Surprise: infected bacteria fight back with “hidden” genes that halt cell growth, slow viral spread

Researchers have uncovered a surprising way bacteria defend themselves: when a bacterium is infected, bacterial enzymes that copy genetic information from RNA into DNA synthesize genes whose protein products help shut down cell growth. This prevents further viral spread in the neighboring bacterial population. The results highlight the potential for other “hidden” genes, like the one found here, to be unearthed in different biological contexts. Bacteria defend themselves from viral infection using diverse immune systems, some of which target and degrade foreign DNA, while others, including defense-associated reverse transcriptase (DRT) systems, take advantage of DNA synthesis. But how the latter approach leads to antiviral defense – including through DNA products produced – remains largely unknown. Focusing on a DRT system from the bacteria K. pneumoniae, Stephen Tang and colleagues discovered that when K. pneumoniae cells were infected with a phage, the DRT2 reverse transcriptases used RNA templates to synthesize a new gene, which the authors dubbed “neo.” Using mass spectrometry, the authors detected Neo peptides in phage-infected cells. The peptides’ presence halted cell growth and restricted viral spread, they say. “It is the Neo protein, we propose,” say the authors, “that acts as the effector arm of the immune system by rapidly arresting cell growth and inducing programmed dormancy, thus protecting the larger bacterial population from the spread of phage.”