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5.4: Helpful Bacteria

Difficulty Level: At Grade Created by: CK-12
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Where does cheese come from?

Bacteria are often used to make cheese from milk. But making foods is not the only beneficial role of bacteria. For example, they also play an essential role in your gut!

Helpful Bacteria

Can we survive without bacteria? Could bacteria survive without us? No and yes. No, we could not survive without bacteria. And yes, bacteria could survive without us.


Bacteria can be used to make cheese from milk. The bacteria turn the milk sugars into lactic acid. The acid is what causes the milk to curdle to form cheese.

Bacteria are also involved in producing other foods. Yogurt is made by using bacteria to ferment milk (Figure below). Fermenting cabbage with bacteria produces sauerkraut.

Yogurt is made from milk fermented with bacteria. The bacteria ingest natural milk sugars and release lactic acid as a waste product, which causes proteins in the milk to form into a solid mass, which becomes the yogurt.


In the laboratory, bacteria can be changed to provide us with a variety of useful materials. Bacteria can be used as tiny factories to produce desired chemicals and medicines. For example, insulin, which is necessary to treat people with diabetes, can be produced using bacteria.

Through the process of transformation, the human gene for insulin is placed into bacteria. The bacteria then use that gene to make a protein. The protein can be separated from the bacteria and then used to treat patients. The mass production of insulin by bacteria made this medicine much more affordable.


Bacteria also help you digest your food. Several species of bacteria, such as E. coli, are found in your digestive tract. In fact, in your gut, bacteria cells outnumber your own cells!


Bacteria are important because many bacteria are decomposers. They break down dead materials and waste products and recycle nutrients back into the environment. This recycling of nutrients, such as nitrogen, is essential for living organisms. Organisms cannot produce nutrients, so they must come from other sources.

We get nutrients from the food we eat; plants get them from the soil. How do these nutrients get into the soil? One way is from the actions of decomposers. Without decomposers, we would eventually run out of the materials we need to survive. We also depend on bacteria to decompose our wastes in sewage treatment plants.


  • decomposer: Organisms that recycle nutrients by breaking down dead materials and wastes.
  • fermentation: Conversion of sugars, or other organic compounds, to simpler compounds.


  • Bacteria can be used to make foods and medicines.
  • Bacteria play an important role in animal digestion.
  • Bacteria recycle nutrients in the environment.


Use the resources below to answer the questions that follow.

  1. How does the gut bacteria differ between the small intestine and the large intestine?
  2. What can happen if something causes a reduction of "good" bacteria in your gut?
  3. How do the number of cells in your intestines compare to the total number of cells in your body?
  4. Would the bacteria in the small intestine be considered aerobic, anaerobic, or facultative aerobic? Explain your reasoning.
  1. What is one of the uses of serotonin in the body?
  2. What have scientists discovered about the relationship between gut bacteria and serotonin?
  3. What do scientists hope to do with this information?
  1. How are bacteria used in making foods? What food are made with bacteria?
  2. How are bacteria used in oil spills?
  3. How are bacteria being used in nanotechnology?


  1. How are bacteria helpful in nature?
  2. How are bacteria beneficial to your health?

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decomposer Organisms that recycle nutrients by breaking down dead materials and wastes.
fermentation Conversion of sugars, or other organic compounds, to simpler compounds; occurs in the absence of oxygen.

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Difficulty Level:
At Grade
7 , 8
Date Created:
Nov 29, 2012
Last Modified:
Aug 30, 2016
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