LYSIS OF GYMNODINIUM SPECIES BY THE FUNGUS VERTICILLIUM-LECANII

Microorganisms were isolated from a major phytoplankton bloom attribut ed to Gymnodinium sp., occurring from January through to March 1993 on the north eastern coast of New Zealand. Among nine groups of microbes isolated, two were prevalent during the decline of the bloom (March t o early April) but were absent or in low numbers in the same site duri ng the remainder of 1993 and in early 1994. These were a marine bacter ium designated str LY and the marine fungus, Verticillium lecanii. Bot h organisms were isolated into pure culture and added to each of eight unialgal dinoflagellate cultures to determine their effects on algal growth. Bacterial strain LY was without effect on any of the dinoflage llates tested, and while V. lecanii was without effect on Alexandrium ostenfeldii (2 strains), Alexandrium minutum and Amphidinium carterae, it slightly inhibited the growth of Heterocapsa triquetra and caused the complete lysis and death of three species of Gymnodinium. Addition s of preparations of culture fluid from the fungus grown on heat-kille d Gymnodinium sp. to cultures of Gymmodinium spp. resulted in their ly sis and death, but were inactive towards the other dinoflagellates tes ted. The lytic system was heat stable, with a molecular weight < 3000.