Interactions between Single-Walled Carbon Nanotubes (SWNT) and Ciliates: SWNT Interfere with Ciliate Ecological Function
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Interactions between Single-Walled Carbon Nanotubes (SWNT) and Ciliates: SWNT Interfere with Ciliate Ecological Functions and Ciliates Transport/Transform SWNT Tiffany S. Y. Chan1, Fatima Nasser1, Christine H. St-Denis2, Niels C. Bols2, and Xiaowu (Shirley) Tang1 1 Department of Chemistry, University of Waterloo, 200 University Ave. West, Waterloo, Ontario, N2L 3G1, Canada 2 Department of Biology, University of Waterloo, 200 University Ave. West, Waterloo, Ontario, N2L 3G1, Canada ABSTRACT We investigated the interactions of water soluble single-walled carbon nanotubes (SWNT) with unicellular organisms, in particular a ciliated protozoan (Tetrahymena thermophila) and a bacteria (Escherichia coli), which are common constituents of natural fresh water. The ciliates could effectively incorporate SWNT into natural organic matter (NOM), and therefore into normal ecological processes. Further, SWNT induced the ciliates to egest viable bacteria in membrane-enclosed vesicles. The egested bacteria aggregates had escaped digestion by the protozoan and were able to proliferate and resist antibiotic/disinfectant treatments, which may have important implications to public health. This work highlights the importance of studies on nanoparticle ecotoxicology. INTRODUCTION Novel nanomaterials, such as CNT, have sparked tremendous interest in a wide range of industrial applications. At the same time, nanomaterials posed new challenges in environmental monitoring and risk assessment [1-4]. Many questions of interest are remained to be answered. What are the routes of transportation and transformation of emerging nanomaterials? What are their distribution in various environmental compartments and how to detect them? What are their ecotoxicity and the risk to public health? Here, we report our study which revealed 1) a potential impact of water soluble SWNT on aquatic microbial ecology and 2) the potential transport and transformation of SWNT by ciliated protozoa. EXPERIMENT SWNT powder (HipCo tube, Carbon Nanotechnologies, Inc) was acid oxidized, purified, and made water soluble [5]. To examine the impact of SWNT on T. thermophila, concentrated SWNT solution in deionized (DI) water was directly dropped into T. thermophila cultures in certified water from lake Superior (M1-02, Environment Canada) or culture media (Osterhout’s buffer, PPYE) to the desired final concentrations. Solution phase SWNT concentration was determined using optical absorbance at 270 nm with a molar extinction coefficient of 2.95 × 107 M-1 cm-1 and a molecular weight of 170 kDa [6]. Stock T. thermophila culture was maintained routinely as described previously in PPYE at room temperature on an orbital shaker [7]. To monitor T. thermophila feeding on bacteria, a green fluorescent protein (gfp) expressing E. coli strain (XL-1) was used, which is referred as pET-gfp in later text. Ingestion, digestion, and excretion of pET-gfp by T. thermophila were observed using a confocal fluorescence
microscope (Zeiss LSM 510). pET-gfp proliferation was recorded by
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