The Influence of Folic Acid, Threonine and Glycine on Serine Synthesis in Tetrahymena

Abstract
Only 1 of 16 strains of Tetrahymena, studied, was found to be completely dependent on an exogenous source of serine for growth. A 2d strain appears to lack threonine aldolase, as it can synthesize serine from added glycine but not from added threonine. The remaining 14 strains will utilize either glycine or threonine (as a source of glycine) for serine synthesis provided the folic acid concentration in the medium is high.