Agaricus Bisporus
Domain: Eukarya
Kingdom: Fungi
Phylum: Basidiomycota
Class: Agaricomycetes
Order: Agaricales
Family: Agaricaceae
Genus: Agaricus
Species: Agaricus bisporus
Agaricus bisporus is classified as part of the kingdom Fungi, and is known by the common names common mushroom or button mushroom, or even just mushroom. There are many characteristics about it that put it under the classification of kingdom Fungi. As part of domain Eukarya, all Fungi are Eukaryotes, including A. bisporus. Like most fungi, they are also multicellular [32]. Another aspect of A. bisporus that fits into the category of all fungi is their mode of nutrition. They are heterotrophs, and break down organic material into carbohydrates and proteins using enzymes outside of their bodies [33]. Additionally, the common mushroom does not have a nervous system. They are not motile, as with all fungi, although some mushrooms can have a motile stage [34]. Finally, almost all fungi can reproduce both sexually and asexually, and this includes the common mushroom. A. bisporus can reproduce asexually by producing spores, and sexually with haploid hyphae and its mycelium that fuse and form a zygospore [35].
During its life, A. bisporus has three different shapes, each one called by a different common name. During its earliest immature stage, this mushroom is white and is called the common mushroom or button mushroom. Once it becomes brown and a little bit bigger, the mushroom can be known as Brown Cap Mushroom or Cremini Mushroom. Finally, in its mature state, it is called a Portobello Mushroom [36]. The shape of the A. bisporus consists of a couple of parts. The cap, which is also called the pileus, is a light brownish color, and it has flat scales that fade at the end of the cap. In earlier stages, the cap is curved, shaped like a hemisphere; however, as the mushroom matures, it becomes a more flattened shape. In its mature state, the pileus of the common mushroom is 5-10 cm in diameter [36]. The next part of the mushroom is the gills. These are at first pink, but with maturity, they turn reddish-brown, then dark brown with a whiter edge. They are organized kind of like the spokes of a wheel [33], [36].Mushrooms also have a stipe, in the shape of a cylinder, which can be as tall as 6 cm and as wide as 1-2 cm. On the stipe is a ring known as an annulus, which has streaks on the upper side of the stipe. The flesh of the button mushroom is white, and can have pink bruising and its spore print is dark brown. The spores on the mushroo
m are ovalish-round and about 5 by 6 micrometers [36]. Most of the mushroom’s body is a bunch of “thread-like, white growth” called the mycelium that spreads out into the mushroom’s environment to absorb food [33].
A. bisporus is found worldwide, but it is native to the grasslands of Europe and North America. It is mainly found in fields and other grassy areas, after rainfall, especially from late spring through the fall [36]. The common mushroom usually will grow on organic matter, such as horse manure, that it can feed on. The best conditions for them to grow is moist, and between 50 and 70 degrees Fahrenheit [33].
Agaricus bisporus
Saccharomyces cerevisiae
Domain: Eukarya
Kingdom: Fungi
Subkingdom: Dikarya
Phylum: Ascomycota
Subphylum: Saccharomycotina
Class: Saccharomycetes
Order: Saccharomycetales
Family: Saccharomycetaceae
Genus: Saccharomyces
Species: Cerevisiae
Saccharomyces cerevisiae is an organism in the kingdom Fungi commonly called Brewer’s Yeast or Baker’s Yeast. Like all Fungi, this yeast is eukaryotic. While most fungi are multicellular, S. cerevisiae falls under the smaller category within Fungi that is unicellular [37]. One of things that adheres to the classification of Fungi is this yeast’s mode of nutrition. Fungi in general get their energy by absorbing organic compounds in their surroundings; Brewer’s Yeast absorbs sugar, mainly glucose, which it metabolizes with both aerobic and anaerobic cellular respiration [38]. As with all Fungi, Brewer’s Yeast also does not have a nervous system and it is not motile. Finally, S. cerevisiae fits in the kingdom Fungi because it can reproduce both sexually and asexually [37].
S. cerevisiae is yellowish green and globular-shaped. There are two main different forms that this yeast can take: haploid and diploid. The form that it usually exists in is diploid, in which it is more ellipsoid shaped, with a diameter of 5-6 micrometers. While in the haploid shape, it is more spherical and has a diameter of about 4 micrometers. This type of yeast also has a cell wall that contains chitin and determines its basic shape [38]. As mentioned earlier, S. cerevisiae absorb sugar that they use for cellular respiration. It is able to metabolize this sugar both with aerobic and anaerobic respiration, so the yeast can survive for some time without oxygen [37].When in the presence of oxygen, the yeast will do aerobic respiration, producing carbon dioxide. It is this process that is utilized when S. cerevisiae is used as baker’s yeast for bread [38]. When there is no oxygen, the yeast will undergo anaerobic respiration, or glycolysis, which produces some energy for the yeast, and gives off ethanol and carbon dioxide. It is anaerobic respiration that is used to brew alcoholic drinks. While S. cerevisiae prefers glucose for these processes, it can also use sucrose or maltose [38].
S. cerevisiae are able to reproduce through both sexual and asexual reproduction. During asexual reproduction, the haploid yeast undergoes mitosis, and eventually forms an ‘a’ strain and an ‘alpha’ strain. One haploid yeast from each cell will then fuse together into a diploid zygote [37]. The new diploid cell then undergoes another type of asexual reproduction called budding, where the daughter cell extends out of the parent cell. In some cases, the daughter cell will stay attached to the parent cell and will not detach after budding [38]. The sexual reproduction that is utilized by S. cerevisiae is called sporulation. During this process, the yeast splits through meiosis into four haploid spores [37], [38]. In this case also, a spore from the 'a' type and a spore from the alpha type will fuse, forming a diploid zygote with two different parent cells [38].
Saccharomyces cerevisiae can be found in places where glucose is available to it, because it needs the sugar to survive. When in the wild, this yeast is often found on the skin of grapes and other fruit, especially is that fruit is broken, with its sugary interior available to the yeast [37], [38]. The yeast has also been known to live on some plants, the gastrointestinal tracts or body surface of insects or homeothermic animal, certain soils, and even some water environments. They can be found all over the world because of their tolerance of extreme conditions such as low pH, high ethanol and high osmotic pressure [38].
S. cerevisiae is considered by many biologists to be among the most important fungi in the world for a couple of reasons. Firstly, it has very good practical uses in baking and brewing. More importantly, biologists often use this yeast as a model organism to run tests on. It is advantageous to use the S. cerevisiae because it is eukaryotic, but also unicellular, and it has a very fast reproduction rate so it is relatively easy to observe.
