Modification de la fonction antibiotique de deux diatomées marines, Asterionella japonica (Cleve) et Chaetoceros lauderi (Ralfs), par le dinoflagellé Prorocentrum micans (Ehrenberg)

Abstract

Two diatoms, Asterionella japonica (Cleve) and Chaetoceros lauderi (Ralfs), produced a similar lipidic antibiotic, whose activity increased after irradiation by visible light. In mixed cultures with the dinoflagellate Prorocentrum micans Ehrenberg, their cells contained higher amounts of the photoactivated antibiotic and a lower quantity of carotenoid pigments. These observations suggest the action of a chemical mediator released into the medium by P. micans, which inhibits the synthesis of pigments, thus leading to an increase of the photoactivation of the lipidic antibiotics in vivo. A similar inverse relationship between the concentration of carotenoids and the antibiotic activity was observed in several clones of Asterionella japonica isolated from different sea-water samples, and in cultures of the same diatom in the presence of diphenylamine. The importance of such phenomenon in a natural environment is discussed.