Cryopreservation refers to the use of a very low temperature (below approximately -130° C [-202° F]) to store a living organism. Organisms (including many types of bacteria, yeast, fungi, and algae) can be frozen for long periods of time and then recovered for subsequent use.

This form of long-term storage minimizes the chances of change to the microorganism during storage. Even at refrigeration temperature, many microorganisms can grow slowly and so might become altered during storage. This behavior has been described for strains of Pseudomonas aeruginosa that produce an external slime layer. When grown on a solid agar surface, the colonies of such strains appear like mucous drops. However, when recovered from refrigeration storage, the mucoid appearance can be lost. Cryopreservation of mucoid strains maintains the mucoid characteristic.

Cryostorage of bacteria must be done at or below the temperature of -130° C (-202° F...