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Abstract
Small heat shock proteins (sHsps) are ubiquitous conserved chaperone-like proteins involved in cellular proteins protection under stressful conditions. In this study, a reverse transcription quantitative PCR (RT-qPCR) procedure was developed and used to quantify the transcript level of a small heat shock gene (shs) in the probiotic bacterium Lactobacillus acidophilus NCFM, under stress conditions such as heat (45 °C and 53 °C), bile (0.3% w/v), hyperosmosis (1 M and 2.5 M NaCl), and low pH value (pH 4). The shs gene of L. acidophilus NCFM was induced by salt, high temperature and acidic stress, while repression was observed upon bile stress. Analysis of the 5′ noncoding region of the hsp16 gene reveals the presence of an inverted repeat (IR) sequence (TTAGCACTC-N9-GAGTGCTAA) homologue to the controlling IR of chaperone expression (CIRCE) elements found in the upstream regulatory region of Gram-positive heat shock operons, suggesting that the hsp16 gene of L. acidophilus might be transcriptionally controlled by HrcA. In addition, the alignment of several small heat shock proteins identified so far in lactic acid bacteria, reveals that the Hsp16 of L. acidophilus exhibits a strong evolutionary relationship with members of the Lactobacillus acidophilus group.
Highlights
During the last decade the use of microorganisms considered probiotic has increased markedly
The biomedical relevance of L. acidophilus is testified by its natural occurrence in the human intestinal microbiota, its probiotic properties, and its possible use as a vaccine delivery system [37,38,39]
Given its use to drive dairy fermentations and in functional probiotic foods, this species is commonly exposed to multiple physiological stresses
Summary
During the last decade the use of microorganisms considered probiotic (health promoting) has increased markedly. Lactobacillus acidophilus is a homo-fermentative LAB species boasting biotechnological applications (i) in the production of dairy foods and (ii) as probiotic (e.g., in the form of yogurts, dietary supplements) It is being considered as a potential vaccine-delivery vehicle to the gastrointestinal tract [4]. Small heat shock proteins (sHsps) are ATP-independent chaperons, whose function is to mediate the correct protein folding in the context of a multi-chaperone network [10] They act as one of the first biological machinery that copes with stress-induced cell damage by binding and maintaining denatured proteins in a disaggregation-competent state [10]. SHsps proteins are induced in response to various kinds of abiotic stress including heat shock, acid stress, and osmotic stress, some sHsps are expressed constitutively, under physiological conditions [12,13] They are usually considered “general” stress proteins. We have focused on these specific stress conditions as they are often encountered by LAB either during food fermentation or gastrointestinal transit
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