Characterization of Streptococcus thermophilus strains that undergo lysis under unfavourable environmental conditions

The autolysis of starter lactic acid bacteria appears as a promising way to enhance the flavour of fermented dairy products. The present work was aime d at investigating the autolysis phenomenon in Streptococcus thermophilus, a thermophilic lactic acid bacteria involved in the starters used for the p roduction of yoghurts, Italian and Swiss-type cheeses. Out of 146 strains s creened for their aptitude to spontaneously lyse at the end of growth in M1 7 medium containing lactose in limited concentration six strains, among whi ch is the type strain CNRZ 1358, were found to be highly autolytic. These a utolytic strains are characterized by a typical bell-shaped growth curve. L ysis of the type strain, which was studied as the model, was triggered unde r unfavourable environmental conditions, such as lactose depletion and NaCl or organic solvents addition. The lysogenic character of this strain was e videnced. Taken together, our results indicate that the autolytic phenotype in S. thermophilus is linked to the lysogenic character but does not resul t from the massive prophage induction under stressing conditions. (C) 2000 Elsevier Science B.V. All rights reserved.