Systematic analysis of the glutamate-dependent acid resistance system in Escherichia coli

Guo, Lingyun (2022): Systematic analysis of the glutamate-dependent acid resistance system in Escherichia coli. Dissertation, LMU München: Fakultät für Biologie

Abstract

Acid resistance is an important feature for all human enterobacteria to survive extreme acid stress in the stomach (pH < 2.5) and to adapt to mild acid stress in the colon (pH 6.0). The glutamate-dependent acid resistance (GDAR) system provides the most robust protection for Escherichia coli strains in extremely acidic environments. The GDAR system consists of the two homologous glutamate decarboxylases GadA/GadB and the glutamate/γ-aminobutyric acid antiporter GadC. Induction of the GDAR system is complex and controlled by many regulatory proteins, but the primary stimuli for its activation are poorly understood. In this work, the dynamics of gadA/gadB expression and GadA/GadB production were systematically analyzed in correlation with alterations of pH, oxygen and several metabolites during the growth of E. coli MG1655 in a bioreactor. The expression profile and further research revealed a transient, fine-tuned activation profile, in which oxygen limitation plays a major role, followed by stationary phase and acid stress. Under oxygen limitation, E. coli switches to mixed acid fermentation. Therefore, in this study, the effect of fermentation products, as well as short-chain fatty acids (SCFAs) on the expression of the gadB and gadA was investigated. The SCFAs acetic acid, propionic acid, and butyric acid were found to be the most important external stimuli of the GDAR system. The MnmG/MnmE-GadE circuit was identified to respond to these SCFAs in E. coli. In addition, a screening of regulators that sense the low pH caused by SCFAs and hydrochloric acid revealed the response regulator of the pyruvate-sensing YpdA/YpdB histidine kinase/response regulator system is important for the expression of gadA and gadB in E. coli. This activation is independent of the expression of the expression of the central regulator gene gadE and does not require the phosphorylation of YpdB. In summary, a systematic analysis of the expression profile of the GDAR system has revealed SCFAs as external stimuli for the MnmG/MnmE-GadE regulatory circuit, as well as a new regulatory component, the response regulator YpdB in this complex regulatory network.

• Dokumententyp: Dissertationen (Dissertation, LMU München)
• Themengebiete: 500 Naturwissenschaften und Mathematik ; 500 Naturwissenschaften und Mathematik > 570 Biowissenschaften, Biologie
• Fakultäten: Fakultät für Biologie
• Sprache der Hochschulschrift: Englisch
• Datum der mündlichen Prüfung: 14. November 2022
• 1. Bericht­erstatter:in: Jung, Kirsten