Differential Growth of and Nanoscale TiO 2 Accumulation in Tetrahymena thermophila by Direct Feeding versus Trophic Transfer from Pseudomonas aeruginosa

Abstract

ABSTRACT Nanoscale titanium dioxide (TiO 2 ) is increasingly used in consumer goods and is entering waste streams, thereby exposing and potentially affecting environmental microbes. Protozoans could either take up TiO 2 directly from water and sediments or acquire TiO 2 during bactivory (ingestion of bacteria) of TiO 2 -encrusted bacteria. Here, the route of exposure of the ciliated protozoan Tetrahymena thermophila to TiO 2 was varied and the growth of, and uptake and accumulation of TiO 2 by, T. thermophila were measured. While TiO 2 did not affect T. thermophila swimming or cellular morphology, direct TiO 2 exposure in rich growth medium resulted in a lower population yield. When TiO 2 exposure was by bactivory of Pseudomonas aeruginosa , the T. thermophila population yield and growth rate were lower than those that occurred during the bactivory of non-TiO 2 -encrusted bacteria. Regardless of the feeding mode, T. thermophila cells internalized TiO 2 into their food vacuoles. Biomagnification of TiO 2 was not observed; this was attributed to the observation that TiO 2 appeared to be unable to cross the food vacuole membrane and enter the cytoplasm. Nevertheless, our findings imply that TiO 2 could be transferred into higher trophic levels within food webs and that the food web could be affected by the decreased growth rate and yield of organisms near the base of the web.