Replication cycle timing determines phage sensitivity to a cytidine deaminase toxin/antitoxin bacterial defense...

Area of Science:

• Bacteriology
• Molecular Biology
• Virology

Background:

• Toxin-antitoxin (TA) systems are crucial genetic elements in bacteria, involved in regulating cellular processes and providing defense mechanisms.
• The avcID system is a novel type III TA system with potential applications in phage resistance.

Purpose of the Study:

• To elucidate the activation mechanism of the avcID toxin-antitoxin system.
• To understand how this system confers resistance to phage infection.

Main Methods:

• Investigated the molecular mechanism of avcID system activation.
• Analyzed the role of phage-induced host transcription inhibition in antitoxin degradation.
• Assessed the impact of AvcD activation on phage replication and virion formation.

Main Results:

• AvcD activation is triggered by phage-induced host transcription inhibition, leading to the degradation of the AvcI antitoxin.
• Activated AvcD deaminates deoxycytidines to deoxyuridines, depleting nucleotides and hindering phage replication.
• While T5 phage (longer replication cycle) is sensitive, T7 phage (shorter replication cycle) exhibits resistance, indicating AvcI depletion alone is insufficient for protection against all phages.

Conclusions:

• The avcID system's activation is dependent on phage-induced antitoxin degradation, not solely on AvcI depletion.
• The system's effectiveness against phages correlates with their replication cycle length.
• This study provides novel insights into TA system-mediated phage defense mechanisms.