Identification de prot?ines de stress chez Lactobacillus delbrueckii bulgaricus par ?lectrophor?se bidimensionnelle

Identification of stress proteins in Lactobacillus delbrueckii bulgaricus by two-dimensional electrophoresis. We studied Lactobacillus bulgaricus adaptation to an acid stress. In L. bulgaricus, adapted cells (30 min incubation at pH 4.75) were ?250 fold 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 35S methionine labeling of exponentially growing cultures, under standard (pH 6) and adaptive (pH 4.75) conditions. After 2 dimensional (2-D) electrophoresis separation, the protein patterns were compared. At least 30 protein spots showed an increased radioactivity level under acidic conditions. We determined the N-terminal amino acid sequence of 3 highly induced proteins. By comparison to databases, they were identified as the heat shock proteins GroES, GroEL and DnaK. A differential induction was observed for GroES and GroEL, suggesting a post-transcriptionnal regulation mechanism. In this report we established a method for the study of acid stress response in L. bulgaricus. This method will also be useful for further studies on the adaptation of this bacterium to environmental variations. Nous avons ?tudi? l'adaptation de la bact?rie lactique Lactobacillus bulgaricus au stress acide. Nous avons montr? que les bact?ries cultiv?es en milieu "neutre " (pH 6) pr?sentaient une forte l?talit? apr?s transfert dans un milieu acide (choc acide ? pH 3,6). En revanche, les bact?ries pr?alablement adapt?es dans un milieu acide non l?tal (pH 4,75) devenaient ?250 fois plus tol?rantes au choc acide. Apr?s marquage ? la m?thionine 35S et s?paration par ?lectrophor?se bidimensionnelle (2-D), les profils prot?iques obtenus en condition d'adaptation (pH 4,75) et en condition standard (pH 6) sont compar?s. On observe une augmentation significative (> 2) de l'intensit? d'environ 30 spots pendant l'adaptation. La d?termination des s?quences peptidiques N-terminales de 3 prot?ines fortement induites ? pH 4,75 permet d'identifier les prot?ines de choc thermique GroES, GroEL et DnaK. Nous observons des niveaux d'induction diff?rents pour GroES et GroEL, qui pourraient ?tre li?s ? une r?gulation post-transcriptionnelle. Au final, nous avons ?tabli une m?thode d'?tude de la r?ponse au stress acide chez L. bulgaricus. De fa?on plus g?n?rale, cette m?thode permettra d'?tudier l'adaptation de cette bact?rie aux variations environnementales.