Parallel Evolution of Enhanced Biofilm Formation and Phage-Resistance in during Adaptation Process in Spatially Heterogeneous Environments.

An opportunistic pathogen has a versatile phenotype and high evolutionary potential to adapt to various natural habitats. As the organism normally lives in spatially heterogeneous and polymicrobial environments from open fields to the inside of hosts, adaptation to abiotic (spatial heterogeneity) and biotic factors (interspecies interactions) is a key process to proliferate. However, our knowledge about the adaptation process of in spatially heterogeneous environments associated with other species is limited. We show herein that the evolutionary dynamics of PAO1 in spatially heterogeneous environments with known to coexist in vivo is dictated by two distinct core evolutionary trajectories: (i) the increase of biofilm formation and (ii) the resistance to infection by a filamentous phage which is retained in the PAO1 genome. Hyperbiofilm and/or pili-deficient phage-resistant variants were frequently selected in the laboratory evolution experiment, indicating that these are key adaptive traits under spatially structured conditions. On the other hand, the presence of had only a marginal effect on the emergence and maintenance of these variants. These results show key adaptive traits of and indicate the strong selection pressure conferred by spatial heterogeneity, which might overwhelm the effect of interspecies interactions.