In Situ Determination of the Intracellular pH ofLactococcus lactisandLactobacillus plantarumduring Pressure Treatment

Abstract

Hydrostatic pressure may affect the intracellular pH of microorganisms by (i) enhancing the dissociation of weak organic acids and (ii) increasing the permeability of the cytoplasmic membrane and inactivation of enzymes required for pH homeostasis. The internal pHs of Lactococcus lactis and Lactobacillus plantarum during and after pressure treatment at 200 and 300 MPa and at pH values ranging from 4.0 to 6.5 were determined. Pressure treatment at 200 MPa for up to 20 min did not reduce the viability of either strain at pH 6.5. Pressure treatment at pH 6.5 and 300 MPa reduced viable cell counts of Lactococcus lactis and Lactobacillus plantarum by 5 log after 20 and 120 min, respectively. Pressure inactivation was faster at pH 5 or 4. At ambient pressure, both strains maintained a transmembrane pH gradient of 1 pH unit at neutral pH and about 2 pH units at pH 4.0. During pressure treatment at 200 and 300 MPa, the internal pH of L. lactis was decreased to the value of the extracellular pH during compression. The same result was observed during treatment of Lactobacillus plantarum at 300 MPa. Lactobacillus plantarum was unable to restore the internal pH after a compressiondecompression cycle at 300 MPa and pH 6.5. Lactococcus lactis lost the ability to restore its internal pH after 20 and 4 min of pressure treatment at 200 and 300 MPa, respectively. As a consequence, pressure-mediated stress reactions and cell death may be considered secondary effects promoted by pH and other environmental conditions.

Standardized Assay Medium To Measure Lactococcus lactis Enzyme Activities while Mimicking Intracellular Conditions

“…The pH of the assay medium was set to 7.5, the reported internal pH (34) at an external pH of 6.5 (the same as in CDMPC). Furthermore, it seems that the internal pH is kept rel- atively constant in vivo in the range of external pHs between 6 and 7 (29). Element concentrations.…”

Protective Effect of Sucrose and Sodium Chloride for Lactococcus lactis during Sublethal and Lethal High-Pressure Treatments

“…The fluorescence method developed by Breeuwer et al (5) was adapted to L. lactis subsp. cremoris MG1363 (22). Cells from an overnight culture were washed and resuspended in 50 mM HEPES buffer (pH 8.0).…”

“…The ATP-dependent multiple-drug-resistance (MDR) transporter HorA is inactivated prior to cell death in Lactobacillus plantarum during high-pressure treatment (38, 39), and the pressure-mediated inactivation of HorA depends on the membrane composition (39). In L. plantarum and L. lactis inactivation of the membrane-bound ATPases and reductions in the intracellular pH were observed after high-pressure treatment (22,44).…”

“…The ATP-dependent multiple-drug-resistance (MDR) transporter HorA is inactivated prior to cell death in Lactobacillus plantarum during high-pressure treatment (38, 39), and the pressure-mediated inactivation of HorA depends on the membrane composition (39). In L. plantarum and L. lactis inactivation of the membrane-bound ATPases and reductions in the intracellular pH were observed after high-pressure treatment (22,44).Since membranes and membrane-bound enzymes are among the main targets of high-pressure inactivation, we directed our attention to the membrane-bound MDR transport enzymes of L. lactis. In L. lactis at least four drug extrusion activities have been detected (3,20).…”

D-Tagatose production by Lactococcus lactis NZ9000 Cells Harboring Lactobacillus plantarum L-arabinose Isomerase

“…The highest dairy products and medicine with broad market prospects. 27 The aim of this work was to investigate the possibility of producing D-tagatose from D-galactose with the recombinant Lactococcus lactis NZ9000 cells harboring araA from lactic acid bacteria. As described previously, the recombinant strain was successfully constructed and D-tagatose is produced efficiently after optimization.…”