The Physiological Response Of Lactobacillus Casei Atcc 393 Under Different Stresses

As a natural microflora from dairy products, Lactobacillus casei always encounters several stressful conditions which will greatly affect its viability, productivity and flavor. In these cases, a series of physiological changes named stress responses appeared in L. casei to fight against the harsh environments. However, various stresses always occur simultaneously thus complicates the defense system, and the traditional research on single-stress is absolutely limited to describe the changes in the stress process. In this study, we investigated the survival and corresponding physiological changes of the L.casei type strain, L.casei ATCC 393, under cross-protection. The results will help us to understand the mechanism of stress tolerance in the complex environment and provide the possibility to improve stress tolerance of cells used as probiotics products.1. We compared the survival rate of L.casei ATCC 393 under varying conditions of heat, acid, oxygen, and bile salt stress. L.casei ATCC 393 exhibited a good acid stress tolerance (pH3.0) and strong resistance to bile (2% bile salt concentration remained 50% survival rate) on the early mid-log phase. In addition, it maintained a high survival rate both in 1 mM hydrogen peroxide treatment and 50oC 90 min, which showed its potential used as probiotics.2. The survival rate of cells with or without cross stresses were compared. Pre-adaptation with mild acid was found to be most effective in improving the viability of cells under both lethal thermal and lethal oxygen stresses. Compared with lactic acid, hydrochloric acid was the better cross-protection inducer which increased the survival to 305-fold and 173-fold respectively under heat and oxygen stress after mild acid preadaption (pH 3.8-4.0 HCl 90 minutes).3. The membrane composition of cells as well as intracellular pH (pHi) was then investigated under cross-protection induced by acid. Different from the cells directly encountered the lethal thermal and oxygen stresses, adapted cells showed a slow decline in both pHi and unsaturation of membrane fatty acids. Such results indicated that the acid- induced cross protection may stabilize the intracellular pH and membrane saturation which related to the cell integrity.4. The proteome changes of L.casei ATCC 393 in cross-protection were then compared by two-dimensional protein electrophoresis and isobaric tags for relative and absolute quantitation (iTRAQ) technology. Results suggested that the strong ability of protein repair and regeneration may be the main reason of cross-protection in improving cells'survival under stresses. In addition, DNA repair system and the maintenance of energy metabolism may play a role in such tolerances.