Cytotoxic effects of delfin insecticide (Bacillus thuringiensis) on cell behaviour, phagocytosis, contractile vacuole activity and macronucleus in a protozoan ciliate Paramecium caudatum

Abstract

The freshwater protozoan ciliate Paramecium caudatum was used to assess the potential cytotoxic effects and functional activities of biological insecticide delfin. Delfin® WG is a biological insecticidebased on the SA-11 strain of Bacillus thuringiensis subspecies kurstaki serotype 3a, 3b. In acute toxicity studies, cell motility was affected slightly at lower concentrations but at higher concentrationscells exhibited rocking movements, later on cells became motionless. LC50 for 3 h exposure was found to be 250.17 ± 15.33 ppm. In acute exposure cells showed deformities such as swelling of cells, ovalshaped deformity, and at higher concentrations shortening of longitudinal axis in the body size with blackening of cytoplasm occurred. Leaking of cytoplasmic contents was also observed. A significantdepletion of phagocytosis was observed on exposure to 100 ppm of delfin for 30 min to 1 h duration and was time dependent. Changes in pulsatory vacuole activity were observed on exposure 25, 50 and100 ppm for 20 min. The macronuclear aberrations increased with increasing concentrations of delfin up to 100 ppm. Macronuclear aberrations such as rod shaped macronucleus, marginalization ofmacronucleus, fragmentation, vacuolization and complete diffusion of macronucleus were observed and were dose dependent. Our findings on phagocytosis, contractile vacuole activity and macronuclearchanges indicate a potential physiological and cytogenetic effect of delfin on P. caudatum. The simplicity in handling, faster generation time, easy maintenance in the laboratory, rapid performance and high reproducibility makes ciliates as suitable tools and tags for physiological, genotoxicity studies and risk assessment