Calprotectin protectsStaphylococcus aureusin coculture withPseudomonas aeruginosaby attenuating quorum sensing and decreasing the production of pseudomonal antimicrobials

Pseudomonas aeruginosaandStaphylococcus aureuscause debilitating polymicrobial infections in diverse patient populations. Studies of these bacterial pathogens in coculture have shown that environmental variables including Fe availability and the host-defense protein calprotectin (CP) impact coculture dynamics. To decipher how CP modulates interactions betweenP. aeruginosaandS. aureus, we employed dual-species RNA-seq to examine the transcriptional responses of both pathogens in coculture to CP treatment and metal depletion. Analysis of these responses revealed that, for bothP. aeruginosaandS. aureus, CP treatment not only induced gene expression changes consistent with single- and multi-metal starvation responses, but also induced gene expression changes that were not observed under metal limitation. ForP. aeruginosa, CP treatment induced gene expression changes pointing to a shift in chorismate flux away from alkylquinolone and phenazine biosynthesis towards folate biosynthesis. These observations were consistent with decreased production of alkylquinolones byP. aeruginosa, including the potent anti-staphylococcal alkylquinolone N-oxides. CP treatment afforded perturbed levels of two quorum sensing molecules, 3-oxo-C₁₂-homoserine lactone and C₄-homoserine lactone, produced byP. aeruginosa. In addition, CP treatment enhanced the ability ofS. aureusto mount Fe starvation responses and causedS. aureusto express host virulence genes. This analysis illuminated physiological consequences of CP treatment that extend beyond metal starvation and that these consequences impact interspecies interactions. Our findings provide a working model in which CP effectively disarmsP. aeruginosaby inhibiting the production of anti-staphylococcal factors and boosts the ability ofS. aureusto protect itself from attack.