The Importance of Understanding the Stress Physiology of Lactic Acid Bacteria

Abstract

Lactic acid bacteria (LAB) are Gram-positive bacteria belonging to the phylum Firmicutes, class III the Bacilli, in order II the Lactobacillales. The LAB are phylogenetically quite diverse, and the genera generally associated with foods include Lactobacillus, Lactococcus, Enterococcus, Streptococcus, Leuconostoc, Weissella, Oenococcus, Pediococcus, Tetragenococcus, and Carnobacterium. They are of tremendous importance in the production of fermented dairy, meat, vegetable, and cereal foods, mainly as a result of their acidification of foods and the associated preservation effect in addition to improving the aroma, taste, and texture. Furthermore, many LAB are associated with the human gastrointestinal tract, and certain strains have been developed as probiotics. Although modern molecular biological methods have enabled us to have a good view of the taxonomy of the LAB, they have also demonstrated that more data are required to obtain a better and more detailed picture and that the taxonomy of genera such as Lactobacillus is still far from satisfactory. The considerable diversity of LAB genera and species is reflected in their occurrence in a wide variety of habitats, which include some niches with quite extreme conditions of (for these bacteria) high temperatures, low temperatures, or high salt concentrations. Unlike other Gram-positive bacteria such as Bacillus or Listeria, dealing with the stresses encountered in such environments does not rely on a global stress-response regulator such as σΒ. LAB respond to stress with several conserved stress proteins (DnaK, GroEL, Clp), which are also involved in cross-protection against various stress conditions. Depending on the type of stress, other, more specific regulators or mechanisms are also utilized to protect from harmful conditions. A better understanding of the stress response of LAB starters and probiotics and the stresses influencing these bacteria in their industrial and health applications can lead to the development of strains better adapted to survival and growth and hence to functionally more effective strains.