Induction ofOenococcus oeniH+-ATPase activity and mRNA transcription under acidic conditions

The profiles of Oenococcus oeni IOB84.13 H(+)-ATPase activity under various conditions of growth were studied. Cells growing at low pH 3.5 had a 1.6-fold higher H(+)-ATPase activity compared to control cells grown at pH 5.3. While the pH of the growth medium was shown to be stable in the presence of malic acid, a drastic decrease in pH from 5.3 down to 3.9 during growth in the absence of malic acid induced an increase in H(+)-ATPase activity by 1.5-fold. This induction was even greater when the initial pH was 3.5. Partial cloning of the genes encoding the beta-subunit and the epsilon-subunit of the H(+)-ATPase suggested a typical F(1)F(0)-ATPase genetic organization in O. oeni. The atp mRNA was detected by slot blots. Cells shocked at acidic pH were shown to contain higher levels of atp mRNA compared to the control cells grown at pH 5.3. Taken together, these results indicate that the H(+)-ATPase of O. oeni is induced at low pH and that regulation seems to occur at the level of transcription. This agrees with the role of this enzyme in the regulation of the cytoplasmic pH and in the acid tolerance of O. oeni.