Abstract
Tolerance to bile stress is crucial for Lactobacillus paracasei to survive in the intestinal tract and exert beneficial actions. In this work, global transcriptomic analysis revealed that 104 genes were significantly changed (log2FoldChange > 1.5, P < 0.05) in detected transcripts of L. paracasei L9 when exposed to 0.13% Ox-bile. The different expressed genes involved in various biological processes, including carbon source utilization, amino acids and peptide metabolism processes, transmembrane transport, transcription factors, and membrane proteins. It is noteworthy that gene mleS encoding malolactic enzyme (MLE) was 2.60-fold up-regulated. Meanwhile, L-malic acid was proved to enhance bile tolerance, which could be attributed to the intracellular alkalinization caused by MLE pathway. In addition, membrane vesicles were observed under bile stress, suggesting a disturbance in membrane charge without L-malic acid. Then, genetic and physiological experiments revealed that MLE pathway enhanced the bile tolerance by maintaining a membrane balance in L. paracasei L9, which will provide new insight into the molecular basis of MLE pathway involved in bile stress response in Lactic acid bacteria.
Highlights
Lactobacillus paracasei is a common constituent of inhabitants in the human and animal gut, and is extensively used in the food industry as a starter culture for dairy fermentation (Sisto and Lavermicocca, 2012; Di Renzo et al, 2018; Stefanovic et al, 2018)
0.13% bile salts was used for further studies of bile stress response in L. paracasei L9
Metabolism changes at the glycolytic level which lead to enhanced energy production could be crucial for bacteria to resist bile salt
Summary
Lactobacillus paracasei is a common constituent of inhabitants in the human and animal gut, and is extensively used in the food industry as a starter culture for dairy fermentation (Sisto and Lavermicocca, 2012; Di Renzo et al, 2018; Stefanovic et al, 2018). Some strains of L. paracasei have attracted additional interest as health-promotion probiotics (De Vrese and Schrezenmeir, 2008). To exert their beneficial effects, high survival rate and stable colonization in the human gastrointestinal tract (GIT) are crucial for L. paracasei strains. During digestion, L. paracasei suffers from various challenges in the GIT, such as acidic pH in the stomach and bile salts in the intestine (Corcoran et al, 2008; Bove et al, 2013). Bile Stress Response in L. paracasei the lipid bilayer structure of cellular membranes. Tolerance to bile stress is essential for L. paracasei to survive and colonize in the GIT
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