Evaluation of antimicrobial, anticancer, and neuroprotective activities of silver nanoparticles (AgNPs) green-synthesized using a red pigment produced by Streptomyces sp. A23 strain isolated from Algerian bee pollen

Abstract

In this work, the red pigment of Streptomyces sp. A23 strain isolated from Algerian bee pollen was used for the green synthesis of silver nanoparticles (AgNPs) as well as for evaluating their antimicrobial, anticancer, and neuroprotective activities. AgNPs were synthesized as a result of the reduction of 1 mM and 5 mM silver nitrate solutions at various pH values (5, 7 and 9), and were subsequently characterized. AgNPs (5 mM, pH 9) exhibited a maximum UV-vis absorbance at 433 nm. DLS revealed that the average diameter was 112 nm. A zeta potential peak was found at -33 mV corresponding to increased stability. XRD analysis confirmed the crystallization nature of the material. Furthermore, FT-IR analysis revealed specific functional groups at 3471 cm^-1 to 478 cm^-1. In addition, FE-SEM showed that the mean size of the spherical AgNPs was 54.5 nm in diameter. The presence of Ag was revealed by EDX analysis. Additionally, good antimicrobial activity was observed against E. faecalis ATCC 19433, C. albicans ATCC 10231, S. aureus ATCC 6538P, P. aeruginosa ATCC 27853, B. subtilis ATCC 6633, K. pneumoniae ATCC 13883 and E. coli ATCC 7839, with inhibition zones of 32, 30, 30, 27, 25, 20 and 19 mm, respectively. The lowest MIC and MBC were recorded against B. subtilis ATCC 6633 with a value of 62.5 μg mL^-1. Intriguingly, all the synthesized AgNPs at concentrations of 2, 4, and 8 μg mL^-1 had cytotoxic effects on SH-SY5Y neuroblastoma cell lines. In addition, AgNPs (1 mM, pH 7) exhibited significant neuroprotective activity at the lowest tested concentration. Finally, AgNPs synthesized using the red pigment of Streptomyces sp. strain A23 are promising therapeutic agents.