Fungi

Abstract

Fungi are eukaryotes in the Opisthokont clade, which also includes animals (metazoans). Most fungi are free-living decomposers of organic matter (saprotrophs). They are essential for nutrient cycling, especially by decomposing wood. Fungi are heterotrophic; they secrete degradative enzymes to break down complex organic molecules (such as cellulose) into simpler molecules (such as simple sugars) they absorb for nutrition. Fungi grow as filamentous cells (hyphae), sometimes in dense colonies (mycelium), or as single cells (yeasts). Fungi reproduce by spores produced asexually by mitosis or sexually by meiosis. Most fungi do not grow well at temperatures above 30 °C, and therefore, relatively few fungi are pathogenic to warm-blooded animals (birds and mammals), except on skin, nails, or feathers, where temperatures are cooler. Most invasive fungal infections in humans occur in immunocompromised hosts. By contrast, fungi are the most common pathogens of insects and plants. Some fungi cause severe diseases in wildlife or natural plant communities; fungal diseases of amphibians (chytridiomycosis) and bats (white-nose syndrome; with lower body temperatures during hibernation) are threatening the extinction of some species. Oomycetes are stramenopiles that are superficially like fungi and have traditionally been studied with fungi. They are prominent plant pathogens although a few cause significant disease in humans or other animals.