6533b7d8fe1ef96bd126b60c

RESEARCH PRODUCT

pH Homeostasis and Citric Acid Utilization: Differences Between Leuconostoc mesenteroides and Lactococcus lactis

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description

This study presents the effects of citric acid and extracellular pH (pHe) on the intracellular pH (pHi) of wild-type and citrate negative variants (cit−) Leuconostoc mesenteroides subsp. mesenteroides (Ln. mesenteroides M) and Lactococcus lactis subsp. lactis bv. diacetylactis (L. lactis LD). A recent method using a pH-sensitive fluorescent indicator carboxyfluorescein succinimidyl ester (cFSE) was adapted to measure the pHi of these two lactic acid bacteria in resting cells. Energized cells with 10 mM lactose of Ln. mesenteroides M and L. lactis LD modified their pH gradient (ΔpH) in the same manner; when the pHe was decreased from 7 to 4, the pHi decreased from 7 to about 5. The adjunction of 10 mM citric acid had no effect on the pHi of wild-type and cit(−) variant of L. lactis LD, nor on the pHi of Ln. mesenteroides cit(−) variant. Nevertheless, in Ln. mesenteroides M wild-type, citric acid utilization increased the pHi, which was maintained at about 6.5–7.0 when the pHe was decreased from 7 to 4. It could be concluded that citric acid allows the maintenance of pH homeostasis in Leuconostoc mesenteroides.