Integrated transcriptomic and proteomic analysis of the bile stress response in probiotic Lactobacillus salivarius LI01.

Lactobacillus salivarius LI01, isolated from healthy humans, has demonstrated probiotic properties in the prevention and treatment of liver failure. Tolerance to bile stress is crucial to allow lactobacilli to survive in the gastrointestinal tract and exert their benefits. In this work, we used a Digital Gene Expression transcriptomic and iTRAQ LC-MS/MS proteomic approach to examine the characteristics of LI01 in response to bile stress. Using culture medium with or without 0.15% ox bile, 591 differentially transcribed genes and 347 differentially expressed proteins were detected in LI01. Overall, we found the bile resistance of LI01 to be based on a highly remodeled cell envelope and a reinforced bile efflux system rather than on the activity of bile salt hydrolases. Additionally, some differentially expressed genes related to regulatory systems, the general stress response and central metabolism processes, also play roles in stress sensing, bile-induced damage prevention and energy efficiency. Moreover, bile salts appear to enhance proteolysis and amino acid uptake (especially aromatic amino acids) by LI01, which may support the liver protection properties of this strain. Altogether, this study establishes a model of global response mechanism to bile stress in L. salivarius LI01.

BIOLOGICAL SIGNIFICANCE: L. salivarius strain LI01 exhibits not only antibacterial and antifungal properties but also exerts a good health-promoting effect in acute liver failure. As a potential probiotic strain, the bile-tolerance trait of strain LI01 is important, though this has not yet been explored. In this study, an analysis based on DGE and iTRAQ was performed to investigate the gene expression in strain LI01 under bile stress at the mRNA and protein levels, respectively. To our knowledge, this work also represents the first combined transcriptomic and proteomic analysis of the bile stress response mechanism in L. salivarius.