Functional characterization of the membrane-depolarizing toxin TisB in Escherichia coli

Abstract

Bacteria are frequently exposed to environmental stressors that threaten their survival. This leads to the activation of stress response systems that adjust gene expression to maintain cellular in- tegrity. However, if these systems are inadequate, bacteria can form persister cells. These are a dormant subpopulation with reduced metabolic activity and increased antibiotic tolerance. Unlike other forms of bacterial dormancy, such as endospores, persister cells are morphologically similar to active cells but are in a transient state of reduced activity. This survival strategy allows bacteria to withstand adverse conditions that can lead to relapse of infection and the spread of antibiotic resistance. This work examines the functionality of TisB, a toxin of the type I toxin-antitoxin system tisB/istR-1 in Escherichia coli (E. coli), and its role in maintaining dormancy through specific physiological mechanisms. The research suggests that insertion of TisB into the inner membrane leads to membrane depolarization and ATP depletion, which can be considered as key triggers for the dormant state associated with antibiotic tolerance. The results presented illustrate the influence of TisB on persister cell physiology and its role in bacterial survival under antibiotic stress. An important aspect of this work is the use of a moderate expression system for TisB, which allows a controlled investigation of its effects without causing excessive toxicity. This allows for an exam- ination of the relationship between TisB-induced dormancy and protein aggregation. The results show that TisB-dependent protein aggregation influences the duration of dormancy during antibi- otic exposure. In addition, amino acids critical for TisB functionality were identified. This provided insight into the structural elements that are essential for its activity. These findings contribute to a deeper understanding of TisB and highlight the importance of specific amino acids in maintaining its functionality within the membrane. In summary, the results presented here deepen our understanding of the tisB/istR-1 system and its role in bacterial persistence. By elucidating the mechanisms by which TisB influences persistence, protein aggregation and energy content, this study provides a foundation of knowledge that can serve as a starting point for developing strategies to curb bacterial persistence and improve the efficacy of antibiotics.