Characterization, Antimicrobial and Antioxidant Evaluation of Biofabricated Silver Nanoparticles from Endophytic Pantoea anthophila

Endophyte mediated nanoparticles fabrication were emerging as a new frontier in nanomedicines that produce high biocompatible and functionalized silver nanoparticles. In this study, silver nanoparticles were successfully biosynthesized from the extracellular extract of endophytic bacterium Pantoea anthophila isolated from the stem of Waltheria indica for the first time. The synthesized nanoparticles showed a strong absorption band at 410 nm in the UV–Visible range. The dynamic light scattering and zeta potential analysis indicated that the average particle size was 16 nm at 5.30 mV. FTIR spectrum displayed the presence of various functional groups at 3423.65, 1633.71, 1022.27, 607.58 cm(−1) that stabilised the nanoparticle. X-ray diffraction peaks were conferred to 100, 200, 220 and 311 planes of a face centred cubic structure. TEM and SEM micrograph revealed the spherical-shaped, polycrystalline nature with the presence of elemental silver analysed by EDAX. Selected area electron diffraction also confirms the orientation of silver nanoparticles with X-ray diffraction analysis. Antimicrobial activity against 10 different human pathogenic bacteria and fungi showed a broad spectrum inhibition against both Gram-positive and Gram-negative bacteria. Among the bacterial pathogens, B. Subtilis exhibited low activity compared to other pathogens. C. albicans was greatly controlled than other fungal species. A strong free radical scavenging activity of silver nanoparticles with IC(50) values 31.29 ± 0.73, 19.83 ± 1.57, 35.64 ± 0.94, 42.07 ± 1.30, 29.70 ± 2.26, 29.10 ± 0.82, 36.80 ± 0.63 μg/ml was obtained in different antioxidant assays that were comparable to the reference. The study suggests that the silver nanoparticles can be biosynthesized from endophytic P. anthophila metabolites with significant therapeutic potential. With proper validation, the biosynthesized silver nanoparticles can be developed as a promising antiviral and anticancer drug candidate.