Sublethal silver nanoparticle exposure promotes an Eut-dependent shift in Escherichia coli-Staphylococcus aureus competition.

Envelope-targeting antimicrobials are widely detected in wastewater and engineered water systems, yet their potential to reshape interspecies interactions through membrane-derived metabolites remains poorly understood. Here, we investigated whether sublethal silver nanoparticles (AgNPs) could bias competitive interactions between Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) toward more balanced coexistence. Repeated exposure to 0.5 mg/L AgNPs for 9 days increased the S. aureus/E. coli ratio threefold. In contrast, untreated co-cultures were dominated by E. coli, with 25% of lineages showing competitive exclusion and an E. coli/S. aureus ratio exceeding 105. During competition with S. aureus, E. coli activated ethanolamine (EA) utilization in bacterial micro compartments (Eut BMCs), resulting in extracellular accumulation of acetate and ammonium. Physiological assays identified nitrogen, rather than carbon, as the principal growth-promoting currency of this cross-feeding interaction. Deletion of eutBC in AgNP-exposed co-cultures abolished the coexistence phenotype and restored an outcome similar to that observed without AgNP exposure. In simulated eutrophic water, sublethal AgNPs also enhanced S. aureus survival through the E. coli Eut pathway, supporting the environmental relevance of this mechanism. Mass-matched Ag⁺ exposure neither induced EA utilization nor promoted more balanced coexistence. These findings indicate that sublethal envelope-targeting nanomaterials can alter microbial metabolism and competitive relationships in this two-species model, with potential implications for interactions in contaminated water systems.