Relationship between the F0F1-ATPase and the K(+)-transport system within the membrane of anaerobically grown Escherichia coli. N,N'-dicyclohexylcarbodiimide-sensitive ATPase activity in mutants with defects in K(+)-transport

Escherichia coli Dcu C4-dicarboxylate transporters dependent proton and potassium fluxes and FOF1-ATPase activity during glucose fermentation at pH 7.5

During fermentation in Escherichia coli succinate is transported via Dcu transporters, encoded dcuA, dcuB, dcuC and dcuD although the role of DcuD protein has not been elucidated yet. It has been shown contribution of Dcu transporters in the N,N'-dicyclohexylcarbodiimide (DCCD) sensitive proton and potassium transport through the cytoplasmic membrane and membrane-associated ATPase activity. Total H^± efflux was decreased ~ 40% while K^± uptake was absent in dcuD mutant. DCCD-sensitive H^± flux was absent in dcuD nevertheless it was increased ~ 3 fold in dcuACB. K^± uptake in dcuACB was stimulated ~ 30% compared to wild type but in DCCD assays K^± ions were effluxed with the rate of 0.15 mmol/min per 10⁹ cells/ml. In dcuACB mutant membrane potential (ΔΨ) was ~ 30 mV higher than in wild type. dcuD gene expression was increased in the dcuACB mutant respect to wild type at pH 7.5 (~120%), suggesting that an increment of DcuD activity compensates the lack of DcuA, DcuC and DcuB carriers. It can be concluded that active DcuD is important for H^± efflux via the F_OF₁-ATPase and K^± uptake at pH 7.5. In addition, DcuA, DcuB and DcuC transporters are crucial for regulating DCCD-sensitive K^± transport and ΔΨ in E. coli.

Evidence for Escherichia coli DcuD carrier dependent FOF1-ATPase activity during fermentation of glycerol

During fermentation Escherichia coli excrete succinate mainly via Dcu family carriers. Current work reveals the total and N,N’-dicyclohexylcarbodiimide (DCCD) inhibited ATPase activity at pH 7.5 and 5.5 in E. coli wild type and dcu mutants upon glycerol fermentation. The overall ATPase activity was highest at pH 7.5 in dcuABCD mutant. In wild type cells 50% of the activity came from the F_OF₁-ATPase but in dcuD mutant it reached ~80%. K⁺ (100 mM) stimulate total but not DCCD inhibited ATPase activity 40% and 20% in wild type and dcuD mutant, respectively. 90% of overall ATPase activity was inhibited by DCCD at pH 5.5 only in dcuABC mutant. At pH 7.5 the H⁺ fluxes in E. coli wild type, dcuD and dcuABCD mutants was similar but in dcuABC triple mutant the H⁺ flux decreased 1.4 fold reaching 1.15 mM/min when glycerol was supplemented. In succinate assays the H⁺ flux was higher in the strains where DcuD is absent. No significant differences were determined in wild type and mutants specific growth rate except dcuD strain. Taken together it is suggested that during glycerol fermentation DcuD has impact on H⁺ fluxes, F_OF₁-ATPase activity and depends on potassium ions.

Comparable effects of low-intensity electromagnetic irradiation at the frequency of 51.8 and 53 GHz and antibiotic ceftazidime on Lactobacillus acidophilus growth and survival

The effects of low-intensity electromagnetic irradiation (EMI) with the frequencies of 51.8 and 53 GHz on Lactobacillus acidophilus growth and survival were revealed. These effects were compared with antibacterial effects of antibiotic ceftazidime. Decrease in bacterial growth rate by EMI was comparable with the inhibitory effect of ceftazidime (minimal inhibitory concentration-16 μM) and no enhanced action was observed with combined effects of EMI and the antibiotic. However, EMI-enhanced antibiotic inhibitory effect on bacterial survival. The kinetics of the bacterial suspension oxidation-reduction potential up to 24 h of the growth was changed by EMI and ceftazidime. The changes were more strongly expressed by combined effects of EMI and antibiotic especially up to 12 h. Moreover, EMI did not change overall energy (glucose)-dependent H(+) efflux across the membrane but it increased N,N'-dicyclohexylcarbodiimide (DCCD)-inhibited H(+) efflux. In contrast, this EMI in combination with ceftazidime decreased DCCD-sensitive H(+) efflux. Low-intensity EMI had inhibitory effect on L. acidophilus bacterial growth and survival. The effect on bacterial survival was more significant in the combination with ceftazidime. The H(+)-translocating F 0 F 1-ATPase, for which DCCD is specific inhibitor, might be a target for EMI and ceftazidime. The revealed bactericide effects on L. acidophilus can be applied in biotechnology, food producing and safety technology.

Relationship of proton motive force and the F(0)F (1)-ATPase with bio-hydrogen production activity of Rhodobacter sphaeroides: effects of diphenylene iodonium, hydrogenase inhibitor, and its solvent dimethylsulphoxide

Rhodobacter sphaeroides MDC 6521 was able to produce bio-hydrogen (H(2)) in anaerobic conditions under illumination. In this study the effects of the hydrogenase inhibitor-diphenylene iodonium (Ph(2)I) and its solvent dimethylsulphoxide (DMSO) on growth characteristics and H(2) production by R. sphaeroides were investigated. The results point out the concentration dependent DMSO effect: in the presence of 10 mM DMSO H(2) yield was ~6 fold lower than that of the control. The bacterium was unable to produce H(2) in the presence of Ph(2)I. In order to examine the mediatory role of proton motive force (∆p) or the F(0)F(1)-ATPase in H(2) production by R. sphaeroides, the effects of Ph(2)I and DMSO on ∆p and its components (membrane potential (∆ψ) and transmembrane pH gradient), and ATPase activity were determined. In these conditions ∆ψ was of -98 mV and the reversed ∆pH was +30 mV, resulting in ∆p of -68 mV. Ph(2)I decreased ∆ψ in concentrations of 20 μM and higher; lower concentrations of Ph(2)I as DMSO had no valuable effect on ∆ψ. The R. sphaeroides membrane vesicles demonstrated significant ATPase activity sensitive to N,N'-dicyclohexylcarbodiimide. The 10-20 μM Ph(2)I did not affect the ATPase activity, whereas 40 μM Ph(2)I caused a marked inhibition (~2 fold) in ATPase activity. The obtained results provide novel evidence on the involvement of hydrogenase and the F(0)F(1)-ATPase in H(2) production by R. sphaeroides. Moreover, these data indicate the role of hydrogenase and the F(0)F(1)-ATPase in ∆p generation. In addition, DMSO might increase an interaction of nitrogenase with CO(2), decreasing nitrogenase activity and affecting H(2) production.

Role of different Escherichia coli hydrogenases in H+ efflux and F₁F(o)-ATPase activity during glycerol fermentation at different pH values

Escherichia coli is able to ferment glycerol and produce H2 by different Hyds (hydrogenases). Wild-type whole cells were shown to extrude H+ through the F1Fo-ATPase and by other means with a lower rate compared with that under glucose fermentation. At pH 7.5, H+ efflux was stimulated in fhlA mutant (with defective transcriptional activator of Hyd-3 or Hyd-4) and was lowered in hyaB or hybC mutants (with defective Hyd-1 or Hyd-2) and hyaB hybC double mutant; DCCD (dicyclohexylcarbodi-imide)-sensitive H+ efflux was observed. At pH 5.5, H+ efflux in wild-type was lower compared with that at pH 7.5; it was increased in fhlA mutant and absent in hyaB hybC mutant. Membrane vesicle ATPase activity was lower in wild-type glycerol-fermented cells at pH 7.5 compared with that in glucose-fermented cells; 100 mM K+ did not stimulate ATPase activity. The latter at pH 7.5, compared with that in wild-type, was lower in hyaB and less in hybC mutants, stimulated in the hyaB hybC mutant and suppressed in the fhlA mutant; DCCD inhibited ATPase activity. At pH 5.5, the ATPase activities of hyaB and hybC mutants had similar values and were higher compared with that in wild-type; ATPase activity was suppressed in hyaB hybC and fhlA mutants. The results indicate that during glycerol fermentation, H+ was expelled also via F1Fo. At pH 7.5 Hyd-1 and Hyd-2 but not FhlA or Hyd-4 might be related to F1Fo or have their own H+-translocating ability. At pH 5.5, both Hyd-1 and Hyd-2 more than F1Fo might be involved in H+ efflux.

Changes in bacterial cells induced by high pressure at subzero temperature

The aim of this study was to examine the effect of pressure treatment at 193MPa and -20°C on membrane damage, changes in activity of membrane-bound ATPases and degradation of nucleic acids. The experiments were carried out with three Escherichia coli strains, in the exponential and stationary phases of growth, and differing in sensitivity to pressure. All E. coli strains subjected to pressure in the exponential phase of growth were inactivated by 6 log cycles, independently of the strain, which was accompanied by a total loss of ability to plasmolyse, an increase in irreversible membrane permeability to PI, and a reduction of cellular ATP by more than 80%. After pressure treatment of stationary phase cells, the relationship between the inactivation level and the ability to plasmolyse was not as evident as in the case of exponential phase cells. Pressure treatment of two strains of E. coli K-12 and Ec160/59 in the stationary phase that decreased viability by no more than one log cycle led only to reversible permeabilization of bacterial membranes, while irreversible permeabilization was observed in the pressure sensitive E. coli IBA72 strain phase that was inactivated by 4.6 log cycles. The reduction of ATP and changes in ATPase activity after pressure treatment of tested E. coli strains in the stationary phase of growth depended on the stage of inactivation of the particular strain. Electrophoretic analysis showed degradation of RNA isolated after pressure treatment from cells of all E. coli strains tested in the exponential phase of growth. The changes of RNA induced by pressure were not visible in the case of cells in the stationary phase. The degradation of DNA isolated from pressure treated E. coli strains from the exponential as well as from the stationary phase of growth was not observed.

Copper (II) ions affect Escherichia coli membrane vesicles' SH-groups and a disulfide-dithiol interchange between membrane proteins

The SH-groups in Escherichia coli membrane vesicles, prepared from cells grown in fermentation conditions on glucose at slightly alkaline pH, have a role in the F0F1-ATPase operation. The changes in the number of these groups by ATP are observed under certain conditions. In this study, copper ions (Cu2+) in concentration of 0.1 mM were shown to increase the number of SH-groups in 1.5- to 1.6-fold independent from K+ ions, and the suppression of the increased level of SH-groups by ATP was determined for Cu2+ in the presence of K+. Moreover, the increase in the number of SH-groups by Cu2+ was absent as well as the inhibition in ATP-dependent increasing SH-groups number by Cu2+ lacked when vesicles were treated with N-ethylmaleimide (NEM), specific thiol-reagent. Such an effect was not observed with zinc (Zn2+), cobalt (Co2+), or Cu+ ions. The increased level of SH-groups was observed in the hycE or hyfR mutants with defects in hydrogenases 3 or 4, whereas the ATP-dependent increase in the number of these groups was determined in hycE not in hyfR mutants. Both changes in SH-groups number disappeared in the atp or hyc mutants deleted for the F0F1-ATPase or hydrogenase 3 (no activity of hydrogenase 4 was detected in the hyc mutant used). A direct effect of Cu2+ but not Cu+ on the F0F1-ATPase is suggested to lead to conformational changes or damaging consequences, increasing accessible SH-groups number and disturbing disulfide-dithiol interchange within a protein-protein complex, where this ATPase works with K+ uptake system or hydrogenase 4 (Hyd-4); breaks in disulfides are not ruled out.

Escherichia coli proton-translocating F0F1-ATP synthase and its association with solute secondary transporters and/or enzymes of anaerobic oxidation–reduction under fermentation

The Escherichia coli proton-translocating F0F1-ATP synthase has a priority in H+ circulation through the membrane in maintaining proton-motive force in the context of ATP synthesis and hydrolysis. Recent advances in the study of this complex under fermentative growth have led to hypothesis that, in the absence of oxidative phosphorylation, F0F1 is implicated as an essential part of H+ movement and ATP hydrolysis, associated with solute secondary transporters and/or enzymes of anaerobic oxidation-reduction. These associations can result from a protein-protein interaction by dithiol-disulfide interchange. In such associations F0F1 has novel functions in bacterial cell physiology.

The number of accessible SH-groups in Escherichia coli membrane vesicles is increased by ATP or by formate

The number of accessible SH-groups was determined in membrane vesicles prepared from Escherichia coli growing in fermentation conditions at slightly alkaline pH on glucose with or without added formate. Addition of ATP or formate to the vesicles caused a approximately 1.4-fold increase in the number of accessible SH-groups. The increase was inhibited by treatment with N-ethylmaleimide or the presence of the F(0)F(1)-ATPase inhibitors N,N(')-dicyclohexylcarbodiimide or sodium azide. The increase in accessible SH-groups was also absent in strains with the ATP synthase operon deleted or with the single F(0) domain cysteine Cysb21 changed to Ala. Using hyc and hyf mutants, it was shown that the increase was also largely dependent on hydrogenase 4 or hydrogenase 3, main components of formate hydrogen lyase, when bacteria were grown in the absence or presence of added formate. These results suggest a relationship between the F(0)F(1)-ATP synthase and hydrogenase 4 or hydrogenase 3 under fermentation conditions.

Formate increases the F0F1-ATPase activity in Escherichia coli growing on glucose under anaerobic conditions at slightly alkaline pH

Escherichia coli growing on glucose under anaerobic conditions at slightly alkaline pH carries out a mixed-acid fermentation resulting in the production of formate among the other products that can be excreted or further oxidized to H(2) and CO(2). H(2) production is largely dependent on formate dehydrogenase H and hydrogenases 3 and 4 constituting two formate hydrogen lyases, and on the F(0)F(1)-ATPase. In this study, it has been shown that formate markedly increased ATPase activity in membrane vesicles. This activity was significantly (1.8-fold) stimulated by 100mM K(+) and inhibited by N,N(')-dicyclohexylcarbodiimide and sodium azide. The increase in ATPase activity was absent in atp, trkA, and hyf but not in hyc mutants. ATPase activity was also markedly increased by formate when bacteria were fermenting glucose with external formate (30mM) in the growth medium. However this activity was not stimulated by K(+) and absent in atp and hyc but not in hyf mutants. The effects of formate on ATPase activity disappeared when cells were performing anaerobic (nitrate/nitrite) or aerobic respiration. These results suggest that the F(0)F(1)-ATPase activity is dependent on K(+) uptake TrkA system and hydrogenase 4, and on hydrogenase 3 when cells are fermenting glucose in the absence and presence of external formate, respectively.

Biochemical analysis of neomycin-resistance in the methanoarchaeon Methanothermobacter thermautotrophicus and some implications for energetic processes in this strain

Methanogenesis-driven ATP synthesis in a neomycin-resistant mutant of Methanothermobacter thermautotrophicus (formerly Methanobacterium thermoautotrophicum strain DeltaH) was strongly inhibited at both pH 6.8 and pH 8.5 by the uncoupler 3,3',4',5 -tetrachlorosalicylanilide (TCS) in the presence of either 1 or 10 mM NaCl. The generation of a membrane potential in the mutant cells at pH 6.8 was also strongly inhibited by TCS in the presence of 1 or 10 mM NaCl. On the other hand, at pH 8.5 in the presence of 10mM NaCl, a protonophore-resistant membrane potential of approximately 150 mV was found. These results indicate that in the mutant cells the process of energy transduction between methanogenesis and membrane potential generation is not impaired. In contrast to the wild-type strain, ATP synthesis in the mutant cells was driven by an electrochemical gradient of H(+) under alkaline conditions. Unlike wild-type cells, the mutant lacks the capacity to transduce an uncoupler-resistant membrane potential energy at pH 8.5 into ATP synthesis. Na(+)/H(+) exchange was comparable in the wild type and the mutant cells. Western blots of sub-cellular fractions with polyclonal antiserum reactive to the B-subunit of the halobacterial A-type H(+)-translocating ATPase confirmed the presence of A-type ATP synthase in the mutant cells. Furthermore, in the mutant cells a protein band of molecular mass about 45 kDa is absent but there was an abundant protein band at about 67 kDa. Based on the observed bioenergetic features of the mutant cells, neither the A(1)A(o) ATP synthase alone nor together with the Na(+)/H(+) antiporter seems to be responsible for ATP synthesis driven by sodium motive force. Rather, some other links between neomycin-resistance and failure of sodium motive force-dependent ATP synthesis in the neomycin resistant mutant are discussed.

The roles of hydrogenases 3 and 4, and the F0F1-ATPase, in H2 production by Escherichia coli at alkaline and acidic pH

The hyc operon of Escherichia coli encodes the H2-evolving hydrogenase 3 (Hyd-3) complex that, in conjunction with formate dehydrogenase H (Fdh-H), constitutes a membrane-associated formate hydrogenlyase (FHL) catalyzing the disproportionation of formate to CO2 and H2 during fermentative growth at low pH. Recently, an operon (hyf) encoding a potential second H2-evolving hydrogenase (Hyd-4) was identified in E. coli. In this study the roles of the hyc- and hyf-encoded systems in formate-dependent H2 production and Fdh-H activity have been investigated. In cells grown on glucose under fermentative conditions at slightly acidic pH the production of H2 was mostly Hyd-3- and Fdh-H-dependent, and Fdh-H activity was also mainly Hyd-3-dependent. However, at slightly alkaline pH, H2 production was found to be largely Hyd-4, Fdh-H and F0F1-ATPase-dependent, and Fdh-H activity was partially dependent on Hyd-4 and F0F1-ATPase. These results suggest that, at slightly alkaline pH, H2 production and Fdh-H activity are dependent on both the F0F1-ATPase and a novel FHL, designated FHL-2, which is composed of Hyd-4 and Fdh-H, and is driven by a proton gradient established by the F0F1-ATPase.

K+ influx by Kup in Escherichia coli is accompanied by a decrease in H+ efflux

Escherichia coli accumulates K+ by means of multiple uptake systems of which Kup is the major transport system at acidic pH. In cells grown under fermentative conditions at pH 5.5, K+ influx by a wild-type strain upon hyper-osmotic stress at pH 5.5 was accompanied by a marked decrease in H+ efflux, with a 1:1 ratio of K+ to H+ fluxes. This was observed with cells treated with N,N'-dicyclohexylcarbodiimide. Similar results with a mutant defective in Kdp and TrkA but with a functional Kup system but not in a mutant defective in Kdp and Kup but having an active TrkA system suggest that Kup operates as a H+ -K+ -symporter.

Redox potential is a determinant in the Escherichia coli anaerobic fermentative growth and survival: effects of impermeable oxidant

Decrease of redox potential (Eh) down to -550-600 mV in the Escherichia coli culture is observed during growth in either anaerobic or aerobic conditions. The E. coli growth and survival under anaerobic fermentative conditions were found to be strongly inhibited by potassium ferricyanide in the concentration of 1 mM, when Eh was decreased to -50-100 mV. This oxidant also resulted in approximately 2-fold decrease of total and N,N'-dicyclohexylcarbodiimide (DCCD)-inhibited H+ efflux, 2.5-fold inhibition in K+ influx, 1.5-fold less K+ accumulation, and delayed a decrease in Eh to negative values by bacteria. K3[Fe(CN)6] was shown to block an ATP-dependent increase in the amount of accessible thiol groups of membrane vesicles that was inhibited by DCCD, and this inhibition by the oxidant could be recovered by dithiothreitol. These effects were not observed with cells growing under aerobic conditions. The effects of K3[Fe(CN)6], an impermeable oxidant, might be explained by the fact that redox potential is a determinant in the E. coli anaerobic fermentative growth and survival that has a regulatory role in maintaining H+ and K fluxes and the number of accessible thiol groups on membrane.

Kup is the major K+ uptake system in Escherichia coli upon hyper-osmotic stress at a low pH

The K+ uptake was observed in washed cells of Escherichia coli, wild-type, upon hyper-osmotic stress at pH 5.5 when glucose was supplemented. This uptake had apparent a Km of 0.58 mM and Vmax of 0.10 micromol K+/min/mg protein. Such a K+ uptake was investigated using a mutant defective in Kdp and TrkA but with a functional Kup and a mutant defective in Kdp and Kup but having an active TrkA. The K+ uptake to reach the steady state level as well as the initial K+ influx rate in the first mutant were at least 3.5-fold greater than these values with the second mutant and similar to those of the wild-type. Such differences in the K+ uptake activity were correlated with K+ requirements for growth of these mutants. Moreover, the K+ uptake in the wild-type was blocked by a protonophore (carbonyl cyanide m-chlorophenylhydrazone). Valinomycin, arsenate and N,N'-dicyclohexylcarbodiimide were not effective in changing the K+ uptake. It is suggested that Kup is the major K+ uptake system in E. coli upon hyper-osmotic stress at a low pH.