0000000000067134
AUTHOR
Christophe Riondet
Effect of reducing agents on the acidification capacity and the proton motive force of Lactococcus lactis ssp. cremoris resting cells.
International audience; Reducing agents are potential inhibitors of the microbial growth. We have shown recently that dithiothreitol (DTT), NaBH(4) and H(2) can modify the proton motive force of resting cells of Escherichia coli by increasing the membrane protons permeability [Eur. J. Biochem. 262 (1999) 595]. In the present work, the effect of reducing agents on the resting cells of Lactococcus lactis ssp. cremoris, a species widely employed in dairy processes was investigated. DTT did not affect the acidification nor the DeltapH, in contrast to the effect previously reported on E. coli. The DeltaPsi was slightly increased (30 mV) at low pH (pH 4) in the presence of 31 mM DTT or 2.6 mM NaB…
Determination of total ribonucleotide pool in plant materials by high-pH anion-exchange high-performance liquid chromatography following extraction with potassium hydroxide
A new, improved method that only requires a potassium hydroxide extraction procedure is presented for the analysis of a full nucleotide pool in plant materials. Quantification was performed by high-pH anion-exchange chromatography (HPAEC) with UV detection after a potassium hydroxide extraction, and allowed the quantification of 13 linear ribonucleotides in a single run. The method has been validated by comparison of six extraction methods and also by measurement of the intracellular nucleotide levels of three plant species (cell cultures and leaves). The evolution of the nucleotide pool of Nicotiana tabacum cell culture during growth has also been measured, and showed an increase in the po…
Changes in the proton-motive force in Escherichia coli in response to external oxidoreduction potential.
International audience; The pH homeostasis and proton-motive force (Deltap) of Escherichia coli are dependent on the surrounding oxidoreduction potential (ORP). Only the internal pH value and, thus, the membrane pH gradient (DeltapH) component of the Deltap is modified, while the membrane potential (DeltaPsi) does not change in a significant way. Under reducing conditions (Eh < 50 mV at pH 7.0), E. coli decreases its Deltap especially in acidic media (21% decrease at pH 7.0 and 48% at pH 5.0 for a 850-mV ORP decrease). Measurements of ATPase activity and membrane proton conductance (CH+m) depending on ORP and pH have shown that the internal pH decrease is due to an increase in membrane prot…
Extracellular oxidoreduction potential modifies carbon and electron flow in Escherichia coli.
ABSTRACT Wild-type Escherichia coli K-12 ferments glucose to a mixture of ethanol and acetic, lactic, formic, and succinic acids. In anoxic chemostat culture at four dilution rates and two different oxidoreduction potentials (ORP), this strain generated a spectrum of products which depended on ORP. Whatever the dilution rate tested, in low reducing conditions (−100 mV), the production of formate, acetate, ethanol, and lactate was in molar proportions of approximately 2.5:1:1:0.3, and in high reducing conditions (−320 mV), the production was in molar proportions of 2:0.6:1:2. The modification of metabolic fluxes was due to an ORP effect on the synthesis or stability of some fermentation enzy…
Influence of lactose-citrate co-metabolism on the differences of growth and energetics in Leuconostoc lactis, Leuconostoc mesenteroides ssp. mesenteroides and Leuconostoc mesenteroides ssp. cremoris
International audience; The biodiversity of growth and energetics in Leuconostoc sp. has been studied in MRS lactose medium with and without citrate. On lactose alone, Ln. lactis has a growth rate double that of Ln. cremoris and Ln. mesenteroides. The pH is a more critical parameter for Ln. mesenteroides than for Ln. lactis or Ln. cremoris; without pH control Ln. mesenteroides is unable to acidify the medium under pH 4.5, while with pH control and as a consequence of a high Y(ATP) its growth is greater than Ln. lactis and Ln. cremoris. In general, lactose-citrate co-metabolism increases the growth rate, the biomass synthesis, the lactose utilisation ratio, and the production of lactate and …
Combined action of redox potential and pH on heat resistance and growth recovery of sublethally heat-damaged Escherichia coli
International audience; The combined effect of redox potential (RP) (from -200 to 500 mV) and pH (from 5.0 to 7.0) on the heat resistance and growth recovery after heat treatment of Escherichia coli was tested. The effect of RP on heat resistance was very different depending on the pH. At pH 6.0, there was no significant difference, whereas at pH 5.0 and 7.0 maximum resistance was found in oxidizing conditions while it fell in reducing ones. In sub-lethally heat-damaged cells, low reducing and acid conditions allowed growth ability to be rapidly regained, but a decrease in the redox potential and pH brought about a longer lag phase and a slower exponential growth rate, and even led to growt…
Regulation of reactive oxygen species production by a 14-3-3 protein in elicited tobacco cells.
International audience; The regulation of the system responsible for the production of reactive oxygen species (ROS) during plant–microorganism interaction is still largely unknown. The protein NtrbohD has been recently demonstrated as the plasma membrane oxidase responsible for ROS production in elicited tobacco cells. Here, its C-terminus part was used as a bait in a two-hybrid screen in order to identify putative regulators of this system. This led to the isolation of a cDNA coding for a member of the 14-3-3 protein family. The corresponding transcript was induced after infiltration of tobacco leaves with the fungal elicitor cryptogein. Tobacco cells transformed with an antisense constru…