The biochemistry of rumen protozoa. 5. The nitrogen metabolism of Entodinium

Blackburn & Hobson (1960a) reported that when stained particles of casein were added to sheep rumen liquor incubated in vitro, oligotrich protozoa could be seen to swallow and digest these particles. One of the most numerous species of such protozoa is Entodinium caudatum. Suspen- sions of this organism containing no other protozoa and almost free from bacteria were used by us in a study of its carbohydrate metabolism (Abou Akkada & Howard, 1960). It was shown that this organism satisfies its carbohydrate needs only by swallowing and digesting starch grains. It seemed of interest to see whether casein particles could also serve as food for the entodinia. Preliminary experiments showed that stained casein particles were readily swallowed and digested by clean, washed suspensions of the entodinia. The work described below is concerned mainly with the decomposition of casein by E. caudatum and with the properties of the enzymes involved, together with some other aspects of nitrogen metabolism by this protozoan.