Virus-like Particles Suppress Growth of theRed-Tide-Forming Marine DinoflagellateGymnodinium mikimotoi

We isolated 2 virus-like agents that suppressed growth of Gymnodinium mikimotoi from coastalwaters of the Uwa Sea, Japan. The agents found in the flagellate cells, named GM6 and GM7, were filterable in a0.22-lm-pore filter with approximately 100-nm shapes. Electron microscopic observation showed the presenceof virus-like particles in severely damaged G. mikimotoi cells infected by GM6. The growth-suppression activityof the agents (GM6 or GM7) was lost by heating at 50°C, with treatments of DNase and protease, and filtrationthrough a 0.05-lm filter. Our results suggest that the agents are DNA viruses infectious to and virulent for G.mikimotoi. This is the first report of a virus-like agent specific to G. mikimotoi.