Proteolytic activity of streptococcus bovis cultured alone or associated with Prevotella albensis, on two kinds of protein substrates: Casein or pea proteins

This work aims at studying in detail, the interaction between two major bac terial species involved in the ruminal proteolysis, Streptococcus bovis and Prevotella albensis. We chose to investigate this interaction by examining their behaviour both alone in monoculture and together in co-culture on tw o kinds of protein substrates. Comparison of the behaviour of S. bovis and P. albensis in monoculture, in terms of growth and total proteolytic activi ty with protein as the sole source of nitrogen, showed that S. bovis grew m ore rapidly and developed a higher total proteolytic activity A higher prop ortion of short peptides was generated at the end of the exponential growth phase on pea protein medium whereas peptide accumulation did not appear on casein medium for both species; peptides of casein origin would be used mo re by species in monoculture than those of pea origin. S. bovis predominate d in number in both co-cultures but the balance between species was greater on pea proteins (S. bovis: 64% and P. albensis: 36%) than on casein (S. bo vis: 86% and P. albensis: 14%). At the same time, the decrease of the prote olytic activity was smaller on pea protein medium than that with casein and the use of proteolysis products was facilitated; peptides liberated by pea protein hydrolysis accumulated less than those obtained from casein. Moreo ver, the diversity of the endopeptidases. expressed increased on pea protei ns and the exopeptidase activities remained rather constant whereas they we re highly stimulated on casein medium. All the results obtained in co-cultu re on pea proteins allowed us to suggest that a greater synergism occurred between the two species for the breakdown of proteins. (C) 2001 Academic Pr ess.