# Filamentous prophage Pf4 promotes genetic exchange in Pseudomonas aeruginosa

## TL;DR

A filamentous prophage called Pf4 helps Pseudomonas aeruginosa cells share genetic material, repair defects, and maintain community stability.

## Contribution

The Pf4 prophage is shown to be actively exchanged among P. aeruginosa cells, enabling defect repair and cost-sharing within the population.

## Key findings

- The Pf4 prophage is frequently exchanged within P. aeruginosa colonies, repairing defective Pf4.
- Pf4 trafficking occurs rapidly in biofilms, artificial sputum, and infected mouse lungs.
- Pf4 can package additional DNA, doubling its genome size and enhancing adaptability.

## Abstract

Filamentous prophages are widespread among bacteria and play crucial functions in virulence, antibiotic resistance, and biofilm structures. The filamentous Pf4 particles, extruded by an important pathogen Pseudomonas aeruginosa, can protect producing cells from adverse conditions. Contrary to the conventional belief that the Pf4-encoding cells resist reinfection, we herein report that the Pf4 prophage is reciprocally and commonly exchanged within P. aeruginosa colonies, which can repair defective Pf4 within the community. By labeling the Pf4 locus with antibiotic resistance and fluorescence markers, we demonstrate that the Pf4 locus is frequently exchanged within colony biofilms, in artificial sputum media, and in infected mouse lungs. We further show that Pf4 trafficking is a rapid process and capable of rescuing Pf4-defective mutants. The Pf4 phage is highly adaptable and can package additional DNA doubling its genome size. We also report that two clinical P. aeruginosa isolates are susceptible to the Pf4-mediated exchange, and the Pf5 prophage can be exchanged between cells as well. These findings suggest that the genetic exchanging interactions by filamentous prophages may facilitate defect rescue and the sharing of prophage-dependent benefits and costs within the P. aeruginosa community.

Microbial communities are crucial ecological entities with complex interactions, among which metabolites and genetic exchange can dictate community composition and stability. Previous studies have focused on metabolites excreted by one cell and used by another. Here, we demonstrate that the Pf4 prophage is frequently exchanged among P. aeruginosa cells, enabling the effective repair of Pf4-defective cells. Given that P. aeruginosa cells build better biofilms and gain increased virulence and antibiotic resistance at the cost of producing phage particles, Pf4 trafficking might effectively prevent potential cheating behaviors and ensure cost-sharing within the population.