Defence heterogeneity in host populations gives rise to pathogen diversity

We tested the role of defence heterogeneity on the evolution of pathogen genetic diversity. We passaged the opportunistic pathogen Pseudomonas aeruginosa through populations of the nematode Caenorhabditis elegans varying in genotypes and symbiont presence for 14 passages. The C. elegans genome encodes for genes involved in immune defence against pathogen infection. One member of this microbiome, Pseudomonas berkeleyensis, was found to improve C. elegans survival upon P. aeruginosa infection by priming host immunity. In this experiment, P. aeruginosa evolution occurred in C. elegans populations either comprised of identical hosts (homogeneous host populations) or comprised of different combinations of host genotypes and symbionts (heterogeneous host populations). The sequences here are the whole genomes of the evolved pathogens, as well as the ancestral clone/reference genome.