Environmental redox conditions and strain variation define phenazine-mediated antagonism in co-infecting bacteria

Manuscript Description

Happy accidents happen all the time! In this study, we initially identified Pseudomonas aeruginosa in the gut of mice with low levels of Klebsiella pneumoniae colonization. Many years later, we characterized these strains and determined that a well-known mediator of P. aeruginosa interspecies bacterial competition, pyocyanin, was restricting K. pneumoniae growth. In it of itself, this was interesting, but not entirely novel. What was really interesting was that when we acquired a heterologous expression system in E. coli, we identified an expression strain that was deep red and completely bactericidal! This secondary metabolite, known as pyorubin, is one step before pyocyanin in its synthesis pathway. Even more interesting, we found that environmental oxygen and redox state tune its activity. As such, the effects of this and related molecules, including pyocyanin, depend on the environmental context in which P. aeruginosa and K. pneumoniae are competing. Finally, we tested the strength of our findings using a large cohort of clinical P. aeruginosa and K. pneumoniae isolates, as well as tested the activity of pyocyanin and pyorubin on a small set of diverse bacterial species.

Link

https://journals.plos.org/plosbiology/article?id=10.1371/journal.pbio.3003809

Abstract

Pseudomonas aeruginosa and Klebsiella pneumoniae are gram-negative opportunistic pathogens that frequently colonize the human body and are major causes of infection. These bacteria are often co-isolated in polymicrobial urinary tract and lung infections, the latter of which is associated with increased disease severity and worse clinical outcomes. Despite their overlapping niches and clinical relevance, little is known about how these two pathogens interact and how those interactions influence human health. Given the growing recognition that microbial interactions are key drivers of disease, we investigated how P. aeruginosa and K. pneumoniae influence one another. We discovered an antagonistic interaction in which P. aeruginosa restricts the growth of K. pneumoniae. This inhibition is driven by phenazine production in P. aeruginosa, specifically the secondary metabolites pyocyanin and pyorubin, which are both necessary and sufficient to suppress K. pneumoniae growth. Using a diverse set of clinical isolates, we found that this antagonism is strain-dependent. Both the susceptibility of K. pneumoniae to phenazines and the ability of P. aeruginosa to restrict K. pneumoniae growth varies between strains. Moreover, the necessity of phenazine production is specific to the site of infection. Together, these findings demonstrate that strain background and environmental context are critical determinants of pathogen interactions. These findings reveal that both strain background and environmental redox conditions govern the ecological rules of pathogen interaction, providing a framework for predicting outcomes.

Citation

Todd K, Schneider O, Lawrence JM, Aronoff JL, Witek B, Velázquez-Colón V, et al. (2026) Environmental redox conditions and strain variation define phenazine-mediated antagonism in co-infecting bacteria. PLoS Biol 24(5): e3003809. https://doi.org/10.1371/journal.pbio.3003809