Biophysical basis of filamentous phage tactoid-mediated antibiotic tolerance in P. aeruginosa

Area of Science:

• Microbiology
• Structural Biology
• Biophysics

Background:

• Inoviruses are filamentous bacteriophages infecting diverse prokaryotes.
• These phages self-assemble into liquid-crystalline tactoids, protecting bacterial cells in Pseudomonas aeruginosa biofilms from antibiotics.

Purpose of the Study:

• To investigate the structural, biophysical, and protective properties of tactoids formed by P. aeruginosa phage Pf4 and Escherichia coli phage fd.
• To understand how phage geometry and packing density influence tactoid morphology and emergent properties.

Main Methods:

• Cryo-electron microscopy (cryo-EM) to determine the structure of the fd phage capsid.
• Comparative analysis of tactoid formation, morphology, and protective capabilities of Pf4 and fd phages.
• Assessment of the diffusion barrier formed by tactoids against antibiotic treatment.

Main Results:

• Cryo-EM revealed distinct biochemical properties of the fd phage capsid compared to Pf4.
• Pf4 and fd phages formed tactoids with different morphologies due to variations in phage geometry and packing density.
• Tactoids formed by both phages demonstrated protective effects against antibiotics for rod-shaped bacteria.
• Direct association with tactoids was essential for bacterial protection, confirming the formation of a diffusion barrier.

Conclusions:

• Inovirus tactoids exhibit distinct structural and emergent properties based on phage characteristics.
• Tactoids serve as effective diffusion barriers, protecting bacteria from external threats like antibiotics.
• This study enhances understanding of how filamentous molecules contribute to bacterial defense in biofilms and host-associated infections.