Basic features of the Streptococcus thermophilus heat shock response

The heat shock response was investigated in the thermophilic acid bacterium Streptococcus thermophilus. The heat resistance (58°C, 30 min) of log-phase cells grown at 42°C was enhanced by pretreatment at 52°C for 15 or 30 min. Concurrently to this acquired thermotolerance, two-dimensional gel electrophoresis indicates that the cells induced the synthesis of at least 22 heat shock proteins after temperature upshift. Furthermore, following SDS-PAGE, Western blotting, and immunological analysis, six proteins were found to be antigenically related to the Escherichia coli heat shock proteins DnaK, DnaJ, GroEL, GrpE, and La and to the Bacillus subtilis ⁴³ factor Among these six proteins, two related to DnaK and GroEL, are clearly overexpressed during this stress. It is concluded that S. thermophilus possesses a heat shock response similar to that known to occur in mesophilic microorganisms.