Influence of environmental parameters on Karenia selliformis toxin content in culture

Karenia selliformisstrain GM94GAB was isolated in 1994 from the north of Sfax, Gabes gulf, Tunisia. This species, which produces gymnodimine (GYM) a cyclic imine, has since been responsible for chronic contamination of Tunisian clams. A study was made by culturing the microalgae on enriched Guillard f/2 medium. The influence of growing conditions on toxin content was studied, examining the effects of (i) different culture volumes (0.25 to 40 litre flasks), (ii) two temperature ranges (17-15°C et 20-21°C) and (iii) two salinities (36 and 44). Chemical analyses were made by mass spectrometry coupled with liquid chromatography (LC-MS/MS). Results showed that (i) the highest growth rate (0.34 ± 0.14 div d -1 ) was obtained at 20°C and a salinity of 36, (ii) GYM content expressed as pg eq GYM cell -1 increased with culture time. The neurotoxicity of K. selliformisextracts was confirmed by mouse bioassay. This study allowed us to cal- culate the minimal lethal dose (MLD) of gymnodimine (GYM) that kills a mouse, as a function of the number of K. selliformiscells extracted.

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