Exocytotic and phagocytotic activities of Tetrahymena pyriformis are not influenced by Clostridium botulinum neurotoxins

The ciliate Tetrahymena pyriformis GL was tested for its applicability to the detection of botulinum neurotoxins. Botulinum neurotoxins attack different proteins of the SNARE-complex, which is involved in fusion processes of the cellular membrane traffic. The exocytosis of enzymes and the phagocytosis of germs include several presumptive SNARE-dependent pathways within T. pyriformis. Acid phosphatase was chosen as indicator enzyme for the quantification of the exocytotic activity. It was determined by photometric measurement after the addition of the substrate pnitrophenylphosphate. The phagocytotic activity was quantified with Escherichia coli as prey germ. Botulinum neurotoxins were produced by cultivating reference strains of the seven Clostridium botulinum toxovars A to G in TPGY broth with and without the addition of trypsin. The success of the neurotoxin production was tested by the mouse bioassay, which is the standard test for botulinum neurotoxins. The neurotoxins were added to the assays used for the determination of the exocytotic and the phagocytotic activity of T. pyriformis in final concentrations of 1.5·102 mouse lethal doses·ml-1, except E: 1.5 mouse lethal doses ·ml-1. No significant influence of the toxins could be detected. Hence, T. pyriformis cannot be used as a test-organism for the detection of botulinum neurotoxins.