Fungus Fact Friday

Tagged: cell biology

#016: Characteristics of the Defunct Phylum Zygomycota 0

Fungus Fact

#016: Characteristics of the Defunct Phylum Zygomycota

It has recently been demonstrated that the four subphyla historically classified as zygomycota do not make up a monophyletic group. As a result, the phylum zygomycota is no longer used. However, it has not yet been replaced by other phyla. The terms “zygomycota” and “zygomycetes” are therefore only used informally to reference this diverse group of fungi. The distinctive characteristic of the zygomycetes is their method of sexual reproduction (if a sexual stage exists). Their hyphae are almost always haploid. When two compatible (and haploid) hyphae meet they form gametangia, which fuse and become diploid. However, the diploid hypha is immediately isolated from the rest of the fungus. This isolated hypha then undergoes meiosis and develops into one zygospore. The zygospore is usually thick-walled and undergoes an obligatory period of dormancy before it germinates. This helps the spore survive for a long time in adverse conditions. Zygos also tend to...

#015: Characteristics of Phylum Glomeromycota [Archived] 1

Archived

#015: Characteristics of Phylum Glomeromycota [Archived]

Note: This is an archived post. You can find the current version of this post here. The Glomeromycota are all fungi which form arbuscular mycorrhizae (AM). Mycorrhizae are a type of mutualism with plants where the fungus gets sugars and gives up hard-to-extract nutrients (especially phosphorous).  AM fungi accomplish this by forming structures within the plant’s root cells while not causing a disease reaction.  Most land plant species form AM, and only a few families are considered non-mycorrhizal.  AM fungi tend to be generalists, colonizing a variety of different plant species.  Each plant is usually colonized by multiple AM species.  This mycorrhizal network has a variety of different roles in an ecosystem.  It supplies nutrients to plants, determines what species make up an ecosystem’s plant community, and allows other plants (like orchids and Indian pipe) to parasitize larger plants via the network.  A recent study has also suggested that plants...

#014: Characteristics of Phylum Chytridiomycota 1

Fungus Fact

#014: Characteristics of Phylum Chytridiomycota

Phylum chytridiomycota is the oldest phylum of fungi, with a fossil record dating back to the Vendian period (around 500 million years ago). It is no surprise, then, that chytrids are the simplest fungi.  Hyphae produced by chytrids can be unicellular, diminutive rhizoids or multicellular and as large as those produced by species in the other fungal phyla.  Chytrids are unique among the fungi in that they produce motile spores.  Each spore is equipped with one whiplash flagellum at its posterior.  Other fungus-like organisms which produce motile spores (often with multiple flagella) but have cellulose cell walls are no longer classified as fungi (chytrids, like all other fungi, have chitin in their cell walls).  Asexual zoospores are formed in a zoosporangium and are released through a pore.  The simplest chytrids form a very small network of rhizoids and produce only one zoosporangium per thallus.  However, more complex chytrids may form...

#013: Characteristics of Phylum Basidiomycota [Archived] 19

Archived

#013: Characteristics of Phylum Basidiomycota [Archived]

Note: This is an archived post. You can find the current version of this post here. Phylum Basidiomycota accounts for about 35% of all described fungal species.* This phylum contains the fungi that people are most familiar with. The classic “Mario mushroom” (based on Amanita muscaria), the grocery store button mushroom and other varieties of Agaricus bisporus, shiitakes, oyster mushrooms, and even the major “magic mushrooms” are all basidiomycetes.  However, basidiomycota also includes rusts and smuts, which are economically important plant pathogens, some yeasts, and a few lichenized fungi.  Like the ascomycota, the basidiomycota fill a variety of different ecological roles.  Many form mycorrhizae with plants (amanitas, chanterelles, russulas, etc.), others parasitize plants (rusts, smuts, honey mushrooms, etc.), a lot decompose organic material (cultivated mushrooms, yeasts, etc.), and some live in a variety of symbioses with insects (this includes some interesting mutualisms with leaf cutter ants and termites).

#012: Characteristics of Phylum Ascomycota 16

Fungus Fact

#012: Characteristics of Phylum Ascomycota

Phylum Ascomycota includes about 75% of described fungal species.*  It includes the baker’s yeast, Saccharomyces ceriviciae, scientifically important fungi such as Neurospora crassa and Penicillium chrysogenum, a number of desirable edible mushrooms, most notably morels and truffles, most lichenized fungi, and many important plant pathogens, such as the causal agent of chestnut blight.  As you can tell from this list, the ascomycetes have a variety of life history strategies and ecological roles.  Many ascomycetes grow as hyphae, others grow as yeasts, and some can even switch between the two.  Some ascomycota only reproduce sexually, others only reproduce asexually, and many do both.  Ascomycetes can be saprophytic (they decompose non-living matter), parasitic (on plants, bugs, humans, etc.), or mutualistic (with algae, plants, or even beetles).  Ascomycota have provided us with penicillin and have helped scientists understand the cell cycle, meiosis, and heredity.  Despite this diversity, Ascomycota is a monophyletic group (it...

#011: Characteristics of Kingdom Fungi [Archived] 61

Archived

#011: Characteristics of Kingdom Fungi [Archived]

Note: This is an archived post.  You can read the current version of the post here. This post begins to answer the age-old question, “What is a fungus?” Fungi are a monophyletic group—meaning that they arose from a single common ancestor—and therefore share a number of traits.  Everyone has their own list of important traits common to all fungi, and I have come up with one that agrees with as many as possible.

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Fungus Fact

#009: Overview of the Fungal Life Cycle

Filamentous fungi begin their lives as sexual spores. Each spore has a haploid (only one copy of each chromosome) nucleus, which is designated “n.” When the spore lands in a favorable environment, it germinates and produces a mycelium. There are two ways that this mycelium can grow vegetatively: through growth of the mycelium or through asexual reproduction. The fungus can produce asexual mitospores (n) which are dispersed and grow a new mycelium that is genetically identical to the parent. When this mycelium encounters another fungus with a compatible mating type they fuse together (plasmogamy). However, their nuclei remain separate and the cells become dikaryotic (meaning “two nuclei,” designated “n+n”). This gives rise to a dikaryotic mycelium. In ascomycetes and some other fungi, the dikaryotic mycelium only results in the production of fruiting bodies. In basidiomycetes, the dikaryotic mycelium grows vegetatively and produces fruiting bodies. Some basidiomycetes form clamp connections to...

#004: Fungal Hyphae Are Not Made Up of Traditional Cells 3

Fungus Fact

#004: Fungal Hyphae Are Not Made Up of Traditional Cells

The mycelium of a fungus is made up of one continuous cytoplasm and is thus said to be coenocytic.  Most hyphae have structures called septa that divide the hyphae into cells.  Each septum has a central pore (or multiple micropores) which allows it to regulate movement of nuclei and other organelles and to allow nutrients and resources to be quickly moved around.  There are a few levels of complexity of septa.  The least complex level has no septa, and the nuclei are free to move around the hyphae.  In this case there are many nuclei in each hyphae and the hyphae are said to be polykaryotic (plant and animal cells are usually monokaryotic*).  In mated fungi, this allows for an interesting situation where you can think about populations of nuclei within an individual.  Other hyphae are septate but have a large pore at the center of each septum.  This pore...

#003: Yeast vs. Hyphae 5

Fungus Fact

#003: Yeast vs. Hyphae

There are two major fungal growth modes: yeast and hyphae.  Yeast are single-celled organisms.  Hyphae are multicellular,*branching tubes that form mycelial networks.  Although “yeast” is commonly used to refer to Saccharomyces cerevisiae, yeast are a very diverse group.  Actually, they are not even a single group: yeast are placed into both Ascomycota and Basidiomycota.  These are the same two phyla that contain mushrooms, which exhibit hyphal growth.  Yeast grow by increasing the volume of the cell and then dividing through mitosis.  This mitosis can follow either a fission or budding pattern.  In fission, the cell divides in half and the cytoplasm is split equally.  In budding, a small bud forms off of the cell.  The nuclei replicate and half of them move into the bud.  The bud grows in size and eventually separates.  At this point the bud is still smaller and the cytoplasm is not divided evenly.  Under certain...