PHYSIOLOGICAL AND METABOLIC RESPONSES OF FUNCTIONAL LACTIC ACID BACTERIA TO STRESS FACTORS

In our study, six functional lactic acid bacterium strains (able to produce bacteriocins, exopolysaccharides, or S-layer proteins) were subjected to different stress conditions in order to evaluate their capacity to adapt to harsh environments. They were cultivated at different temperatures, below and above their optimal growth temperatures. Moreover, they were grown in presence of bile salts or NaCl, or in acidic media. Total proteins, lactic acid production, enzymatic activities and synthesis of the metabolites of biotechnological interest were evaluated for all growth conditions. Over expression of some proteins was detected in the electrophoretic pattern of the total protein extracts from the stressed cultures compared to the control cultures. Enzymatic activities and lactic acid production were, in general, directly related with growth. The tested strains maintained their capacity to synthesize the assayed metabolites under almost all stress conditions. Bacteriocin production of two strains and exopolysaccharides production of both Leuconostoc strains were correlated with growth, while the S-layer production and the bacteriocin production by strain L. helveticus 34.9 were enhanced under stress conditions.