Interaction of silver nanoparticles with pure nitrifying bacteria

► N. europaea and electrolytes contributed to AgNPs aggregation in the medium. ► The inhibitory effect of AgNPs on N. europaea was size- and coating-dependent. ► AgNPs caused the damage of cell wall of N. europaea and made the nucleoids disintegrated and condensed next to cell membrane. ► AgNPs inhibited activity of N. europaea via repressing the expression of selected functional proteins.