Isolation and characterization of lethal proteins in nematocyst venom of the jellyfish Cyanea nozakii Kishinouye

Cyanea nozakii Kishinouye, a jellyfish widely distributed in coastal areas of China, has garnered attention because of its stinging capacity and the resulting public health hazard. We used a recently developed technique to extract jellyfish venom from nematocysts; the present study investigates the lethality of C. nozakii venom. The nematocyst contents were extremely toxic to the grass carp, Ctenopharyngodon idellus, producing typical neurotoxin toxicity. The ID50 was about 0.6 μg protein/g fish. Toxin samples were stable when kept at −80 °C, but after 48 h, an 80% decline in lethality occurred at −20 °C. Poor stability of the venom was observed within the range of 65–80 °C and at pH 3.5. The venom was hydrolyzed by a proteolytic enzyme, trypsin. Fractionation of the venom yielded two protein bands with molecular weights of 60 kDa and 50 kDa. Our results provide the first evidence that C. nozakii produces lethal toxins. These characteristics highlight the need for the isolation and molecular characterization of new active toxins in C. nozakii.