BACKGROUNDMicroorganisms with high tolerance to toxic metal effects are essential for such processes as bioremediation, bioaccumulation, sewage and wastewater treatment, and also biosynthesis of metal nanoparticles (NPs). RESULTSA brief and simple method for formation of synthetic activated sludge granules with high resistance to toxic metal ions is reported. The symbiotic granules formed had much more resistance to toxic metals than the initial native activated sludge or its pure culture isolates. The microbial survival assessed at concentration 20mgL(-1) of Ag+ was 7% for the initial activated sludge; it being 9, 13 and 12% for granules of the pure cultures of Fusarium oxysporum, Fusarium nivale, and Penicillium glabrum, respectively, while the survival of the three-layered synthetic granules formed on the basis of these cultures reached 24%. CONCLUSIONThe method is based first on selection of cultures of activated sludge of wastewater treatment facilities which had the most resistance to silver ions, and then on creation of multilayered activated sludge granules. Microbial cultures with low resistance to metal ion toxicity were protected by layers of microorganisms with higher resistance. (c) 2014 Society of Chemical Industry