Cold Shock Proteins and Low-Temperature Response of Streptococcus thermophilus CNRZ302

Low-temperature adaptation and cryoprotection were studied in the thermophilic lactic acid bacterium Streptococcus thermophilus CNRZ302. S. thermophilus actively adapts to freezing during a pretreatment at 20°C, resulting in an approximately 1,000-fold increased survival after four freeze-thaw cycles compared to mid-exponential-phase cells grown at an optimal temperature of 42°C. No adaptation is observed when cells are exposed to a temperature (10°C) below the minimal growth temperature of the strain (just below 15°C). By two-dimensional gel electrophoresis several 7-kDa cold-induced proteins were identified, which are the major induced proteins after a shift to 20°C. These cold shock proteins were maximally expressed at 20°C, while the induction level was low after cold shock to 10°C. To confirm the presence of csp genes in S. thermophilus, a PCR strategy was used which yielded products of different sizes. Sequence analysis revealed csp-like sequences that were up to 95% identical to those of csp genes of S. thermophilus ST1-1, Streptococcus dysgalactiae, Streptococcus pyogenes, and Lactococcus lactis. Northern blot analysis revealed a seven- to ninefold induction of csp mRNA after a temperature shift to 20°C, showing that this thermophilic bacterium indeed contains at least one cold-inducible csp gene and that its regulation takes place at the transcriptional level.