pH Homeostasis in Lactic Acid Bacteria

The ability of lactic acid bacteria to regulate their cytoplasmic or intracellular pH is one of the most important physiological requirements of the cells. Cells unable to maintain a near neutral intracellular pH during growth or storage at low extracellular pH may lose viability and cellular activity. Despite the importance of pH homeostasis in the lactic acid bacteria, however, an understanding of cytoplasmic pH regulation has only recently begun to emerge. This review describes the specific effects of low pH on lactic acid bacteria, reports recent research on the physiological role of intracellular pH as a regulator of various metabolic activities in lactic acid bacteria, and presents the means by which lactic acid bacteria defend against low intracellular pH. Particular attention is devoted to the proton-translocating ATPase, an enzyme that is largely responsible for pH homeostasis in fermentative lactic acid bacteria

pH Homeostasis in Lactic Acid Bacteria

The ability of lactic acid bacteria to regulate their cytoplasmic or intracellular pH is one of the most important physiological requirements of the cells. Cells unable to maintain a near neutral intracellular pH during growth or storage at low extracellular pH may lose viability and cellular activity. Despite the importance of pH homeostasis in the lactic acid bacteria, however, an understanding of cytoplasmic pH regulation has only recently begun to emerge. This review describes the specific effects of low pH on lactic acid bacteria, reports recent research on the physiological role of intracellular pH as a regulator of various metabolic activities in lactic acid bacteria, and presents the means by which lactic acid bacteria defend against low intracellular pH. Particular attention is devoted to the proton-translocating ATPase, an enzyme that is largely responsible for pH homeostasis in fermentative lactic acid bacteria

Intracellular pH Effects in Lactic Acid Bacteria

The objectives of this research were to determine the effect of lactic acid and low pH on the intracellular pH in three species of lactic acid bacteria. A pH gradient (intracellular pH minus the extracellular pH) of .9 to 1.4 pH units was achieved by several strains of lactic acid bacteria, including Streptococcus thermophilus 19258 and 573, Lactococcus lactis ssp. lactis C2, and Lactococcus lactis ssp. cremoris HP during log phase of growth in various media. A noticeable decline of the pH gradient occurred at an internal pH of 5.5 to 6.0. In late stationary phase, the pH gradient was generally reduced to .5 pH units or less. In contrast, the aciduric Lactobacillus casei 685 maintained a large pH gradient (\u3e 1.0 pH units) even when the medium pH was reduced to less than 4.0. Rapid growth of lactococci and streptococci in media containing excess lactose did not occur when the intracellular pH was reduced below a critical pH of 5.0 or at a neutral pH when proton-uncoupling agents were present

Optimisation of Perioperative Cardiovascular Management to Improve Surgical Outcome II (OPTIMISE II) trial: study protocol for a multicentre international trial of cardiac output-guided fluid therapy with low-dose inotrope infusion compared with usual care in patients undergoing major elective gastrointestinal surgery.

INTRODUCTION: Postoperative morbidity and mortality in older patients with comorbidities undergoing gastrointestinal surgery are a major burden on healthcare systems. Infections after surgery are common in such patients, prolonging hospitalisation and reducing postoperative short-term and long-term survival. Optimal management of perioperative intravenous fluids and inotropic drugs may reduce infection rates and improve outcomes from surgery. Previous small trials of cardiac-output-guided haemodynamic therapy algorithms suggested a modest reduction in postoperative morbidity. A large definitive trial is needed to confirm or refute this and inform widespread clinical practice. METHODS: The Optimisation of Perioperative Cardiovascular Management to Improve Surgical Outcome II (OPTIMISE II) trial is a multicentre, international, parallel group, open, randomised controlled trial. 2502 high-risk patients undergoing major elective gastrointestinal surgery will be randomly allocated in a 1:1 ratio using minimisation to minimally invasive cardiac output monitoring to guide protocolised administration of intravenous fluid combined with low-dose inotrope infusion, or usual care. The trial intervention will be carried out during and for 4 hours after surgery. The primary outcome is postoperative infection of Clavien-Dindo grade II or higher within 30 days of randomisation. Participants and those delivering the intervention will not be blinded to treatment allocation; however, outcome assessors will be blinded when feasible. Participant recruitment started in January 2017 and is scheduled to last 3 years, within 50 hospitals worldwide. ETHICS/DISSEMINATION: The OPTIMISE II trial has been approved by the UK National Research Ethics Service and has been approved by responsible ethics committees in all participating countries. The findings will be disseminated through publication in a widely accessible peer-reviewed scientific journal. TRIAL REGISTRATION NUMBER: ISRCTN39653756.The OPTIMISE II trial is supported by Edwards Lifesciences (Irvine, CA) and the UK National Institute for Health Research through RMP’s NIHR Professorship

Proton-Translocating Adenosine Triphosphatase Activity in Lactic Acid Bacteria

Streptococcus thermophilus 19258 and 573, Luctococcus luctis ssp. lucris C2, Lactococcus luctis ssp. cremoris HP, and Luctobucillus cusei 685 were grown in various media and assayed for protontranslocating ATPase (H+-ATPase) activity. The H+-ATPase was extracted from the membrane fractions of protoplasted cells using a French pressure cell, and activity was measured by the release of inorganic phosphate from ATP. The pH optima for the H+-ATPase, assayed in vitro, were 7.5 for S. thermophilus and Lactococcus luctis ssp. cremoris HP and 5.0 for Lactobacillus casei 685. In contrast, for cells grown in batch culture the H+-ATPase activity was always greatest when the cytoplasmic pH was less than the optimum for the enzyme. The H+- ATPase activity generally increased as the pH decreased until an extracellular pH of 5.0 was reached. Below an extracellular pH of 5.0, activities of this enzyme dropped markedly. The aciduric lactic acid bacterium, Lactobacillus casei 685, had higher basal levels of this enzyme than the streptococci and lactococci. Results suggest that this enzyme may be involved in regulation of the intracellular pH in lactic acid bacteria