Comparative amino acid metabolism of Tetrahymena geleii.

The ciliated protozoan, Tetrahymena geleii, is known to be similar to higher animals in its nutritional requirements. Thus it may utilize glycogen, starch, and galactose, as well as glucose and sucrose for its carbohydrate supply (1). In addition, it requires for optimal growth very nearly all of the B vitamins known at present and all of the amino acids essential to mammalian growth and maintenance (2-4). However, T. geleii differs in requiring certain purines and pyrimidines (5), the amino acid, serine (3), and an unknown growth factor, protogen (6). The protozoan also differs in that it does not absolutely require an unsaturated fatty acid or any of the fat-soluble vitamins (7). These nutritional data do not constitute an entirely valid basis for comparison of T. geleii with vertebrates. The various cells exist under widely different physiological conditions and the nutritional data from higher animals are complicated by the general phenomenon of symbiosis with microorganisms. However, the nutritional similarities do suggest metabolic studies which would allow a more critical comparison of these extreme phylogenetic types within the animal kingdom. Such metabolic studies are of much interest from the standpoint of comparative biochemistry. Also they offer the possibility of recommending T. geleii further as a convenient experimental animal. This paper presents comparative studies of amino acid metabolism in T. gebeii. The general method has been to replace or supplement the essential amino acids with compounds which are related, either structurally or metabolically, to the various amino acids. The results have emphasized the similarities of T. geleii to vertebrate organisms and have, in some cases, differentiated it from other microorganisms.