Response mechanisms of lactic acid bacteria to alkaline environments: a review

Regulation of the cytoplasmic or internal pH (pHin) is a fundamental requirement for the survival and viability of bacteria. The optimum pHin for most bacteria is near the neutral point (pH 7.0). Therefore, bacteria may have some strategies to adapt themselves to the acidity or alkalinity of cytoplasm. As other microorganisms, lactic acid bacteria (LAB) are able to maintain a neutral or near neutral cytoplasmic pH even when the pH of the external medium varies. Mechanisms facilitating survival and growth under alkaline conditions of LAB are reviewed. These mechanisms are: (i) the active potassium extrusion and the potassium-proton antiport system, (ii) the sodium-proton antiport system, (iii) the proton-translocating adenosine triphosphatase (ATPase), (iv) the formation of transmembrane proton gradients (ΔpH) in a reversed direction, and (v) the adaptation, cross-protection, and changes in protein synthesis.