Mode of action of an antialgal agent produced by a marine gammaproteobacterium against Chattonella marina

A marine gammaproteobacterium, strain MS-02-063, was able to kill Chattonella marina, a noxious red tide phytoplankton. However, the algicidal activity of bacterial cells washed with the planktonic medium was significantly reduced. These results suggest that strain MS-02-063 produces an extracellular substance, the pigment, PG-L-1, that showed a potent algicidal effect on C. marina. The LD50 value of PG-L-1 was calculated to be approximately 8.5 mu g ml(-1). At the approximate LD50 concentration of 10 mu g ml(-1), a morphological change, which seemed to be due to the inhibition of cell division, was observed in C. marina. Almost all cells of C. marina were destroyed readily at 100 mu g ml(-1) of PG-L-1, and the cytostatic activity of PG-L-1 against this phytoplankton was observed at a concentration of 1 mu g ml(-1) during the 5 d of incubation. A sublethal concentration of PG-L-1 of 10 mu g ml(-1) significantly inhibited the reactive oxygen species (ROS) production by C. marina. ROS production has been previously reported to be essential for normal growth of C. marina (Oda et al. 1995; Biosci Biotechnol Biochem 59:2044-2048). Therefore, the inhibitory effect of PG-L-1 on ROS production may lead to growth inhibition of C. marina, at least in part. The pigment, PG-L-1, may be a useful compound not only as an applicable agent for the mitigation of harmful algal blooms, but also as an experimental tool to analyse the ROS production system in a red tide phytoplankton such as C. marina.