Identification and functional characterization of type II toxin/antitoxin systems in Aggregatibacter...

Area of Science:

• Microbiology
• Molecular Biology
• Genetics

Background:

• Type II toxin/antitoxin (TA) systems are crucial for bacterial survival strategies like persister cell formation and biofilm development.
• Aggregatibacter actinomycetemcomitans inhabits the dynamic oral environment, yet the role of its TA systems in adaptation remains largely unexplored.
• Understanding TA systems in A. actinomycetemcomitans is key to deciphering its persistence mechanisms within dental biofilms.

Purpose of the Study:

• To identify and characterize type II TA systems in Aggregatibacter actinomycetemcomitans.
• To investigate the function of these TA systems in response to environmental conditions relevant to the oral cavity, particularly low pH.
• To determine the contribution of specific TA systems to A. actinomycetemcomitans' metabolic activity, biofilm formation, and persistence under acidic stress.

Main Methods:

• Bioinformatic analysis to identify conserved type II TA systems across A. actinomycetemcomitans serotypes.
• Gene expression analysis to assess TA system induction under various environmental conditions.
• Construction and analysis of deletion mutants to evaluate the impact on metabolic activity and biofilm formation under acidic stress.
• In vitro assays to determine the translational inhibition and RNA degradation activity of toxin/antitoxin components.

Main Results:

• Eleven conserved type II TA systems, including RelBE, MazEF, and HipAB families, were identified in A. actinomycetemcomitans.
• Two RelBE-like systems (D11S_1194-1195 and D11S_1718-1719) were induced by low pH.
• Deletion of D11S_1718-1719 significantly reduced metabolic activity and biofilm biomass under acidic conditions.
• Toxin proteins D11S_1194 and D11S_1718 inhibited in vitro translation and degraded ribosome-associated RNA.

Conclusions:

• D11S_1194-1195 and D11S_1718-1719 function as RelBE-like type II TA systems activated by acidic conditions.
• These systems likely inhibit translation by degrading ribosome-associated mRNA, aiding bacterial adaptation.
• The identified TA systems play a significant role in the adaptation and persistence of A. actinomycetemcomitans in acidic dental biofilm environments.