The Use of Tetrahymena to Evaluate the Effects of Gamma Radiation on Essential Nutrilites*

Abstract

The complete synthetic medium for the growth of Tetrahymena pyriformis E was subjected to gamma‐radiation from cobalt 60. A dose‐response curve indicated the range of radiation which damaged the medium so that growth of Tetrahymena was inhibited. The essential vitamins and amino acids which comprise the medium were individually irradiated in solution. Media were prepared with single irradiated components and tested for their ability to support growth of the protozoa. Thiamine, riboflavin, pantothenate, pyridoxine, folic acid, and thioctic acid were destroyed by less than 1 × 10 6 rep, while 2 × 10 6 rep was required to inactivate nicotinic acid. Most amino acids proved to be relatively radiation‐resistant. At the high radiation levels of 1 × 10 7 rep and 2.3 × 10 7 rep respectively, only serine and methionine were damaged. All other amino acids remained biologically active even after receiving 2.3 × 10 7 rep, the highest level of radiation employed. Organoleptic observations, however, showed radiation‐caused color and odor changes in many of those amino acids whose biological activity for Tetrahymena was unaffected. The nucleotide, guanylic acid, was also inactivated at 2.3 × 10 7 rep.