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Negative frequency-dependent selection and asymmetrical transformation stabilise multi-strain bacterial population
Gabrielle L Harrow1, John A Lees1, William P Hanage2
1MRC Centre for Global Infectious Disease Analysis, Department of Infectious Disease Epidemiology, Imperial College London, Norfolk Place, London, W2 1PG, UK.
The ISME Journal
|January 7, 2021
Summary
Negative frequency-dependent selection (NFDS) combined with asymmetrical recombination explains how Streptococcus pneumoniae strains co-exist. This model prevents genome loss and maintains bacterial diversity within host populations.
Area of Science:
- Microbiology
- Evolutionary Biology
- Population Genetics
Background:
- Streptococcus pneumoniae exists as diverse strains with distinct genomes co-circulating within hosts.
- Vaccine-associated dynamics suggest multi-locus negative frequency-dependent selection (NFDS) maintains S. pneumoniae strain variation.
- Previous models explored NFDS's role in stabilizing multi-strain populations but struggled with recombination's impact.
Purpose of the Study:
- To investigate the combined effects of multi-locus NFDS and different recombination models on bacterial population structure.
- To determine if asymmetrical recombination can explain the maintenance of distinct bacterial strains.
- To model the evolutionary dynamics underlying the co-existence of Streptococcus pneumoniae strains.
Main Methods:
- Utilized long-term simulations of bacterial population evolution.
- Compared outcomes of multi-locus NFDS with symmetrical versus asymmetrical recombination.
- Analyzed population structure, genetic variation, and fitness based on genomic data.
Main Results:
- Symmetrical recombination under NFDS led to unstructured populations.
- Asymmetrical recombination, favoring deletion over insertion, successfully recreated distinct strains.
- This combination resulted in outbreeding depression, where recombinants with reduced genomes had lower fitness, thus maintaining strain separation.
Conclusions:
- The combination of multi-locus NFDS and asymmetrical recombination effectively models the emergence and maintenance of bacterial strains.
- Asymmetrical recombination, potentially common in bacteria, is crucial for understanding strain co-existence.
- This model provides a plausible mechanism for the long-term stability of diverse bacterial populations within a niche.
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