Na+ transporters critical for infection and adaptation of Pseudomonas aeruginosa in Drosophila melanogaster

Abstract

We found that the Na+-NQR deletion produced no change in the bacterium’s ability to kill the flies, while the Mrp deletion produced a significantly reduced virulent rate in the bacterium. The reason for altered infectivity was not due to the altered pyocyanin production or biofilm formation because there was no observed correlation with mortality. Bacterial load assays measuring viable P. aeruginosa in the infected fly showed that the Mrp deletion mutant was unable to grow as well in the fly as wild type and the Na+-NQR mutant. We conclude that the ability to kill is dependent on the ability to survive and grow in the host environment as Drosophila mortality was correlated with bacterial growth in the fly. These findings support Mrp’s role in Na+ regulation as crucial in infection and colonization in Drosophila.

Pseudomonas aeruginosa is a highly opportunistic pathogen that has the ability to adapt to a wide variety of host environments, a characteristic that is crucial in causing infections particularly in individuals with weakened immune systems. In order to understand P. aeruginosa virulence, the underlying physiology that enables this bacterium to survive and spread in an environment, and at the sites of infection, needs to be better understood. P. aeruginosa’s robust adaptability is hypothesized to be due to the bacterium’s diverse respiration and ion transporters. In P. aeruginosa, multiple ion pumps have the biological role of transporting Na+ ions. These enzymes are responsible for creating ion gradients that are necessary for maintenance of ion homeostasis, ATP synthesis, locomotion and the transport of nutrients. To determine individual roles of the Mrp and Na+-NQR proteins in infection, we infected Drosophila melanogaster with single deletion mutants of these enzymes and assessed their abilities to colonize and kill the host. In order to measure P. aeruginosa acute infection, we developed a fly pricking assay that results in a short infection period prior to death.