Fungi

Background Information:

Fungi are eukaryotes and are heterotrophs that absorb (not ingest) their food. They secrete digestive chemicals into their environment, where the food is “digested”, after which they absorb the nutrients. Most fungi are multicellular (yeast are secondarily unicellular). Fungi can be saprophytes, parasites, or mutualistic symbionts.

Saprophytic Mushrooms in Log Saprophytes absorb nutrients from dead organic matter (dung, corpses, etc.). These are important, necessary decomposers.

Parasites absorb nutrients from the body fluids of a host organism, to the detriment of the host.

Mutualistic symbionts absorb nutrients from a host, but reciprocate with some beneficial function(s). For example, mycorrhiza (-ae) (rhizo = root) are special fungi that live in/on the roots of plants, especially trees. This mutualistic association of plant roots and fungi is beneficial to both organisms because, through their digestive enzymes, the fungi help make minerals available to the plant and help in water absorption (they are smaller diameter than any of the tree roots) in return for organic “food” from the plant. About 90% of all trees depend on micorrhizae and bare-root trees often don’t do as well because all of the smaller roots where the micorrhizal fungi would normally live are pruned off. I have seen suggestions in various gardening books that when bare-root trees are planted, a couple shovel-fuls of forest soil should be put around their roots to inoculate them with the necessary fungi.

The “body” of a fungus is called a mycelium (pl = mycelia) (myce = fungus). A mycelium is a tangled network of filaments, each of which is called a hypha (pl. = hyphae; hypha = web, weaving). Some species of fungi have their hyphae divided into individual cells while others have hyphae that are multinucleate tubes without individual cells. Growth of a mycelium (the hyphae therein) can be very rapid, hence mushrooms (which are composed of densly-packed hyphae) can pop up in a lawn overnight.

The normal condition for fungal nuclei is 1n, and mitosis happens slightly differently than in other groups of eukaryotes. “Normal” fungal reproduction is asexual by just making spores that are disseminated by wind or water. However, especially under adverse conditions, many fungi also have some form of sexual reproduction with the formation of a different kind of spores, and fungi are grouped/classified based on what type of sexual reproduction they use.

Fankhauser Blue Cheese A number of fungi are commercially important: yeast and all the various edible mushrooms are fungi; blue, Roquefort, Camembert, and Brie cheeses are made using Penicillium roqueforti or Penicillium camemberti; and P. notatum is the source of penicillin. A variety of other molds are used for drugs, cheeses, etc.; other edible mushrooms are used in Oriental cooking; some mushrooms like truffles, puffballs, morels are considered to be delicacies: and various strains of the yeast, Saccharomyces cerevisiae, are used for beer, wine, and bread.

On the other hand, a number of fungi are pathogenic and adversely affect humans. Some mushrooms are toxic so you should never eat wild mushrooms unless you are absolutely, positively sure what they are. Ergot of rye grows in rye and if infected rye is milled into flour and ingested, people who eat that flour will ingest the chemical ergotine, which is both toxic and hallucinogenic (and also contains lysergic acid from which LSD is made). Ergotine can cause spasms and a burning sensation. Currently, ergotine is used in very small (dilute) amounts to stop postpartum bleeding.

Candida albicans is normally a a single-celled, yeast-type fungus which lives in our large intestines. Normally, it is a small part of the intestinal flora and is kept in check by the good bacteria that live in our colons. If for some reason it becomes necessary for a person to take antibiotics, as we previously discussed, these antibiotics will kill the good bacteria, allowing Candida and other such invaders to multiply. Also, if the person eats too much sugar or other simple carbohydrates, these will serve as food for the Candida, helping it to multiply, grow, and/or travel to other parts of the body, where it is called “vaginal yeast infection” (both partners must be treated simultaneously or they’ll just pass it back and forth) or “thrush” (if it’s in someone’s mouth and/or throat). There is also some evidence that Candida can turn into a mycelium with hyphae invading body tissues. To help fight against a “yeast” infection, a number of people have suggested eating yogurt daily, especially if a person is on antibiotics, and I read, somewhere, that women who consume a cup of yogurt a day have less problems with “yeast” infections. If a person has a number of bacterial infections, and antibiotics are frequently prescribed and/or if a person is prone to “yeast” infections, that person should insist that his/her doctor prescribe a fungicide (nystatin, which goes by brand names like Mycostatin, or Nilstat, Nystex, etc.) along with any antibiotics that are prescribed. From what I’ve read, it is strongly suggested that such a person also avoid foods either naturally or artificially high in sugar and simple carbohydrates (grapes, bananas, pop, candy, cookies, etc. white flour, white rice) which just serve as food for the Candida, making things worse. Rather, this person should replace these with a high fiber, adequate protein diet. There is also evidence that taking garlic on a daily basis helps — garlic is a known fungicide. I have heard that some people put yogurt on an infected site and that some women use a yogurt douche, but it would probably be a good idea to discuss these options with your physician first. It is important to keep the infected area as dry as possible, and open to fresh air if possible. If the site is normally covered by clothing, wear cotton clothing because polyester holds in body moisture — women with vaginal yeast infections shouldn’t wear nylons.

Fungal Classification

Division Zygomycota:

Rhizopus Reproduction (zygo = yoke; myco = fungus). In this group of fungi, sexual reproduction produces a zygosporangium (containing zygospores) which can remain dormant through unfavorable weather and release the spores when weather is suitable. An example is Rhizopus (rhizo = root; pus = foot) which is black bread mold.

Division Ascomycota (Ascomycetes):

Peziza Reproduction

Click for More Photos (ascus = little sac, bag, bladder) Fungi in this Division primarily reproduce asexually by forming chains of spores called conidia (conid = dust). In their sexual reproduction, a cup-like “fruiting” structure is formed called an ascocarp (carpo = fruit). This contains a number of asci (ascus), each of which contains eight ascospores. The ascospores are always lined up in the order in which they did meiosis, thus are used by some biologists to study meiosis. Examples of fungi in this Division include Peziza, Morels (Morchella) — considered a delicacy and one of the few that’s “safe” to collect because few other things look like them. Yeast and Ergot are also Ascomycetes. For many years, mycologists (people who study fungi, myco = fungus) suspected that Penicillium belonged here, and recently the genus was officially moved from the Deuteromycota to here.

Division Basidiomycota (Basidiomycetes):

Mushroom Reproduction

Click for More Photos (basidium = a small pedestal) Often the mycelium of mushrooms starts in one place (wherever the initial spore landed) and spreads out from there in a circle. Around the edge of the circle, specialized, densely-packed hyphae form fruiting structures each of which is called a basidiocarp (or mushroom). The gills of mushrooms are lined with basidia (sing. = basidium) each bearing four basidiospores which result from meiosis. Some members of this group (like Polyporus squamosus — poly = many; porus referring to the pores on the underside, squamo = scale referring to the shaggy top side) have pores rather than gills. In a puffball, spores are produced inside the puffball, then “wait” for a hole or tear in it so they can get out. A ring of mushrooms forms at the outer edge of the mycelium. Mushrooms can rapidly appear and use nutrients in the area of the immediate growth ring, so the grass appears stunted and is called a fairy ring (people thought the fairies were dancing and trampling down the grass there).

Part of a Fairy Ring

Division Deuteromycota

(deutero = second, i.e. other) This is a general category for fungi in which humans have not yet observed sexual reproduction (which would qualify a fungal species to be classified in any of the other Divisions). This Division is also called Fungi Imperfecti or the imperfect fungi (botanists use “perfect” to refer to a plant with flowers with all their sexual parts and functions — while fungi do not have flowers, the method(s) of sexual reproduction used by members of this Division is/are unclear). Until recently, Penicillium used to be classified as an imperfect fungus because, while humans had observed asexual reproduction by means of asexually-produced spores, no one had ever seen evidence of sexual reproduction (fertilization and meiosis) in any species of Penicillium. For many years, it was suspected that Penicillium belonged in the Ascomycota, and recently it was officially moved to that Division.

Lichens:

Lichen = Alga + Fungus

Click for More Photos The “bodies” of lichens are made of a mixture of fungus (often an Ascomycete) and either a green alga (Division Chlorophyta) or a bluegreen alga (Cyanobacteria). The fungus and alga live in a symbiotic relationship, that is, they are closely associated with each other. More specifically, their relationship is called mutualistic, because both benefit from the relationship. The fungus holds water to keep the alga moist, “digests” rock and makes the minerals available for both to use, and generally serves as protection for the alga. The alga produces organic “food” for both by the process of photosynthesis. The scientific names for lichens usually are based on the type of fungus (each “species” of lichen consists of its own kind of fungus and its own kind of alga). The scientific names for lichens apply to each type of lichen — there are not separate names for the fungus and alga in a lichen. Lichens are often a grayish-green color, but may be brightly colored. They are an important food source for a number of animals (notably reindeer), while some species are used by humans for dye. Lichens are good at colonizing bare rock and starting to break it down into soil. Because lichens depend on rainwater as a source of moisture and air as a source of CO₂ from which to make sugar, they are extremely sensitive to pollution and are among the first to die. Thus, these fungi are indicator species for poor air quality.