STUDY OF PRODUCTION AND TOXICITY OF CULTURED GAMBIERDISCUS TOXICUS

¹ Inserm Unité 303, "Mer et Santé," La Darse—B. P. 3, 06230 Villefranche-sur-Mer, France

Gambierdiscus toxicus has been described as the chief producer of ciguateric toxins: ciguatoxin (CTX) and maitotoxin (MTX). Dr. R. Bagnis (Malardé Institute, Tahiti) provided us with a strain of this benthic dinoflagellate in 1981 to study its cytological, physiological, and toxicological characteristics.

The growth of G. toxicus has been studied under various chemical and physical conditions enabling us to define optimal culture conditions. Since then, we have improved the cultivation procedure and have obtained large scale cultures of some clones and strains in different culture media.

All the experiments showed that G. toxicus has complex nutritive requirements and a large inertia to response at some non-drastic environmental variations. Increased growth rates were observed when cultures were treated with antibiotics.

The classical extraction procedure of the toxins has been adapted to our algal material. The method was simplified and resulted in enhanced toxinic yield.

Our principal results have demonstrated that G. toxicus in culture remained very toxic; 600 to 2000 cells were sufficient to kill a 20 g female mouse within 24 hours (MLD = 1-3 mg/kg). No variation of the degree of toxicity has been observed for three years.

A linear relationship between the number of G. toxicus cells (Coulter counted) and the weight of corresponding algal pellet has been found. This leads to an easier evaluation of the quantity of toxic extract required to calculate the minimum lethal dose (MLD).

The extraction procedure results in two toxic fractions: a water-soluble (MTX-like) and a lipid-soluble (CTX-like). The latter corresponds to 10 to 25% of the total toxicity.

A dose-time to death curve has been established with our CTX-like extracts.