The Sterol Requirement of Tetrahymena paravorax RP

Tetrahymena paravorax RP was cultured axenically in a medium of known chemical composition (within the limits of contemporary standards of chemical purity). In this medium, it required 12 amino acids, 6 B‐complex vitamins, a purine, a pyrimidine, and inorganic salts. A sterol or sterol ester was necessary for optimal growth. Plant and animal 3 β‐OH sterols with saturated and unsaturated ring systems, and with a variety of side chain structures, were active. Several methylated sterols suggested as intermediates in cholesterol synthesis were inhibitory.