Effect of Genetic Background on Diversification of Pseudomonas aeruginosa

Abstract

Life on Earth is incredibly diverse. The process of diversification that gives rise to this diversity is not the same for all lineages. Diversification is often driven by ecological opportunity. Pseudomonas aeruginosa is an opportunistic pathogen present in a variety of environments that causes chronic lung infections in cystic fibrosis (CF) patients. It diversifies rapidly within the CF lung and CF lung-like environments. Here we aim to assess both ecological and genetic factors in diversification of several strains of P. aeruginosa. We evolved 12 replicate populations of 8 different strains of P. aeruginosa in a nutritionally complex (LB) and simple environment (MIN) for 750 generations. We then measured diversity over time by observing the number of colony morphologies in each population every 250 generations. We also measured competitive fitness relative to the ancestor for endpoint populations. To provide a more complete analysis, phylogeny was factored into our statistical models. First, we found no significant differences in diversification between populations evolved in LB versus MIN media. Ancestor population size had no significant effect on diversification. We found that in both selection environments, CF strains diversified less than environmental strains, but this difference was marginally significant and only present when comparing these two niches directly and excluding acute strains. Finally, we found no correlation between gains in fitness and endpoint diversity. Our results suggest that diversification is limited by niche specialization (domestication) of P. aeruginosa to the CF lung.