nTiO₂ induced changes in intracellular composition and nutrient stoichiometry in primary producer--cyanobacteria

The widely and increasing use of nano-titanium dioxide (nTiO2) has led to its release in the environment and concerns of consequent impact on aquatic eco-relevant biota. Previous studies indicated possible physiological changes (i.e., nitrogen storage) induced by nano-titanium dioxide (nTiO2) exposure in algae, which will likely have ecological implications. This study investigated the short- (96 h) and long-term (21 days) ecotoxic impact of environmentally relevant nTiO2 concentrations on the cellular biochemical pools and nutrient stoichiometry in the nitrogen-fixing cyanobacteria Anabaena variabilis. Changes in nutrient element ratios and cellular composition were analyzed using both chemical elemental analysis and Fourier Transform Infrared (FT-IR) spectroscopy. Chemical elemental analysis showed that exposure to nTiO2 at varying dose concentrations and exposure duration led to statistically significant changes in intracellular C:N, C:P and N:P stoichiometries compared with those in the controls. In general, there seemed to be a decreasing trends of cellular C:N ratio and increase in the cellular C:P and N:P ratios with the increasing level of nTiO2 exposure. Further FT-IR analysis results revealed both temporal and dose-dependent change patterns of major macromolecules, including protein, lipids, nucleic acids and carbohydrates, in A. variabilis upon nTiO2 exposure. The relative ratio of amide II, lipids, nucleic acids and carbohydrates to the cellular protein content (quantified as amide I stretch) changed significantly within the initial 96 h of exposure and, both the magnitude of changes and levels of recovery seemed to be nTiO2 dose-dependent. This study, for the first time, demonstrated that the intracellular composition and nutrient stoichiometry changes could be induced by long-term and short-term exposures to nTiO2 to primary producers, which may have ecological implications for interspecies equilibriums and community dynamics in aquatic ecosystems.