off as a spore, a sort of seed. This seed can sprout and this results in a hyfus structure, which we call a mycelium. This is what you see on your sandwich when it is moldy. Then you can perfectly see the little fungal threads. This will grow and become a mycelium body. That body will then meet another mycelium, with which it can reproduce. This does not happen in the same way as it happens with mammals, where an egg and a seed come together, but here two entire mycelia come together. And what happens then is that two cells fuse and that subsequently the two nuclei are able to migrate, can move through each other’s body. So actually, you already have the body and it later becomes a product of two halves. So, we develop from an egg cell and a sperm cell and grow into an entire body, the product of two parents, while for fungi the bodies are already present and thereafter it becomes a product of the two of them. This fungus structure could, when there is a certain trigger, for example the sudden presence of light, or that there is too little oxygen, or the remark there is a lack of food, then start to create mushrooms. Mushrooms are essentially the fruits of the fungus. There the spores are again created. When you cut a mushroom in two, what everybody sure has done sometime, then you can see little brown pieces in the middle These are lamellas and there spores are made. Mushrooms can do another cool trick. I can get a piece of mushroom and put it onto nutritious soil. Another mycelium structure will then grow, which is able to form a mushroom. A clone of the former mushroom. This process can be endlessly repeated. This is what a mushroom is. We cultivate them, because we know how to cultivate mushrooms. This is something I think we are doing for almost 600 years now. We accidentally found out how to cultivate them. Then the question that I got in response to this talk: “Are mushrooms a suitable replacement for meat?” I thought to myself: what is the definition of a suitable replacement for meat? I went to the website of the Voedingscentrum to look for a definition and I read that a suitable replacement for meat should have enough protein, iron and vitamin B1 and/or B12 Now I know that mushrooms at least the ones we know but also lots of other sorts, contain a lot of protein and essential amino acids. They also contain vitamin B1 but what they not contain is vitamin B12, which is only present in products of animals. They also do not contain enough iron. Luckily, we can get iron from a lot of other vegetables and we can produce vitamin B12 even for vegans with help of yeast. So, following the strict definition mushrooms are not a suitable replacement for meat. However, like Adsean mentioned I think that we need a more varied diet and this is a very suitable source of protein. Enough about meat replacements. I promised to tell more about the biggest mushrooms in the world. Here they are. As big as an umbrella: they can be a about a meter in intersection. They are very delicious, are eaten by humans and seen as a local delicacy. They have loads of protein and have sort of meat-like structure, they are described as such. Unfortunately, they grow only once a year in the wild. They are quickly and happily picked by local people which is also the only moment you could buy them at the local market and with local I mean Africa and Asia. We, humans, are not yet able to cultivate those mushrooms. However, there is something, or someone else, that was able to do so namely insects: termites. Termites succeeded in creating this fungus about 30 million years ago for their own consumption. They do this in a process that is very similar as our agricultural practices. This is what a termite hill looks like. This is me, still completely rested on top of a termite hill; this is me three hours later, because it takes so much time to cut open such a hill. Here you can see what the inside of the hill looks like. I made a schematic picture to better explain the situation. You see that everything above the ground are corridors and tunnels. That is the system that keeps the climate of such a termite hill constant. The temperature is regulated, the humidity is regulated, the oxygen flow is regulated. I have seen videoclips on YouTube where people pump CO2 inside termite hills. And what they then see is that the termites restructure the tunnels to make sure air circulation stays constant to maintain their fungus. Really cool. Every hill is created by a king and a queen. They are the only ones in the nest able to reproduce. Together they make all employees and soldiers that take care of the nest. When they die, the whole nest dies. The workers they create look after the fungus garden. They sow, they harvest and they look after the fungus. They even remove weeds. When other fungus enter, there are stories that they really eat those. This is what that fungus garden looks like. I again have a scheme for that but I did not make it myself. It is a schematic picture made by my supervisor and what there actually happens is that the workers leave the hill and fetch dead plant material: leaves, pieces of wood, grass, which they bring back to the nest. Those are very complex plant materials and termites are unable to get a lot of energy from them. Just like when we eat lettuce: we cannot get much energy from it. This is because the sugars are hidden in too complex forms for us to break apart. A fungus however is able to do so. Termites eat the material together with small pieces of fungus from the nest, which they excrete. This way, they are sowing the fungus, and now, in a perfectly inoculated substrate, we would say, a very perfectly sown soil which is already a bit humid and a bit pre-grinded the fungus can grow. There it creates hyfus structures and when that is done the fungus garden is again eaten by termites. That is how they eat fungi and get their energy. This way, they convert a nutrient poor source into a nutrient rich, protein rich source for themselves. You can see here beautifully – this is a photo where you can see that at the top – at the top, there still is very dark material. It has just been deposited recently, this is the fresh excrement of termites. As the fungus has grown through more of the material, you see it becomes lighter. This is a sign that the complex structures of the plant material are broken down by the fungus. It brings along a change in colour. And then these little things. I can imagine you think these are those mushrooms but they are not. They are a sort of evolutionary adjustment of the fungus to make sure they can go through the intestine system of termites without being broken down. These are a sort of clones in the fungus, we call them asexual spores, spores that did not go through meiosis. So no… How can I put that? Hmm, that is a tough one. Do you know what meiosis is? No? Okay. They are, genetically seen, exactly the same as this fungus. This is different than sexual spores, that is the same as when I would make egg cells. All my egg cells are different. Every time I would get babies, they would be different. That is the result of meiosis. That is the difference. These are clones, which are eaten by termites to inoculate again. The people that pay attention will have noticed that I still did not speak about the mushrooms. In these nests they have no use. They just are a waste of resources. To explain this I have to go back to the beginning of the hills. Once a year the king and queen make winged offspring. These are the princes and princesses that will start new hills. They fly away, a male and female meet, lose their wings and start to dig themselves in. For the first few weeks they do not need food from the outside, because they have enough fat reserves. In that time they start their new nest. They create the first workers. The problem is that they did not take the fungus from their previous nest and without that fungus they will not survive. It is a coincidence, and the question is if it’s a coincidence, that exactly at the moment the workers leave the nest to get food, also the mushrooms come from the existing hills. They spread their spores in the whole area, which ends on plant material that is brought by the first workers to their new nest. This is how every nest gets inoculated. It seems that there is a strong connection between the creation of mushrooms and the creation of winged descendants to start new hills. Somewhere there is the key for me to find out how to cultivate these mushrooms myself. The existing hypothesis was that these little spore balls, these little clones that this structure would also be the beginning of a new mushroom. You can imagine that the king and queen can only make a limited amount of new termites a day. When you have to partly create winged termites, you have less workers to look after the nest. This would mean that the small balls are not being eaten and that they can grow into mushrooms. This is what we always assumed. I thought, I have seen this with other mushrooms, you can in a very early stage see if it will be mushrooms in the end. So the only thing I need to do is to cut that in half and make microscopical images. Then I can see if a mushroom grows inside. I also thought that when I mimic the situation that there would be no workers to eat those little balls then mushrooms should be formed. So, what I did: I went to South Africa, cut open a lot of nests and parts of it I took with me to a laboratory to put into little pots without termites. I made sure there was some moist, that it was warm enough, dark enough, just like their own nests. I just had to wait. And this is what I saw. I indeed saw that mushrooms were being formed. However, I also saw something else. I saw irregular little balls were present, as we know of, and I saw very clearly structured balls with the same size. I called them pointy – well, we call the balls nodules and I named them pointy nodules as they are pointy. They clearly have a point like a mushroom. What happened when I had them in the laboratory in little boxes to see what would happen without workers present was indeed that the irregular shaped little balls only increased in size. The ones that already looked like a mushroom really turned into mushrooms. It looks thus like that – no first, I wanted to show you what they looked like from the inside and that is something you can all see very clearly that these really are two different things. This is a cross section from a irregular one and this is a cross section from a pointy one. Here, you can already see the mushroom growing. The same pattern proceeded when it enlarged. You could see both the mushroom and the one with no structure more and more clearly. This means, for now, that it seems that it is no coincidence that the little balls they use in the nest also can grow into mushrooms. This means I have to go back to the drawing table to think about a new idea. I still think there is a connection between the flying termites and the loss of workers in the nest: that then mushrooms can be formed. How this is really taking place I will later in my PhD try to model to see if I could really show it. But for now I have to owe you the details, the triggers of these mushrooms, but I have told you about how termites work and I hope you find this system as fascinating as I do. Thank you for your attention.

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