Biotechnological potential of silver nanoparticles synthesized by green method to control phytopathogenic bacteria: contributions from a proteomic analysis.

Silver nanoparticles (AgNPs) synthesized through green synthesis routes are widely used as antimicrobial agents due to their advantages such as biocompatibility, stability, sustainability, speed and cost-effectiveness. Although AgNPs appear to be more potent than silver ions, the mechanisms related to their antibacterial activity are not yet fully understood. The most common proposed mechanism of AgNPs' toxicity so far is the release of silver ions and/or specific functions of the particles. In this context, the present study aimed to investigate the mechanisms of action of AgNPs synthesized using noni fruit peels (Morinda citrifolia) against the phytopathogen Xanthomonas campestris pv. campestris (Xcc) through proteomics. Xcc was treated with AgNPs (32 µM), AgNO₃ (32 µM), or received no treatment (Ctrl - control condition), and its proteomic response was comprehensively characterized to elucidate the antimicrobial mechanisms of AgNPs in the phytopathogenic microorganism. A total of 352 differentially abundant proteins were identified. Most proteins were regulated in the AgNPs × Ctrl and AgNPs × AgNO₃ comparisons/conditions. When Xcc treated with 32 µM AgNPs were compared to controls, the results showed 134 differentially abundant proteins, including 107 increased and 27 decreased proteins. In contrast, when Xcc treated with 32 µM AgNO₃ were compared to Ctrl, the results showed only 14 differentially abundant proteins, including 10 increased proteins and 4 decreased proteins. Finally, when Xcc treated with 32 µM AgNPs were compared to Xcc treated with 32 µM AgNO₃, the results showed 204 differentially abundant proteins, including 75 increased proteins and 129 decreased proteins. Gene ontology enrichment analysis revealed that most of the increased proteins were involved in important biological processes such as metal ion homeostasis, detoxification, membrane organization, metabolic processes related to amino acids and carbohydrates, lipid metabolic processes, proteolysis, transmembrane transport, and others. The AgNPs used in this study demonstrated effective antimicrobial activity against the phytopathogenic bacteria Xcc. Furthermore, the obtained results contribute to a better understanding of the mechanisms of action of AgNPs in Xcc and may aid in the development of strategies to control Xcc in brassica.