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Characterization of a stress tolerance-defective mutant of Lactobacillus rhamnosus LRB.

ABSTRACT: Lactobacillus rhamnosus is a lactic acid bacterium that survives diverse ecological niches, including the human oral cavity and gastrointestinal tract. L. rhamnosus is an acidogenic bacterium that produces copious amounts of lactic acid. The organism is also considered as aciduric, since it can survive prolonged exposure to an acidic environment. For a probiotic bacterium such as L. rhamnosus, it is necessary to understand how this organism survives acid stress. In this study we used L. rhamnosus LRB to isolate one spontaneous mutant that was sensitive to acid stress. The mutant, which we named RBM1, also displayed sensitivity to a wide range of stresses including osmotic, thermal, and others. Using whole genome sequencing, we mapped the putative mutations in the mutant strain. It appears that three single nucleotide substitutions occurred in the mutant as compared to the wild-type LRB strain. Among those, the most relevant mutation occurred in the ftsH gene that created a single amino acid change in the protein. We performed a comparative proteomic study to understand the molecular basis for stress sensitivity and found that ~15% of the proteome is altered in the mutant strain. Our study suggests that generation of spontaneous mutants during L. rhamnosus colonization could drastically affect bacterial physiology and survival under stress conditions.

SUBMITTER: Biswas S

PROVIDER: S-EPMC6688488 | biostudies-literature | 2019 Aug

REPOSITORIES: biostudies-literature

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Characterization of a stress tolerance-defective mutant of Lactobacillus rhamnosus LRB.

Biswas Saswati S Keightley Andrew A Biswas Indranil I

Molecular oral microbiology 20190607 4

Lactobacillus rhamnosus is a lactic acid bacterium that survives diverse ecological niches, including the human oral cavity and gastrointestinal tract. L. rhamnosus is an acidogenic bacterium that produces copious amounts of lactic acid. The organism is also considered as aciduric, since it can survive prolonged exposure to an acidic environment. For a probiotic bacterium such as L. rhamnosus, it is necessary to understand how this organism survives acid stress. In this study we used L. rhamnosu ...[more]

PMID: 31056830

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Project description:Lactobacillus rhamnosus GG (GG) is a widely used and intensively studied probiotic bacterium. Although the health benefits of strain GG are well documented, the systematic exploration of mechanisms by which this strain exerts probiotic effects in the host has only recently been initiated. The ability to survive the harsh conditions of the gastrointestinal tract, including gastric juice containing bile salts, is one of the vital characteristics that enables a probiotic bacterium to transiently colonize the host. Here we used gene expression profiling at the transcriptome and proteome levels to investigate the cellular response of strain GG toward bile under defined bioreactor conditions. The analyses revealed that in response to growth of strain GG in the presence of 0.2% ox gall the transcript levels of 316 genes changed significantly (p < 0.01, t test), and 42 proteins, including both intracellular and surface-exposed proteins (i.e. surfome), were differentially abundant (p < 0.01, t test in total proteome analysis; p < 0.05, t test in surfome analysis). Protein abundance changes correlated with transcriptome level changes for 14 of these proteins. The identified proteins suggest diverse and specific changes in general stress responses as well as in cell envelope-related functions, including in pathways affecting fatty acid composition, cell surface charge, and thickness of the exopolysaccharide layer. These changes are likely to strengthen the cell envelope against bile-induced stress and signal the GG cells of gut entrance. Notably, the surfome analyses demonstrated significant reduction in the abundance of a protein catalyzing the synthesis of exopolysaccharides, whereas a protein dedicated for active removal of bile compounds from the cells was up-regulated. These findings suggest a role for these proteins in facilitating the well founded interaction of strain GG with the host mucus in the presence of sublethal doses of bile. The significance of these findings in terms of the functionality of a probiotic bacterium is discussed.

Dataset Information

Characterization of a stress tolerance-defective mutant of Lactobacillus rhamnosus LRB.

Publications

Characterization of a stress tolerance-defective mutant of Lactobacillus rhamnosus LRB.

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