Characterization of Two Component Systems of Lactobacillus casei BL23 and their involvement in stress response

• Autores: Ainhoa Revilla Guarinos
• Directores de la Tesis: Manuel Hernández Pérez (dir. tes.), Manuel Zuñiga Cabrera (dir. tes.)
• Lectura: En la Universitat Politècnica de València ( España ) en 2014
• Idioma: inglés
• Tribunal Calificador de la Tesis: Alberto Marina Moreno (presid.), Mª Antonia Ferrús Pérez (secret.), Josef Deutscher (voc.)
• Enlaces
  • Tesis en acceso abierto en: RiuNet
• Resumen

  • Lactobacillus casei is a species naturally found in the gastrointestinal and genital tracts of animals and humans. It has been traditionally employed in the production of fermented foods and recent studies have demonstrated the probiotic properties of certain strains of this species, as L. casei BL23, the strain subject of the present study. Probiotics are defined as live micro¿organisms which, when administered in adequate amounts, confer a health benefit on the host. In order to exert their beneficial effect, they must reach the intestine in sufficient amounts and in a viable state. Thus, they must be able to survive to the variety of adverse conditions ¿ stress ¿ encountered during industrial food processing and during their transit through the gastrointestinal tract. Among these stress conditions are the presence of antimicrobial peptides (used as food preservatives, produced by the innate immune system of the host or produced by other microorganisms present in the intestinal microbiota) and acid stress (during industrial processing or during passage through the stomach). Signaling systems are critical to detect adverse changes in the environmental conditions and to activate specific responses to counteract them. Among these signaling mechanisms, the signal transduction Two Component Systems (TCS) play a major role in bacteria. They typically consist of an intramembrane sensor protein, histidine kinase, and a response regulator which controls the expression of specific genes involved in the adaptive response to the stress condition that activated the system. TCS have been extensively studied in model microorganisms like Escherichia coli and Bacillus subtilis, as well as in other pathogen microorganisms like Staphylococcus aureus where they have a major role during the processes of invasion and colonization of the host. Probiotic bacteria must face essentially the same environmental conditions as pathogens do, however, the information about the signal transduction mechanisms operating in probiotic bacteria like L. casei is scarcer. This work aims to gain insight into the role of TCS in the physiology and stress response of the probiotic microorganism L. casei. The investigations carried out during this PhD thesis showed that 17 TCS were encoded in L. casei BL23 genome. Mutants defective in the 17 response regulators of each of the TCS were obtained and they were phenotypically characterized. Our results highlighted the importance of some of these TCS in the general physiology as well as in the stress response of this strain. A deeper study was performed in the response to stress by antimicrobial peptides. The results showed that TCS09 and TCS12, belonging to the BceRSlike TCS group which have been described to be involved in the antibiotic stress response in other microorganisms, are also involved in the antimicrobial peptide stress response of L. casei BL23. Furthermore, our results have shown that TCS12 is controlling systems involved in maintenance of cell surface properties: Dlt system and MprF protein. Our work proves that a correct functionality of the Dlt system is crucial in the maintenance of the barrier properties of the cell wall of L. casei BL23, which is determinant in its ability to survive in acid media. This work has led to an increased understanding not only of the mechanisms regulating signal transduction, but also of the specific response mechanisms that allow L. casei BL23 to adapt its physiology to different environmental conditions.