Biosynthesis of silver nanoparticles from macroalgae Hormophysa triquetra and investigation of its antibacterial activity and mechanism against pathogenic bacteria.

In this study, brown macroalgae Hormophysta triquetra (HT) collected from the Qatari coast is used to biosynthesize silver nanoparticles (AgNPs) from its aqueous (AQ), chloroform: methanol (MCF), and ethanolic extracts (ET). The NPs are characterized using Transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), Gas chromatography/Mass spectrometry (GC/MS) and X-ray photoelectron spectroscopy (XPS). The NPs were evaluated for their antibacterial activities by disc-diffusion method and their minimum inhibitory concentrations (MIC) were assessed. The NPs synthesized through biological process exhibited significant antibacterial efficacy against Escherichia coli, Bacillus subtilis, Staphylococcus aureus, Pseudomonas stutzeri, and Pseudomonas fragi for all the three NPs. AQ-AgNP and ET-AgNP showed higher zones of inhibition for P. fragi with inhibitory zones of 22.5 mm and 25 mm respectively. On the other hand, MCF-AgNP showed a higher zone of inhibition for E. coli with an inhibition zone of 23.5 mm. The NPs inhibited the growth of bacterial strains by deforming their structure and forming pits. The results revealed that macroalgae HT could be used as a potential candidate to produce AgNPs and have efficient antibacterial activities against both types of bacteria i.e., Gram-positive (B. subtilis and S. aureus) and Gram-negative (E. coli, P. stutzeri, and P. fragi).