title: The nature of the stimulation of the growth of Streptococcus lactis by yeast extract.
abstract: Yeast extract was fractionated on Sephadex G-25 into 7 fractions. The fraction most stimulatory to the growth of Streptococcus lactis C10 contained over 70% of the amino N present in yeast extract and consisted of a wide variety of free amino acids and a small amount of peptide material. Examination of possible replacement factors for this fraction revealed that the amino -acid material present was largely responsible for the stimulation of Str. lactis C10. Purine and pyrimidine bases and inorganic constituents also contributed to the stimulation. In addition, yeast extract contained a component which decomposed H2O2, a metabolite which accumulates in the growth medium under aerobic conditions and inhibits growth. The nature of the stimulation was studied by isolating slow and fast acid-producing colonies of Str. lactis C10. It appeared that yeast extract and other amino-acid supplements prevented an observed inhibition of the growth of the slow variants below pH 6.0, apparently by satisfying a nutritional deficiency caused by a drop in pH.
mesh_terms: D000332:Aerobiosis; D000596:Amino Acids / Q000032:analysis / Q000494:pharmacology; D000818:Animals; D003470:Culture Media; D006863:Hydrogen-Ion Concentration; D013294:Lactococcus lactis / Q000187:drug effects / Q000254:growth & development*; D008892:Milk; D010455:Peptides / Q000494:pharmacology; D011687:Purines / Q000494:pharmacology; D011743:Pyrimidines / Q000494:pharmacology; D015002:Yeast, Dried
chemical_list: D000596:Amino Acids; D003470:Culture Media; D010455:Peptides; D011687:Purines; D011743:Pyrimidines