Role of choline in the nutrition of the rumen protozoon Entodinium caudatum.

A requirement of choline for growth of Entodinium caudatum in a simplified culture medium has been demonstrated. Ethanolamine, N-methylethanolamine, or N-dimethylethanolamine were ineffective as substitutes. In the rumen, the normal environment of this organism, levels of free choline were virtually zero even after ingestion of pasture containing phosphatidylcholine which was rapidly catabolized. Free [Me-14C]choline is very rapidly cleared from rumen fluid, a little being incorporated into the phosphatidylcholine of protozoa, but the clearance also occurs in animals with defaunated rumens. It is suggested that E. caudatum obtains choline for growth mainly from plant membrane material which it has ingested, rather than from the free base in the rumen liquor.