Mechanism of the toxic action of cationic G5 and G7 PAMAM dendrimers in the cyanobacterium Anabaena sp. PCC7120

Abstract

Nowadays, nanomaterials are extensively used worldwide in many different fields and their potentially serious effects on aquatic ecosystems have become a global concern. In this study, we have investigated the effect of two nanometric manufactured polymers, high-generation cationic G5 and G7 poly(amidoamine) dendrimers, in a prokaryotic primary producer of aquatic ecosystems, the filamentous cyanobacterium Anabaena sp. PCC7120. Dendrimers significantly decreased the growth of the cyanobacterium and they induced morphological alterations both at the filament and the single-cell level. Furthermore, the exposure to dendrimers induced significant alterations in several physiological parameters of the cyanobacterium: intracellular reactive oxygen species overproduction, damage in membrane integrity, membrane potential alterations, increase of metabolic activity, acidification of intracellular pH, oxidative DNA damage and alteration of intracellular free Ca²⁺ homeostasis. Dendrimers also induced alterations in the photosynthesis of Anabaena: decrease in oxygen evolution and in PSII activity, alteration in different photochemical events and in chlorophyll a content. Moreover, both dendrimers were internalized into cyanobacterial cells. In conclusion, high-generation cationic dendrimers exhibited high toxicity towards Anabaena, severely affecting several physiological, morphological and photosynthetic parameters.