Response of Leuconostoc œnos to environmental changes

Malolactic fermentation, a spontaneous step in vinification, is frequently controlled by use of malolactic bacterial starters of Leuconostoc œnos. Strains isolated from fermenting wines and then submitted to industrial processes to obtain freeze-dried preparations lose their natural adaptation to survive and to grow in wine. However, culture conditions influence their adaptability as well as their survival after exposure to stress. As the plasma membrane was considered as the primary target for the deleterious effects of the environment, the changes of its components after cell heating and incubation in hostile conditions were studied. The ratio of phospholipids to proteins of the membrane decreased significantly when cells were submitted to any kind of stress. Phospholipids decreased while the protein content increased up to fivefold. Only some membrane proteins were over-synthesized compared to control cells. Seventeen protein bands were separated by gel electrophoresis of which three in particular were always over-expressed after the cells were shocked. Some also appeared when the cells entered the stationary phase. These results show that Leuc. œnos responded to environmental stresses by changing its membrane composition. Stress proteins appeared whatever the nature of the shock. This phenomenon may be involved in the acquisition of resistance of Leuc. œnos to harsh conditions in wine.