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SUMMARY: Streptococcus lactis was grown in batch culture in a complex organic medium. Growth of the culture was followed by estimating the extinction, the dry weight, protein, DNA and RNA of the organism; basic peptides were estimated by electrophoresis and nisin by bio-assay. By the end of the lag phase of growth when active DNA and RNA synthesis were already proceeding, the nisin which had been introduced with the inoculum could not be recovered, although the cocci contained other basic peptides. Rapid nisin synthesis started after an increase of about 50 % in the dry weight of the cocci had taken place. Initially, high molecular weight nisin was made, the concentration of which decreased as the incubation proceeded. This was followed by the production of lower molecular weight nisin which could be recovered 24 hr after the end of the incubation. Inocula of organisms derived at intervals from the parent culture were tested in secondary cultures for length of lag of growth by re-inoculation into fresh medium of the same composition. During the lag phase of growth of the parent culture, the length of lag of growth of the secondary cultures fell to about half the original time. The shortest lag of the secondary cultures coincided with commencement of logarithmic growth of the parent culture and with the disappearance of cellular nisin from the parent culture. The length of the lag of the secondary cultures returned to their original value as the parent culture reached stationary phase and coincided with maximum nisin concentration in the parent culture. It is suggested that the length of lag of growth is related to the presence of basic peptides.

Biosynthesis of the Antibiotic Nisin and Other Basic Peptides by Streptococcus lactis Grown in Batch Culture