Characterization of proteolytic activities of rumen bacterial isolates from forage‐fed cattle

The proteolytic activities of eight strains of ruminal bacteria isolated from New Zealand cattle were characterized with respect to their cellular location, response to proteinase inhibitors and hydrolysis of artificial proteinase substrates. The Streptococcus bovis strains had predominantly cell‐bound activity, which included a mixture of serine and cysteine‐type proteinases which had high activity against leucine p‐nitroanilide (LPNA). The Eubacterium strains had a mainly cell‐associated activity with serine and metallo‐type proteinases which showed high activity against the chymotrypsin substrate, N‐succinyl alanine alanine phenylalanine proline p‐nitroanilide (NSAAPPPNA) and some LPNA activity. A Butyrivibrio strain, C211, had a cell‐bound mixture of cysteine and metallo‐proteinase activities and strongly hydrolysed NSAAPPPNA and LPNA while the high activity Butyrivibrio‐like strain, B316, had a cell‐bound, mainly serine proteinase activity which strongly hydrolysed NSAAPPPNA. A Prevotella‐like strain, C21a, had a mixture of cysteine, serine and metallo‐proteinase activities which were cell‐bound and hydrolysed LPNA. The activities of these strains did not match those of the bacterial fraction of rumen fluid, which contained activities mainly of the cysteine type with specificity towards the substrate N‐succinyl phenylalanine p‐nitroanilide. The contribution of these strains to proteolysis in the rumen is discussed.