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.

中文翻译：

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鼠李糖乳杆菌LRB的胁迫耐受缺陷型突变体的表征。

鼠李糖乳杆菌是一种乳酸菌，可在包括人类口腔和胃肠道在内的各种生态环境中存活。鼠李糖乳杆菌是产酸细菌，可产生大量的乳酸。该生物也被认为是酸性的，因为它可以长时间暴露在酸性环境中生存下来。对于益生菌，例如鼠李糖乳杆菌，有必要了解这种生物如何在酸胁迫下生存。在这项研究中，我们使用了鼠李糖乳杆菌LRB分离出一种对酸胁迫敏感的自发突变体。我们将其命名为RBM1，该突变体还表现出对多种压力的敏感性，包括渗透压，热应力和其他应力。使用全基因组测序，我们绘制了突变菌株中的推定突变。与野生型LRB菌株相比，突变体中出现了三个单核苷酸取代。其中最相关的突变发生在fts H基因中，该基因在蛋白质中产生了一个氨基酸变化。我们进行了比较蛋白质组学研究，以了解应激敏感性的分子基础，发现突变株中约有15％的蛋白质组发生了改变。我们的研究表明鼠李糖乳杆菌自发突变体的产生 在压力条件下，定植会严重影响细菌的生理和生存。