Stress response of Pseudomonas species to silver nanoparticles at the molecular level

In recent years, silver nanoparticles (AgNPs) have been shown to possess broad antibacterial activity. The present study investigated the cytotoxicity of AgNPs to a common soil bacterium, Pseudomonas sp. The molecular mechanism involved in its stress response to AgNPs was also studied. The minimum inhibitory concentration (MIC) of AgNPs was found to be 0.2 mg/L. At a sublethal concentration of 0.1 mg/L AgNPs, the protein expression profile of Pseudomonas showed overexpression of stress proteins such as ribosomal proteins S2 and L9, alkyl hydroperoxide reductase/thiol-specific antioxidant (AhpC/TSA) family protein, and keto-hydroxyglutarate aldolase (KHGA). The upregulation of these proteins was further confirmed by quantitative polymerase chain reaction. The results showed increased expression of ribosomal protein S2, KHGA, AhpC/TSA, and ribosomal protein L9 by 1.09-, 3.41-, 1.52-, and 1.56-fold, respectively (p < 0.05), after AgNP exposure compared with control. The present study clearly demonstrates that AgNPs are toxic to soil bacteria and induce oxidative and metabolic stress.