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. 2006 Jul 7:4:21.
doi: 10.1186/1741-7007-4-21.

Cooperation and virulence in acute Pseudomonas aeruginosa infections

Freya Harrison  1 , Lucy E Browning, Michiel Vos, Angus Buckling
Affiliations

Cooperation and virulence in acute Pseudomonas aeruginosa infections

Freya Harrison et al. BMC Biol. .

Abstract

Background: Efficient host exploitation by parasites is frequently likely to depend on cooperative behaviour. Under these conditions, mixed-strain infections are predicted to show lower virulence (host mortality) than are single-clone infections, due to competition favouring non-contributing social 'cheats' whose presence will reduce within-host growth. We tested this hypothesis using the cooperative production of iron-scavenging siderophores by the pathogenic bacterium Pseudomonas aeruginosa in an insect host.

Results: We found that infection by siderophore-producing bacteria (cooperators) results in more rapid host death than does infection by non-producers (cheats), and that mixtures of both result in intermediate levels of virulence. Within-host bacterial growth rates exhibited the same pattern. Crucially, cheats were more successful in mixed infections compared with single-clone infections, while the opposite was true of cooperators.

Conclusion: These data demonstrate that mixed clone infections can favour the evolution of social cheats, and thus decrease virulence when parasite growth is dependent on cooperative behaviours.

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Figures

Figure 1
Figure 1
Time to death in hours of waxmoth larvae inoculated with pure cooperator, pure cheat or mixed clone infections of P. aeruginosa. Mixed inocula contained cheats and cooperators in a 1:1 ratio. Error bars show ± one standard error.
Figure 2
Figure 2
The effect of single versus mixed cooperator and cheat infections on the number of bacterial doublings (per gram fresh weight). Mixed inocula contained cheats and cooperators in a 1:1 ratio. Error bars show ± one standard error.
Figure 3
Figure 3
The number of doublings (per gram fresh weight) or cooperator (black) and cheat (white) clones in single and mixed infections. Mixed inocula contained cheats and cooperators in a 1:1 ratio. Error bars show ± one standard error.
Figure 4
Figure 4
The relative fitness of the cheat in mixed infections decreases as its frequency in the inoculum increases. Error bars show ± one standard error.
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