Protect thy host: Pf4 phages shield Pseudomonas aeruginosa from antibiotics.

Bacterial viruses or bacteriophages exert profound effects on host cell lifestyle and evolution. The prophage Pf4 in Pseudomonas aeruginosa is highly induced in biofilms and is shown to confer antibiotic resistance to the bacterium. A novel study has now revealed that Pf4 forms crystalline structures that serve to physically wall off antibiotics from the bacterium. This represents an entirely novel mechanism involving liquid-liquid phase separation in prokaryotic systems. Furthermore, the toxin-antitoxin system PfiAT, which is encoded within the prophage Pf4, represents a unique production mechanism for Pf4. Combined, these two studies broadened our knowledge on the antibiotic resistance mechanisms used by P. aeruginosa.