Serum-Induced Endocytic Vacuole in the Nonphagocytic Tetrahymena Pyriformis Strain NP1

Abstract

Tetrahymena pyriformis strains WH6, W, HSM, and GLC, after exposure to normal human serum, give rise to large membrane-bounded endocytic vacuoles, as visualized by transmission electron microscopy (TEM). These vacuoles do not resemble ordinary food vacuoles formed in the oral apparatus. Nor do they appear to be vacuoles containing protein concentrated from the serum: Albumin solutions induce a different type of vacuole (Brenner et al., 1976). The large bodies take a stain (PAS) that indicates the presence of polysaccharide. TEM micrographs show the presence of lipid in some of the large bodies. It is not yet known if these large body vacuoles are formed in the oral apparatus like food vacuoles or result from the fusion of pinocytic vacuoles.Although the mutant T. pyriformis strain, NP1, is unable to form a functional oral apparatus at 37° C and cannot form food vacuoles (Rasmussen and Orias, 1975), it multiplies in 2% proteose peptone medium supplemented with vitamins and heavy metal salts.