Characteristics of virus-like growth suppression agents against phytoplankton obtained from seawater at the mouth of Funka Bay, Hokkaido, Japan

Abstract

Eighteen samples of virus-like growth suppression agents against the marine phytoplankton Alexandrium catenella, Gymnodinium mikimotoi and Tetraselmis sp., obtained from the coastal waters at the mouth of Funka Bay, Hokkaido, Japan, from 1993 to 1995, were characterized on size estimation, heat stability, nuclease sensitivity, proteinase K sensitivity, stability under acidic condition, titration, diethyl ether sensitivity, and ultraviolet (UV) sensitivity. All agents were affected by heating at 50°C for 30 min, exposure to acidic conditions below pH5.0, passing through a 0.05 μm filter, RNase treatment, and irradiation of UV dosage at 5×104 μW/s per cm2. The growth suppression effects of 11 agents from Tetraselmis sp. and A. catenella disappeared after proteinase K treatment, however, seven agents from G. mikimotoi were unaffected by this treatment. Furthermore, 11 agents against Tetraselmis sp. and A. catenella were collected from the bottom fraction by ultracentrifugation, while seven agents against G. mikimotoi were collected from the upper fraction, not from the precipitated fraction. These results suggest that at least two types exist in the virus-like agents showing growth suppression for phytoplankton.