Biosynthesis, characterization and biological potential of microbe-mediated silver nanoparticles using thermophilic actinomycetes, Streptomyces nigra.

Silver nanoparticles (AgNPs) were synthesized using the cell-free extract of Streptomyces nigra (GenBank Accession: PP565016), a thermophilic actinobacterium isolated from scorched stubble environment, a previously unexplored ecological niche. The nanoparticle (NPs) formation was confirmed through the appearance of strong Surface Plasmon Resonance (SPR) peak at 422 nm. The characterization of biogenic AgNPs includes SEM (Scanning Electron Microscope), Zeta potential, XRD (X-ray Diffraction), FT-IR (Fourier Transform Infrared Spectroscopy), along with EDAX (Energy Dispersive X-ray Analysis) which confirms their spherical morphology, crystalline nature and surface functionalization with biological molecules. AgNPs show significant antibacterial activity against both Gram positive and negative bacteria with zone of inhibition ranging from 10 to 18 mm. The particles exhibited notable antioxidant activity indicating their potential to neutralize oxidative stress. Anti-inflammatory activity was confirmed by the denaturation of protein with the IC50 value of 41.8 ± 0.64 μg/mL. Antidiabetic potential was assessed via α-amylase inhibition assay, which was dose dependent (IC50 49.61 ± 0.56 μg/mL). The MTT assay demonstrated dose-dependent cytotoxicity against prostate cancer cell lines (PC3), with significant reduction in cell viability and colony formation. Apoptosis induction was confirmed visually by AO/EtBr dual staining. This study highlights that S. nigra is a promising microbial source for the biosynthesis of multifunctional AgNPs possessing potential biological activity.