Characterization of the Heat Shock Response in Lactococcus lactis subsp. lactis

The heat shock response in Lactococcus lactis subsp. lactis was characterized with respect to synthesis of a unique set of proteins induced by thermal stress. A shift in temperature from 30 to 42°C was sufficient to arrest the growth of L. lactis subsp. lactis, but growth resumed after a shift back to 30°C. Heat shock at 50°C reduced the viable cell population by 10³; however, pretreatment of the cells at 42°C made them more thermoresistant to exposure at 50°C. The enhanced synthesis of approximately 13 proteins was observed in cells labeled with ³⁵S upon heat shock at 42°C. Of these heat shock-induced proteins, two appeared to be homologs of GroEL and DnaK, based on their molecular weights and reactivity with antiserum against the corresponding Escherichia coli proteins. Therefore, we conclude that L. lactis subsp. lactis displays a heat shock response similar to that observed in other mesophilic bacteria.