[Mechanisms of the protective action of cryoprotectors on Escherichia coli cells]

Two classes of cryoprotectors, namely, glycerol (penetrating the cell) and dextran with a mol. mass of 15-20,000 Da (non-penetrating the cell), were tested for their ability to exert a protective effect on the permeability and viability of Escherichia coli M 17 cells subjected to different freezing conditions. Cell permeability assayed in terms of the release of low-molecular-weight compounds into the surrounding medium was shown to be disordered to a far less extent when dextran was used as a cryoprotective agent than in the case of glycerol. The cells were found to be resistant to lysis stimulated by the detergent sodium lauryl sulfate (0.02%) in the presence of dextran. The cells were still capable of forming colonies after their freezing to -10 degrees C in the presence of the cryoprotectors in media containing the detergent (2%). Once the cells had been frozen to -196 degrees C, only those protected by glycerol were resistant to the detergent in the growth medium. Different mechanisms of the cryoprotective action on E. coli cells are discussed.