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Sac Fungi (Ascomycota), includes approximately 75% of all fungi. They are either single celled (yeasts), filamentous (hyphal) or both (dimorphobic). They are the largest phylum of fungi, having over 64,000 species.

Common fungi: baker's yeast (saccharomyces cerevisiae), used in baking and brewing industries, the alcohol evaporates and the carbon dioxide makes the dough rise to make bread.

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Common fungi: Candida albicans, causes diaper rash in babies

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What defines the ascomycota is the ascus, in which nuclear fusion and meiosis take place. In the ascus, 1 round of mitosis follows meiosis to leave 8 nuclei, and eventually 8 ascospores. Ascospores are formed within the ascus by an enveloping membrane system, which packages each nucleus with its cytoplasm and provides the site for ascospore wall formation.

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The body of the ascomycota is shared by other fungi and consists of a eukaryotic cell surrounded by a wall. The body can be a single cell, like yeasts, or a filament divided into cellular segments, called hypha.

Nutrition and symbiosis:

Sac fungi are heterotrophs and obtain nutrients from dead or living organisms. Some species take over plants, animals, or other fungi as parasites and receive their energy in form of nutrients from the tissues of their hosts. Their biggest role is recycling dead plant material. As parasites, they count for most of the plant and animal pathogens including pneumocystis carinii, that is responsible for pneumonia in humans and ophiostoma ulmi, the Dutch elm disease fungus responsible for losses of many elm trees in North America and Europe.

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It occurs through reproductive spores like the conidia. Sac fungi can make spores sexually (ascospores or meiospores) and asexually (conidia or mitospores) where ascospores are not formed. Following meiosis, the ascopores take shape inside the ascus when new cell walls surround each nucleus. Conidia contain mitotic nuclei, and their cell wall is a made of hyphal or yeast.

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Asexual spores can be recognized by their color, shape, and how they are released as spores. In Sexual reproduction,the ascus is formed.

Classification of Sac fungi:
  • Pezizomycotina, largest subphylum and includes all sac fungi that produce fruiting bodies. Examples: cup fungi, caterpillar fungus, and powdery mildew.

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  • Saccharomycotina, includes most yeasts like baker's yeast and candida which are single celled fungi that reproduce by budding.

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  • Taphrinomycotina, includes both hyphal fungi (neolecta, taphrina), fission yeasts (schizosaccharomyces), and mammalian lung parasite (pneumocystis).

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Sac fungi grow as a hyphae and later form a mycelium, that when it is visible it is mold. Some grow as single celled yeasts which, during sexual reproduction develop into an ascus and do not form fruiting bodies. The cell walls and septa give stability and rigidity to the hyphae and may prevent lost of cytoplasm in case of local damage to cell wall and membrane.

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They fulfill a central role in most ecosystems. They are important decomposers, which break down organic materials, and help the detritivores (animals that feed on decomposing material), to obtain their nutrients. Sac fungi along with other fungi break down large molecules and have important roles in nutrient cycling.

Their fruiting bodies provide food for many animals. Many ascomycetes also form symbiotic relationships with other organisms including plants and animals. They can be found anywhere on land.

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Harmful effects:

One of their most harmful roles is in many plant diseases

  • Blue-green, red and brown molds attack and spoil foods, ex. penicillium italicum rots oranges.

  • Ergot (claviceps purpurea) is a menance to humans because it attacks wheat or rye and produces poison causing ergotism if consumed. Some of the symptoms include hallucinations, stomach cramp, and a burning feeling in the limbs.

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Positive effects:

  • Penicillium chrysogenum, produced an antibiotic (pencillin), that attacked bacteria and caused a change in the treatment of bacteria diseases in the 20th century.

  • The medical importance of tolypocladium niveum as an immune suppressor.

  • Some asomycete fungi can be changed through engineering procedures. They can produce useful proteins like insulin, human growth hormones, or tpa, used to dissolve blood clots.

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Created by: Nidia Rodriguez & Francesca Torres