Growth requirements and the effect of organic components of the synthetic medium on the biosynthesis of the antibiotic nisin in Streptococcus lactis strain.

A synthetic medium SM-3 has been elaborated for growth of Streptococcus lactis strain 51, which contains the minimal number of organic components required for the growth of this strain and nisin production. This medium contains 9 amino acids, 4 vitamins from B group, glucose and mineral salts. Addition of biotin to the medium stimulated the growth of the strain, while the addition of purines and/or pyrimidines had no effect. Hitherto biotin has been considered to be necessary for the growth of S. lactis and purines and pyrimidines were believed to stimulate the growth of these bacteria. In strain 51 the minimal requirements for growth were also the minimal requirements for nisin biosynthesis. Strain 51 produced 3-4 times less nisin in medium SM-3 than in a complex medium. The addition of one of four amino acids (serine, proline, cysteine or cystine) to SM-3 medium increased the amount of antibiotic produced. The addition of all four amino acids simultaneously, caused formation of nisin amounts similar to those produced in complex medium.