title: Proteolytic activities of the starch-fermenting ruminal bacterium, Streptococcus bovis.
abstract: The objective of this study was to characterize the extracellular proteolytic activity of Streptococcus bovis. Strains KEG, JB1, NCFB 2476, and K11.21.09.6C produced very similar large molecular weight (160-200 kDa) extracellular proteases that were specifically inhibited by PMSF, a serine protease inhibitor. Further experiments with S. bovis KEG indicated that cultures grown with casein as the sole added N source produced the greatest level of proteolytic activity, and the level of proteolytic activity was independent of growth rate. Clarified ruminal fluid (CRF) decreased proteolytic activity by 54% compared with cultures grown with casein alone, and addition of exogenous peptides and carbohydrates (CHO) to the CRF further reduced the level of proteolytic activity by 44% and 52%, respectively. These results suggested that the proteolytic activity of S. bovis KEG was modulated by available N source and that the proteolytic activity was present for reasons other than providing N for growth. The role of S. bovis in ruminal proteolysis requires further definition, but phenotypic similarity among some ruminal strains would suggest a common niche in ruminal proteolysis. The uniformity of proteolytic activities could make S. bovis a prime candidate for manipulation in ruminal proteolysis control strategies.
authors.affiliation: Department of Animal Sciences, University of Illinois, 1207 W. Gregory Dr., Urbana, IL 61801, USA.
authors.forename: K E
authors.initials: KE
authors.lastname: Griswold
authors.forename: B A
authors.initials: BA
authors.lastname: White
authors.forename: R I
authors.initials: RI
authors.lastname: Mackie
mesh_terms: D000818:Animals; D003470:Culture Media; D004591:Electrophoresis, Polyacrylamide Gel / Q000379:methods; D010450:Endopeptidases / Q000378:metabolism*; D009584:Nitrogen / Q000378:metabolism; D012417:Rumen / Q000382:microbiology*; D015842:Serine Proteinase Inhibitors / Q000494:pharmacology; D013213:Starch / Q000378:metabolism; D016985:Streptococcus bovis / Q000201:enzymology* / Q000254:growth & development
chemical_list: D003470:Culture Media; D015842:Serine Proteinase Inhibitors; D013213:Starch; D010450:Endopeptidases; D009584:Nitrogen