Interplay between the mechanics of bacteriophage fibers and the strength of virus-host links

TL;DR

This study investigates the mechanical properties of bacteriophage fibers, revealing how three fibers provide sufficient strength to secure the virus to bacteria, supported by high-resolution imaging and finite element analysis.

Contribution

The paper combines atomic force microscopy and finite element modeling to explain why bacteriophages use exactly three fibers for host attachment, linking mechanics to biological function.

Findings

Radial stiffness of gp37 fibers is ~0.08 N/m

Breaking force of fibers is ~120 pN

Young's modulus of fibers is ~20 MPa

Abstract

Viral fibers play a central role in many virus infection mechanisms since they recognize the corresponding host and establish a mechanical link to its surface. Specifically, bacteriophages have to anchor to bacteria through the fibers surrounding the tail before starting the viral DNA translocation into the host. The protein gene product (gp) 37 from bacteriophage T4 long tail fibers forms a fibrous parallel homotrimer located at the distal end of the long tail fibers. Biochemical data indicate that, at least three of these fibers are required for initial host cell interaction, but do not reveal why three and no other number. By using Atomic Force Microscopy we obtained high-resolution images of gp37 fibers adsorbed on mica substrate in buffer conditions and probed their local mechanical properties. Our experiments of radial indentation at the nanometer scale provided a radial stiffness of ~0.08 N/m and a breaking force of ~120 pN. In addition, we performed Finite Element Analysis and determined a Young's modulus of ~20 MPa. From these mechanical parameters, we hypothesize that three viral fibers provide enough mechanical strength to prevent a T4 virus from being detached from the bacteria by the viral particle Brownian motion, delivering a biophysical justification of the previous biochemical data.