Extremely high level of reactive oxygen species (ROS) production in a newly isolated strain of the dinoflagellate <i>Karenia mikimotoi</i>

Abstract

We found that the newly isolated dinoflagellate strain Karenia mikimotoi NGU04 generates O2– at a level almost equal to that of the raphidophycean flagellate Chattonella marina, and much higher than those of other strains of K. mikimotoi. Fluorescence microscopy observation of strain NGU04 suggested that ROS such as O2– and H2O2 are generated in certain intracellular compartments. As in C. marina, a significant increase in O2– generation was observed in the presence of lectins suggesting that K. mikimotoi has a signalling system that can respond to extracellular stimuli. The NGU04 strain showed a greater lethal effect on rotifers than other strains, but the toxicity was not inhibited by ROS-scavenging enzymes. Our findings indicate that different strains of K. mikimotoi can generate different amounts of ROS depending on the strain, but certain toxic factors other than ROS may be responsible for rotifer toxicity.