Microbial Storage at Low Temperature Quiz

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Questions and Answers

What is the purpose of covering deep tubes with 1 cm mineral oil during storage at low temperature?

To prevent contamination

How long can bacteria be successfully stored at low temperatures using the agar deep tubes method?

2-3 weeks

What is the term for the process in which water is removed from a product after it is frozen?

Lyophilization or freeze-drying

What temperature range is the dense cell suspension frozen at in the Lyophilization method?

-60 to -78°C Signup and view all the answers

What is the main reason why most bacteria die during the Lyophilization process?

Desiccation Signup and view all the answers

How do spore- and cyst-formers differ in terms of viability during Lyophilization?

They can remain viable for many years Signup and view all the answers

What cryoprotective agents are commonly used in the preservation of microbial cultures?

Glycerol or dimethyl sulfoxide (DMSO) Signup and view all the answers

Describe the advantages of using the liquid nitrogen method for preserving microbial cultures.

It has been successful with many species that cannot be preserved by lyophilization. Most species can remain viable for 10 to 30 years without changing characteristics. Signup and view all the answers

What is a disadvantage of the liquid nitrogen method for preserving microbial cultures?

It is relatively expensive due to the need for regular replenishment of liquid nitrogen in the refrigerators. Signup and view all the answers

Explain the process of sealing a cell suspension into small vials during the preservation of microbial cultures.

The cell suspension is sealed into small vials before freezing at controlled temperatures. Signup and view all the answers

How are the vials containing the frozen cell suspension stored after the preservation process?

They are stored in a liquid nitrogen refrigerator, either by immersion in the liquid nitrogen or in the gas phase above the liquid nitrogen. Signup and view all the answers

What role does the cryoprotective agent play in the preservation of microbial cultures?

It prevents cell damage due to ice crystal formation during the freezing process. Signup and view all the answers

What is the main advantage of freeze-drying in preserving bacteria?

Preservation of bacterial viability for more than 30 years Signup and view all the answers

How are lyophilized cultures revived?

By opening the vials, adding liquid medium, and transferring the rehydrated culture to suitable growth medium Signup and view all the answers

How long can sporulating fungi remain viable when protected by skim milk and stored on silica gel?

4-5 years Signup and view all the answers

What is the role of silica gel in the preservation of microbes?

To adsorb moisture and keep the culture dried Signup and view all the answers

What is the simple method for reviving cultures preserved using silica gel?

Scatter some silica gel crystals on an agar plate Signup and view all the answers

What is the main benefit of cryopreservation using liquid nitrogen?

Long-term preservation of cultures Signup and view all the answers

Study Notes

Storage of Microorganisms

Agar deep tubes covered with 1 cm mineral oil can be used for short-term storage at low temperatures (0-40°C) in refrigerators or cold rooms.
This method slows down metabolic activity, but does not stop it, and growth continues slowly, leading to eventual death of the microorganisms.

Lyophilization (Freeze-Drying)

Lyophilization or freeze-drying is a process that removes water from a product after it is frozen, allowing the ice to change directly from solid to vapor without passing through a liquid phase.
The process consists of three separate and interdependent processes: freezing, sublimation, and desorption.
The method involves freezing a dense cell suspension at -60 to -78°C, then connecting it to a high-vacuum line, and finally, sealing the suspension into small vials.
This method dehydrates the bacteria with a minimum of damage to delicate cell structures.
Most bacteria die due to desiccation, but spore- and cyst-formers can remain viable for many years.

Cryopreservation (using liquid nitrogen)

Cryopreservation involves freezing cells at a controlled rate using liquid nitrogen (-196°C) or other cryoprotective agents.
The cells are prepared as a dense suspension in a medium containing glycerol or dimethyl sulfoxide (DMSO), which prevents cell damage due to ice crystal formation.
The vials are then stored in a liquid nitrogen refrigerator, either by immersion in the liquid nitrogen (-196°C) or by storage in the gas phase above the liquid nitrogen (-150°C).
Advantages of this method include:
- Ability to preserve many species that cannot be preserved by lyophilization.
- Most species can remain viable for 10 to 30 years or more without undergoing change in their characteristics.
Disadvantages include:
- The method is relatively expensive due to the need to replenish liquid nitrogen at regular intervals.

Storage in Silica Gel

Sporulating fungi can be stored by this method, protected by skim milk and stored on silica gel.
Sporulating fungi can remain viable for 4-5 years, and spores and microcysts can be preserved for up to 11 years on silica gel.
Viability of fungi depends on the strain of fungi and the media used to grow it before preservation.
Advantages of this method include:
- Inhibition of fungal growth and metabolism.
- Simple revival of culture by scattering silica gel crystals on an agar plate.

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Description

Test your knowledge on storing pure microbial cultures at low temperatures to slow down metabolic activity. Learn about the duration of storage for bacteria and fungi, as well as the eventual death of microbes due to continued growth and nutrient utilization.