Host immune stress reveals a role for potassium homeostasis in Pseudomonas aeruginosa aggregate stability

Pseudomonas aeruginosa (Pa) forms multicellular aggregates during chronic airway infection, yet the physiological processes that regulate aggregate organization and dispersal remain incompletely understood. Here, we investigated how Pa aggregates respond to human neutrophil elastase (HNE), a host-derived protease abundant in the cystic fibrosis airway. Transcriptomic analysis of HNE-exposed aggregates identified strong induction of the kdpFABC high-affinity potassium transport system, with greater induction in aggregate than planktonic populations. Functional analysis of kdpA revealed a broader role in aggregate physiology: loss of kdpA increased total biomass while reducing average aggregate volume and accelerating dispersal, including in the absence of HNE. Genetic complementation restored key kdpA-dependent phenotypes, whereas co-culture with wild-type cells did not rescue the mutant. Increasing extracellular potassium modified aggregate volume, biomass, and dispersal in the kdpA mutant but did not uniformly restore these phenotypes to wild-type levels, demonstrating that kdpA-dependent aggregate behavior is potassium-responsive. Together, these findings identify KdpA as a link between potassium homeostasis and Pa aggregate behavior and suggest that host-derived stress increases engagement of a homeostatic system that contributes to the coordination of population growth, aggregate organization, and dispersal.