2.3.1: Introduction to Fungi

The word fungus is from the Latin word for mushroom, which is also similar to the Greek word for sponge. Indeed, the familiar mushroom is a reproductive structure used by only some of the fungi. There are many fungal species that don't produce mushrooms at all. The kingdom Fungi includes an enormous variety of living organisms collectively referred to as Eucomycota, or true Fungi. While scientists have identified almost 150,000 species of fungi as of 2020,¹ this is only a fraction of the millions of fungal species likely present on Earth.

Though understudied, kingdom Fungi is filled with fascinating organisms. An individual Armillaria ostoyae fungus in Oregon is one of the oldest and largest organisms on Earth, spreading across almost 10 km² of forest, with a mass anywhere from 6,800 to 30,000 metric tons and an estimated age between 1,900 to 8,500 years old, depending on estimates of growth rate. The fungus Pilobolus can shoot its spores twice as fast as a rifle bullet, many fungal species glow in the dark, others control the minds of insects, and still others negotiate the distribution of carbon, nitrogen, phosphorus, and other materials between trees in the world's forests.

Figure \(\PageIndex{1}\): Most people associate fungi with the reproductive structures they make. The rainbow of mushrooms shown in this image belong to the Basidiomycota, just one of the major lineages of fungi. On the right hand side, a few Ascomycota fruiting bodies can be seen: bright blue apothecia of Chlorociboria and the black, spatulate fruiting bodies of the earth tongues Trichoglossum and Geoglossum. The Ascomycota and Basidiomycota are generally considered macrofungi because most make fruiting bodies that we can see. The other fungi are often called the microfungi, forming microscopic fruiting structures. Photo by Maria Morrow, CC-BY-NC. Note: These were all found in my backyard on a single outing.

Fungi were once considered plant-like organisms and so are studied under the umbrella of botany. Though they are more closely related to animals than plants, fungi were not moved into their own kingdom until 1969, the same year we landed on the moon. Fungi are not capable of photosynthesis: they are heterotrophic, using complex organic compounds as sources of energy and carbon. These sources of carbon are digested externally, then absorbed. Some fungal organisms multiply only asexually, whereas others undergo both asexual reproduction and sexual reproduction. Most fungi produce a large number of spores, which are haploid cells that can undergo mitosis to form multicellular, haploid individuals. Like bacteria, fungi participate in nearly every role in an ecosystem. They are often decomposers and participate in the cycling of nutrients by breaking down organic materials to simple molecules.

Fungi are frequently found in symbiotic relationships with other organisms. For example, most terrestrial plants form a mutualistic symbiosis with fungi; the roots of the plant connect with the underground parts of the fungus forming mycorrhizae. Through mycorrhizae, the fungus and plant exchange nutrients and water, greatly aiding the survival of both species. Lichens are another association between a fungus and a photosynthetic partner (usually an alga), where they form a single body that might contain two to many different organisms. Fungi also cause serious infections in plants and animals. For example, Dutch elm disease, which is caused by the fungus Ophiostoma ulmi, is a particularly devastating type of fungal infection that destroys many native species of elm (Ulmus sp.) by infecting the tree’s vascular system. The elm bark beetle acts as a vector, transmitting the disease from tree to tree. Accidentally introduced in the 1900s, the fungus decimated elm trees across the continent. Many European and Asiatic elms are less susceptible to Dutch elm disease than American elms.

The close evolutionary relationship between fungi and animals makes fungal infections in humans a challenging to treat. Unlike bacteria, fungi do not respond to traditional antibiotic therapy because they are eukaryotes. Fungal infections may prove deadly for individuals with compromised immune systems.

Fungi have many commercial applications. The food industry uses yeasts in baking, brewing, and wine making. Cheeses and cured meats are products of fungal metabolism. Many industrial compounds are byproducts of fungal fermentation. Fungi are the source of many commercial enzymes, as well s the main source of citric acid production. Fungi are important to the health industry. Antibiotics were originally discovered in the fungus Penicillium notatum and many current medications, such as some antibiotics or the immunosuppressant Cyclosporine, are derived from fungi.

What is a mycologist?

Mycologists are biologists who study fungi. Many mycologists start their careers with a degree in botany, microbiology, or even ecology. To become a lab mycologist, a bachelor's degree in a biological science (preferably majoring in microbiology) and a master's degree in mycology are often necessary. Mycologists can specialize in taxonomy and fungal genomics, molecular and cellular biology, plant pathology, fungal ecology, biotechnology, or biochemistry. Some medical microbiologists concentrate on the study of infectious diseases caused by fungi (mycoses). Mycologists collaborate with zoologists and plant pathologists to identify and control difficult fungal infections, such as the devastating chestnut blight, the mysterious decline in frog populations in many areas of the world, or the deadly epidemic called white nose syndrome, which is decimating bats in the Eastern United States.

Government agencies hire mycologists as research scientists and technicians to monitor the health of crops, national parks, and national forests. Mycologists are also employed in the private sector by companies that develop chemical and biological control products or new agricultural products, and by companies that provide disease control services. Because of the key role played by fungi in the fermentation of alcohol and the preparation of many important foods, scientists with a good understanding of fungal physiology routinely work in the food technology industry. Oenology, the science of wine making, relies not only on the knowledge of grape varietals and soil composition, but also on a solid understanding of the characteristics of the wild yeasts that thrive in different wine-making regions. It is possible to purchase yeast strains isolated from specific grape-growing regions. The great French chemist and microbiologist, Louis Pasteur, made many of his essential discoveries working on the humble brewer’s yeast, thus discovering the process of fermentation.

Perhaps because mycology is often given short shrift within higher education (many institutions do not even offer mycology courses), many mycologists become teachers. This includes those employed as professors, as well as those who write books, teach workshops, give lectures, or provide other forms of education. As the field of mycology grows, so to do the possibilities for mycologists!

Footnote

¹ Figure from the 2020 Species Fungorum database. More information can be found in this open-access paper.

Attribution

Curated and authored by Maria Morrow, CC-BY-NC, using the following sources:

• 19.1.7 Fungi from Biology by John. W. Kimball (licensed CC-BY)
• 24 Fungi and 24.0 Prelude to Fungi from Biology 2e by OpenStax (licensed CC-BY). Access for free at openstax.org.
• 5.3 Fungi from Microbiology by OpenStax (licensed CC-BY). Access for free at openstax.org.