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 andwashed
biomass of microalgae and cyanobacteria into the AgNO3 solution and (ii) by adding AgNO3 into a cellfree
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 embedd 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.