Authors : Joana Silva , Ana Sofia Carvalho , Rita Ferreira , Paula Teixeira and Paul Gibbs
Abstract: The degree of thermotolerance conferred on Lactobacillus delbrueckii ssp. bulgaricus, by an acid shock or a heat shock, when cells were grown in controlled and non-controlled pH conditions, during exponential and stationary growth phases, was evaluated. For exponential phase cells, thermotolerance was enhanced by submitting the cells to prior heat or acid shocks independently of the pH of growth conditions. Stationary phase cells were significantly more resistant to heating than cells in the exponential phase but only when growth occurred under non-controlled pH. Induced thermotolerance in stationary phase cells, was only observed for cells grown under controlled pH. Except for cells in the stationary growth phase grown under non-controlled pH, the heat or acid shock treatments resulted in an intracellular increase in the well - known heat shock proteins, GroES and GroEL. The presence of chloramphenicol negated the heat shock response and production of GroES and GroEL, confirming that de novo protein synthesis was involved in cell protection. These proteins were also identified in stationary phase cells grown under non-controlled pH, suggesting their involvement in induced thermotolerance during growth at low pH. Very few studies have investigated the response of stationary phase cells. The evaluation development of the response to sub-lethal stresses as a function of the pH conditions during growth is a new insight;. In fact, it was demonstrated that the pH of growth is a crucial factor.
Joana Silva , Ana Sofia Carvalho , Rita Ferreira , Paula Teixeira and Paul Gibbs , 2006. Stress Response of Lactobacillus Delbrueckii ssp. Bulgaricus: The Importance of The Growth pH. Journal of Food Technology, 4: 166-171.