The Relation of the Length of Lag Phase of Growth to the Synthesis of Nisin and Other Basic Proteins by Streptococcus lactis Grown Under Different Cultural Conditions

Abstract

A nisin-producing strain of S. lactis was grown in batch culture and at intervals during growth secondary cultures were derived from the parent culture and the length of lag of growth was estimated. Two media were used: a highly buffered ''medium 22'' and an unbuffered (LTB) medium both without pH control and with pH controlled at about 6.7. In ''medium 22'' the dry weight doubling time was 95 min. and at the end of growth the pH was 5.2. Neutralization of the culture in this medium did not markedly affect nisin production or dry weight. The total and cell-bound nisin formed/unit dry wt of organism tended to correlate with the length of lab phase of growth. In LTB medium the dry wt doubling time was 45 min. and the terminal pH was 4.5. Of the total nisin formed >80% was in the culture fluid when the pH was allowed to decrease below 6.0; total nisin in cultures without pH control did not correlate with length of lag phase of growth. Neutralization of the culture increased the dry weight of organism about threefold. Neutralization also increased the cell-bound nisin/unit dry wt organism in stationary phase and the length of lag of growth of such organisms was longer than comparable stationary-phase organisms grown in unneutralized culture. Chloramphenicol (1 ug./ml. medium) decreased the nisin/unit dry wt organism at stationary phase and the length of lag of growth of such cultures was shorter than in comparable cultures without chloramphenicol. Frequently the start of growth was characterised by a decrease of bio-assayable nisin and a shortening of the lag phase; these changes could be mimicked by a culture which had reached the stationary phase through glucose depletion. The characteristics of early growth were reproduced after the addition of more glucose.