Nature 2021 October

A foray for fungi

Autumn is the traditional time of year to go in search of edible mushrooms. There is much more to fungi than adding some interesting flavours to a meal. We are never very far from fungi. The 150,000 known species are found in every niche on earth from mountains to the deepest sea trench, woodlands, in deserts and rainforests, from the Tropics to the Antarctic, or simply under a rock, in the soil or in a puddle and the extremes of space or on and inside all animals and plants.

Typically, our first encounters are the sights of mushrooms and toadstools that appear suddenly in fields and on woodland trees. Secondly, a characteristic smell might attract our attention along a footpath, or the mould on rotten woodwork or decomposing food. Thirdly, our taste buds might delight in the like of the exotic truffle or the well-matured stilton or simply the refinements of yeasts used in bread and beer.

Aside from contributing in all sorts of ways to your diet, they have shared our bodies forever and their spores are to be found in every breath you take, or swallow you make. Our daily life is rife with fungal encounters: in the alcohol we drink; the bread, cheese, yoghurt not to mention the soy sauce in your last Chinese meal. However, their toxic and deadly poisonous qualities have had as long a history, be it involuntarily, for ‘recreational pleasure’ or as an intentional deadly weapon. The medicines we rely on and miscellaneous chemicals we voluntarily consume are the result of mycological synthesis, most notably antibiotics. However fresh the food is we eat, fungi are ahead of us starting the process of decomposition and conversion into food they need. Industrial processes use fungi to produce acids, enzymes, detergents, dyes and paints.

A vital ecological role Fungi play that we do not notice, nor give grateful thanks for, is their activity in the decomposition of dead animals and plants. Without this global clean-up the world would otherwise be so overwhelmed by mile high piles of biological material it would be too toxic for us to survive.

Meanwhile, in ways that we do not notice or yet fully understand, fungi are the bricks and the cement that bind the living world together. Sometimes we catch a glimpse of this infrastructure in the form of the exquisitely fine fibres of the mycelium which bind and aerate the soil. In turn this entanglement of mycelia and substrate enhances water retention and restricts the forces of erosion. Fungi are not just limited to construction. They are called the ‘primary decomposers’ as they kick off the processing of dead or dying organisms. In woodland it would be trees or leaf litter, or in the sea it could be the discarded fronds from a seaweed forest, or any other organic detritus that has been discarded from the living part of the ecosystem.

A highly-regarded current-day mycological researcher has coined the term ‘molecular keys’ to denote the enzymes that give fungi the ability to unlock or release an unbelievably expansive range of chemicals that might be unique to certain plant or animal groups or even to just one species. For example, beetle species each have their own particular carbohydrates and proteins from which fungi have evolved enzymes so they can digest all variations. This soup of chemicals is the powerhouse behind every ecosystem. Fungi (and bacteria) are the equivalent of industrial chemical plants churning the soup and freeing up vital elements like magnesium, nitrogen, calcium and phosphorous. In simple terms fungi unlock ‘nutrients’ which are recycled by being fed back into the ecosystem’s food chain. In this way Fungi effectively connect through the food webs with all living things across the entire ecosystem.

In other ways, fungi exemplify the dependence on them of all organisms. Our bodies rely on a surprisingly wide range of bacterial and fungal communities which are called our microbiome. Scarily, microbiologists have computed that at most only 43 percent of the cell count that make up our bodies are actually of human origin. In other words around 60% of the cells are bacterial and fungal in origin.

I am reminded that, until relatively recently, fungi were considered a marginal subset of the kingdom of plants. Even when I was studying them in the 1970s it was breaking news when they were awarded their own kingdom based on their scale, variety and ecological importance and were put on a par with animals, plants and bacteria. More significantly, the reclassification of fungi into its own grouping, which is, in part, based on genetic studies, finds them more closely related to animals than plants. A significantly large number of physiological processes discovered so far in some fungi, for example the production of Vitamin D, is no mere coincidence. It points to an ancestral alignment of fungi biological systems with those of animals.

The oldest confirmed fungal fossil is dated at about 800 million years old. Evolutionary biologists believe the animal and fungi evolutionary trees separated from each other around a billion years ago.

Until 400 million years ago life on earth was still confined to the oceans. Terrestrial life was just beginning to populate the land. It is thought fungi were in the vanguard of that initial, tentative invasion from the sea, probably in a symbiotic relationship with simple plants. Though now extinct, the descendants of both algal and fungal parties to the symbiotic relationship can be found today. Ancestors of today’s lichens, the ‘prototaxites’ were at 25 feet, the largest living land ‘organisms’: the ‘trees’ of their day.

Fungi closely interact with plants in all environments, exchanging nutrients and transmitting chemical information between fungal mycelia and plant root systems, which has been described as a single shared circulatory and nervous system in one. Associated with plant roots, the filaments are called mycorrhizae or ‘fungal roots’ that dissolve and extract minerals from the soil in exchange for plant sugars produced by photosynthesis. In woodlands, fungal networks are not just alongside but actually inside trees, with their filaments threaded and woven in and among all the tree stem, leaf, flower and fruit cells securing and exchanging nutrients.

As humans we arrogantly see ourselves sitting above all other animals, consider plants as there only for our benefit and pleasure and fungi as largely irrelevant. Measured in terms of longevity, survival, adaptability in every ecosystem, fungi could be measured as scoring highest of them all. A foray for fungi can be much more than just a way to gather tasty food.

Chris Brown
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