Navigating a Fine Balance: Point-Mutant Cheater Viruses Disrupt the Viral Replication Cycle.

Area of Science:

• Virology
• Evolutionary Biology
• Molecular Biology

Background:

• Cheater viruses possess a replication defect but exhibit a selective advantage during coinfection with wild-type (WT) viruses.
• Two point-mutant cheaters of the MS2 bacteriophage have been previously identified.
• Understanding the full range of cheater virus evolution is crucial for comprehending viral dynamics.

Purpose of the Study:

• To explore the potential repertoire of cheater MS2 bacteriophage viruses.
• To investigate the evolutionary mechanisms and genetic basis of cheater virus emergence.

Main Methods:

• Experimental evolution of MS2 bacteriophage at a high multiplicity of infection.
• Identification and characterization of emergent point-mutant cheater viruses.
• Genomic analysis to identify secondary mutations and their locations.

Main Results:

• A third distinct point-mutant cheater MS2 bacteriophage was discovered, arising in multiple independent experimental replicas.
• Each of the three identified cheaters disrupts viral replication through unique defect + advantage mechanisms.
• Point-mutant cheaters acquired secondary mutations that complemented initial defects, often located near the original mutation site due to overlapping genomic functions.

Conclusions:

• Viruses with dense, functionally overlapping genomes are prone to evolving point-mutant cheaters.
• Cheater mutations can readily alter the complex balance of the viral replication cycle.
• The proximity of cheater and secondary mutations highlights the pleiotropic effects of mutations in overlapping genomic regions.