Bacterial toxin-antitoxin systems: Novel insights on toxin activation across populations and experimental
Luis R Pizzolato-Cezar1, Beny Spira2, M Teresa Machini1
1Department of Biochemistry, Institute of Chemistry, University of São Paulo, São Paulo, Brazil.
Abstract:
The alarming rise in hard-to-treat bacterial infections is of great concern to human health. Thus, the identification of molecular mechanisms that enable the survival and growth of pathogens is of utmost urgency for the development of more efficient antimicrobial therapies. In challenging environments, such as presence of antibiotics, or during host infection, metabolic adjustments are essential for microorganism survival and competitiveness. Toxin-antitoxin systems (TASs) consisting of a toxin with metabolic modulating activity and a cognate antitoxin that antagonizes that toxin are important elements in the arsenal of bacterial stress defense. However, the exact physiological function of TA systems is highly debatable and with the exception of stabilization of mobile genetic elements and phage inhibition, other proposed biological functions lack a broad consensus. This review aims at gaining new insights into the physiological effects of TASs in bacteria and exploring the experimental shortcomings that lead to discrepant results in TAS research. Distinct control mechanisms ensure that only subsets of cells within isogenic cultures transiently develop moderate levels of toxin activity. As a result, TASs cause phenotypic growth heterogeneity rather than cell stasis in the entire population. It is this feature that allows bacteria to thrive in diverse environments through the creation of subpopulations with different metabolic rates and stress tolerance programs.
Insights
Toxin-antitoxin systems (TASs) create bacterial subpopulations with varied metabolic rates and stress tolerance. This phenotypic growth heterogeneity, not cell stasis, aids survival in challenging environments and informs new antimicrobial therapies.
Area of Science:
- Microbiology
- Molecular Biology
- Bacterial Pathogenesis
Background:
- Rising hard-to-treat bacterial infections necessitate novel antimicrobial strategies.
- Toxin-antitoxin systems (TASs) are bacterial defense mechanisms involving toxins and antitoxins.
- The precise physiological roles of TASs remain debated, impacting therapeutic development.
Purpose of the Study:
- To elucidate the physiological functions of TASs in bacteria.
- To identify experimental limitations causing discrepancies in TAS research.
- To understand how TASs contribute to bacterial survival and competitiveness.
Main Methods:
- Review of existing literature on bacterial toxin-antitoxin systems.
- Analysis of proposed functions and experimental evidence for TASs.
- Discussion of regulatory mechanisms controlling TAS activity.
Main Results:
- TASs induce phenotypic growth heterogeneity, not population-wide stasis.
- Subsets of cells transiently express toxins, creating diverse subpopulations.
- These subpopulations exhibit varied metabolic rates and stress tolerance.
Conclusions:
- TASs facilitate bacterial adaptation and survival in diverse, challenging environments.
- Understanding TASs' role in heterogeneity is key to developing effective antimicrobial therapies.
- Addressing experimental shortcomings is crucial for advancing TAS research.
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