What are Fungi?

Fungi are a diverse group of organisms that include mushrooms, molds, and yeasts. Unlike plants, fungi cannot make their own food through photosynthesis. Instead, they absorb nutrients from their surroundings by breaking down dead plants, animals, or even rocks. Scientists estimate that there are between 2.2 and 3.8 million fungal species on Earth but can only identify around 150,000 of them so far.

Fungi can be found almost everywhere on our planet (perhaps even on the planet Mars): in soil, water, air, and even inside other living things. Fungi are remarkably tough organisms that can survive in some of the most extreme environments. Scientists call organisms that thrive in harsh conditions extremophiles, and fungi are among the best at this survival game. Some fungi can survive freezing temperatures far below zero. In boiling hot springs or in water high in acid or salt. Perhaps most incredibly, scientists found fungi growing inside the damaged Chernobyl nuclear reactor in Ukraine, where radiation levels are extremely high and dangerous to most life forms. These radiation-resistant fungi do not just survive they seem to use radiation as an energy source, much the same as plants convert sunlight to energy.

They range from microscopic single cells, like the yeast used to make bread, to enormous organisms. In fact, the largest known living organism on Earth is a fungus! In Oregon’s Blue Mountains, a honey fungus (Armillaria ostoyae) spreads underground across an area of about 1,665 football fields and is estimated to be thousands of years old, larger than a blue whale, the biggest animal on Earth.

Beneath our feet, fungi create vast underground networks that help plants connect and share resources. While we use cables and wires to connect our computers and phones, nature has its own system. In forests, fungi form living threads in the soil that link the roots of many different plants. These fungal threads, called mycelium, stretch out in all directions, connecting one plant to another.

This network allows plants to support each other. For example, when a large tree has extra nutrients, it can pass them to a smaller tree nearby with the help of fungi. The nutrients move from the tree’s roots into the fungal threads and then into the roots of another tree. In this way, the fungi act as a bridge for exchanging nutrients between plants.

Plants also use this system to share information. If a plant is being attacked by insects, it can release chemical signals into the soil. These signals travel through the fungal threads to reach neighboring plants, which can then start preparing their defenses before the insects arrive. Just like the Internet brings people together across continents, the “Wood Wide Web” connects plants throughout forests and ecosystems.

A Lucky Accident That Changed Medicine

Many great scientific discoveries happen by accident! One famous example is the discovery of penicillin. In 1928, a British scientist named Alexander Fleming made a discovery that would revolutionize medicine. Fleming was studying bacteria in his laboratory at St. Mary’s Hospital in London when he left for a vacation. When he returned, he noticed that one of his bacterial culture dishes had been accidentally contaminated by mold. Surprisingly, wherever the mold grew, the bacteria around it had died. This mold was a fungus called Penicillium chrysogenum (Figures 1A, B), and from it, scientists developed a medicine called penicillin (Read more in this Young Minds article). Penicillin is a very important medicine that fights harmful bacteria that make people sick. It has saved countless lives by treating bacterial infections that were once deadly.

Over the years, fungi have shaped modern medicine in many other ways, too. For example, organ transplants would be nearly impossible without cyclosporine, which is a medicine derived from a fungus called Tolypocladium inflatum (Find more info in this Young Minds article). This drug suppresses the immune system, preventing organ rejection and enabling successful transplantation. Thousands of patients worldwide benefit from this discovery every year. Heart attacks and medicines called statins, derived from fungi, can reduce cholesterol levels and help prevent heart attacks and strokes, saving lives around the world. Some fungi are even used to produce chemotherapy medicines that help fight various types of cancer. For example, several Taxol® and Taxotere® drugs are derived by the fungi Penicillium raistrickii and Pestalotiopsis pauciseta (Figures 1C, D). These drugs save thousands of lives every year

Fungi also show promise for treating some mental health conditions. Psychedelic compounds such as psilocybin (from Psilocybe mushrooms) are being studied for the treatment of depression, post-traumatic stress disorder, and addiction, offering new hope where other medical secrets fungi might hold.

Friendly Fungi Partnerships

In the “Wood Wide Web” section above, we saw how underground fungal networks can connect many plants in a forest. A big part of this network is formed by special fungi called mycorrhizal fungi (See more in this Young Minds article). These fungi live in close association with plant roots and form partnerships that benefit both sides.

Their tiny threads, called hyphae, collect water and nutrients from places that plant roots cannot easily reach, and they can even help protect roots against harmful microbes. In return, plants share some of the sugars they produce through photosynthesis with these fungi. This partnership helps plants grow stronger, keeps forests healthy, and can be found beneath almost every plant you see [1–4].

Nature’s Cleanup Crew and Garden Guards

One of fungi’s most important jobs in nature is recycling. Fungi play a key role in recycling organic matter in ecosystems. They break down fallen leaves, dead trees, and other plant material. To do this, fungi use special chemicals called enzymes, which cut large, complex molecules into smaller pieces. Once the material has been broken down, fungi use it as food and release nutrients back into the soil.

Scientists have also discovered that fungi can help clean up pollution. Some fungi used in processes called mycoremediation can break down pollutants such as oil, certain plastics, and industrial chemicals. In some cases, fungi can transform dangerous substances into less harmful forms. Researchers are now exploring how to use these fungi to help restore polluted soils and water and to make environments healthier.

Farmers and gardeners have also discovered that some fungi can be used as natural pesticides. Instead of relying only on synthetic chemicals to keep harmful insects away, they can use fungal products called biopesticides to help protect crops. Certain fungi live around plant roots and can help protect plants from insect pests and diseases. Some of these fungi produce substances that harm or repel specific insects, while remaining safe around organisms, including important pollinators like bees and butterflies. Farmers are increasingly using these beneficial fungi to protect their crops while reducing their reliance on synthetic chemical pesticides.

Glowing Fungi: Nature’s Night Lights

Imagine walking through a dark forest at night and seeing the ground, fallen logs, and even tree trunks glowing with an eerie green light (without any batteries or electricity), just living mushrooms producing their own light! This is not science fiction; it is the amazing ability of bioluminescent fungi (Figure 2).

Just like fireflies, bioluminescent fungi transform chemical energy into light energy using an enzyme called luciferase. So far, more than 120 species of bioluminescent fungi have been identified. In some cases, their glow may help attract insects that spread their spores, while in other cases it may help deter animals that might eat them. Scientists study these glowing fungi not just because they are beautiful, but also because the light-producing chemicals have potential uses in biotechnology and medical research.

The Tasty World of Fungi

Many familiar foods depend on fungi. When bakers make bread, they add tiny, safe fungi called yeast that makes the dough rise and become soft. The yeast does this by producing bubbles of carbon dioxide gas (CO₂) inside the dough.

Fungi are also essential for making many types of cheese. Different friendly fungi help turn milk into cheeses with very different textures and flavors, from stretchy mozzarella to strong blue cheese, in which the blue veins are made of fungal growth.

Beyond bread and cheese, fungi help produce several other foods. For example, specific fungi are used to ferment soybeans to make soy sauce, and others are involved in the production of chocolate from cocoa beans. Some fungi are also used to ferment drinks like beer and wine. In these beverages, yeast consume sugars and produce alcohol and CO₂, which give these drinks their characteristic flavors and bubbles. Many of the foods and drinks people enjoy every day would not exist without the work of fungi (Figure 3).

Important Safety Warning

However, not all fungi are safe to touch or eat. Some wild mushrooms and other fungi contain dangerous toxins that can cause serious illness. Children should never pick unknown wild mushrooms or any other fungi they find outside, unless a trained adult, such as a scientist who studies fungi, called a mycologist, confirms that they are safe. It is always best to eat only fungi that come from reliable sources, such as food bought at a store.

Conclusions: Why Fungi Matter

Fungi are everywhere, quietly shaping our world in ways most people never notice. A lucky lab accident led to the discovery of penicillin, and since then fungi have helped us develop medicines that protect transplanted organs, lower cholesterol, fight cancer, and may even offer new hope for treating mental health conditions. Underground, their mycelial “Wood Wide Web” allows plants to exchange nutrients and warning signals, keeping forests healthy and connected. Fungi decompose dead organic matter and return nutrients to the soil, help remove some kinds of pollution through mycoremediation, protect crops as natural biopesticides, and make everyday foods like bread, cheese, soy sauce, and pizza possible.

Understanding fungi is important because they connect many parts of life on Earth (and extraterrestrial) healthy forests, healthy people, and healthy ecosystems. By learning how fungi work, scientists can find new medicines, improve farming in more sustainable ways, and discover better methods to restore polluted environments.

Fungi may even help us face future challenges, such as feeding a growing population, dealing with climate change, and exploring space. Just like animals and plants, some fungi are rare and need protection. Climate change and habitat loss threaten fungal diversity, which is why scientists are working to identify and protect endangered fungal species.

The fungal kingdom still holds countless mysteries. With more than 90% of fungal species yet to be discovered, who knows what amazing abilities the next fungus might have? Perhaps one day you will become a mycologist and discover the next life-saving wonder fungus or find a new way fungi can help solve the world’s problems. Stay curious about the many secrets that the fungal world still holds!

Glossary

Extremophiles: ↑ Organisms that thrive in extreme conditions, such as very high or low temperatures, strong acidity, high salt levels, high pressure, dryness, or radiation. These organisms inhabit the most inhospitable places on Earth (extraterrestrial), including volcanic vents and frozen environments.

Mycelium: ↑ A network of microscopic threads (hyphae) that forms the main body of a fungus. Mycelium spreads through soil or other materials to absorb nutrients, sometimes shares resources with plants, and can produce mushrooms for reproduction.

Penicillin: ↑ A group of antibiotics derived from fungi. Penicillin was the first antibiotic medicine discovered that was effective against many bacterial infections.

Mycorrhizal Fungi: ↑ Fungi that have a symbiotic (mutually beneficial) relationship with the roots of plants. They help plants absorb water and nutrients, and in return they receive sugars from the plants.

Mycoremediation: ↑ A method of cleaning up pollution in which fungi, especially certain mushrooms, are used to break down or remove environmental contaminants such as petroleum hydrocarbons (oil spills) or polychlorinated biphenyls (PCBs).

Biopesticides: ↑ A natural pest-control product made from living organisms or natural materials, used to protect plants while reducing the use of synthetic chemicals.

Bioluminescent Fungi: ↑ Fungi that produce and emit light through chemical reactions inside their cells, like fireflies and some deep-sea organisms.

Mycologist: ↑ A scientist who specializes in the study of fungi, including mushrooms, molds, and yeasts. Mycologists investigate many aspects of fungi, such as their classification, ecology, genetics, and useful applications.

Conflict of Interest

The author(s) declared that this work was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

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