GELIFES Seminars - Sandra Breum Andersen

Sandra Breum Andersen (University of Copenhagen)

Social interactions drive evolution of pathogenic bacteria

All of life is social, from genes cooperating to form organisms, to animals cooperating to form societies. Omic approaches offer exceptional opportunities to solve major outstanding problems in the study of how social interactions contribute to evolution. A challenge is to apply these approaches to a wider range of non-model organisms, and to move from exploratory analyses to the testing of evolutionary theory. I will present work on the evolution of pathogenic bacteria causing long-term infections of cystic fibrosis patients, using a large collection of longitudinally sampled Pseudomonas aeruginosa isolates. P. aeruginosa can acquire iron through cooperative and private mechanisms, using specific receptors for direct uptake or uptake via cooperative public goods. With whole genome sequencing and phenotypic assays we identify a shift in iron acquisition strategy during infection, from cooperative to private uptake. Loss of cooperation during infection has been suggested to be a host adaptation. Yet experimental work shows that cheats may invade a population of cooperators, even if this leads to extinction in the long run. By analysing the order of mutations across and within iron uptake systems we disentangle the effects of social interactions and host adaptation. We show that cooperation is favoured at the initiation of infection, and even frequently increased. This, however, facilitates the invasion of cheats and the breakdown of cooperation. In response, a private uptake system is upregulated – but not without costs. We find that the upregulation is detrimental if iron availability increases during infection, which likely explain subsequent accumulation of mutations in the receptor gene. With this we demonstrate the power of genomics for identifying social interactions, in a natural population of clinically important pathogenic bacteria.

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