Acidophilic behaviour of the malolactic bacterium Oenococcus oeni

Abstract

Oenococcus oeni is a lactic acid bacterium most often responsible for malolactic fermentation in wine. Acidity appears as a crucial parameter that limits bacterium growth in wine. The high concentration of ethanol and sulphite enhanced this deleterious effect of this medium. Many mechanisms contribute to the acid tolerance of O. oeni. The cytoplasmic membrane is the first target of such stress. After a mild acid shock, the membrane fluidity is regulated to control exchange with the medium. This adaptation process involves the modification of the membrane composition and probably the synthesis of stress proteins allowing the maintenance of enzymatic activities associated to the membrane. Moreover, the activation of protons-ATPase and the consumption of protons during the malolactic fermentation participate to the adaptation at acid pH. The study of acid sensitivity of neomycin resistant mutants of Oenococcus oeni has demonstrated a relationship between reduction of ATPase activity and lack of malolactic activity.