Influence of ionophores and energy inhibitors on peptide metabolism by rumen bacteria

Ionophores and inhibitors of bacterial energy metabolism were added to mixed rumen bacteria prepared from sheep receiving grass hay plus concentrate diets, and their influence on the rate of metabolism of alanine (Ala) peptides was determined. Dicyclohexylcarbodiimide (DCCD) had no influence on the rate of breakdown of Ala2, Ala3, Ala4 or Ala5, indicating that the metabolism of these peptides did not require ATP. The protonophores tetrachlorosalicylanilide (TCS) and carbonyl cyanide m-chlorophenyl-hydrazone (CCCP) inhibited peptide breakdown to a minor extent (< 15%), whereas the ionophores monensin and tetronasin had greater, but still small (12–31%), inhibitory effects. Toluene stimulated peptide breakdown, consistent with a permeability barrier having been removed. Thus, at least some peptide metabolism depends on transport into bacteria; transport appears not to be ATP-linked, and may well be coupled to the uptake of mineral cations rather than protons. Rumen fluid from sheep receiving a similar diet with added monensin (33 mg/kg) or tetronasin (10 mg/kg) hydrolysed Ala3 and Ala4 at rates that did not differ significantly from controls. Nevertheless, the peak concentration of free peptides in rumen fluid after feeding was more than doubled in ionophore-fed sheep, and peptides persisted for longer than in control animals.