Screening of cyanobacteria and microalgae for their ability to synthesize silver nanoparticles with antibacterial activity

The aim of this study was to assess the ability of selected strains of cyanobacteria and microalgae to biosynthesize silver nanoparticles (Ag-NPs) by using two procedures; (i) suspending the live and washed biomass of microalgae and cyanobacteria into the AgNO3 solution and (ii) by adding AgNO3 into a cell-free culture liquid. Ag-NPs were biosynthesized by 14 out of 16 tested strains. In most of the cases Ag-NPs were formed both in the presence of biomass as well as in the cell-free culture liquid. This indicates that the process of Ag-NPs formation involves an extracellular compound such as polysaccharide. TEM analysis showed that the nanoparticles were embedded within an organic matrix. Ag-NPs varied in shape and sizes that ranged between 13 and 31 nm, depending on the organism used. The antibacterial activity of Ag-NPs was confirmed in all but one strain of cyanobacterium (Limnothrix sp. 37-2-1) which formed the largest particles.