Effect of cold shock on protein synthesis and on cryotolerance of cells frozen for long periods in Lactococcus lactis.

Aspects of the cold-shock response in Lactococcus lactis subsp. lactis LL41-1 were investigated. First, it was determined whether new proteins were synthesized in response to cold shock. Cell-free extracts were prepared from a cold-shocked (exposed to 10 degreesC for 5 h) culture (cfe-cs) and from a non-cold-shocked (held at 30 degreesC continuously) culture (cfe-non), and were subjected to sodium dodecyl sulphate-polyacrylamide gel electrophoresis. A protein of approximately 6.3 kDa was present in the cfe-cs and appeared not to be present in the cfe-non. No other changes were evident. Second, the effect of cold shock on cryotolerance of cells that have been frozen at -20 degreesC for up to 1 year was examined. Without the cold-shock treatment prior to freezing the cell viability following freezing for 1 day was 34%, 14 days 32%, 182 days 7%, and 364 days 0.2%. However, with the cold shock treatment it was 83%, 82%, 12%, and 0.8%, respectively. It appears that cold shock significantly improves cryotolerance of the cells for short periods of freezing, but the protective effect was less marked following longer storage periods.