Impact of nano titanium dioxide exposure on cellular structure of Anabaena variabilis and evidence of internalization

Abstract

The present study investigated the impact of nano titanium dioxide (nTiO2) exposure on the cellular structures of the nitrogen-fixing cyanobacteria Anabaena variabilis. Results of the present study showed that nTiO2 exposure led to observable alteration in various intracellular structures and induced a series of recognized stress responses, including production of reactive oxygen species (ROS), appearance and increase in the abundance of membrane crystalline inclusions, membrane mucilage layer formation, opening of intrathylakoidal spaces, and internal plasma membrane disruption. The production of total ROS in A. variabilis cells increased with increasing nTiO2 doses and exposure time, and the intracellular ROS contributed to only a small fraction (<10%) of the total ROS measured. The percentage of cells with loss of thylakoids and growth of membrane crystalline inclusions increased as the nTiO2 dose and exposure time increased compared with controls, suggesting their possible roles in stress response to nTiO2, as previously shown for metals. Algal cell surface morphology and mechanical properties were modified by nTiO2 exposure, as indicated by the increase in cell surface roughness and shifts in cell spring constant determined by atomic force microscopy analysis. The change in cell surface structure and increase in the cellular turgor pressure likely resulted from the structural membrane damage mediated by the ROS production. Transmission electron microscopy (TEM) analysis of nTiO2 aggregates size distribution seems to suggest possible disaggregation of nTiO2 aggregates when in close contact with microbial cells, potentially as a result of biomolecules such as DNA excreted by organisms that may serve as a biodispersant. The present study also showed, for the first time, with both TEM and Raman imaging that internalization of nTiO2 particles through multilayered membranes in algal cells is possible. © 2010 SETAC © 2011 SETAC.