Toxic and Phototoxic Properties of the Protozoan Pigments Blepharismin and Oxyblepharismin*

Abstract

Abstract— The toxic and phototoxic properties of blepharismin and oxyblepharismin that were purified from the pigments of a ciliated protozoan, Blepharisma japonicum , by thin‐layer chromatography, were investigated in detail. The toxicity was tested against the ciliated protozoan Dileptus margaritifer , which is relatively sensitive to blepharismin. Although oxyblepharismin has been believed to be neither toxic nor phototoxic, it was found that oxyblepharismin is toxic in the dark and is also phototoxic. This shows that oxyblepharismin can act as a photosensitizer. The toxicity and phototoxicity of these pigments were compared with those of hypericin, which is known to be a typical, strong photosensitizer from plants. It was concluded that blepharismin and oxyblepharismin have strong intrinsic toxicities in the dark compared with hypericin, but their phototoxicities are slightly weaker than that of hypericin. This strong intrinsic toxicity supports our proposal that blepharismin acts as a defensive device against predators in the dark as well as in the light. The decrease in the defensive ability and the increase in the resistance to photokilling of Blepharisma concomitant with its color change from red to blue‐purple in response to weak illumination can be explained by the decrease in toxicity and phototoxicity of the pigment itself and by the decrease in amount of the pigment.