Iron starvation induced by vacidobactin A impairs the growth of pyoverdine-deficient Pseudomonas aeruginosa

ABSTRACT Iron acquisition is a crucial step for bacterial survival that shapes bacterial fitness and ecological interactions within microbial communities. Pseudomonas aeruginosa , an opportunistic clinical and environmental bacterium, relies on high-affinity siderophores such as pyoverdines to scavenge iron. Understanding these pathways provides vital insights into siderophore specificity, bacterial resource competition, and iron metabolism in bacteria. Here, we report vacidobactin A (VacA), a siderophore produced by the soil bacterium Variovorax paradoxus , identified through a screen of natural product extracts targeting a clinical multi-drug-resistant strain of P. aeruginosa . Rather than functioning as a direct antimicrobial agent, VacA impairs the growth of P. aeruginosa by imposing iron starvation. This is observed exclusively in strains that are unable to produce pyoverdine, their native siderophore. To determine whether VacA-mediated inhibition resulted from restricted access to iron, we heterologously expressed a TonB-dependent transporter from V. paradoxus in a pyoverdine- and pyochelin-deficient P. aeruginosa strain. Transporter expression enabled utilization of VacA-bound iron and restored growth, demonstrating that the antagonistic effect of VacA is governed by selective siderophore recognition and uptake rather than iron sequestration alone. Additionally, VacA synergized with thiostrepton, which hijacks pyoverdine receptors to enter the cell and inhibit protein synthesis. This investigation demonstrates how environmental microorganisms exploit siderophore specificity to compete for iron and establish antagonistic relationships within microbial communities. IMPORTANCE Iron acquisition is fundamental to bacterial survival and shapes ecological interactions within microbial communities, yet the mechanistic principles governing siderophore specificity and iron competition remain incompletely understood. Here, we demonstrate that vacidobactin A, a siderophore produced by Variovorax paradoxus , suppresses P. aeruginosa growth by limiting iron availability, particularly in strains deficient in pyoverdine production. By demonstrating that heterologous expression of a TonB-dependent transporter restores iron utilization from vacidobactin A, we establish that siderophore-mediated antagonism is governed by selective recognition and uptake pathways. Furthermore, the synergy between vacidobactin A and thiostrepton illustrates how siderophore systems integrate with other cellular vulnerabilities. These findings illuminate fundamental principles of bacterial resource competition and highlight how environmental microorganisms exploit iron metabolism as a competitive strategy, advancing our understanding of microbial community dynamics and bacterial physiology.