A study on the mate-killer toxin by microinjection in Paramecium

The killing action by mu toxin, which is contained in the cytoplasm of stock 540, Paramecium primaurelia, was demonstrated against the various stocks of paramecia by means of microinjection. Most of the toxin is present in the soluble fraction of the host cytoplasm. The toxin was precipitated by ammonium sulphate at 50–80% saturation, and was almost completely inactivated by incubation at 60 °C for 30 min. Pre-autogamous paramecia were more sensitive than post-autogamous ones to the toxin. Paramecia which bear endosymbionts were generally resistant to the mate-killer toxin.