To microbes in the frozen state, make its metabolism to stop in order to achieve the purpose of preservation.
Most microorganisms are able to save by freezing, cell volume supplied than outsiders more sensitive to low temperature, without the cell than the cell wall is sensitive at all.
The reason and the low temperature will make the moisture inside the cell formation of ice crystals, causing cell, especially the cell membrane damage.
During freezing, take appropriate quick-frozen method, can be produced by the ice crystals are small and reduce the damage to cells.
When out of the low temperature down and began to heat up, ice crystals grow up again, so the rapid heating can also reduce the damage to cells.
Frozen when the medium is have a significant effect on cellular damage.
For example, 0.
About 5 mol/L glycerol or dimethyl maple can penetrate into cells, and by reducing the strong dehydration effect and protect the cells;
Macromolecular substances such as dextrin, serum protein, skim milk or polyvinylpyrrolidone (
PVP)
Cannot penetrate the cell, but can be by way of combined with cell surface and prevent the membrane from frostbite.
Therefore, when using freezing preservation strains, general should join various protective agent in order to improve the survival rate of cultures.
in general, the storage temperature is lower, the better preservation effect.
In freezing preservation methods, liquid nitrogen preservation can be achieved
196℃。
Therefore, from the applicable scope of microbes, survival period, the character of stability, the method using in various microbial preservation methods to date is one of the ideal.
But the liquid nitrogen preservation need to use special equipment, only suitable for some professional preservation institutions commonly use.
Accordingly, ultra-low temperature freezer preservation more common use.
In a variety of genetic engineering in the manual, for example, are generally recommended in -
70 ℃ cryogenic refrigerator save strains or some special physiological state of cells (
Adding glycerol do protective agent)
, such as the induction of competent cells is established.
Under the condition of no overtemperature refrigerator, also can use -
Ordinary refrigerator strains of 20 ~ 30 ℃.
But should pay attention to the eutectic point of cells with protective agent added mixture in this temperature range, due to the small temperature refrigerator may change cause the repeated melting and recrystallization of cultures, and damage in sharp contrast to the bacteria.
So the effect of using common strains of fridge cryopreservation often is far lower than the ultra-low temperature freezer, should pay attention to check the survival condition of preservation thing often, switched to. Cultivation at any time
