Variations in the uptake and metabolism of peptides and amino acids by mixed ruminal bacteria in vitro

Ian Armstead, John Ling

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Mixed ruminal bacteria, isolated from sheep (Q and W) fed a concentrate and hay diet, were anaerobically incubated with either 14C-peptides or 14C-amino acids. Experiment 1 showed that uptake of both 14C-labeled substrates was rapid, but the rate for amino acids was twofold greater than for peptides (molecular weight, 1,000 to 200) initially but was similar after 10 min. Experiment 2 demonstrated that metabolism was also rapid; at least 90% of either 14C-labeled substrate was metabolized by 3 min. Of the radioactivity remaining in bacteria, approximately 30% was in the form of 14C-amino acids, but only in leucine, tyrosine, and phenylalanine. Supernatant radioactivity was contained only in tyrosine, phenylalanine, and mostly proline for incubations with 14C-amino acids but in up to 10 amino acids when 14C-peptides were the substrates. Short-term incubations (<5 min; experiment 3) confirmed previous uptake patterns and showed that the experimental system was responsive to substrate competition. Experiment 4 demonstrated that bacteria from sheep Q possessed initial and maximum rates of 14C-amino acid uptake approximately fourfold greater (P < 0.01) than those of 14C-peptides, but with no significant differences (P > 0.1) between four 14C-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 14C-peptides and 14C-amino acids. Calculations 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 bacteria. The variations of these findings and their implications for future research are discussed.

Original languageEnglish
Pages (from-to)3360-3366
Number of pages7
JournalApplied and Environmental Microbiology
Issue number10
Publication statusPublished - Oct 1993


  • Amino Acids/metabolism
  • Animals
  • Bacteria/isolation & purification
  • Biological Transport, Active
  • Dietary Proteins/metabolism
  • In Vitro Techniques
  • Kinetics
  • Male
  • Peptides/metabolism
  • Rumen/metabolism
  • Sheep


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