['Heat and cold shock response are normally considered as independent phenomena. A small amount of evidence suggests instead that interactions may exist between them in two Lactococcus strains.', 'We show the occurrence of molecular relationships between the mechanisms of cold and heat adaptations in Streptococcus thermophilus, a lactic acid bacterium widely used in dairy fermentation, where it undergoes both types of stress. We observed that cryotolerance is increased when cells are pre-incubated at high temperature. In addition, the production of a protein, identified as ClpL, a member of the heat-shock ATPase family Clp A/B, is induced at both high and low temperature. A knock-out clpL mutant is deficient in both heat and cold tolerance. However lack of production of this protein does not abolish the positive effect of heat pre-treatment towards cryotolerance.'] Is expression of the heat shock gene clpL of Streptococcus thermophilus induced by both heat and cold shock?