REGULATION OF PROTEINASE SYNTHESIS IN LACTOCOCCUS-LACTIS

The synthesis of extracellular serine proteinase of Lactococcus lactis was studied during the growth in a batch and a continuous culture on chemically defined media. In a batch culture the proteinase synthesis started during the exponential phase of growth and the highest proteinase concentrations were found at the end of the exponential and beginning of the stationary phase of growth. During the growth in a lactose-limited chemostat with amino acids as the sole source of nitrogen, the specific rate of proteinase synthesis was maximal at a mu of 0.23 h-1. At higher growth rates the proteinase production declined. The proteinase synthesis was dependent on the amino acid sources in the medium. In batch cultures of L. lactis grown on a chemically defined medium with amino acids, the proteinase production was increased four-fold compared to media containing casein or a tryptic digest of casein as the sole source of nitrogen. The inhibition of the rate of proteinase synthesis by casein and peptides was also observed during the growth in a chemostat. The addition of the dipeptide leucylproline (final concentration of 100 muM) to a lactose-limited continuous culture during the steady state (D = 0.23 h-1) resulted in a transient inhibition of the rate of proteinase synthesis. This suggested that exogenously supplied peptides control the regulation of proteinase synthesis of L. lactis.