• Microbiology is the branch of biology that deals with the study of organisms that are invisible to the naked eye, or microorganisms. These include bacteria, viruses and some fungi. While microorganisms are perhaps best known for their negative effects, such as causing diseases, they can also be quite beneficial. There are a number of microbiology science fair ideas that demonstrate the various impacts microorganisms can have.
  
  

Trapping Microorganisms

• This science fair project is designed to introduce you to the invisible world of microorganisms that surrounds you on a daily basis. You will need to choose a number of different test sites where you can set up microorganism "traps," such as in a bathroom, kitchen, bedroom, outside on a patio or inside the refrigerator.
  
  These traps are Petri dishes, which you should fill up halfway with agar, a gelatinous substance made from seaweed that is used as medium for biological cultures (and as a food thickener). According to sciencebuddies.org, you should leave the open Petri dishes in their test sites for 48 hours before observing your results under a microscope. Note the color, size and amount of microbial colonies that appear in each.
  
  

Pumpkin Preservation

• Many individuals have observed the dreadful decomposition that occurs in pumpkins a few weeks---and in some times days---after carving them. This decomposition is caused by thousands of invading microorganisms, which were previously held at bay by the pumpkin's unbroken skin. Thus, exploring ways to extend the life of jack-o-lanterns is really a search for microbial repellent.
  
  For this experiment, you will need to carve a number of different-sized pumpkins---the more the better---making sure to vary carving patterns/styles to observe their impact on microbial growth. Then you can cover your pumpkins with a number of different substances, making sure to leave some untreated as controls. Some substances you can apply are vinegar, bleach, cooking oil, salt, hairspray and pesticides. Observe which substances do the best job preventing decomposition.
  
  

Microorganisms and Plant Growth

• Another microbiology science fair idea, from sciencemadesimple.com, is to study the effects of microorganisms on plant growth. To do this, the website recommends gathering two samples of fertile soil from the same source, and then baking one of the samples in an oven to kill any microorganisms.
  
  Next, plant the same amount of the same type of plant seeds in each soil sample, and provide the samples with the same amount of light and water. Which plants grow faster or healthier? A variation on this experiment is to purchase a specialized, nitrogen-producing bacteria and add it to one soil sample but not the other. Observe which sample produces the best results.