Identification of a stimulant for Lactobacillus casei produced by Streptococcus lactis

A compound stimulatory to the growth of Lactobacillus casei was isolated from cell extracts of Streptococcus lactis, purified, and characterized. The stimulant was identified as a small peptide with a molecular weight of approximately 4,500 daltons. The purified peptide gave negative tests for nucleic acids, phosphorus, glucosamine, and carbohydrates. Sixteen amino acids were detected in acid hydrolysates of this peptide. Serine, proline, glycine, alanine, leucine, and glutamic acid were present in hydrolysates in greatest abundance.