🍄 Fungi Blog 🍄

What are Fungi?

Fungi are eukaryotic organisms that can be multicellular or unicellular. Fungi are absorptive heterotrophs, meaning they obtain food by secreting digestive enzymes from their surroundings and then absorbing the organic molecules produced by the external digestion. This allows fungi to break down cellulose and lignin. Multicellular fungi consist of thin threadlike cells called hyphae that form mycelium. This mycelium allows the fungus to grow through and digest substrate. Fungi can be symbionts (pathogenic or mutualistic), saprophytes, or predators. 

Arthrobotrys dactyloides using its hypha to constrict and catch a nematode.

Fungal cell walls include chitin, which is a strong polysaccharide, also commonly found in the exoskeletons of arthropods.

Fungi have three distinct life stages. Haploid spores and hyphae, dikaryotic hyphae and fruiting bodies, and diploid spore-producing cells. Spores are the most common means of reproduction among fungi. Spores can form from both sexual and asexual processes. Most of these spores are dispersed by wind or by insects. 

Different Types of Fungi Phyla.

When it comes to phyla, fungi are taxonomically diverse, having seven monophyletic phyla and two polyphyletic phyla. The phyla are organized based on how they reproduce and typically end in mycota. The seven monophyletic phyla are microsporidia, blastocladiomycota, neocallismastigamycota, chytridiomycota, glomeromycota, basidiomycota, and ascomycota. The two polyphyletic phyla are zygomycota, and deuteromycota.

Microsporidia

Microsporidia are obligate, intracellular, animal parasites. Microsporidia lack mitochondria, having reduced mitochondrion-like organelles. Microsporidia have long polar tubes, which commonly cause disease in immunosuppressed patients. Microsporidia will use their polar tube to infect a host with their spores, and these spores also contain a polar tube. Microsporidia infest intestinal and neuronal cells, leading to diarrhea and neurodegenerative disease.

A microsporidian spore with an extruded polar tube inserted into a cell.

Chytridiomycota

Chytridiomycota, also known as chytrids, are aquatic, flagellated fungi. They are closely related to ancestral fungi. Chytrids produce motile spores from pot-shaped sporangia. Chytrids have flagellated gametes; their reproductive cells have a flagellum that allows them to swim. Batrachochytrium dendrobatidis, also known as BD, causes an infectious amphibian disease called chytridiomycosis.

Several sporangia of Batrachochytrium dendrobatidis.

Blastocladiomycota

Blastocladiomycota, also known as blastoclads, have uniflagellated zoospores. Blastoclads are the production of ornate, thick-walled resting sporangia, which produce zoospores when they germinate. Blastocladiomycota are fungi to go through alternation of generations. Blastocladiomycota are the only fungal group that have been found to exhibit a true haploidiplontic life cycle, with an alternation between haploid and diploid generations.

Zoosporangia of an Allomyces. A fungus in the Blastocladiomycota phylum.

Neocallimastigomycota

Neocallimastigomycota are in the rumen of mammalian herbivores, where they enzymatically digest the cellulose and lignin of the plant biomass. Mammals depend on fungi for sufficient calories.  Horizontal gene transfer brought the cellulase gene from bacteria into the Neocallimastix genome. Neocallimastigomycota are anaerobic and have greatly reduced mitochondria. Their zoospores have multiple flagella.

Mycelium of Anaeromyces sp. strain KF8 stained by lugol solution.

Zygomycota

Zygomycota are named for producing diploid zygote nuclei by fusion of haploid nuclei. Zygomycetes are not monophyletic and are still under research regarding their origin. Zygomycota includes the common bread molds and a few human pathogens. Zygomycota have chemotropic hyphae, which are attracted to opposite types in unfavorable conditions for sexual reproduction.

Rhizopus stolonifer, also known as black bread mold.

Glomeromycota

Glomeromycota are a tiny group of fungi. Their obligate symbiotic relationship with the roots of many extant plants appears to be ancient and may have made it possible for terrestrial plants to evolve. Currently, there is no evidence of sexual reproduction.

Flax root cortical cells containing arbuscular mycorrhizal fungi. Arbuscular mycorrhizae are potentially capable of increasing crop yields with lower phosphate and energy inputs.

Basidiomycota

Basidiomycota are some of the most familiar fungi. This phylum is named for their sexual reproductive structure called a basidium. A basidium is a club-shaped structure found inside the inner surface of the gills. In basidiomycota, the four haploid products of meiosis are incorporated into basidiospores. Some examples of basidiomycota are shelf fungi, puffballs, toadstools, mushrooms, as well as some important plant pathogens. Mushrooms are formed entirely of dikaryotic mycelium.

The fruiting bodies of a Coprinus.

Ascomycota

Ascomycota contains about 75% of the known fungi. Ascomycota are named for their characteristic reproductive structure, the microscopic, saclike ascus. Ascomycota includes bread yeasts, common molds, cup fungi, truffles, morels, as well as serious plant pathogens. 

Saccharomyces cerevisiae, also known as brewer's yeast, is a unicellular ascomycete. Most yeasts reproduce by budding. Yeasts ferment carbohydrates by breaking down glucose into ethanol and carbon dioxide.

Deuteromycota

Deuteromycota are also known as imperfect fungi or form taxa. Deuteromycota can only reproduce asexually because they lack a sexual stage. This is a polyphyletic group, not closely related to each other, hence named form phylum. Deuteromycota is a phylum that is no longer accepted, but the term is still used to refer to certain fungi.

This is Aspergillus and this fungi was originally in the deuteromycota phylum. Some species, like the Aspergillus, were reclassified as ascomycetes based on molecular analysis.