Pseudomonas aeruginosasenses and responds to epithelial potassium flux via Kdp operon to promote biofilm biogenesis

Abstract

AbstractMucosa-associated biofilms are associated with many human disease states, but the mechanisms by which the host promotes biofilm biogenesis remain unclear. In chronic respiratory diseases like cystic fibrosis (CF),Pseudomonas aeruginosaestablishes chronic infection through biofilm formation.P. aeruginosacan be attracted to interspecies biofilms through potassium currents emanating from the biofilms. We hypothesized thatP. aeruginosacould, similarly, sense and respond to the potassium efflux from human airway epithelial cells (AECs) to promote biofilm biogenesis. Using respiratory epithelial co-culture biofilm imaging assays ofP. aeruginosagrown in association with CF bronchial epithelial cells (CFBE41o-), we found thatP. aeruginosabiofilm biogenesis was increased by potassium efflux from AECs, as examined by potentiating large conductance potassium channel, BKCa(NS19504) potassium efflux. This phenotype is driven by increased bacterial attachment and increased coalescence of bacteria into aggregates. Conversely, biofilm formation was reduced when AECs were treated with a BKCablocker (paxilline). Using an agar-based macroscopic chemotaxis assay, we determined thatP. aeruginosachemotaxes toward potassium and screened transposon mutants to discover that disruption of the high-sensitivity potassium transporter, KdpFABC, and the two-component potassium sensing system, KdpDE, reducesP. aeruginosapotassium chemotaxis. In respiratory epithelial co-culture biofilm imaging assays, a KdpFABCDE deficientP. aeruginosastrain demonstrated reduced biofilm growth in association with AECs while maintaining biofilm formation on abiotic surfaces. Collectively, these data suggest thatP. aeruginosabiofilm formation can be increased by attracting bacteria to the mucosal surface via a potassium gradient and enhancing coalescence of single bacteria into microcolonies through aberrant AEC potassium efflux sensed through the bacterial KdpFABCDE system. These findings suggest that electrochemical signaling from the host can amplify biofilm biogenesis, a novel host-pathogen interaction, and that potassium flux could be a potential target for therapeutic intervention to prevent chronic bacterial infections in diseases with mucosa-associated biofilms, like CF.Author SummaryBiofilm formation is important forPseudomonas aeruginosato cause chronic infections on epithelial surfaces during respiratory diseases, like cystic fibrosis (CF). The host factors that promote biofilm formation on host surfaces are not yet fully understood. Potassium signals from biofilms can attractP. aeruginosa, but it is unknown if potassium from the human cells can influenceP. aeruginosabiofilm formation on a host surface. We found thatP. aeruginosabiofilm formation on human airway cells can be increased by the potassium currents from airway cells, and determined bacterial genes related to potassium uptake and sensing that contribute to biofilm formation on airway cells. These findings suggest thatP. aeruginosacan respond to host potassium signals by forming increased biofilm and that reducing chronic infections may be accomplished by reducing potassium coming from airway cells or blocking the bacterial proteins responsible for the biofilm enhancement by potassium currents.