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The Variety and Roles of Microbes

Author(s): Barbara Tharp, MS, and Nancy Moreno, PhD

A Closer Look at Microbes’ Roles

Food - One of the most common uses of microbes in food preparation is the process of fermentation. Although oxygen usually is necessary to transform food into energy, some species of bacteria and fungi are able to complete this transformation in an oxygen-free environment. Even without oxygen, these microbes break down food, often sugar and other carbohydrates, thereby creating by-products such as CO2, ethyl alcohol and lactic acid. This naturally-occurring process has been utilized by humans to prepare many kinds of food products.

In ethanol fermentation, for example, microbes release ethyl alcohol and CO2. This process is used to produce many alcoholic beverages, including wine (from fermented grapes), as well as foods like bread (in which the alcohol is baked off, and CO2 causes the bread dough to rise during baking). The other most common type of fermentation used in food production is lactic acid fermentation, which gives foods like yogurt and pepperoni sausages their slightly sour flavors.

Disease - Pathogens are microbes that infect and cause disease in host organisms, which may be humans, plants, animals or even other microbes. Many species have immune system responses designed to slow or stop the growth of different microbes. However, in some cases, it is necessary to use additional antimicrobial agents. 

The majority of microbes are not harmful, and many are helpful to humans and other organisms. For example, vitamin K—which is required to form one of the blood clotting factors (prothrombin) in the liver—is produced by bacteria in the large intestine.

Environment - Microbes are naturally occurring almost everywhere. From backyard compost piles to acidic hot springs, they play a role in every ecosystem. Most microbes help the environment, living peacefully and symbiotically with the other organisms on the planet.

Microbes play a major role in converting the essential element, nitrogen, into a usable form. Although nitrogen is the most common gas in our atmosphere and is used in the DNA and other important molecules in plants and animals, neither plants nor animals are capable of converting it from its unusable, gaseous form (N2) into other, usable compounds. However, through a process called nitrogen fixation, several microbes in the soil and in water are able to change nitrogen gas into forms that plants can use, such as ammonium (NH4+). Animals then obtain this important element by eating plants.

Microbes also are responsible for decomposing organic material (plants, animals, insects, etc.). Through decomposition, microbes break down dead organisms and deposit nutrients back into the soil for other organisms to use. This “recycling” of organic material is vital to sustain life on Earth.

Funded by the following grant(s)

Science Education Partnership Award, NIH

Science Education Partnership Award, NIH

Grant Number: 5R25RR018605