Abstract
The evolution of host–parasite interactions could be affected by intraspecies variation between different host and parasite genotypes. Here we studied how bacterial host cell‐to‐cell signaling affects the interaction with parasites using two bacteria‐specific viruses (bacteriophages) and the host bacterium Pseudomonas aeruginosa that communicates by secreting and responding to quorum sensing (QS) signal molecules. We found that a QS‐signaling proficient strain was able to evolve higher levels of resistance to phages during a short‐term selection experiment. This was unlikely driven by demographic effects (mutation supply and encounter rates), as nonsignaling strains reached higher population densities in the absence of phages in our selective environment. Instead, the evolved nonsignaling strains suffered relatively higher growth reduction in the absence of the phage, which could have constrained the phage resistance evolution. Complementation experiments with synthetic signal molecules showed that the Pseudomonas quinolone signal (PQS) improved the growth of nonsignaling bacteria in the presence of a phage, while the activation of las and rhl quorum sensing systems had no effect. Together, these results suggest that QS‐signaling can promote the evolution of phage resistance and that the loss of QS‐signaling could be costly in the presence of phages. Phage–bacteria interactions could therefore indirectly shape the evolution of intraspecies social interactions and PQS‐mediated virulence in P. aeruginosa.
Highlights
The evolution of host–parasite interactions is sensitive to the underlying characteristics of the coevolving host and parasite genotypes (Lively & Dybdahl, 2000; Sorci, Moller, & Boulinier, 1997; Thompson, 2005; Vrijenhoek, 1986)
We found that a quorum sensing (QS)-signaling-positive strain evolved higher levels of phage resistance during a short-term selection experiment
This difference was unlikely to be driven by demographic effects as the nonsignaling strains reached generally higher population densities in the absence of phages—resistance mutations arise generally faster in large populations due high mutation supply rates and frequent host–parasite encounter rates (Lopez-Pascua & Buckling, 2008)
Summary
The evolution of host–parasite interactions is sensitive to the underlying characteristics of the coevolving host and parasite genotypes (Lively & Dybdahl, 2000; Sorci, Moller, & Boulinier, 1997; Thompson, 2005; Vrijenhoek, 1986). Co-evolutionary dynamics can follow either an arms race or fluctuating selection dynamics depending on the interacting parasite species (Betts, Kaltz, & Hochberg, 2014), while considerable variation exists in host species sensitivity to a one given parasite species (Thompson, 2005). This is especially true with bacteria, where small differences between different genotypes can have large effects on fitness. Additional experiments were conducted to study whether activation of different QS systems with exogenously added signal molecules affects bacterial growth in the presence of a phage
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