These resistance mechanisms then place greater selection pressure on the infecting bacteriophages, which develop counter-strategies in a perpetual 'arms race' between virus and host. Toxin-antitoxin (TA) loci are widespread in bacteria and can confer multiple benefits, including resistance to bacteriophages.
The study by Otsuka and Yonesaki, published in this issue of Molecular Microbiology, describes a new plasmid-encoded TA system, lsoAB, which confers resistance to a dmd(-) mutant of bacteriophage T4 through the activity of the LsoA toxin.
Infections with wild-type T4, however, are unaffected as the Dmd protein acts as an alternative antitoxin to LsoA, thus preventing its anti-bacteriophage activity.
Dmd has also been shown to negate the activity of a related toxin, RnlA. This is a striking result indicating that Dmd can act as a promiscuous antitoxin, binding and inhibiting multiple toxin partners, when antitoxin activity is generally considered to be limited to a single cognate toxin.
This study is an exciting addition to both the bacteriophage resistance and TA fields, and suggests a greater role for TA system-based resistance and counter-resistance in the world's oldest predator-prey relationship.