Yeast cells are members of the Fungus Kingdom. They are
single celled microorganisms (eukaryotic) classified under phyla Ascomycota
(sac fungi) and Basidiomyota (higher fungi) both of which fall under the
Kingdom - Fungus
Subkingdom - Kikarya
Phyla - Ascomycota and
* Budding yeast, also referred to as true yeast
fall under the Phylum Acomycota and in the Order Saccharomycetales
Yeast are very diverse (over 1,500 species) with
most forming the phylum Ascomycota while only a few are classified as
Basidiomycota. Yeast cells reproduce through budding or binary fission which are both
methods of asexual reproduction (Horst, 2010).
Budding - A new yeast cell is formed through mitotic cell division and remains
attached as a bud on the old cell until it splits and becomes independent.
Here, the parent cell produces an outgrowth that finally splits to become an
independent identical cell as the parent cell.
Binary Fission - In binary fission, no outgrowth (bud) is
formed. Rather, through mitosis, the genome replicates and divides followed by
the formation of a new plasma membrane and ultimately the cell dividing in to
two to form two new cells from the parent cell.
* Some of the fungi referred to as dimorphic tend
to alternate between the yeast and hyphal phase which means that they can also
grow as hyphae (thread like)
Because they are very diverse, yeast can be
found in a wide variety of habitats particularly in environments with
sugar-rich materials. They are likely to be found on flowers, plant leaves, and
fruits as well as on soil, deep-sea environments, skin surface and even
intestinal tracts of animals (warm blooded).
While they can be found in many
environments, yeast require moist environments with sufficient amounts of simple
and soluble nutrients to support growth and multiplication (Horst, 2010).
While such yeast as the Candica can cause
infections (Candidiasis) there are useful yeast such as:
Distiller’s and Wine Yeast
Yeast Under the Microscope
Glass slides and cover
Stains (stated below)
Yeast cake contains Saccharomyces Cerevisiae
(sugar-eating fungus) and can therefore be used to obtain the yeast to observe
under the microscope. The following is a procedure that can be used to prepare
the specimen for observation.
Obtain yeast cake (this can
be bought from bakery specialty stores or a supermarket)
Cut a small piece of yeast
cake and mix with water to form a pasty texture
Add a little more water to
form a solution
Using a dropper, collect
and place a drop of the solution on a microscope slide
Place a microscope cover
slip and observe under high power objective
When viewing the specimen under high
magnification (1000x and above) one will see oval (egg shaped) organism, which
are the yeast. It is also possible to observe the buds, which can be seen on
some of the yeast cells.
If the solution had some sugar, one will also
notice some bubbles in the specimen, which are as a result of the fermentation
process by the microorganisms.
Fluorescence microscopy can be used for the
purposes of observing the organelles inside the yeast cells. This is particularly
a great method through which students can get to view the intracellular
distribution of the cell and identify the different types of cell organelle.
This may prove a little challenging when it comes to yeast given that
they are very small in size (compared to other cells) and have a cell wall
(Chalfie and Kain, 2005).
For living yeast cells, a number of dyes have to
be used in order to increase contrast and be able to differentiate the
different organelles in the cells.
Martin Chalfie and Steven R. Kain (2005) Green
Fluorescent Protein: Properties, Applications and Protocols.
Jiří Hašek (2006) Yeast Fluorescence Microscopy.
Volume 313 of the series Methods in Molecular Biology pp 85-96.
Feldmann, Horst (2010). Yeast. Molecular and
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