Genomic and phenotypic diversification of <i>Pseudomonas aeruginosa</i> during sustained exposure to a ciliate predator

Many bacterial pathogens spend much of their evolutionary history outside hosts, where they face intense ecological pressures such as predation. How these pressures shape pathogen evolution and disease potential remains unclear. Using experimental evolution, genomics, and phenotypic analyses, we show that prolonged exposure to a eukaryotic predator drives predictable genetic and phenotypic changes in the opportunistic pathogen <i>Pseudomonas aeruginosa</i> . Predator exposure altered regulatory, metabolic, and virulence-associated pathways, yet much adaptation was shared with predator-free populations, highlighting the dominant role of abiotic environments. Although predator-driven evolution reshaped traits linked to motility and growth, its effects on virulence were modest and context dependent. These findings clarify how environmental interactions influence pathogen evolution and underscore the importance of studying pathogens across diverse ecological settings.