| Summary: | The synthesis of silver nanoparticles (AgNPs) by microorganisms recently gained a greater interest due to its potential to produce them in various sizes and morphologies. In this study, for AgNP biosynthesis, we used a new <i>Pseudomonas</i> strain isolated from a consortium associated with the Antarctic marine ciliate <i>Euplotes focardii</i>. After incubation of <i>Pseudomonas</i> cultures with 1 mM of AgNO<sub>3</sub> at 22 °C, we obtained AgNPs within 24 h. Scanning electron (SEM) and transmission electron microscopy (TEM) revealed spherical polydispersed AgNPs in the size range of 20−70 nm. The average size was approximately 50 nm. Energy dispersive X-ray spectroscopy (EDS) showed the presence of a high intensity absorption peak at 3 keV, a distinctive property of nanocrystalline silver products. Fourier transform infrared (FTIR) spectroscopy found the presence of a high amount of AgNP-stabilizing proteins and other secondary metabolites. X-ray diffraction (XRD) revealed a face-centred cubic (fcc) diffraction spectrum with a crystalline nature. A comparative study between the chemically synthesized and <i>Pseudomonas</i> AgNPs revealed a higher antibacterial activity of the latter against common nosocomial pathogen microorganisms, including <i>Escherichia coli, Staphylococcus aureus</i> and <i>Candida albicans</i>. This study reports an efficient, rapid synthesis of stable AgNPs by a new <i>Pseudomonas</i> strain with high antimicrobial activity.
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