Growth and toxin production of the toxic dinoflagellate Pyrodinium bahamense var. compressum in laboratory cultures

Toxin production of a Malaysian isolate of the toxic red tide dinoflagellate Pyrodinium bahamense var. compressum was investigated at various stages of the batch culture growth cycle and under growth conditions affected by temperature, salinity, and light intensity variations. In all the experiments conducted, only 5 toxins were ever detected. Neosaxitoxin (NEO) and gonyautoxin V (GTX5) made up 80 mole percent or more of the cellular toxin content and saxitoxin (STX), GTX6 and decarbamoylsaxitoxin (dcSTX) made up the remainder. No gonyautoxins I‐IV or C toxins were ever detected. In nutrient‐replete batch cultures, toxin content rapidly peaked during early exponential phase and just as rapidly declined prior to the onset of plateau phase. Temperature had a marked effect on toxin content, which increased 3‐fold as the temperature decreased from the optimum of 28°C to 22°C. Toxin content was constant at salinities of 24%° or higher, but increased 3‐fold at 20%°. Toxin content decreased 2‐fold and chlorophyll content increased 3‐fold when light intensity was reduced from 90 to 15 μE m‐2 s‐1. This accompanied a 30% decrease in growth rate. Toxin composition (mole % individual toxin cell‐1) remained constant throughout the course of the nutrient‐replete culture and during growth at various salinities, but varied significantly with temperature and light intensity changes. At 22°C, GTX5 was 25 mole % and NEO was 65 mole %, while at 34°C, GTX5 increased to 55 mole % and NEO decreased proportionally to 40 mole %. When light intensity was reduced from 90 to 15 μE m‐2 s‐1, NEO decreased from 55 to 38 mole %, while GTX5 increased from 40 to 58 mole %. These data suggest that low light and high temperature both somehow enhance sulfo‐transferase activity. In general, toxin content and composition in P. bahamense were both influenced by factors that alter the growth rate of the species. The data show, however, that toxin content was not determined solely by growth rate but, more likely, by the manner in which the cells allocate their nitrogen and carbon to various cellular components and processes under various growth conditions. Several of the toxin production patterns observed in this P. bahamense isolate were similar to those of PSP toxin‐producing Alexandrium and Gyrnnodinium species, but there were also significant differences.