Stress Responses of Lactococcus lactis
Lactococcus lactis is a Gram-positive bacterium widely used as a starter culture in the food industry due to its health-promoting and nutritional properties. However, L. lactis, similar to other lactic acid bacteria, encounters various stress conditions both during industrial processes and in the gastrointestinal tract. In response to environmental stresses, L. lactis employs numerous mechanisms to survive under stressful conditions. In this chapter, the stress responses of L. lactis, including alterations in the metabolic activities and energy state as well as the intracellular stress signals are summarized and discussed. In general, environmental stresses result in decreased glycolytic activity and in shifts of the metabolic pathways to counteract the harsh environment encountered. In addition, the intracellular stress-response signals such as the maintenance of intracellular pH homeostasis and the accumulation of specific intermediates are elucidated. Finally, we summarize the cross-protection phenomenon in L. lactis, which leads to increased stress resistance by pre-exposure of the cells to a mild stress. We believe that by addressing the overall stress responses of L. lactis, we are contributing to a deeper understanding of the tolerance mechanisms in this microorganism to environmental stresses that may provide new strategies to enhance the industrial utility of this species.
KeywordsLactic Acid Bacterium Cholic Acid Glycine Betaine Proton Motive Force Acid Tolerance Response
Preparation of this chapter was supported in part by a grant from the Major Program of National Natural Science Foundation of China (No. 20836003) and the National Natural Science Foundation of China (No. 30900013). We also thank Chongde Wu and Feng Xue for their numerous contributions to this work.
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