Changes in the proton‐motive force in <i>Escherichia coli</i> in response to external oxidoreduction potential

Riondet, Christophe; Cachon, Rémy; Waché, Yves; Alcaraz, Gérard; Diviès, Charles

doi:10.1046/j.1432-1327.1999.00429.x

Cited by 63 publications

(37 citation statements)

References 41 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…These two enzymes are known to be overexpressed in acidic conditions (4), but chemostat is pH regulated and the higher activity observed cannot be due to extracellular pH variations. However, we have shown recently that on resting cells of E. coli, reducing conditions permeabilized the cytoplasmic membrane mainly to protons (28).…”

Section: Discussionmentioning

confidence: 96%

Extracellular Oxidoreduction Potential Modifies Carbon and Electron Flow in Escherichia coli

et al. 2000

Self Cite

View full text Add to dashboard Cite

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 enzymes; thus, in high reducing conditions, lactate dehydrogenasespecific activity increased by a factor of 3 to 6. Those modifications were concomitant with a threefold decrease in acetyl-coenzyme A (CoA) needed for biomass synthesis and a 0.5-to 5-fold decrease in formate flux. Calculations of carbon and cofactor balances have shown that fermentation was balanced and that extracellular ORP did not modify the oxidoreduction state of cofactors. From this, it was concluded that extracellular ORP could regulate both some specific enzyme activities and the acetyl-CoA needed for biomass synthesis, which modifies metabolic fluxes and ATP yield, leading to variation in biomass synthesis.A wealth of information is available on the response of Escherichia coli cellular metabolism to pH, water activity, or temperature variations, but little is known about the action of extracellular oxidoreduction potentials (ORP) on metabolism, although numerous reactions and regulations are of the oxidoreduction type. Previous studies have shown that substrates with different oxidation states yield a specific product spectrum. Thus, with glucose (oxidation state ϭ 0), the spectrum of main end products (formate:acetate:ethanol:lactate) is equal to 2:1:1:2, with glucitol (oxidation state ϭ Ϫ1), it is equal to 2:1:6:0.5, and with glucuronate (oxidation state ϭ 2), it is equal to 1:5:1:1, with small amounts of succinate also being produced in each case (1). Those metabolic flux modifications are also observed when the nature of external electron acceptors varies (7). In the same way, the NADH/NAD ϩ ratio, which is responsible for regulation of enzymes (8) or genes (16), can be influenced by the oxidation level of the substrate (36) or by the availability and nature of electron acceptors (7). In addition, protein folding and disulfide bond formation are regulated and modified by different oxidoreductase enzymes and oxidoreduction couples (glutathione, thioredoxin) (26). Recently, Taylor and Zhulin in their review have shown that ORP influences or could influence numerous regulations of cell functions controlled via Per-Arnt-Sim (PAS)-containing receptors (signaling modules that monitor changes in light, ORP, oxygen, and the overall energy level of a cell), transducers, and regulators (34). Thus, E. coli senses the medium ORP and swims to a preferred ORP niche by redox...

show abstract

Section: Discussionmentioning

confidence: 96%

Extracellular Oxidoreduction Potential Modifies Carbon and Electron Flow in Escherichia coli

et al. 2000

Self Cite

View full text Add to dashboard Cite

show abstract

“…Transformed standard Gibbs energies of reactions were taken from Kümmel et al (38), and different membrane potentials as well as ⌬pH values were considered to calculate the proton motive force (1,23,32,33,36,39,53,61). The Gibbs energy of the energy-independent transhydrogenase reaction was calculated with the same equation lacking the third term (proton motive force).…”

Section: Methodsmentioning

confidence: 99%

Different Biochemical Mechanisms Ensure Network-Wide Balancing of Reducing Equivalents in Microbial Metabolism

2009

View full text Add to dashboard Cite

To sustain growth, the catabolic formation of the redox equivalent NADPH must be balanced with the anabolic demand. The mechanisms that ensure such network-wide balancing, however, are presently not understood. Based on 13 C-detected intracellular fluxes, metabolite concentrations, and cofactor specificities for all relevant central metabolic enzymes, we have quantified catabolic NADPH production in Agrobacterium tumefaciens, Bacillus subtilis, Escherichia coli, Paracoccus versutus, Pseudomonas fluorescens, Rhodobacter sphaeroides, Sinorhizobium meliloti, and Zymomonas mobilis. For six species, the estimated NADPH production from glucose catabolism exceeded the requirements for biomass synthesis. Exceptions were P. fluorescens, with balanced rates, and E. coli, with insufficient catabolic production, in which about one-third of the NADPH is supplied via the membrane-bound transhydrogenase PntAB. P. versutus and B. subtilis were the only species that appear to rely on transhydrogenases for balancing NADPH overproduction during growth on glucose. In the other four species, the main but not exclusive redox-balancing mechanism appears to be the dual cofactor specificities of several catabolic enzymes and/or the existence of isoenzymes with distinct cofactor specificities, in particular glucose 6-phosphate dehydrogenase. An unexpected key finding for all species, except E. coli and B. subtilis, was the lack of cofactor specificity in the oxidative pentose phosphate pathway, which contrasts with the textbook view of the pentose phosphate pathway dehydrogenases as being NADP ؉ dependent.For all combinations of prevalent carbon substrates, the approximately 60 reactions of heterotrophic central carbon metabolism provide the building blocks and energy at appropriate rates and stoichiometries to fuel about 300 anabolic reactions (43). Additionally, redox equivalents must be appropriately balanced between large numbers of producing and consuming reactions. Aerobically, the primary role of the redox cofactor NADH is respiratory ATP generation via oxidative phosphorylation. The chemically very similar redox cofactor NADPH, in contrast, drives anabolic reductions. To fulfill these rather distinct functions, the two redox couples are generally not in thermodynamical equilibrium and the NADPHto-NADP ϩ ratio is in a more reduced state than the NADHto-NAD ϩ ratio (25). During heterotrophic growth on glucose, the major NADPH-generating reactions are considered to be the oxidative pentose phosphate (PP) pathway, the Entner-Doudoroff (ED) pathway, and the isocitrate dehydrogenase step in the tricarboxylic acid (TCA) cycle (Fig. 1A). The precise rate of formation of NADPH, however, depends on the actual carbon fluxes through these catabolic pathways, which can vary significantly with environmental conditions. The anabolic demand for NADPH, in contrast, is coupled to the rate of biomass formation (46) and, to various extents, to the reduction of thioredoxin for maintaining an appropriate redox state (3). Thus, in the absence of reacti...

show abstract

“…Indeed, the ability of microorganisms to adjust the amount of energy conserved during respiration to meet cellular energetic and physiological demands is well known (14,26,28). A microorganism can, for example, decrease the effective value of m by synthesizing alternative redox enzymes that translocate fewer protons than normal.…”

mentioning

confidence: 99%

A New Rate Law Describing Microbial Respiration

Jin

Bethke

2003

Appl Environ Microbiol

168

132

View full text Add to dashboard Cite

The rate of microbial respiration can be described by a rate law that gives the respiration rate as the product of a rate constant, biomass concentration, and three terms: one describing the kinetics of the electron-donating reaction, one for the kinetics of the electron-accepting reaction, and a thermodynamic term accounting for the energy available in the microbe's environment. The rate law, derived on the basis of chemiosmotic theory and nonlinear thermodynamics, is unique in that it accounts for both forward and reverse fluxes through the electron transport chain. Our analysis demonstrates how a microbe's respiration rate depends on the thermodynamic driving force, i.e., the net difference between the energy available from the environment and energy conserved as ATP. The rate laws commonly applied in microbiology, such as the Monod equation, are specific simplifications of the general law presented. The new rate law is significant because it affords the possibility of extrapolating in a rigorous manner from laboratory experiment to a broad range of natural conditions, including microbial growth where only limited energy is available. The rate law also provides a new explanation of threshold phenomena, which may reflect a thermodynamic equilibrium where the energy released by electron transfer balances that conserved by ADP phosphorylation.Understanding the rate at which microbes respire in biological and geochemical systems is central to developing quantitative descriptions of a broad range of problems in microbiology, from the propagation of disease to the attenuation of contaminants in drinking-water supplies. Microbiologists have in recent years expended considerable effort in investigating microbial respiration rates under specific conditions (22,33,36,41).In virtually all cases, the results of such studies have been cast in terms of a semi-empirical rate law such as the Monod equation (15). Application of such rate laws is limited in two senses. First, because of their semi-empirical nature, they are best suited to interpolating the results of a set of experiments within the range of chemical conditions tested (7). Second, none of the laws accounts for the thermodynamic effects of the energy available in the cell's environment. As such, there is no basis for applying a rate law derived for a laboratory experiment, where the available energy is typically maintained at a high level to provide for microbial growth at acceptable rates, to natural conditions, where much less energy may be available. As a result, the rate laws invariably predict positive activities even where there is no energy available to drive the cell's metabolism forward.In a recent paper (13), we performed, on the basis of the chemiosmotic model of cellular respiration (19) and nonlinear nonequilibrium thermodynamics (6), a rigorous analysis of the problem of respiration in eukaryotic cells by mitochondria. In our analysis, we accounted for a simultaneous forward and backward flux of electrons through the respiratory chain. The resultin...

show abstract

Changes in the proton‐motive force in Escherichia coli in response to external oxidoreduction potential

Cited by 63 publications

References 41 publications

Extracellular Oxidoreduction Potential Modifies Carbon and Electron Flow in Escherichia coli

Extracellular Oxidoreduction Potential Modifies Carbon and Electron Flow in Escherichia coli

Different Biochemical Mechanisms Ensure Network-Wide Balancing of Reducing Equivalents in Microbial Metabolism

A New Rate Law Describing Microbial Respiration

Contact Info

Product

Resources

About