Carbon nanotube compared with carbon black: effects on bacterial survival against grazing by ciliates and antimicrobial treatments

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.

Keywords::

• Carbon nanotube
• carbon black
• protozoa
• bacterial survival
• toxicity
• ecotoxicology

Acknowledgements

The authors would like to thank D. Weber for his assistance in confocal microscopy and SEM sample preparation. This work is supported by a Leaders Opportunity Fund from the Canada Foundation of Innovation (CFI) and Ontario Research Foundation (ORF) to Dr. Tang, and a Strategic grant from the Natural Science and Engineering Research Council (NSERC) of Canada to Drs Bols and Tang.