Evolution of bacteriophage T7 in a growing plaque

Area of Science:

• Microbiology
• Virology
• Evolutionary Biology

Background:

• Bacteriophage T7 amplification involves complex host-pathogen interactions.
• The emergence and selection of phage mutants are critical for understanding viral evolution.
• Host-expressed enzymes can influence phage adaptation and fitness.

Purpose of the Study:

• To spatially resolve the emergence and selection of bacteriophage T7 mutants.
• To investigate the evolutionary dynamics of phage mutants during high-multiplicity amplification.
• To determine the adaptive advantages conferred by genomic deletions in phage mutants.

Main Methods:

• Spatially resolved analysis of phage mutants within a growing plaque using stab sampling.
• Quantification of phage replication rates through one-step growth cultures.
• Characterization of mutant genomes, including deletions and gene content.

Main Results:

• Mutant phage T7, utilizing host-expressed T7 RNA polymerase, emerged at 10^8 replications and outgrew the wild type.
• Spatial analysis revealed differential selection rates of mutants along plaque radii, influenced by host range and restriction patterns.
• Identified mutants with genomic deletions up to 11%, including the gene for their own RNA polymerase.

Conclusions:

• Phage mutants can rapidly emerge and gain a selective advantage through genomic streamlining and efficient replication.
• Spatial heterogeneity within a plaque facilitates the selection of diverse mutant lineages.
• The study provides insights into the mechanisms of viral adaptation and evolution under strong selective pressure.