Filamentous phage entry — A filamentous bacteriophage infects male E. coli by attaching specifically to which structure?

Introduction / Context:
Host recognition by bacteriophages depends on precise receptor binding. Filamentous phages (e.g., M13, fd) target the F pilus on “male” E. coli cells, which carry the F plasmid and express conjugative pili.

Given Data / Assumptions:

• Male E. coli cells present F pili on their surface.
• Filamentous phages initiate infection by binding the pilus tip.
• Attachment triggers DNA entry without lysing the host.

Concept / Approach:
The defining receptor for these phages is the F pilus tip. Binding and pilus retraction or dynamics promote delivery of the phage genome through the pilus into the bacterium, leading to chronic infection rather than immediate lysis.

Step-by-Step Solution:

Verification / Alternative check:
Classic M13 systems in molecular cloning rely on this pilus-specific entry mechanism.

Why Other Options Are Wrong:

• LPS/cell wall/membrane can be receptors for other phages, but not for filamentous F-specific phages.

Common Pitfalls:
Confusing F-pilus-dependent phages with LPS-binding tailed phages.

Final Answer:
the tip of the pilus