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Adaptive molecular evolution for 13,000 phage generations: a possible arms race
Holly A Wichman1, Jack Millstein, J J Bull
1Department of Biological Sciences, University of Idaho, Moscow, 83844-3051, USA. hwichman@uidaho.edu
Genetics
|February 3, 2005
Summary
Bacteriophage phiX174 evolved rapidly over 180 days, showing sustained adaptive molecular evolution. This suggests an ongoing genomic arms race driven by host-phage interactions, rather than adaptation to a static environment.
Area of Science:
- Microbiology
- Evolutionary Biology
- Genetics
Background:
- Bacteriophage phiX174 is a well-studied model organism.
- Understanding viral evolution is crucial for predicting pathogen adaptation.
- Previous studies on phage evolution have been of shorter duration.
Purpose of the Study:
- To investigate the long-term molecular evolution of bacteriophage phiX174.
- To quantify the rate and nature of nucleotide substitutions over an extended period.
- To explore the adaptive significance of genetic changes in a continuous culture system.
Main Methods:
- Bacteriophage phiX174 was cultured on a continuous supply of sensitive hosts for 180 days.
- Approximately 13,000 phage generations were monitored.
- Nucleotide substitutions were analyzed over time and across different genes.
Main Results:
- A sustained, high rate of nucleotide substitution (approx. 0.2% per 20 days) was observed, accumulating in a clock-like manner.
- Rates of silent and missense substitutions varied, with a high rate of parallel substitutions early on.
- Most observed genetic changes, including silent ones, appeared to be adaptive.
Conclusions:
- The sustained adaptive evolution challenges models of adaptation to constant environments.
- Continuous molecular evolution suggests an indefinite arms race between phages and hosts.
- High levels of co-infection and intra-host genome competition likely drive this ongoing evolutionary process.