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

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 stab ility, nuclease sensitivity, proteinase K sensitivity, stability under acid ic condition, titration, diethyl ether sensitivity, and ultraviolet (UV) se nsitivity. All agents were affected by heating at 50 degrees C for 30 min, exposure to acidic conditions below pH 5.0, passing through a 0.05 mu m fil ter, RNase treatment, and irradiation of UV dosage at 5 x 10(4) mu W/s per cm(2). The growth suppression effects of 11 agents from Tetraselmis sp, and A. catenella disappeared after proteinase K treatment, however, seven agen ts from G. mikimotoi were unaffected by this treatment. Furthermore, 11 age nts against Tetraselmis sp. and A. catenella were collected from the bottom fraction by ultracentrifugation, while seven agents against G, mikimotoi w ere collected from the upper fraction, not from the precipitated fraction. These results suggest that at least two types exist in the virus-like agent s showing growth suppression for phytoplankton.