Fungi

Background Information on Fungi

Fungi are eukaryotes and are heterotrophs that absorb (not ingest) their food. They secrete digestive chemicals into the 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.

Saprophytes in Beech 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 shovelfuls 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; -ium = small). 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. Even solid-looking muchrooms are made of masses of densely-packed hyphae.

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.

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; while 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 in making beer, wine, andxfs 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 terated 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

Like botanists, mycologists (myco = fungus; -ology = to study) use the term “Division” instead of “Phylum” and there are five Divisions in Kingdom Fungi: Zygomycota, Ascomycota, Basidiomycota, Deuteromycota, and Lichens. Most of the fungi with which we are familiar are Basidiomycetes or Ascomycetes. Almost all fungi reproduce asexually by producing some kind of spores. The various Divisions are separated by the type of sexual reproduction done by their members.

Examine, draw large, labeled pictures of, and take notes on each of the following examples of fungi. Optionally, observe “wild” fungi and bring back samples for microscopic examination. Certain other wild fungi like morels or blackleg can be brought back and sautéed. Also, examine any plastic mounts and/or other live or preserved specimens that are available.

Division Zygomycota:

Diagram of 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 stolonifera (rhizo = root; pus = foot; stoloni = twig, shoot; fer = to bear, carry), commonly known as black bread mold. Hyphae are typically 1n. When opposite mating strains come into contact, portions of the hyphae of each will grow toward each other, eventually joining together to form a 2n zygote. The zygote develops a tough protective coat and is then called a zygospore. Eventually, this undergoes meiosis to form four 1n daughter cells.

Prepared Slide of Rhizopus Examine the slide containing Penicillium, Aspergillus, and Rhizopus (Carolina #B223). The Rhizopus is the one that’s stained red and bears large, knobby structures which contain spores.

Division Ascomycota (Ascomycetes):

Diagram of Peziza Reproduction (ascus = little sac, bag, bladder, hence commonly called “sac fungi”) 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 and other cup fungi, as well as 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. When two opposite mating strains come into contact, a special structure, the ascocarp (carpo = a fruit) is produced for sexual reproduction. This consists of several specialized hyphae which terminate in structures called asci (the sacs). Within each ascus, a zygote undergoes meiosis to form four cells, each of which divides once more by mitosis. Thus there is a total of eight ascospores in an ascus. Interestingly, these have been used for genetic studies because they are lined up in the order in which the chromosomes separated in meiosis.

Prepared Slide of Aspergillus
Prepared Slide of Penicillium
Examine the Aspergillus (stained blue) and the Penicillium (stained purple) on the same slide mentioned above.

Peziza cross section
Peziza — 8 Ascospores
If available, cut a thin cross-sectional slice from a cup fungus (Peziza) or morel and examine under the microscope to see the asci and ascospores. If neither of those is available (as is likely in mid-winter) examine the prepared slide of Peziza (Carolina #B255 — pictured here), instead. Notice that there are eight (8) ascospores per ascus. If morels are available, sautée; and enjoy. If blue cheese or Camembert is available, you may wish to taste some. Optionally, if there are any left-over agar plates sitting around, P. roqueforti could be cultured for later examination.

Follow this link (picture to the right) to view more photographs of Ascomycota.

Examples of other Ascomycota include:

Half-free Morel
Prepared Slide of Yeast Budding

Division Basidiomycota (Basidiomycetes):

Diagram of Mushroom Reproduction (basidium = little pedestal) This Division includs things like mushrooms, shelf fungus, and puffballs: You may have already observed and tasted some of these fungi in a previous Biology lab class. A mushroom is actually a specialized reproductive structure arising from a large underground mycelium. Technically, a mushroom is a basidiocarp. The gills of mushrooms are lined with special structures called basidia. Within each basidium a zygote undergoes meiosis to form four nuclei. The basidium then grows four appendages and a nucleus goes into each to make four basidiospores. 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).

Mushroom Gills
Gills Close-up
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).

Growth of Mushrooms:

1. Small Buttons	2. Larger Buttons
3. Caps Open Leaving Vellum Behind
4. Velum Left by Opening caps	6. Decomposing Basidiocarps
5. Caps, Stalk, and Velum

Coprinus Slice Through Cap
Coprinus Gills Close-up

Coprinus Basidiospores on Basidia If available, cut a thin cross-sectional slice from mushroom gills and examine under the microscope to see the basidia and basidiospores. If no live specimens are available (as is likely in mid-winter) examine the prepared slide of Coprinus (Carolina #B270 - pictured here), instead.

Polyporus Section
Polyporus Close-up of Basidiospores

Polyporus Section of One Pore
Polyporus is another member of the Basidiomycota. However, these do not form gills like other mushrooms, but rather as their genus name might suggest, make many, small, rounded pores in which the basidia and basidiospores develop. Examine the prepared slide of a cross section through a Polyporus (Carolina #B276).

Draw and label the general structure of a mushroom, including cap, gills, stalk, and annulus (= velum). If appropriate species of mushrooms are available, sautée; and enjoy.

Follow this link (picture to the right) to view more photographs of Basidiomycota.

Examples of other Basidiomycota include:

Bird’s-Nest Fungus
Small Puffballs

Division Deuteromycota

(deutero = second, i.e. other) This is a general, catch-all 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 to human observers). 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.

This group is mentioned just because it fits in, here, but we will not be examining them.

Lichens:

Diagram of Lichen Composition The “body” of each species of lichen is made of a very specific mixture of one kind of fungus (often an Ascomycete) and one kind of 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.

Microscopic View of Lichen Examine the prepared slide of a cross section of a lichen (Carolina #B294). In general, as shown here, the fungus is stained blue, and the alga is stained red.

Follow this link (picture to the right) to view more photographs of lichens.

Examples of other lichens include:

Lichens on Tree Trunk
Lichen on Tree Trunk

Other Things to Include in Your Notebook

Make sure you have all of the following in your lab notebook:

• all handout pages (in separate protocol book)
• all notes you take as you read through the Web page and/or during the introductory mini-lecture
• all notes and data you gather as you perform the lab
• labeled drawings (yours!) of all fungi examined with all body parts labeled
  • Zygomycota (Rhizopus)
  • Ascomycota (Peziza)
  • Ascomycota (Penicillium)
  • Ascomycota (Aspergillus)
  • Basidiomycota (Coprinus)
  • Basidiomycota (Polyporus)
  • Lichen
  • any others that are available
• answers to all discussion questions, a summary/conclusion in your own words, and any suggestions you may have
• any returned, graded pop quiz