Impact of Titanium Dioxide Nanomaterials on Nitrogen Fixation Rate and Intracellular Nitrogen Storage in Anabaena variabilis

摘要

This study comprehensively investigated the impact of titanium dioxide nanomaterials (nTiO_2) exposure on cell growth, nitrogen fixation activity, and nitrogen storage dynamics in the primary producer cyanobacteria Anabaena variabilis at various dose concentrations and exposure time lengths. The results indicated that both growth rate (EC_(50)-96 h of 0.62 mgTiO_2/ L) and nitrogen fixation activity (EC_(50)-96 h of 0.4 mgTiO_2/L) were inhibited by nTiO_2 exposure. The Horn's law (C~nT~m) was used as inactivation model to predict the concentration- and time-dependent inhibition of growth and nitrogen fixation activity. The kinetic parameters determined suggested that the time of exposure has a greater influence than the nTiO_2 concentration in toxicity. We observed, for the first time, that nTiO_2 induced a dose (concentration and timel-dependent increase in both the occurrence and intracellular levels of the nitrogen-rich cyanophycin grana proteins (CGPs). The results implied that CGPs may play an important role in the stress response mechanisms of nTiO_2 exposure and can serve as a toxicity assessment endpoint indicator. This study demonstrated that nitrogen-fixing activity could be hampered by the release of nTiO_2 in aquatic environments; therefore it potentially impacts important biogeochemical processes, such as carbon and nitrogen cycling.