The production of extracellular amino acids by rumen bacteria.

One hundred and sixteen freshly isolated rumen bacteria and 10 laboratory strains were studied for the production and excretion of free amino acids during growth in a basal medium containing glucose, cellobiose, and soluble starch as the energy sources, (NH4)2SO4 as the prime nitrogen source, volatile fatty acids, hemin, vitamins, Na2CO3, and cysteine as the reducing agent. Amino acid analyses of 48-h culture fluids of the isolates indicated the presence of alanine, glutamic acid, valine, aspartic acid, glycine, serine, lysine, methionine, leucine, isoleucine, threonine, histidine, arginine, phenylalanine, and tyrosine. Most isolates excreted some free amino acids. Alanine, glutamic acid, valine, aspartic acid, and glycine were found in the greatest concentrations with some isolates accumulating between 50 and 295 microgram/ml of one or more of these compounds. Concentrations of the remaining amino acids rarely exceeded 20 microgram/ml of culture fluid. Growth studies demonstrated that the amino acids were excreted during active growth of the bacteria and ceased shortly after growth became limited.