Science—group 3/4, 7A. Bread Mold Information.
When observing mold colonies on bread, you should define
the following characteristics:
1. What is the color of the mold? Some molds have hyphae (or branching elements)
that are non-pigmented. These types of molds are called hyaline molds, whereas others
(commonly the ones you see on the bathroom tiling) are "demetiaceous" or darkly
pigmented - commonly black in color.
2. Is the center of the mold a different color from the edges? Many light-colored
molds, also called Hyphomycetes, produce pigmented spores as they grow. For instance,
Aspergillus fumigatus produces a green center (coloration from the spores) with a white
edge. The white edge is called an "apron" - this area has just hyphal elements (branches
of mold filaments), that have not yet developed spores. Pencillium species tend to
produce bluish-colored spores, while the spores produced by Aspergillus niger are black
3. Copious quantites of white-grey, cottony material suggests species of
"Zygomycetes", namely Rhizopus, Mucor or Rhizomucor. In the lab, we refer to these
species as "lid-lifters" as they will push the lid of a Petrie plate over if left to grow
unchecked (for this reason, we tape the lid shut if we isolate one of these).
Why does Bread Mold Grow Quicker in Warm, Dark and
Like all living things, molds (or fungi) need food, water, and proper
temperature in order to grow.
Just like humans, molds are mostly water. Water is used in some processes,
but all of the biochemical reactions necessary for life must take place in a watery solution
(the cytoplasm) of the cell. (More on these reactions later.) The water environment of
the cell allows all of the components to move and mix properly. It also prevents the mold
from drying out, since water is critical for normal survival.
As for temperature, molds are different from us. We control the temperature of
our body so that all of the reactions have the proper conditions to go forward. We are
called "warm blooded". Molds cannot control their temperature, so they must grow and
develop at whatever temperature their environment is. In the watery solution inside
mold cells are proteins called "enzymes" which direct the biochemical processes of the
cells. These enzymes work faster when the temperature is higher (as long as it doesn't
get too hot!) If you can do a growth experiment at several temperatures, you can
probably find the temperature at which these enzymes work best for molds. For
humans, it's 98.6 degrees Fahrenheit, which is our body temperature. (When
biochemists take these enzymes out of the body, they still work best at 98.6 degrees.)
For most molds, the optimal temperature is around 80 degrees.
Molds do not need light for normal growth, because they do not
make their own food like plants do. Molds are eating (using
extracellular digestion) food that was at some point produced by
plants. At some point in their life, most molds do need light to start
a different life stage, such as spore production. The main reason for
growing molds in the dark is that they might get dried out by sun or
other bright lights.
What Makes Mold have Color?
The color of molds comes from their ascospores, which are the structures that
these organisms use to reproduce. Ascospores are like seeds of plants, but remember
molds are not plants or animals. They are part of their own kingdom called "Fungi".
Mushrooms are part of this same kingdom.
Generally mold color is determined by the genetics of the organism, and not the
environment. Before we had more modern genetic techniques to analyze DNA,
mycologists (these are the microbiologists that study molds) classified molds according
to color. Many molds still have colors in their names...
Information Courtesy of <http://www.madsci.org/FAQs/micro/molds.html>