Science and Technology

What are the Requirements for Microbial Growth?


Microorganisms require carbohydrates, proteins fats, vitamins, and metals to grow in culture media. The process of taking nutrients and transforming them into cellular material needs energy. Let’s discuss the basic requirements microbes need for their growth.

Physical requirements

The growth of the microbes is dependent on several physical factors. These physical requirements play a significant role in understanding the growth pattern of microbes.

1. Temperature

Temperature includes minimum growth temperature, optimum growth temperature, and maximum growth temperature. Other categories in temperature are:

  • Psychrophiles– they are cold-loving and grow between 0°C and 20 to 30°C. Psychrophiles can cause food spoilage.
  • Mesophiles—moderate-temperature-loving and grow between 25- 400C.
  • Thermophiles—heat-loving with optimum growth temperature of 50 to 60°C. typically they found in found in hot springs and organic compost.
  • Hyperthermophiles– grow at the optimum growth temperature >80°C.

2. pH      

Majority of the bacteria grow between pH 6.5 and 7.5 while molds and yeasts grow between pH 5 and 6. At the end, acidophiles usually grow in acidic environment.

3. Osmotic Pressure

Plasmolysis is caused by the hypertonic environments (higher in solutes than inside the cell). This happens because of the high osmotic pressure. For example, extreme or obligate halophiles need high osmotic pressure (high salt) while facultative halophiles can tolerate high osmotic pressure.

Chemical Requirements

In order to grow microbes successfully, they must have a good supply of water along with numerous other substances including sources of carbon and nitrogen, minerals, oxygen, and organic growth factors.

1. Carbon

It is a structural backbone of organic molecules. Chemoheterotrophs use organic molecules as energy while autotrophs use CO2.

2. Nitrogen

Nitrogen is a major component of proteins, DNA, and ATP. Most bacteria decompose protein material as a nitrogen source while some other bacteria may use NH4+ or NO3– from organic material. A couple of bacteria also use N2 in organic processes.

3. Sulfur

It is utilized in amino acids, thiamine, and biotin. Most bacteria decompose protein for the sulfur source while other bacteria use SO42– or H2S.

4. Phosphorus

Phosphorous is present in DNA, RNA, and ATP and is found in membranes. PO43 is a major source of phosphorus used.

5. Trace Elements

These are inorganic elements required in small amounts. They perform their functions usually as enzyme cofactors. Common examples include iron, copper, molybdenum, and zinc.

6. Oxygen

Singlet oxygen boosts to a higher energy level and is reactive. Superoxide radicals, peroxide anion hydroxyl group are also required. Obligate aerobes need oxygen. Facultative anaerobes grow via fermentation or anaerobic respiration when oxygen isn’t available. Obligate anaerobes do not have the ability to use oxygen and are harmed by it. Aerotolerant anaerobes tolerate but cannot use oxygen. Microaerophiles require oxygen concentration less than air.

7. Organic Growth Factors

Organic compounds can be obtained from the environment such as vitamins, amino acids, purines, and pyrimidines, are necessary for microbial growth on culture media.

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