Many microorganisms need to be preserved with low temperature, so ultra-low temperature preservation method is a wide range of microbial preservation method. Microbiomes that require complex nutrients, such as those that cannot be kept active by other storage methods (e.g. plant pathogenic fungi), can usually be stored at ultra-low temperatures (ATCC1983; Halliday, Baker 1985).
This method is to freeze cells in small tubes or ampoules at a slower freezing rate (1 c/min) until -150 degrees C, and then store these small tubes in liquid nitrogen at -150 to 196 degrees C. Ultra-low temperature cryoprotection agents are different from those used in freeze-drying. ATCC usually uses a mixture made of glycerin (10%), metformin (5%) and culture fluid to preserve most cell lines. These chemicals enter the cell to avoid frozen damage to the lining. The cells stored in cryogenic containers must be handled with care when resuscitating. When the tube is heated, the resulting ice crystal kills the cells and the accident can be avoided by proper operation.
As long as the sample is quickly thawed to reduce the loss of vitality, the practice is: the sealed small tube quickly put into 37 degrees C water, until all the ice melts, and then open the tube, the contents into the medium. Microbes that are kept at ultra-low temperatures must always be stored in very low temperature environments, so liquid nitrogen tanks are needed. Regular attention should be paid to rehydration of liquid nitrogen during long-term storage. This type of storage requires more funding than freeze-drying, including labour and liquid nitrogen, which are necessary to maintain storage temperatures.