Biology subjects

Nolan, E. M.

Publications and source records attributed to Nolan, E. M..

2 recordsLinked to original sources

bioRxiv2026

Metal-independent effects of calprotectin on cocultures of Pseudomonas aeruginosa and Staphylococcus aureus involve alkylquinolone production

The current working model of the innate immune protein calprotectin (CP) focuses on its metal-sequestering activity, which contributes to host defense against infection. Recently, CP was reported to enhance the survival of Staphylococcus aureus in coculture with Pseudomonas aeruginosa in a metal-independent manner. This prior work indicated that the CP protein scaffold, even in the absence of its metal-binding sites, possesses activities that impact interspecies dynamics between these bacterial pathogens. In this study, we employ {Delta}{Delta}, a CP variant lacking both functional metal-binding sites, to assess the responses of each pathogen to the CP protein scaffold in monoculture and coculture. Using dual-species transcriptomics, we report that {Delta}{Delta} treatment induced gene expression changes indicative of cell envelope modifications for both P. aeruginosa and S. aureus during coculture. The presence of the CP protein scaffold also attenuated the production of the quorum sensing molecule C4-homoserine lactone and the anti-staphylococcal alkylquinolone (AQ) metabolite 2-heptyl-4-hydroxyquinoline N-oxide. Cocultures with S. aureus and P. aeruginosa mutants defective in AQ biosynthesis demonstrated that AQ production was required for {Delta}{Delta} to impact expression of membrane remodeling genes in both species during coculture. Furthermore, we showed that in the absence of AQ production, the effect of CP on S. aureus in coculture resembled that of Fe depletion. Collectively, our findings demonstrate that the functional versatility of CP extends beyond multi-metal sequestration and that its intertwined metal-dependent and -independent activities have important consequences for bacterial physiology and polymicrobial interactions. IMPORTANCERecent studies of the innate immune protein calprotectin (CP), which is known for its metal-sequestering ability and contributions to nutritional immunity, have uncovered that the protein also exerts metal-independent activities on bacterial pathogens. In this work, we investigate the metal-independent effects of CP on the interspecies dynamics of Pseudomonas aeruginosa and Staphylococcus aureus, two high-priority pathogens that co-colonize various polymicrobial infection sites. We report that the ability of the CP protein scaffold to attenuate the anti-staphylococcal activity of P. aeruginosa results from perturbed quorum sensing and reduced production of alkylquinolone (AQ) metabolites. We further show that pseudomonal AQs contribute to cell envelope remodeling responses exhibited by both pathogens in the presence of the CP protein scaffold. These results afford an updated working model wherein both canonical metal-dependent and noncanonical metal-independent activities of CP elicit physiological changes in both pathogens, resulting in perturbed coculture dynamics.

microbiology↗

bioRxiv2025

Calprotectin protects Staphylococcus aureus in coculture with Pseudomonas aeruginosa by attenuating quorum sensing and decreasing the production of pseudomonal antimicrobials

Pseudomonas aeruginosa and Staphylococcus aureus cause 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 between P. aeruginosa and S. 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 both P. aeruginosa and S. 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. For P. 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 by P. 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 by P. aeruginosa. In addition, CP treatment enhanced the ability of S. aureus to mount Fe starvation responses and caused S. aureus to 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 disarms P. aeruginosa by inhibiting the production of anti-staphylococcal factors and boosts the ability of S. aureus to protect itself from attack. ImportanceThe innate immune protein calprotectin (CP) defends the host against bacterial pathogens by sequestering multiple essential nutrient metal ions at infection sites. In addition to this role in nutritional immunity, CP promotes the survival of Staphylococcus aureus in coculture with Pseudomonas aeruginosa, an effect that is independent of its metal-sequestering function. In this work, we sought to understand how CP modulates this interspecies interaction by evaluating the transcriptional responses of P. aeruginosa and S. aureus to CP and metal limitation in cocultures. Our study revealed that CP attenuates the ability of P. aeruginosa to attack S. aureus with anti-staphylococcal factors and enhances the capacity of S. aureus to withstand this assault, effects that are not recapitulated by metal limitation. This work provides new understanding of how CP modulates microbial interactions that are relevant to human health.

microbiology↗