The in vitro uptake and metabolism of peptides and amino acids by five species of rumen bacteria

Streptococcus bovis JB1, Prevotella ruminicola B1 4, Selenomonas ruminantium Z108, Fibrobacter succinogenes S85 and Anaerovibrio lipolytica 5S were incubated with either 14C‐peptides (mol. wt, 200–1000) or 14C‐amino acids to compare their rates of uptake and metabolism. In experiment 1, the bacteria were grown and incubated in a complex medium, but no uptake of 14C‐labelled substrates occurred. When casein digest was omitted, uptake rates of 14C‐peptides were different (P < 0·01) with each species, but nil for 14C‐amino acids. In experiment 2, to minimize the effects of non‐radiolabelled peptides and amino acids, defined and semi‐defined media were used. Patterns of 14C‐peptide uptake resembled those of experiment 1. The 5‐min rate for Strep. bovis JB1 was almost twice that of P. ruminicola B14, though by 15 min they were similar and threefold greater than other species; that of A. lipolytica 5S was especially low. Incubations with 14C‐amino acids resulted in a wide range (P < 0·01) of uptake rates; after 5 min P. ruminicola B14 possessed the lowest and Strep. bovis JB1 the highest, but after 15 min, that of Sel. ruminantium Z108 was even higher. All bacteria, with the exception of P. ruminicola B14, assimilated 14C‐amino acids faster (P < 0·01) than 14C‐peptides. Only Strep. bovis JB1 and P. ruminicola B14 were capable of extensively metabolizing 14C‐peptides, but all five species metabolized 14C‐amino acids; there was evidence of substantial degradation and some synthesis. Calculations suggest that peptides could supply up to 43%, and amino acids 62% of the N requirements of rumen bacteria.