Isolation of proteolytic rumen bacteria by use of selective medium containing leaf fraction 1 protein (ribulosebisphosphate carboxylase).

The principle proteolytic bacteria isolated from bovine rumen contents by virtue of the ability to obtain nitrogen from the proteolysis of leaf fraction 1 protein (ribulosebisphosphate carboxylase, EC 4.1.1.39) were identified as Streptococcus bovis and Butyrivibrio spp. Substitution of fresh fodder, rich in soluble protein, for a hay-concentrates diet resulted in enhanced ruminal proteolytic activity and a significant increase in the number of bacteria able to use fraction 1 protein as the sole nitrogen source. Isolated proteolytic bacteria degraded fraction 1 protein and casein readily. Bovine serum albumin was attacked by Butyrivibrio spp. but was resistant to proteolysis by the streptococci.