DEGRADATION OF PROTEIN AND UTILIZATION OF THE HYDROLYTIC PRODUCTS BY A PREDOMINANT RUMINAL BACTERIUM, PREVOTELLA-RUMINICOLA B(1)4

Degradation and utilization of protein by Prevotella ruminicola B(1)4, a proteolytic bacterium that is prominent in the rumen, was examined. In preliminary experiments, proteinaceous N sources produced faster g rowth rates than did NH4Cl, based on changes in optical density over t ime. However, ammonium chloride produced a greater maximum cell densit y than did proteinaceous N sources. Of the proteinaceous N sources, an enzymatic hydrolysate of soybean protein with a relative peptide size of 3 AA residues produced a greater growth rate and maximum cell dens ity compared with the other proteinaceous N sources. Further experimen ts revealed that P. ruminicola B(1)4 grew faster and to a greater fina l dry weight with soybean protein than with casein. Degradation of bot h proteins was low as was indicated by the slow disappearance of solub le protein, low concentrations of free AA and peptides, and the decrea se in ammonia concentrations over time. Patterns of degradation did di ffer between the two proteins, however. Accumulation of peptides and f ree AA from soybean protein peaked 2 h earlier than those from casein, and concentrations of free AA and peptides from soybean protein were lower on average than those from casein. Prevotella ruminicola B14 pre ferentially utilized Asp, Ile, Leu, Lys, and Arg from soybean protein compared with casein. The relative size of peptides that accumulated f rom both proteins, as determined by the ratio of ninhydrin reaction af ter HCl hydrolysis to ninhydrin reaction before HCl hydrolysis, sugges ted that part of the proteolytic activity of P. ruminicola B14 is a di peptidase. Our findings suggest that P. ruminicola may have a greater impact on peptide degradation than on protein degradation in the rumen .