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

Abstract

dNanoscale 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.

Considerations of Environmentally Relevant Test Conditions for Improved Evaluation of Ecological Hazards of Engineered Nanomaterials

“…276 Other indirect physical effects derive from ENMs adhering to the organism surface, 277 light shading, 278 or internal food displacement. 99 Near-field exposures (Fig. 3) can result in biological hazards from specific ENMs based on their properties (e.g., electronic).…”

Heteroaggregation of nanoparticles with biocolloids and geocolloids

“…For instance, NPs-microorganism heteroaggregation can lead to increased removal of NPs from wastewater during secondary treatment [106,[115][116][117][118]. Interactions between cell walls of microorganisms and NPs are also thought to precede uptake and toxicity [107,108,[110][111][112]116,119], and may be important for trophic transfer of NPs in both aquatic and terrestrial environments [108,[119][120][121].…”

Toxicity-based toxicokinetic/toxicodynamic assessment of bioaccumulation and nanotoxicity of zerovalent iron nanoparticles in <em>Caenorhabditis elegans</em>

“…[60][61][62][63] However, several NPs with conflicting results have been reported to have no biomagnification effects in food chains. [64][65][66][67] Tangaa et al 68 and Unrine et al 69 suggested that the discrepancies among BMFs could be due to both abiotic (eg, environmental parameters) and biotic (eg, organism physiology and life-history traits, foodweb structure, and analyses of whole-body vs single-organ concentration) that affect the efficiency of trophic transfer.…”