Pseudomonas aeruginosa biofilm deficient mutant experiences parallel evolution during chronic infection

In our prior work we used a porcine full-thickness thermal injury model to identify beneficial mutations that promote P. aeruginosa persistence in this model of chronic infection (Gloag et al. 2019-PRJNA491911; Marshall et al. 2021 - PRJNA633671). Using variant colony morphology as an indicator for adaptation, we identified hyperbiofilm variants, specifically rugose small-colony variants (RSCVs), as the only variant colony phenotype to emerge across the 28 day infection (Gloag et al. 2019, PRJNA491911). Whole genome sequencing revealed that mutations in the wsp chemosensory system were the first mutations leading to the RSCV phenotype that were selected (Gloag et al. 2019, PRJNA491911). In the current study, we were interested in identifying other pathways under evolutionary selection and the fitness benefits of these mutations, during chronic infection. Particularly of interest here are mutations that allow P. aeruginosa to compensate for the deletion of psl and pel while still having high cyclic-di-GMP levels. The background strain for all isolates was a mutant where wspF and psl and pel operons were removed from the genome.