Within-host evolution decreases virulence in an opportunistic bacterial pathogen
Lauri Mikonranta1, Johanna Mappes2, Jouni Laakso3,4
1Centre of Excellence in Biological Interactions, Department of Biological and Environmental Science, University of Jyväskylä, P.O. Box 35, 40014, Jyväskylä, Finland. lauri.mikonranta@jyu.fi.
BMC Evolutionary Biology
|August 19, 2015
Summary
Opportunistic pathogens like Serratia marcescens db11 can evolve reduced virulence when adapting to hosts, even without transmission constraints. This adaptation may involve immune evasion or trade-offs from fluctuating environments.
Area of Science:
- Evolutionary biology
- Microbial pathogenesis
- Host-pathogen interactions
Background:
- Pathogen evolution is often linked to host transmission efficiency.
- Opportunistic pathogens can survive outside hosts, facing different selection pressures.
- Conflicting selection pressures may shape virulence in opportunistic pathogens.
Purpose of the Study:
- To investigate the role of within-host selection on virulence evolution in opportunistic pathogens.
- To compare virulence of Serratia marcescens db11 after evolution within hosts versus in an external environment.
Main Methods:
- Sequential infection of Drosophila melanogaster with Serratia marcescens db11.
- Experimental evolution of the pathogen within hosts and in an outside-host environment.
- Comparison of bacterial life-history traits and virulence between evolved strains.
Main Results:
- The pathogen adapted to both host and external environments, altering traits like motility and growth rate.
- Selection within hosts led to decreased virulence without reducing bacterial load.
- External environment selection maintained ancestral virulence levels.
Conclusions:
- Within-host adaptation does not inevitably increase virulence, even without transmission limits.
- Attenuated virulence may result from immune evasion or trade-offs in fluctuating environments.
- Opportunistic pathogen life cycles can drive evolution towards lower virulence.
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