MadSci Network: Microbiology

Re: Questions about bread mold

Date: Thu Nov 1 15:04:57 2007
Posted By: Shireef Darwish, Grad student, Department of Plant Science, McGill University
Area of science: Microbiology
ID: 1193103623.Mi

Hi Rebecca,

Great project idea! Here are some suggestions in regard to your questions.

The bread should be left uncovered to allow the fungus to grow at its natural growth rate. You want the only variable to be bread type, so try to avoid wrapping the bread, which could cause variability in oxygen availability and humidity. Place the breads in identical large plastic containers (e.g., Tupperware), or better yet place all of the bread types in a single large plastic container (e.g., a Rubbermaid bin) to minimize environmental differences (humidity, oxygen, CO2, temperature). This arrangement will be safe, but try to avoid disturbing the air inside of the container, which will cause millions of spores to be released! This could be unhealthy for you if you inhale a large amount of spores, and could effect your experiment by introducing new molds to your bread.
[It would be a good idea to wear a dust mask (covering your mouth and nose) and safety goggles to protect yourself from exposure to mold spores when working on this project. You might also want to wear a smock or something similarly covering and disposeable to protect your clothes. A shower-cap would similarly protect your hair. -- SM, Moderator]

To measure growth, you should calculate the square area (how many inches or centimeters squared) of the mold on each piece of bread. Fungi usually grow as circular colonies (think of the circular patches of mold growing on a moldy fruit or floating in an old juice bottle!), so you will have to measure the radius of each mold patch to calculate its area (A = r2) where A=area, =3.14, and r= the radius of the mold patch. To obtain the radius, simply use a ruler to measure the distance from the edge of the mold to the center. See my simple diagram of a moldy piece of bread.

Scientists that are interested in the growth of molds usually measure the radius (or diameter) of molds every day to determine how fast their mold is growing (the growth rate). For example, you take the following measurements from bread mold growing on whole wheat over 5 days: day1=1cm; day2=3cm, day3=6cm; day4=10cm; day5=14cm. Now you can plot this data on a simple graph (x axis=time/day; y axis=radius of mold patch). You can plot the growth rate of all of the breads you tested on the same graph to determine which bread had the fastest rate of mold growth. Here is an example of the type of data you could record and how it would look when graphed (see picture of line graph):

	       Total Area of Mold Growth (cm square)
Day	White bread	Whole wheat	Sourdough bread
1	1	        1	        1
2	8	        4              	2
3	24	        12       	6
4	56	        34	        14

You can easily see that bread mold grew fastest on white bread and slowest on the sourdough.

OK, so does bread mold grow on anything besides bread? Well, there are several types of mold that will happily grow on bread, such as Aspergillus and Penicillium (the source of penicillin!). However, the species Rhizopus stolonifera is what is commonly known as black bread mold and I think it is this fungus that you will be working with. Check out this link to the University of Winnipeg for some detailed biological info about R. stolonifera ( Also try the following link for an overview of the kingdom Fungi (my personal favorite kingdom of life!), which also has some great info about Rhizopus ( 2520notes.doc+rhizopus+stolonifera).

The short answer is YES!!! R. stolonifera will grow on a variety of fruits, such as peaches, plums and cherries. The fungus is attracted to simple sugars (like glucose, fructose and sucrose), which are abundant in foods like processed breads and sweet juicy fruits! Based on this fact, what would be your hypothesis regarding the type of bread most susceptible to bread mold?

Hope this helps! Good luck and have fun, Rebecca!


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