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Growth Requirements for Microorganisms

Instructor: Adrianne Baron

Adrianne has taught high school and college biology and has a master's degree in cancer biology.

All living organisms have requirements in order to live, and this includes microbes. In this lesson, we discuss the physical, chemical, and gaseous growth requirements of microorganisms.

Microorganisms

There are all types of organisms in our world. Many are very large and easily seen. Other organisms are so tiny that you cannot see them with the naked eye. These tiny organisms are known as microorganisms.

Bacteria are microorganisms
Picture of a micrograph of a microorganism

Interestingly, while microorganisms are so tiny, they outnumber us and have existed longer than we have. There are a handful of microorganism types. These include bacteria, viruses, fungi, parasites, and protozoa.

Growth Requirements

In order for you to grow, certain requirements had to be met. If your environment was different, then there is a chance that you would not have grown. The same is true for microorganisms. Their environments have to be just right for them to grow. The growth requirements are divided into two categories: physical and chemical.

While all microorganisms share the characteristic of being tiny, their specific environmental requirements are quite different. They have the same type of requirements, but there are huge differences in what is needed to meet them.

Physical

The first physical requirement is temperature. There are some microbes that only grow at very high temperatures and do not like the cold at all. These microbes are classified as thermophiles, meaning heat-loving. Other microorganisms like anything from moderate to cold temperatures and are called mesophiles and psychrophiles, respectively. The correct temperature for growing microorganisms is maintained using incubators, cold rooms, and refrigerators.

Another physical requirement is pH, which is the acidity or alkalinity of a substance. The pH of the growth medium must be suitable for the specific type of microorganism being grown.

pH determines the acidity of a substance
picture of the pH scale

Most fungi grow best at a lower pH, somewhere between pH 4 to 6, while bacteria thrive in a more neutral pH around 6.5 to 7. There are some species of bacteria that are classified as acidophiles because they grow best at a more acidic pH than other bacteria.

Chemical

Microorganisms use chemicals to make everything they need to survive. Therefore, it is very important to have the proper chemicals available for them to grow. By far the most important chemical is carbon. This is because microbes need organic material for food and to make other biological macromolecules that allow them to grow and reproduce. Carbon is normally added to the growth medium by adding carbon dioxide if the microbe is an autotroph, meaning they make their own food. If the microbe is a heterotroph, they cannot make their own food. Organic compounds such as carbohydrates are added for them to break down and extract the carbon. Fungi require a higher concentration of carbon than bacteria and other microbes.

Another important chemical is nitrogen. The growth medium needs nitrogen so the microorganisms can use it to make nucleic acids, which is a necessary step in the duplication of DNA. DNA have to be duplicated for cellular replication in multicellular microbes and reproduction in bacteria and multicellular microbes. Nitrogen is usually added to a medium by adding ammonium.

A growth medium also needs hydrogen; this is important for microbes to generate energy for themselves. Bacteria use the hydrogen to generate energy across their membranes. Autotrophic microbes use the hydrogen in the process of making their food, which they then convert into energy. Hydrogen is added to the medium when ammonium and carbohydrates are added. The microbes break down the ammonium and carbohydrates to release hydrogen.

There may be other elements added to growth medium in trace amounts. These include copper, iron, potassium, magnesium, manganese, and zinc. The presence of these elements will vary tremendously depending on what type of microorganism is being grown. In some cases, none of these will be added to the medium. In fact, most microorganisms grow just fine without some or all of these.

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