Identification of stress proteins in Lactobacillus delbrueckii bulgaricus by two-dimensional electrophoresis

We studied Lactobacillus bulgaricus adaptation to an acid stress. In L. bul garicus, adapted cells (30 min incubation at pH 4.75) were similar to 250 f old more tolerant to lethal acid stress (30 min at pH 3.6) than non adapted ones. In order to identify proteins induced during the adaptation, de novo protein synthesis was monitored by S-35 methionine labeling of exponential ly growing cultures, under standard (pH 6) and adaptive (pH 4.75) condition s. After 2 dimensional (2-D) electrophoresis separation, the protein patter ns were compared. At least 30 protein spots showed an increased radioactivi ty level under acidic conditions. We determined the N-terminal amino acid s equence of 3 highly induced proteins. By comparison to databases, they were identified as the heat shock proteins GroES, GroEL and DnaK. A differentia l induction was observed for GroES and GroEL, suggesting a post-transcripti onnal regulation mechanism. In this report we established a method for the study of acid stress response in L. bulgaricus. This method will also be us eful for further studies on the adaptation of this bacterium to environment al variations.