Molecular features underlying Pseudomonas aeruginosa persistence in human plasma

Pseudomonas aeruginosa, an opportunistic Gram-negative pathogen, is a leading cause of bacteremia with a high mortality rate. We recently reported that P. aeruginosa forms a persister-like sub-population of evaders in human plasma and blood. However, the molecular mechanisms underlying the formation of evaders remained unknown. Here, using a gain-of-function genetic screen, we examined the molecular determinants of P. aeruginosa persistence in plasma. We found that, among other factors, ATP and biotin availability greatly influence bacterial survival in plasma; mutants in pur and bio genes display higher tolerance and persistence, respectively. Electron microscopy combined with energy-dispersive X-ray spectroscopy (EDX) revealed the formation of polyphosphate granules upon incubation in plasma in several clinical strains, implying the bacterial response to a low-energy stress signal. Indeed, mutants with transposon insertions in ppk genes were eliminated in the plasma. Analysis of several steps of the complement cascade and exposure to an outer-membrane-impermeable drug, nisin, suggested that the mutants impede membrane attack complex (MAC) activity per se. Through this study, we shed light on P. aeruginosa response to the plasma conditions and discovered the multifactorial origin of bacterial resilience to MAC that provides a comprehensive picture of the complex interplay between P. aeruginosa and the human complement system.