VARIATIONS IN THE UPTAKE AND METABOLISM OF PEPTIDES AND AMINO-ACIDS BY MIXED RUMINAL BACTERIA IN-VITRO

Mixed ruminal bacteria, isolated from sheep (Q and W) fed a concentrat e and hay diet, were anaerobically incubated with either C-14-peptides or C-14-amino acids. Experiment 1 showed that uptake of both C-14-lab eled substrates was rapid, but the rate for amino acids was twofold gr eater than for peptides (molecular weight, 1,000 to 200) initially but was similar after 10 min. Experiment 2 demonstrated that metabolism w as also rapid; at least 90% of either C-14-labeled substrate was metab olized by 3 min. Of the radioactivity remaining in bacteria, approxima tely 30% was in the form of C-14-amino acids, but only in leucine, tyr osine, and phenylalanine. Supernatant radioactivity was contained only in tyrosine, phenylalanine, and mostly proline for incubations with C -14-amino acids but in up to 10 amino acids when C-14-peptides were th e substrates. Short-term incubations (<5 min; experiment 3) confirmed previous uptake patterns and showed that the experimental system was r esponsive to substrate competition. Experiment 4 demonstrated that bac teria from sheep Q possessed initial and maximum rates of C-14-amino a cid uptake approximately fourfold greater (P < 0.01) than those of C-1 4-peptides, but with no significant differences (P > 0.1) between four C-14-peptide substrate groups with molecular weights of 2,000 to <200 . By contrast, bacteria from sheep W showed no such distinctions (P > 0.1) between rates for C-14-peptides and C-14-amino acids. Calculation s suggested that peptides could supply from 11 to 35% and amino acids could supply from 36 to 68% of the N requirements of mixed ruminal bac teria. The variations of these findings and their implications for fut ure research are discussed.