A continuous evolution system for contracting the host range of bacteriophage T7.

Area of Science:

• Microbiology
• Virology
• Bacteriophage Biology

Background:

• Bacteriophage T7 recognizes bacterial hosts using receptor-binding proteins (RBPs) on its tail fibers.
• RBPs bind to specific lipopolysaccharide (LPS) structures on the host cell surface.
• Previous research focused on phage host range expansion, with limited studies on host range contraction.

Purpose of the Study:

• To investigate bacteriophage T7's ability to alter its host range when exposed to a mixed population of bacterial hosts.
• To understand the role of receptor-binding proteins (RBPs) in host range modification.
• To explore potential applications of host range contraction in bacterial detection and elimination.

Main Methods:

• Culturing bacteriophage T7 in the presence of a permissive host and multiple restrictive bacterial strains with varying LPS structures.
• Monitoring phage evolution and host range changes over successive growth cycles.
• Sequencing genes encoding RBPs to identify mutations responsible for altered host specificity.

Main Results:

• Phage T7 populations gradually evolved to avoid recognition of restrictive bacterial strains when grown in a mixed-host environment.
• This host range contraction was consistently observed across experiments with different permissive hosts.
• Sequencing revealed mutations in RBP genes that altered phage specificity, leading to avoidance of previously restrictive hosts.

Conclusions:

• Receptor-binding proteins (RBPs) play a crucial role in narrowing bacteriophage T7's host range, particularly in complex host environments.
• The observed host range contraction demonstrates an adaptive mechanism to avoid futile infections.
• This system offers a potential platform for engineering bacteriophages for targeted bacterial serotype detection or elimination.