ABSTRACT
The ingestion and digestion of Escherichia coli by the ciliated protozoan, Tetrahymena thermophila, was investigated after an initial exposure to either water-soluble single-walled carbon nanotubes (SWNT) or to carbon black (CB). Both SWNT and CB were internalised and visible in food vacuoles of ciliates. When presented with E. coli expressing green-fluorescent protein (GFP), these ciliates internalised bacteria as well. However, ciliates that had first internalised SWNT but not CB subsequently externalised or egested vesicle-like structures with fluorescent bacteria inside. These egested bacteria were viable and less susceptible than planktonic E. coli to killing either by the antibiotic, chloramphenicol or the disinfectant, glutaraldehyde. These results suggest that SWNT can alter the intracellular trafficking of vesicles within ciliates, leading to bacterial prey being packaged externally and protected for a time from environmental killing, which could have implications for sewage treatment and for public health.
Subject(s)
Anti-Infective Agents/toxicity , Nanotubes, Carbon/toxicity , Soot/toxicity , Tetrahymena thermophila/drug effects , Tetrahymena thermophila/microbiology , Cell Count , Chloramphenicol/toxicity , Coculture Techniques , Disinfectants/toxicity , Ecotoxicology , Escherichia coli/drug effects , Glutaral/toxicity , Green Fluorescent Proteins/metabolism , Microbial Viability/drug effects , Tetrahymena thermophila/physiology , Vacuoles/microbiologyABSTRACT
Research on the toxicity of carbon nanotubes has focused on human health risks, and little is known about their impact on natural ecosystems. The ciliated protozoan Tetrahymena thermophila has been widely studied by ecotoxicologists because of its role in the regulation of microbial populations through the ingestion and digestion of bacteria, and because it is an important organism in wastewater treatment and an indicator of sewage effluent quality. Here we show that single-walled carbon nanotubes are internalized by T. thermophila, possibly allowing the nanotubes to move up the food chain. The internalization also causes the protozoa to aggregate, which impedes their ability to ingest and digest their prey bacteria species, although it might also be possible to use nanotubes to improve the efficiency of wastewater treatment.