Differential Growth of and Nanoscale TiO2Accumulation in Tetrahymena thermophila by Direct Feeding versus Trophic Transfer from Pseudomonas aeruginosa
ABSTRACTNanoscale titanium dioxide (TiO2) is increasingly used in consumer goods and is entering waste streams, thereby exposing and potentially affecting environmental microbes. Protozoans could either take up TiO2directly from water and sediments or acquire TiO2during bactivory (ingestion of bacteria) of TiO2-encrusted bacteria. Here, the route of exposure of the ciliated protozoanTetrahymena thermophilato TiO2was varied and the growth of, and uptake and accumulation of TiO2by,T. thermophilawere measured. While TiO2did not affectT. thermophilaswimming or cellular morphology, direct TiO2exposure in rich growth medium resulted in a lower population yield. When TiO2exposure was by bactivory ofPseudomonas aeruginosa, theT. thermophilapopulation yield and growth rate were lower than those that occurred during the bactivory of non-TiO2-encrusted bacteria. Regardless of the feeding mode,T. thermophilacells internalized TiO2into their food vacuoles. Biomagnification of TiO2was not observed; this was attributed to the observation that TiO2appeared to be unable to cross the food vacuole membrane and enter the cytoplasm. Nevertheless, our findings imply that TiO2could 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.