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Cryopreservation is a process that preserves biological materials like cells, tissues, or organs by freezing them to very low temperatures.
This process helps keep biological material stable at cryogenic temperatures for extended periods of time and preserves the original cell structures.
At low temperatures, any cell metabolism that might damage the biological material is effectively stopped.
Cryopreservation is typically done at sub-freezing temperatures, below −80°C and typically below −140°C. At a temperature of −196°C, that of liquid nitrogen, all chemical reactions, biological processes, and physical intra and extracellular activities are suspended.
The concept of cryopreservation in microbiology dates back to the mid-20th century.
Cryopreservation typically involves several steps
Preparation of the Culture
Microorganisms are cultured and grown under optimal conditions until they reach a desired stage of growth or density.
Preparation of Cryoprotectant
A cryoprotectant solution is prepared, which typically includes substances like glycerol or dimethyl sulfoxide (DMSO). This solution helps protect the cells from damage during freezing by reducing ice crystal formation.
Mixing
The cryoprotectant solution is mixed with the microbial culture in a suitable ratio to ensure proper protection during freezing.
Aliquoting
The mixture is divided into small aliquots to facilitate easy storage and revival of individual samples as needed.
Freezing
The aliquots are gradually cooled down to very low temperatures, typically using a controlled-rate freezer or a combination of freezing methods. Slow cooling allows the cells to adjust to the decreasing temperature and minimizes damage from ice crystal formation.
Storage
Once frozen, the samples are stored in specialized cryogenic storage containers, such as liquid nitrogen tanks, at ultra-low temperatures (-80°C to -196°C) to maintain their viability over long periods.
The earliest documented use of cryopreservation techniques in microbiology can be traced to the work of researchers like Christopher Polge, who in the 1940s discovered the protective properties of glycerol in preserving sperm cells. This laid the foundation for later advancements in preserving various types of cells, including microorganisms.
