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  • P.K. Peterson

The Fungus Among Us

“The world depends on fungi, because they are major players in the cycling of materials and energy around the world.”

- E.O. Wilson, American biologist, naturalist and writer


“Globally, the total length of fungal mycelium in the top 10cm of soil is more than 150 quadrillion km: about half the width of our galaxy.”

- Toby Kiers, professor of evolutionary biology, Vrije Universiteit Amsterdam and Merlin Sheldrake, biologist and author



We read or hear mostly about microbes that make us sick, aka, pathogens. Yet a vast majority of microbes (bacteria, archaea, viruses, protists, and fungi) are either harmless or beneficial to humans. In this Germ Gems post I highlight five positive facts about fungi or what I refer to as “Fun Facts.”

What exactly are fungi? Like the other members of the domain of life called Eukarya (namely, plants, animals, and protists), fungi are organisms whose cells possess a nucleus. This intracellular structure distinguishes the eukaryotes from prokaryotes, that is, bacteria and archaea. As of 2020, taxonomists had described around 148,000 species of fungi. The global biodiversity of fungi is, however, estimated to be far greater—between 2.2 and 3.8 million species.


The majority of fungal species are microscopic yeasts and molds. One group of fungi, mushrooms, are easily visible. Fun Fact 1: the largest organism on Earth is a fungus, a mushroom called Armaillaria ostoyae, that occupies more than 2,000 acres of forest floor in Eastern Oregon.


The field of ecosystems biology has mushroomed (pun intended) in recent years. At the same time that a greater understanding has emerged of ecosystems—defined as interacting communities of living organisms (plants, animals, and microbes) with nonliving components of their environment, such as, air, water, and mineral soil—the essential role of fungi in decomposition of organic matter as well as in provision of nutrients is better appreciated.


In human biology, one of the most exciting areas of research in the past decade is the study of the human microbiome. Of the five human ecosystems being examined, the gut captures the most attention. Fun Fact 2: assuming you’re healthy, your gut fungiome (also called the mycobiome) contains about 100 different fungal species. A yeast, Candida albicans, is the most prominent fungus inhabiting the human gut.


While the roles of the gut fungiome in health and disease are just beginning to be defined, it is already clear that yeasts like C. albicans elicit the induction of T helper cells, pivotal orchestrators of protective immune responses. Because the healthy gut also contains more than 2,000 species of bacteria and a myriad of viruses, research on how interactions between different microbial species affect human health (eubiosis) and disease (dysbiosis) is in its infancy. (Research of these complex interactions is daunting, to say the least.)


Fun Fact 3: “Otzi the Iceman,” a well-preserved mummy of a 5,300 year-old Neolithic man found in the Austrian Alps, carried two species of mushrooms, one on cords around his neck and the other in a special pouch, suggesting they had a special purpose such as serving as a food source. Ancient peoples used strains of microscopic fungal strains (often unknowingly) for millennia in the preparation of leavened bread and fermented juices. Mushrooms are not the only kind of fungi we eat. A partial list of common foods made with fungi includes: cheese, bread, chocolate, coffee, tea, pickles, olives, salami, soy sauce, tempeh, miso and others. (Alcoholic drinks are produced with the aid of fungal yeasts.)

Fungi are important not only for human health. Fun Fact 4: fungi are the unsung heroes of tree and plant health. Without fungi, there is no healthy soil, and without soil, there are no happy trees (and for that matter, no happy humans). One specific kind of fungus, the Mycorrhizal fungus, forms an essential symbiotic relationship with plant roots. This fungus helps tree and shrub roots find water and nutrients. In return, the roots give the fungi needed carbon, carbohydrates, and other nutrients.


In an interview published in the April 2021 NewScientist magazine, Suzanne Simard, a professor of forest ecology at the University of British Columbia, tells how she uncovered the hidden language of trees. After discovering what she called the “Wood Wide Web,” she found that underground connections in a forest are like a brain that allows trees to form societies – and look out for their kin. It appears that their symbiotic partners, mycorrhizal fungi, provide the language that warns other trees of pests, droughts, and disease.


Fun Fact 5: fungi are a virtual medicine cabinet of agents to treat and prevent human ailments. With all of the well-deserved publicity about mRNA vaccines manufactured for the prevention of COVID-19, many people don’t know that about 15% of all vaccines and therapeutic proteins are made in yeast. And many fungal species produce metabolites that are sources of pharmacologically active drugs, including statins (HMG-CoA reductase inhibitors) that inhibit cholesterol synthesis, cyclosporin (an immunosuppressive agent widely used in organ transplantation), and a host of anti-cancer agents, including doxorubicin, bleomycin, and mitomycin C.

The fungus psilocybin is gaining increased recognition for its potential role in the treatment of severe depression, substance abuse, and post-traumatic stress disorder. Commonly known as “magic mushrooms” or “shrooms,” psilocybin are naturally occurring mushrooms that are consumed for their hallucinogenic effects. They belong to a group of drugs known as psychedelics, which trigger changes in perception, mood, and thought.


Psilocybin is the key ingredient in magic mushrooms. When psilocybin is ingested, it’s converted in the body to psilocin, which is the chemical with the psychoactive properties. After a checkered early history of psychedelics such as LSD, magic mushrooms now appear to be a potential game changer for some patients with serious mental disorders. (Their popularity, and serious research attention, are discussed in a November 24 MedPage Today article, “Academic Centers Start to Take Psychedelics Seriously.”) In 2018, the Food and Drug Administration granted psilocybin “breakthrough” therapy designation for severe depression.


Probably the best known of the medicinal fungi is the mold, Penicillium chrysogenum. In one of the most remarkable examples of serendipity, in 1928 Dr. Alexander Fleming, a professor of bacteriology in London, accidentally discovered that when some of his petri dishes became contaminated with mold, this fungus produced the antibiotic penicillin. (The discovery of this “miracle drug” netted professor Fleming a Nobel Prize for Physiology or Medicine and 30 honorary degrees). Subsequently, other structurally related beta-lactam antibiotics were derived from fungi.


By definition, antibiotics are a medicine that treats bacterial infections. They are of no value, and in fact can be detrimental, when used in patients with viral infections. But just as we desperately need new antibiotics to treat bacterial superinfections caused by antibiotic-resistant bacteria, there is an equally urgent need for new antivirals to treat SARS-CoV-2 infections. It wouldn’t amaze me if such new treatments were found in mushrooms. For SARS-CoV-2 infections, we may soon get an answer (see Journal American Medical Association November 3, 2021, “Trials Test Mushrooms and Herbs as Anti-COVID-19 Agents; and Medscape November 8, 2021, “Early Trials Underway to Test Mushrooms as COVID Treatment”).


Moral of the story. Don’t ever count the fungi out.

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Main Page images courtesy of Shuxian Hu, MD. Dr. Hu is a scientist in the Neuroimmunology Research Laboratory at the University of Minnesota.

 

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