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Preservation of Microbial Cultures

Preservation of microbial culture is important because it helps to maintain the viability and genetic stability of microorganisms over time. In addition, it allows for the study of their behavior and characteristics and for the production of microbial products. Moreover, it helps prevent the loss of rare or valuable microorganisms. Preserving microorganisms also ensures their consistent and reliable use for research and other purposes. Overall, microbial preservation is crucial in keeping microorganisms alive and stable while maintaining their genetic traits, allowing for their study and use, and preventing loss of rare or valuable specimens.

Principle of microbial preservation

The principle of microbial preservation is all about keeping microorganisms alive and stable for future use. To achieve this, scientists choose methods that can slow down or stop the growth and reproduction of the microorganisms, while still preserving their unique traits.

By preserving microorganisms, we can continue to study them and use them for all sorts of things, like making new medicines or improving food production. So, in a way, microbial preservation is like a time capsule for microorganisms, keeping them alive and ready for use in the future!

Techniques of Preservation of Microbial Culture

There are several ways to preserve microorganisms, such as:


This technique involves putting the microorganisms in a special solution to prevent damage during freezing. The stroage is at very low temperatures (-80°C or lower) to maintain their viability. Freezing is common for preserving bacteria and fungi. The cryoprotective solution used in freezing typically contains a combination of salts, sugars, and organic compounds that protect the cells during freezing. Researchers commonly use glycerol, dimethyl sulfoxide (DMSO), and trehalose as cryoprotectants. After freezing, researchers store the samples in liquid nitrogen (-196°C) or a deep freezer (-80°C) for long-term preservation.

Freeze-drying or Lyophilization

Both freeze drying and lyophilization are methods for preserving microbes for long-term storage. Researchers grow microbes in a culture medium, harvest them, and suspend them in a solution with a cryoprotectant. Next the solution with microbe is frozen, then dried in a vacuum chamber, and finally, a special agent is added to prevent damage from freezing. The dry powder or pellet can be stored at room temperature for a long time. Freeze-drying is useful for preserving bacterial cultures, yeast, and some types of viruses.


While refrigeration is a simple and effective method of preserving microorganisms, it is not suitable for long-term storage. The shelf life of refrigerated samples can vary depending on the microorganism and the medium used but is typically limited to a few weeks or months. This method involves storing microorganisms at a temperature between 2-8°C to slow down their metabolic processes. It’s useful for short-term storage of microorganisms, typically up to a few weeks or months.

Mineral oil overlay

This technique is common for preserving bacterial cultures in liquid media. This method is useful for short-term storage of bacterial and fungal cultures. This technique involves covering the surface of a culture with mineral oil to prevent evaporation and contamination. Firstly, the microorganisms are grown in a liquid medium and then the medium is covered with mineral oil to prevent evaporation and contamination. The mineral oil forms a layer on top of the culture, preventing air from coming into contact with the cells and reducing the risk of contamination. Mineral oil overlay can also help to maintain the pH of the medium and prevent evaporation of the culture.

Glycerol stocks

Glycerol stocks are useful for preserving bacterial and fungal cultures for many years. This technique involves mixing the microorganisms with a glycerol solution and storing the samples in a freezer for long-term preservation. Glycerol mainly prevents ice crystal formation during freezing that can damage the cells. The concentration of glycerol used in the solution can vary depending on the microorganism and the intended use of the preserved sample. Typically, concentrations of 10-20% glycerol are used for bacterial cultures, while concentrations of up to 50% are used for fungal cultures. After mixing the cells with glycerol, the samples are usually stored at -80°C or in liquid nitrogen for long-term preservation. The samples can be revived by thawing and plating on appropriate growth media.

These methods are commonly used to preserve microorganisms for research, industry, and medicine. So, by preserving microorganisms, we can study their behavior, characteristics, and use them to create microbial products. It also helps in preventing the loss of rare or valuable microorganisms.

Advantages of microbial preservation

  • Keeping microorganisms alive and stable for future use
  • Ensuring that important traits and characteristics are maintained
  • Providing a steady supply of microbial products
  • Preventing the loss of rare or valuable microorganisms
  • Allowing researchers to study microorganisms over time
  • Saving time and money on acquiring and cultivating microorganisms

Overall, preserving microorganisms is important for many research, industrial, and medical purposes

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