Effect of rapid cooling and acidic pH on cellular homeostasis of Pectinatus frisingensis, a strictly anaerobic beer-spoilage bacterium.

Pectinatus frisingensis is a strictly anaerobic mesophilic bacterium involved in bottled beer spoilage. Cellular volume, adenylate energy charge, intracellular pH and intracellular potassium concentration measurements were performed in late exponential-phase cell suspensions placed in different physiological conditions, to evaluate the capability of this bacterium to maintain cellular homeostasis. The intracellular pH was calculated from the intracellular accumulation of a [carboxyl-14C]benzoic acid. Optimum physiological conditions were the presence of a carbon source and pH of 6.2, hostile conditions were a pH 4.5, absence of a carbon source, and rapid cooling treatment. The cell was able to maintain a higher intracellular pH than the external pH under all conditions. Intracellular volume was lower at pH 4.5 than at pH 6.2. A low net potassium efflux rate was routinely measured in starving cells, while glucose addition promoted immediate net potassium uptake from the medium. Cooling treatment resulted in sudden net potassium efflux from the cell, a decrease of the intracellular pH, and low modifications of the adenylate energy charge in metabolizing-glucose cell suspensions. Thus, cold treatment perturbs the P. frisingensis homeostasis but the bacteria were able to restore their homeostasis in the presence of a carbon source, and under warm conditions.