A bacterial toxin-antitoxin system as a native defence element against RNA phages

Area of Science:

• Microbiology
• Virology
• Bacterial Genetics

Background:

• Bacteria possess diverse defense mechanisms against bacteriophages (phages).
• Existing antiphage systems primarily target DNA phages, leaving RNA phage defense mechanisms less understood.
• Bacterial toxin-antitoxin (TA) systems, known for cleaving intracellular RNA, present a potential but unexplored defense against RNA phages.

Purpose of the Study:

• To investigate the role of the MazEF toxin-antitoxin system in protecting *Escherichia coli* against RNA phages.
• To determine if bacterial RNA-degrading TA systems contribute to antiphage defense.

Main Methods:

• Experimental challenge of *Escherichia coli* strains with and without the native *mazEF* system against two RNA phage species.
• Assessment of bacterial population susceptibility and individual cell survival rates.
• Genomic analysis of RNA phages to identify potential MazF cleavage sites.

Main Results:

• The native presence of the *mazEF* system conferred moderate protection to *E. coli* populations against RNA phages.
• Individual *E. coli* cells with the *mazEF* system exhibited increased survival rates when exposed to RNA phages.
• Genomic analysis revealed an underrepresentation of the MazF cleavage site in infecting RNA phage genomes, suggesting evolutionary pressure against it.

Conclusions:

• RNA-degrading toxin-antitoxin systems, exemplified by MazEF, can function as a defense mechanism against RNA phages.
• These findings expand the known roles of TA systems beyond stress response and programmed cell death.
• The study highlights a potential evolutionary arms race between bacteria and RNA phages involving specific cleavage sites.