Biosynthesis and Characterization of Silver Nanoparticles Produced by and Cyanobacteria.

The world faces a challenge with the pervasion of multidrug-resistant bacteria that encourages scientists to develop and discover alternative, ecofriendly, and easy-to-produce new antibacterial agents. Our work is part of the greater effort of scientists around the world to achieve this goal by the biological synthesis of silver nanoparticles using cyanobacterial extracellular and intracellular components as nonchemical reducing agents. Two Egyptian cyanobacteria were isolated and identified according to 16S rRNA gene sequencing as and a novel species . The sequences were deposited with accession numbers MW762709 and MW762710 for and , respectively, in the GenBank. The results of UV-Vis analysis showed promising extracellular Ag-NPs synthesis by and under light conditions. Therefore, these Ag-NPs were characterized and evaluated for antibacterial and antioxidant activity. TEM and SEM analyses revealed the spherical crystals with face-centered cubic structures and size range of 6.24-11.4 nm and 6.46-12.2 nm for Ag-NPs of and , respectively. XRD and EDX results confirmed the successful synthesis of Ag-NPs in their oxide form or chloride form. The FTIR spectrum data confirmed the presence of hydroxyl and amide groups. Ag-NPs displayed the largest inhibition zone that ranged from 9 mm against ATCC 10240 to 25 mm against methicillin-resistant (MRSA) ATCC 43300. For Ag-NPs, the inhibition zone diameter was in the range of 9 mm to 18 mm. The biosynthesized Ag-NPs significantly inhibited the growth of medically important resistance-pathogenic Gram-positive and Gram-negative bacteria. The Ag-NPs of exhibited the highest scavenging activity of 48.7% when compared with that of , which displayed 43.753%.