Fungi are defined as eukaryotic organisms with chitinous cell walls and no chloroplasts; they are heterotrophs, usually deriving their carbon from dead matter (as a decomposer) or parasitically from other living things. Fungi also require a source of moisture, be it humidity in the air, water from the cells they attack, or the sweat that comes out of the skin on your feet. The fungal life cycle is somewhat complex; all true fungi go through a haploid (1n) stage, a diploid (2n) stage, and a dikaryotic (n+n) stage. (In some fungi, the dikaryotic stage is reduced; in some, it is largely extended.)

Originally, the fungi were grouped with Kingdom Plantae. Recently, it has been shown that if anything, fungi are more closely related to animals than plants.

Kingdom Fungi is broken into 4 major phyla: Deuteromycota, Basidiomycota, Ascomycota, and Zygomycota. Chytridiomycota are sometimes included in this kingdom as a 5th phylum, and some molecular biologist group the Deuteromycota with their closest relatives in the other phyla rather than separating them into their own. According to current accepted theories, slime molds and water molds (Oomycota, Myxomycota, and Acrasiomycota are not phylogenetically related to the fungi, and therefore, they will not be covered here).

Deuteromycota
These "fungi imperfecti" generally do not exhibit a sexual reproductive function. If they are found to do so, they are then grouped with their proper phylum.

Basidiomycota
The "club fungi" include mushrooms, smuts, puffballs, shelf fungi, and many others. Beginning with the haploid spore, the life cycle starts by the spore germinating into a hypha, or long filament. The hypha divides and grows, and when it meets with another hypha, some of the cells in the hyphae will fuse by plasmogamy. The dikaryotic cells will continue to form hyphae, and at the tip, they will form basidiocarps, or fruiting bodies. Certain cells in the fruiting bodies can have their nuclei fuse (karyogamy) to make diploid cells, which can then go through meiosis to make 4 basidiospores. The spores are released, and the cycle repeats.

Ascomycota
These "cup fungi" include the common molds and mildews that spoil food and attack plants, yeasts, truffles, and morels. An ascomycete Claviceps purpurea is also the cause of ergot, which is the source of lysergic acid diethylamide, everyone's favourite LSD. The life cycle of the ascomycete begins with the release of the haploid spore. The spore then germinates, forming a hypha. Several hyphae often come together, forming a mycelium. In this mycelium, many hyphae branch through asexual reproduction, but some of the hyphae may go through plasmogamy to become dikaryotic. The dikarya can then go through karyogamy to form a zygote, which then goes through meiosis to form between 2 and 8 ascospores encased in an ascus. The spores are released, and the cycle starts over.
In the single-celled ascomycetes, such as the yeasts, the cycle is the same, save the formation of hyphae.

Zygomycota
The zygomycetes include the common black bread mold Rhizopus. The life cycle of zygomycetes is simpler than the other fungi. The spore, once liberated, germinates and forms a mycelium of hyphae. Some of the hyphae can grow erect and form sporangia filled with haploid spores. This is its more common asexual reproductive stage. If conditions are adverse, and compatible opposite mating types are near each other, the hyphae will form gametangia. The gametangia fuse, forming a zygote, which immediate goes through meiosis to form four zygospores.

Chytridiomycota
The chytrids are primitive, single-celled, colonial, or mycelial fungi that appear to reproduce asexually most of the time, only reproducing sexually in times of dire need.

Diseases caused by fungi

Some of the more well-known diseases caused by fungal infections include:

  • Ringworm -- actually several different types of infections of the hair, scalp, skin, beard, or nails -- usually caused by Trichophyton spp.
  • jock itch (tinea cruris) -- caused by Epidermophyton or Trichophyton spp.
  • athlete's foot (tinea pedis) -- caused by Trichophyton or Epidermophyton spp.
  • histoplasmosis -- affects the phagocytes, which are white blood cells -- caused by Histoplasma spp.
  • candidiasis -- opportunistic; affects the mouth (thrush), the vagina (yeast infection), or the skin on the butt (diaper rash) most often -- caused by Candida albicans
  • pneumocystis pneumonia -- while most pneumonia is bacterial or mycoplasmic, this is the only fungal pneumonia -- caused by Pneumocystis carinii

Fungi in Biochemistry and Molecular Biology

Several fungi are important as models for genetic and biochemical phenomena, including:

Fungi are one of the strangest of life's kingdoms. They are ubiquitous and very important to science and commerce. Fungi are responsible for everything from the creation of beer and cheese and life-saving pharmaceuticals such as penicillin. They are also the cause of deadly diseases like histoplasmosis and they can cause severe damage to crops and material goods.

Fungi may be more closely related to animals than plants. They are a taxonomical nightmare, however, because of their inherent variability. Along with this variability, which often entails multiple alleles for a single locus, other characteristics which make fungi special are:


From the BioTech Dictionary at http://biotech.icmb.utexas.edu/. Used with permission. For further information see the BioTech homenode.

Overview

Fungi are one of the five types of microbes1.

Fungi are plant-like organisms, but unlike plants they do not have chlorophyll. Because of this they cannot make their own food. Instead, fungi absorb food from dead organic matter. The function of fungus in the ecosystem is to break down complex organic substances and recycle carbon and other elements. Some fungi are biotrophic, meaning they feeding from living cells; others are necrotrophic, meaning they kill cells and then feed on them. Most fungi feed on plant material rather than animal material.

The main types of fungus are:

  • Moulds (also spelled mold), which have filaments; and
  • Yeasts, which are usually single cells.

Some common fungal Diseases that affect humans are listed below.

Taxonomy

The approximately 100,000 species of the Fungus kingdom are divided into four phyla, based on sexual characteristics.

  • Sac or Cup Fungi (Ascomycota) - 50,000 species including Hemiascomycetae (Brewer's yeast, bakers yeast, and nutritional yeast) and Truffle mushrooms;
  • Club Fungi (Basidiomycota) - most other mushrooms (a.k.a. basidiocarp);
  • Conjugation Fungi (Zygomycota) - including common bread mould;
  • Imperfect Fungi (Deuteromycota) - fungi that are not easily classified, including most of the ones cited below under Diseases.

The lichens (Mycophycophyta) were formerly considered to be a fifth fungus pyhla, but this is no longer true.

Structure and form

The visible part of a fungus is usually a "fruiting body" such as a mushroom. This is usually a small portion of the overall organism. The main body of most fungi is a web called the mycelium. The mycelium is made of very fine threads called hyphae. The hyphae branch and intertwine throughout the fungus' food source (such as soil or wood). A fungal mycelium is generally too fine to be seen by the naked eye, unless the hyphae are packed densely together.

The cell wall of a fungus is made of chitin, which is also found in insects. This is something that distinguishes fungi from plants - the cell walls of plants are made of cellulose.

Reproduction (Replication)

Fungi are capable of two types of reproduction:

  • Asexual:
    • Fungi reproduce asexually by forming spores. When conditions are right the spore starts to grow. A hypha grows from the spore, and begins to branch and weave to form the mycelium. If growing conditions continue to be are favorable, the mycelium develops fruiting bodies, which produce new spores.
    • Fungi can also reproduce asexually by fragmentation. If pieces of the mycelium or hyphae are broken off, those portions can grow into a complete fungus.
    • Yeasts, which are single cells, reproduce by yet another asexual process called budding. A yeast cell splits at the tip to produce a small offspring cell.
  • Sexual

    Each of the fungi phyla have a different form of sexual reproduction.

    • Ascomycota make spores sexually inside a bag or sac called the ascus. In the ascus, meiosis and usually also a mitotic division take place, resulting in spores called ascospores. Asexual spores are made at the tips of the hyphae.
    • Basidiomycota make a structure called the basidium by fusing hyhae, and place spores on the outside. Reproduction results in the forcible discharge of a spore called a ballistospore. Most Basidiomycota do not reproduce asexually.
    • Zygomycota generate their sexual spores inside a thick-walled compartment (the zygosporangium) which is created when 2 hyphae of appropriate mating types fuse together, and then are walled off from the rest of the hypha. Asexual spores are made in a sporangium.
    • In Deuteromycota, the sexual structures are unknown or don't exist. This is a "leftover" category and lacks a single defining characteristic. Most reproduce asexually.

Diseases

The types of diseases caused by fungi can be divided into 3 major categories:

  • Allergic reactions (sensitivity to fungal proteins);
  • Toxicity reactions (consumption of fungal toxins); and
  • Fungal infections (invasion of living tissue by a fungus)

The most well-known example of an allergic reaction to fungus is "toxic mould" and "sick building syndrome" in buildings. (This was in the news in April 2002. Celebrity Ed McMahon sued his insurance company over a botched repair that caused fungus to spread throughout his home, making his family ill and allegedly killing his dog, Muffin. On doctor's orders, the McMahons moved out of their six-bedroom home in September 2001. The suit was settled in May 2003 for $7.2 million US.) The resulting condition is Allergic fungal sinusitis which causes a variety of symptoms, and in extreme cases can result in anaphylactic shock. Note that while moulds are very common in buildings, and will grow anywhere that there is moisture, 'toxic' moulds such as Stachybotrys chartarum are very rare. More common indoor moulds include Penicillium (the basis for the drug Penicillin).

The most well-known examples of fungal toxins are toadstool poisoning. Toadstools such as the Death cap (Amanita phalloides) and Destroying angel (Amanita virosa, A. verna, A. bisporigera, A. ocreata) ultimately cause death due to kidney and liver failure. Another famous example is the Liberty Cap or Magic Mushroom ( Psilocybe semilanceata) which affects the central nervous system inducing a hallucinogenic response. Another example is ergotism, a syndrome which can cause gangrene, hallucinations, and death. It is caused by consumption of rye products contaminated with toxins produced by the mould Claviceps purpurea. This fungus' toxins may have caused illness and delirium in Salem, Mass. leading to the Salem witch trials!

Some fungal infections, called primary pathogens, can cause disease regardless of the previous health of the victim. Others, referred to as opportunistic, affect people with immune systems that are already weakened by other factors. Diseases caused by fungal infection include:

  • Tinea including Ringworm (an infection of the hair, skin, or nails); jock itch (tinea cruris); and athlete's foot (tinea pedis) -- caused by mould fungi called dermatophytes
  • Oral thrush, yeast infection, diaper rash -- Technical name candidiasis -- caused by Candida albicans
  • Histoplasmosis -- Begins in the lungs, spreads through the body -- caused by Histoplasma capsulatum
  • Pneumocystis pneumonia -- Lung infection2 in people who are HIV-positive, especially children. -- caused by Pneumocystis carinii

Fungi are the major cause of disease in plants, accounting for over 70% of major crop diseases. The Irish Potato Famine was caused by a fungus an oomycete*, Phytophthora infestans. (The distinction between fungus and oomycete is fairly recent.) Although P. infestans did not infect humans, humans were certainly affected by it!

* oomycete correction by cordyceps.


Footnotes

  1. The others are bacteria, viruses, protozoans, and helminths (worms).
  2. Most pneumonia is bacterial or mycoplasmic, this is the only fungal pneumonia.

Primary references

  • Other writeups in this node. This writeup began life as high school biology lecture outline. Some redundancies exist with other writeups in this node, both for completeness and because they were used as a source for this work. Care has been taken to minimize the redundancies.
  • The remarkable Tom Volk's Fungi pages http://botit.botany.wisc.edu/toms_fungi/
  • http://www.perspective.com/nature/fungi/
  • http://www.mercksharpdohme.com/pro/fungal_disease/info/facts/home.html
  • http://www.howe.k12.ok.us/~jimaskew/bfungi.htm
  • http://www.achrnews.com/CDA/ArticleInformation/RegionalNews_Item/1,4149,75953-West,00.html
  • http://helios.bto.ed.ac.uk/bto/microbes/applerot.htm#crest
  • Salem: http://botit.botany.wisc.edu/toms_fungi/oct99.html
  • Destroying angel: http://www.bluewillowpages.com/mushroomexpert/amanita_bisporigera.html

The name given to a dolphin who decided, about 14 years ago, to make his home in the harbour of Dingle, a small town in County Kerry, Ireland. He has understandably become quite a tourist attraction, as he is quite friendly. Apparently he has a companion now.

Fungi, The Game

"FUN-gee". A two player game derived from John Horton Conway's "sprouts". All you need to play is a sheet of paper and one or two pencils/pens.

The name comes from an analogy of how some fungi ("FUN-guy") mate: by extending "tentacles" to meet each other and exchange genetic information.

Begin by drawing a horizontal line across the center of the paper, extending from one edge to the other. Agree on an even number of "diamonds" (usually 6 or 8), and draw half that number of diamonds on either side of the line. Place one less than that number of dots on the line itself. For example, for a game with 6 diamonds:

        <>    <>    <>

<----*----*----*----*----*---->

        <>    <>    <>

That's called a 6/5 game, for there are 6 diamonds and 5 dots. Note that if the number of dots is not exactly one less than the number of diamonds, it is a wildly unfair game. Leave a good amount of space between the line and the diamonds.

A valid move (for either player) is connecting two dots, considering diamonds as dots as well, with a line and then placing another dot somewhere along that line. "Line" here is used in a topological sense, in that it can curve and bend and twist (?), so long as it passes through no other lines. A dot may have no more than three lines emerging from it, considering a line passing through a dot as two emerging lines, one on either side. I know it seems very complicated, but it's quite simple; you just have to see it. Bear with me.

There are two players, the "offense" and the "defense". The goal of the offense is to interconnect all diamonds. So if the offense wins, you could start at any of the diamonds and run your finger down some series of line segments to get to any other diamond. The defense's goal is to stop this from happening. Offense goes first.

So, on the board above, a simple opening move could be:

    <>    <>    <>
     \
      *
       \
<---*---*---*---*---*--->



    <>    <>    <>

Don't forget to put the dot on your new line!

An example of a situation in which this game would be considered an offense win would be:

           /------\
    <>    <>-*--<> |
     \             /
      *-------*---/
       \
<---*---*---*---*---*--->
    \              /
     \------*-----/
            |
    <>   /<>|   <>
     \--*---*   /
            \--/

Admittedly, the defense played rather poorly in this game. A similar game in which the defense won would look something like:

           /------\
    <>    <>-*--<> |
     \             /
      *-------*---/
       \
<---*---*---*---*---*--->
    \        /*/   /
     \------*-----/
            
    <>    <>    <>

Connecting that dot back into the line made it impossible for any of the three lower diamonds to connect in with the rest of the crowd. Thus, it's an offense lose.

Play a little with a friend or just experiment with it by yourself. At first it will seem like either the offense or the defense is greatly biased toward (for me, it seemed impossible to defend), but soon new strategies will emerge and you will see that it is, in fact, quite balanced.

Two defensive strategies to get you started:

  • Don't forget that you can connect a diamond to itself. This is often a good idea, as it reduces the number of possible emergences ("lives") by one. If you can connect a diamond to itself, and then connect that diamond to the dot you just made, you have automatically won. This is also something to watch out for when you're playing offense.
  • Subdivide space as much as you can. Put two of their diamonds in one section of space, and the third in another. (That is, drawing a line from one point on the baseline, around one of their diamonds, and back to another point on the baseline is a good idea.)

And two offensive strategies:

  • Think in terms of the baseline. "What do I have to do to connect this line to the baseline?" Remember, connected is a loose word; a line connected to a line connected to the baseline is just the same as a line directly connect to the baseline.
  • Think also in terms of "exits" to a particular space. "Which dots are on the border of this space?" Make sure that you always have more than one "way out" of a space, if your diamonds are in it.

One more tip: Start at a 2/1 game, and observe why that is an obvious defense win. Move to a 4/3 game, and analyze its strategy before going to the more challenging 6/5 and 8/7. I played on 20/19 once, and that wasn't too fun: too much to keep track of. But maybe I just don't understand its strategy yet :)

Happy gaming!

Fun"gi (?), n. pl. (Bot.)

See Fungus.

 

© Webster 1913


Fun"gi (?), n. pl. (Bot.)

A group of thallophytic plants of low organization, destitute of chlorophyll, in which reproduction is mainly accomplished by means of asexual spores, which are produced in a great variety of ways, though sexual reproduction is known to occur in certain Phycomycetes, or so-called algal fungi.

⇒ The Fungi appear to have originated by degeneration from various algæ, losing their chlorophyll on assuming a parasitic or saprophytic life. By some they are divided into the subclasses Phycomycetes, the lower or algal fungi; the Mesomycetes, or intermediate fungi; and the Mycomycetes, or the higher fungi; by others into the Phycomycetes; the Ascomycetes, or sac-spore fungi; and the Basidiomycetes, or basidial-spore fungi.

 

© Webster 1913

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