The Fungus Among Us
Fungi were formerly classified as plants. Many have cell walls (made of chitin, not cellulose) and grow in soil. BUT they do not have roots, stems or leaves and don’t make their own food.
Fungal Structure
· Hyphae (singular is hypha)—thread-like filaments that make up the main structure of fungi.
· Mycelium—a branched network of hyphae filaments.
In a mycelium, different types of hyphae can: 1. act as anchors (attachment).
2. obtain food.
3. form reproductive structures (fruiting bodies).
Fungal Function
Obtaining Food—all fungi are heterotrophs. Specialized hyphae secrete enzymes to digest food outside cells and then absorb the digested nutrients. Many fungi are saprophytes (decomposers) and important to the environment. Others can be parasites, digesting living cells. A few are mutualists (lichen, mycorrhizae).
Reproduction—mostly asexual, but sometimes sexual.
Asexual only
· fragmentation: broken pieces of mycelia can grow into whole new mycelia.
· budding—single celled fungi (like yeast) pinch off smaller parts of their cell that develop into another organism.
Asexual or Sexual
· spores—a reproductive cell that develops into a complete organism. Can form either way. Sexual spores develop only when two different mycelia (gametangia) fuse to form a diploid cell. The structure that forms spores (fruiting body) is the only part seen for most mushrooms.
Divisions (Phyla) of Fungi
Zygomycota
Common name: mold and mildew
Need to know:
Reproduce by spores. Develop spores asexually during good growth conditions (on moist food). Develop zygospores sexually during dry conditions. Zygospores can survive harsh conditions.
Example: black bread mold, Rhizopus stolonifer.
Ascomycota
Common name: sac fungi
Need to know: Structure that holds spores called an ascus, which is a sac. Most important member of this group is yeast. Yeasts ferment sugar to make alcohol and carbon dioxide, so they are used to make wine, beer and bread.
Other examples: morels and truffles (edible), chestnut blight, Dutch elm disease, apple scab (plant diseases).
Basidiomycota
Common name: club fungi
Need to know: Spore producing structure is called the basidia and it is a club shaped cell. Basidia develop on the gills of the visible fruiting bodies (reproductive structures) that most people call “mushrooms”.
Examples: Portobello, shiitake etc. mushrooms, shelf fungi, puffballs, rusts.
Deuteromycota
Common name: imperfect fungi
Need to know: Have no sexual reproduction phase. Some are useful to humans; some cause problems. Most are small and mold-like.
Examples: Penicillin, bleu cheese and citric acid (used in candy and drinks) are made from various imperfect fungi.
Athlete’s foot, jock itch, ringworm and vaginal “yeast” infections are also caused by infections of various imperfect fungi.