Determination of optimal culture conditions for toxin production by a Prorocentrum lima complex strain with high diarrhetic shellfish toxins yield

Abstract

Diarrhetic shellfish poisoning (DSP) is caused by the consumption of shellfish contaminated by diarrhetic shellfish toxins (DSTs) such as okadaic acid (OA) and dinophysistoxins (DTXs) produced by some species of dinoflagellates. To prevent the occurrence of human intoxication cases, inspection of DSTs (OA and DTXs) in shellfish is important. An instrumental method using liquid chromatography-tandem mass spectrometry (LC/MS/MS) has been recently employed in Japan for the monitoring of OA and DTXs in shellfish. For such analysis, reference materials (RMs) of OA and DTXs are essential. Demand for the reference materials, especially dinophysistoxin-1 (DTX1), is recently increasing in Japan. Production of the materials has been performed by mass cultivation of a dinoflagellate (Prorocentrum lima) strain that produces DTXs and OA, which indicates that the efficiency of production depends on the toxin production of the strain used. In this study, P. lima complex subclade 1e strain MIO12P was determined to be a high DTX1 producer among the three Japanese strains of the P. lima complex (subclades 1e, 1f, and 1i). It was clarified that the culture medium suitable for toxin production by strain MIO12P was metals mix SWII medium, and the optimal temperature and salinity for toxin production were 25 °C and salinity 30, respectively. The DTX1 yield (1265.3 ng ml−1) of strain MIO12P cultured under the conditions described above was the highest reported worldwide. Prorocentrum lima complex subclade 1e strain MIO12P is expected to be useful for the sustainable production of DTX1 as a source of RMs for chemical and biochemical methods in the future.