Proteomic analysis of the probiotic Lactobacillus reuteri CRL1098 reveals novel tolerance biomarkers to bile acid-induced stress

Abstract

Lactobacillus (L.) reuteri CRL1098 is a probiotic bacterium with a proven hypocholesterolemic effect, moderate immune stimulant effect and ability to produce cobalamin. The CRL1098 strain survives the passage through the gastrointestinal tract where the exposure to bile acids (BA) causes deleterious effects. In order to characterize the molecular mechanisms through which L. reuteri CRL1098 adapts to bile, its proteomic response was evaluated in the presence of conjugated (glycodeoxycholic acid-GDCA-) and free (deoxycholic acid-DCA-) bile acids (BA). Cell growth inhibition was observed only in the presence of DCA. Two-dimensional gel electrophoresis coupled to mass spectrometry allowed us to identify 25 protein spots differentially expressed in response to both BA. The main functional categories assigned to the proteins were metabolism of nucleotides and glycerolipids, transcription and translation, pH homeostasis and stress-responses. Remarkably, cytosine triphosphate(CTP) synthetase, enzyme related to the repair of oxidative DNA, was over-expressed in the presence of GDCA and significantly repressed by DCA; also three proteins related to protein transcription and translation were over expressed in the presence of the conjugated BA and one, was repressed by the free BA. This differential expression could explain the delayed growth of the cells challenged with the free BA and the unaffected growth in the presence of GDCA. Moreover, some general stress proteins were triggered in the presence of both BA. In addition, the bile salt hydrolase (BSH) enzyme regulation in response to BA was analyzed using real time-PCR to determine its contribution to cell tolerance. An up-regulation of the bsh gene in response to BA was observed, suggesting that this enzyme could be a specific biomarker of bile adaption in L. reuteri CRL1098. The present work proposes that BA induce a complex physiological response in L. reuteri and provide new insights into the mechanisms involved in BA tolerance.