Cryoprotection and cryosterilization effects of type I antifreeze protein on E. coli cells.

To establish the effects of type I antifreeze protein (AFP) on E. coli cells, we have focused on the survival rate of the E. coli cells using type I AFP at various concentrations under rapid cooling conditions using liquid N2 at atmospheric or low pressure. The survival rate of E. coli was enhanced by the addition of type I AFP at a concentration of 10 microg/ml, and its value shifted from 0.73% to 2.96%. When the concentration of type I AFP was 100 microg/ml, the cell survival rate markedly decreased to 0.090%. This low survival rate was further decreased (0.022%) by the application of the same freeze-thaw treatment for four times. Also, the effect of type I AFP as a bactericidal agent did not vary according to the varying initial cell densities from 10(4) to 10(8) cells / ml. Furthermore, the effects of using type I AFP at 1.0 MPa with N2 gas under conditions of low pressure and low oxygen tension using a simple device were examined. When the actions of type I AFP as a cryoprotectant were stimulated, the survival rate of the E. coil cells increased to 57.8%. In addition, the bactericidal effect of type I AFP at 100 micro g/ml of protein concentration could also be enhanced. The survival rate using 100 g/ml of type I AFP under low pressure was 0.35% of that using 10 microg/ml under the same conditions. This is the first report on the cryoprotectant and cryosterilization effects of type I AFP of E. coli cells under various conditions.