Introduction: The synthesis of nanoparticles by green nanotechnology processes is an eco-friendly and coste-ffective method and, accordingly, is regarded as an alternative technique to physical and chemical technologies. Microorganisms including bacteria are used to produce adequate amount of nanoparticles with biomedical applications. The present study reveals the hydrothermal cell lysate supernatant process of copper oxide nanoparticles (CuONPs) by psychrotolerant bacterium and evaluate the antibacterial activity of these nanoparticles against gram negative and positive bacteria. Methods: CuONPs were extracted from Stenotrophomonas sp. BS95 by centrifugation.The UV-visible was used to determine the purity and size of the nanoparticle. The morphology of the CuONPs was further examined by means of atomic force microscopy (AFM). Antibacterial activity was tested against two types pathogenic of bacteria, Escherichia coli PTCC1860 and Staphylococcus aureus ATCC25923. These bacteria were exposed to different concentrations of biosynthesized nanoparticles in Muller Hinton broth medium and incubated at 37 °C for 24 hours. Results and conclusion: The UV-VIS spectra of the CuONPs exhibit the maximum absorption peak at 284 nm suggesting CuONPs formation. In the AFM carried out to examine the topological appearance and provided a threedimensional (3D) profile of the surface on the nanoscale. CuO nanoparticles have a minimum inhibitory concentration (MIC) of 500 μg/mL and 250 μg/mL for E.coli and S.aureus respectively. This study demonstrated that Stenotrophomonas sp. BS95 is a promising source for biosynthesis of CuONPs.This biocompatible method could be a desirable method for synthesis of biogenic nanoparticle and consequently has the ability to use in biomedical applications.

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