Relationship between acid tolerance, cytoplasmic pH, and ATP and H+- ATPase levels in chemostat cultures of Lactococcus lactis

Abstract

The acid tolerance response (ATR) of chemostat cultures of Lactococcus lactis subsp. cremoris NCDO 712 was dependent on the dilution rate and on the extracellular pH (pH(o)). A decrease in either the dilution rate or the pH(o) led to a decrease in the cytoplasmic pH (pH(i) of the cells, and similar levels of acid tolerance were observed at any specific PH(i) irrespective of whether the pH(i) resulted from manipulation of the growth rate, manipulation of the pH(o), or both. Acid tolerance was also induced by sudden additions of acid to chemostat cultures growing at a pH(o) of 7.0, and this induction was completely inhibited by chloramphenicol. The end products of glucose fermentation depended on the growth rate and the environmental pH(o) of the cultures, but neither the spectrum of end products nor the total rate of acid production correlated with a specific pH(i). The rate of ATP formation was not correlated with pH(i), but a good correlation between the cellular level of H+-ATPase and pH(i) was observed. Moreover, an inverse correlation between the cytoplasmic levels of ATP and pH(i) was established. Each pH(i) below 6.6 was characterized by unique levels of ATR, H+-ATPase, and ATP. High levels of H+ATPase also coincided with high levels of acid tolerance of cells in batch cultures induced with sublethal levels of acid. We concluded that H+-ATPase is one of the ATR proteins induced by acid pH(i) through growth at an acid pH(o) or a slow growth rate.