Have you ever thought about how yeast reproduces? That’s what you’ll learn in this lesson! We will look at the reproduction of Ascomycota, a group of fungi that includes yeast.
A Variety of Fungi
What do yeast, penicillin, and Dutch Elm disease have in common? They are all fungi! Specifically, these fungi are all members of the phylum Ascomycota. Ascomycota is a huge group, including more than 32,000 different species of fungus. In addition to yeast and penicillin, it also includes edible fungi such as morel mushrooms and truffles, as well as less appetizing fungi such as bread molds (penicillin is actually made from a type of mold that can grow on bread). Despite the wide range of species within this group, all the members share a few common characteristics, particularly their methods of reproduction.
Ascomycota have two methods of reproduction: asexual and sexual. Most Ascomycota can reproduce using either method or even using both. In asexual reproduction, the fungus undergoes budding or fission, where cells from the fungus divide and split, forming new, genetically identical fungi that can then break off and grow on their own. The spores, or fungal seeds, formed by asexual reproduction are called conidia, and this process allows the fungus to reproduce more quickly than sexual reproduction alone.
All Ascomycota fungi can reproduce sexually. In fact, the ascus, a sac-shaped cell formed as part of the sexual reproduction process, is what gives this group its name. In sexual reproduction, two different gametes, or sex cells, have to combine for reproduction to begin. In some species, the second gamete has to come from another fungus. In other species, a single fungus contains both male and female gametes and can self-fertilize.
The microscopic ascus forms as part of sexual reproduction after the two gametes have combined. The zygote (the single cell created when the gametes combine) develops inside the ascus and divides two to three times, eventually creating either four or eight new cells, each of which is an individual spore.
A single fungus can have many separate asci. In a number of Ascomycota species, the asci all grow in the same place, within a cup or bulge on the surface of the fungus, which is called the ascocarp. Unlike asci, an ascocarp can be seen without having to use a microscope. An ascocarp can look like an open cup, it can be a completely closed bulge on the fungal surface, or it can be only partially open. The shape of the ascocarp depends on the species of fungus.
The spores formed inside the ascus as a product of sexual reproduction are called ascospores. There are typically only eight ascospores in each ascus, but since there can be many asci, each fungus might have hundreds of ascospores.
Ascospores are released when they are mature. The ascus breaks open with enough force to propel the spore up to a foot away from the original fungus. That may not seem like much, but considering the ascospores are too small to see with the naked eye, a foot is a really long way! Spores are sometimes transported even further away on the wind. They can also be transported by water or on the fur of animals. Once it reaches a suitable habitat, the ascospore is ready to grow into an adult fungus.
Ascomycota is an enormous group of fungi containing more than 32,000 species. Members range from yeast and penicillin to morel mushrooms to the fungus that causes Dutch Elm disease. Many members of this group can reproduce asexually. This method produces many conidia, a type of spore, and allows the fungus to reproduce more quickly than sexual reproduction alone. All Ascomycota can reproduce sexually, though, and it is this method that they are best known for. During sexual reproduction, two gametes combine to form a zygote, which develops inside of the sac-shaped ascus that gives the group its name. A single fungus can have many asci, and they develop inside an ascocarp, which can be seen with the naked eye. The zygote develops by dividing itself, typically producing eight separate ascospores. These spores are released when the ascus breaks open, and they can be propelled up to a foot away. They can also be carried further by wind, water, or animals.