External succinate and potassium ions influence Dcu dependent FOF1-ATPase activity and H+ flux of Escherichia coli at different pHs.

During fermentation Escherichia coli transport succinate mainly via Dcu family carriers. Current paper describes the role of externally added succinate on N'N'-dicyclohexylcarbodiimide (DCCD) sensitive ATPase activity and H+ flux depending on potassium ions. At pH 7.5 in wild type membrane vesicles DCCD-sensitive ATPase activity was the same as in dcuACBD quadruple mutant. In dcuACB it was increased ~ 3.3 fold while in dcuD DCCD-sensitive ATPase activity was absent. The DCCD-sensitive H+ efflux was fully dependent on FOF1 only in dcuACB mutant. This activity depended on potassium ions and only in dcuACBD mutant DCCD-sensitive ATPase activity was stimulated ~ 3 fold. At pH 5.5 DCCD-sensitive ATPase activities were determined in dcuACB or dcuD mutants but not in wild type. Interestingly, addition of potassium ions enhanced DCCD-sensitive ATPase activity in dcuD mutant ~ 3-fold compared to wild type. In dcuD mutant ~ 3-fold higher H+ uptake was registered, compared to wild type. Taken together it can be concluded that at pH 7.5 the FOF1-activity depends on DcuACB. Moreover, DcuACB but not DcuD are working towards H+ uptake direction. DcuD contributes to H+ efflux at pH 7.5 while at pH 5.5 it affects H+ influx when external succinate is present.

Ultrastructural investigation of acidocalcisomes and ATPase activity in yeast Candida guilliermondii NP-4 as 'complementary' stress-targets.

As a result of electron microscopic studies of morphogenesis in yeast Candida guilliermondii NP-4, the formation of new structures of volutin acidocalcisomes has been established within the cell cytoplasm. Under influence of X-irradiation, the changes in morphometric and electron-dense properties of yeast cells were identified: in yeast cytoplasm, the electron-dense volutin granules were increased up to 400 nm in size. After 24-h post-irradiation incubation of yeasts, the large volutin pellets are fragmented into smaller number particles in size up to 25-150 nm. The ATPase activity in yeast mitochondria was changed under X-irradiation. In latent phase of growth, ATPase activity was decreased 1·35-fold in comparison with non-irradiated yeasts. In logarithmic phase of growth, ATPase activity was three times higher than in latent phase, and in stationary phase of growth it has a value similar to the latent phase. Probably, the cells receive the necessary energy from alternative energy sources, such as volutin. Electron microscopy of volutin granule changes might serve as convenient method for evaluation of damages and repair processes in cells under influence of different environmental stress-factors.

Novel approach to combat antibiotic resistance: evaluation of some Armenian herb crude extracts for their antibiotic modulatory and antiviral properties.

AIMS: One of the strategies to combat antibiotic resistance can be the use of plant materials in combination with antibiotics, taking into account that phytochemicals can act as antibiotic resistance-modifying agents. This can give a second life to the traditional antibiotics. The aim was to evaluate antibiotic modulatory effect of crude extracts from Agrimonia eupatoria, Hypericum alpestre, Rumex obtusifolius and Sanguisorba officinalis herbs towards several commercial antibiotics using some Gram-positive and Gram-negative bacteria. METHODS: The antibiotic modulatory activity was tested by determining MICs of antibiotics in the absence and presence of plant crude extracts at subinhibitory concentrations. Antiviral potential of different extracts of tested plant materials was also explored by double overlay plaque assay. RESULTS: The tested plant crude extracts exhibited high modulatory activity towards used antibiotics. Particularly, high modulatory activity was observed with extracts of H. alpestre and R. obtusifolius. Many plant-antibiotic combinations induced the decrease in MICs of antibiotics up to ~fourfold indicating synergy. Moreover, the similar change was observed at both subinhibitory concentrations (MIC/2 and MIC/4) of the same plant crude extract. High anti-phage activity of plants with the exception of Lilium armenum against T4 phage of Escherichia coli C-T4 was also shown. CONCLUSIONS: Plant crude extract or commercial antibiotic combinations significantly increased the efficiency of antibiotics. Tested plant materials with exception of L. armenum have antiviral property. SIGNIFICANCE AND IMPACT OF THE STUDY: For the first time, antibiotic modulatory activity of tested herb extracts was shown, which could have potential in practical applications. Tested plant materials with exception of L. armenum could have prospective, as a source of new antiviral compounds.

Effects of iron oxide (Fe3 O4 ) nanoparticles on Escherichia coli antibiotic-resistant strains.

AIMS: Antibiotic resistance of different bacteria requires the development of alternative approaches for overcoming this phenomenon. The antibacterial effects of iron oxide (Fe3 O4 ) nanoparticles (NPs) (from 50 to 250 µg ml-1 ) on Escherichia coli antibiotic-resistant strains have been aimed. METHODS AND RESULTS: The study was performed with ampicillin-resistant E. coli DH5α-pUC18 and kanamycin-resistant E. coli pARG-25 stains. Specific growth rate of bacteria (µ), lag phase duration and colony-forming units (CFU) were determined to evaluate growth properties. Fe3 O4 NPs (average size of 10·64 ± 4·73 nm) coated with oleic acid and synthesized by modified co-precipitation method were used. The medium pH, H+ efflux, membrane H+ conductance, redox potential determinations and H2 yield assay were done using potentiometer methods. Growth properties were changed by NPs in concentration-dependent manner. NPs decreased (up to twofold) H+ -fluxes through bacterial membrane more in E. coli in the presence of the N,N'-dicyclohexylcarbodiimide, inhibitor of ATPase, indicating that antibacterial activity of these NPs was connected with ATP-associated metabolism. Membrane-associated H2 production was lowered up to twofold. Moreover, the synergetic interactions of NPs and antibiotics were found: combination of NPs and antibiotics provided the higher H+ conductance, lower H+ -fluxes and H2 yield. CONCLUSIONS: Fe3 O4 NPs can be suggested as alternative antibacterial agents, which can substitute antibiotics in different applications. SIGNIFICANCE AND IMPACT OF THE STUDY: The antibacterial effects of Fe3 O4 NPs on the growth properties and membrane activity of E. coli antibiotic-resistant strains have been demonstrated. These NPs have potential as antibacterial agents, which can substitute for antibiotics in bacterial disease treatment in biomedicine, pharmaceutical and environmental applications.

The survival of irradiated lactobacilli in the simulated gastrointestinal conditions with antibiotic ceftazidime.

Lactobacillus acidophilus is one of the widespread probiotic bacteria that can overcome acid and bile barrier of stomach and intestine, respectively, and then have beneficial effects on the host improving its intestinal microbial balance. The cell membrane FO F1 -ATPase is an important factor in the response and tolerance to low pH through the action of controlling the H+ concentration between the cell cytoplasm and external medium. In this study, the effects of extremely high-frequency EMI at the frequencies of 51·8 GHz and 53 GHz and cetfazidime ( µmol l-1 ) on survival of L. acidophilus VKM B-1660 in the gastrointestinal model in vitro and on ATPase activity of their membrane vesicles were investigated. Irradiated L. acidophilus survived in media with acid pH; the irradiation stimulated N,N'-dicyclohexylcarbodiimide-sensitive FO F1 -ATPase activity under acidic conditions, but enhanced the inhibitory effects of ceftazidime. Probably irradiated L. acidophilus is overcoming the acid barrier even in the presence of ceftazidime due to the FO F1 -ATPase. The obtained results can allow the use of L. acidophilus in food industry, veterinary and medicine. SIGNIFICANCE AND IMPACT OF THE STUDY: The probiotic property of lactobacilli is defined with survival in different conditions of human digestive tract even in the presence of antibiotics and subjected to electromagnetic irradiation (EMI) at the extremely high frequency. Despite the fact that EMI and antibiotic ceftazidime affected Lactobacillus acidophilus; the viable number of bacterial cells was decreased in in vitro gastrointestinal model, but they could to grow in fresh growth medium. The changes in the FO F1 -ATPase activity were obtained at acidic pH. Thus, these bacteria can overcome acid barrier due to the FO F1 -ATPase: the irradiation stimulates the FO F1 -ATPase activity in the acidic conditions, but enhances the effects of ceftazidime. The results are important for identifying the mechanisms of lactobacilli survival for physical and chemical factors and valuable for use.

The distinguishing effects of low-intensity electromagnetic radiation of different extremely high frequencies on Enterococcus hirae: growth rate inhibition and scanning electron microscopy analysis.

A low-intensity electromagnetic field of extremely high frequency has inhibitory and stimulatory effects on bacteria, including Enterococcus hirae. It was shown that the low-intensity (the incident power density of 0·06 mW cm-2 ) electromagnetic field at the frequencies of 51·8 GHz and 53 GHz inhibited E. hirae ATCC 9790 bacterial growth rate; a stronger effect was observed with 53 GHz, regardless of exposure duration (0·5 h, 1 h or 2 h). Scanning electron microscopy analysis of these effects has been done; the cells were of spherical shape. Electromagnetic field at 53 GHz, but not 51·8 GHz, changed the cell size-the diameter was enlarged 1·3 fold at 53 GHz. These results suggest the difference in mechanisms of action on bacteria for electromagnetic fields at 51·8 GHz and 53 GHz. SIGNIFICANCE AND IMPACT OF THE STUDY: A stronger inhibitory effect of low-intensity electromagnetic field on Enterococcus hirae ATCC 9790 bacterial growth rate was observed with 53 GHz vs 51·8 GHz, regardless of exposure duration. Scanning electron microscopy analysis showed that almost all irradiated cells in the population have spherical shapes similar to nonirradiated ones, but they have increased diameters in case of irradiated cells at 53 GHz, but not 51·8 GHz. The results are novel, showing distinguishing effects of low-intensity electromagnetic field of different frequencies. They could be applied in treatment of food and different products in medicine and veterinary, where E. hirae plays an important role.

Adhesive Properties and Acid-Forming Activity of Lactobacilli and Streptococci Under Inhibitory Substances, Such as Nitrates.

One of the main requirements for probiotics is their ability to survive during passage through gastrointestinal tract and to maintain their activity at different adverse conditions. The aim of the study was to look for the strains of lactobacilli and streptococci with high adhesive properties even affected by inhibitory substances, such as nitrates (NO3 (-)). To study the adhesion properties hemagglutination reaction of bacterial cells with red blood cells of different animals and humans was used. The acid formation ability of bacteria was determined by the method of titration after 7 days of incubation in the sterile milk. These properties were investigated at different concentrations of NO3 (-). The high concentration (mostly ≥2.0 %) NO3 (-) inhibited the growth of both lactobacilli and streptococci, but compared with streptococcal cultures lactobacilli, especially Lactobacillus acidophilus Ep 317/402, have shown more stability and higher adhesive properties. In addition, the concentrations of NO3 (-) of 0.5-2.0 % decreased the acid-forming activity of the strains, but even under these conditions they coagulated milk and, in comparison to control, formed low acidity in milk. Thus, the L. acidophilus Ep 317/402 with high adhesive properties has demonstrated a higher activity of NO3 (-) transformation.

Protective effect of some amino acids synthesized derivatives and their chelates on Escherichia coli under X-ray irradiation.

The protective effects of novel synthesized derivatives of some amino acids--nicotinyl-L-tyrosinate and nicotinyl-L-tryptophanate schiff bases and their Cu(II) and Mn(II) chelates on growth, survival and membrane-associated ATPase activity of E. coli under X-ray irradiation were investigated. The specific growth rate and survival of E. coli were decreased at 10, 20 and 30 Gy doses. However, as 30 Gy was found to be the most effective irradiation dose, it was chosen for studying the radio-protective properties of different compounds. These compounds could increase the bacterial cell protection against X-ray irradiation in concentration-dependent manner. They had a role in stimulation of synthesis or regulation of activity of metal-dependent enzymes, required for reversing the X-ray irradiation damage. The study may prove useful for further estimation of the effectiveness of different compounds as radio-protectors on bacteria and other cells, especially mammalian cells under X-ray irradiation.

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 FOF1-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 FOF1-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, FOF1-ATPase activity and depends on potassium ions.

Aggregation and Adhesion Activity of Lactobacilli Isolated from Fermented Products In Vitro and In Vivo: a Potential Probiotic Strain.

Approximately 25 strains of lactobacilli isolated from different dairy products and fermented vegetables were screened according to their possibility to show the high auto-aggregation and co-aggregation. The strains Lactobacillus helveticus INRA-2010-H11, Lactobacillus rhamnosus INA-5.1, and Lactobacillus acidophilus JM-2012 were determined to have the high auto-aggregation (approximately 73, 46, and 70.5% correspondingly). A high co-aggregation capacity (75.53%) for strains INRA-2010-H11 and JM-2012 was shown. The adhesion degree of INRA-2010-H11 on the surface of buccal epithelial cells was 88.23%. The study of INRA-2010-H11, JM-2012, and both strains' mixture (1:1) adhesion capacity on the surface of epithelial HeLa cells revealed the adhesion of 1.1 × 106, 6.3 × 104, and 2.3 × 105 CFU, respectively, from starter amount of CFU 107 and 108 for both strains. In vivo experiments of LAB adhesion in gastrointestinal tract of mouse revealed the presence of 2.5 × 109, 1.2 × 109, and 1.5 × 109 CFU of LAB in control and groups of mouse, fed by INRA-2010-H11 and mixture, respectively. Feeding by investigated lactobacilli was suggested to lead to microbiota biodiversity reduction in small intestine and colon and its augmentation in stomach. Thus, INRA-2010-H11 demonstrated a high aggregation and adhesion activity so it has the potential as a good probiotic strain.

The Effects of Low Doses of Gamma-Radiation on Growth and Membrane Activity of Pseudomonas aeruginosa GRP3 and Escherichia coli M17.

Microorganisms are part of the natural environments and reflect the effects of different physical factors of surrounding environment, such as gamma (γ) radiation. This work was devoted to the study of the influence of low doses of γ radiation with the intensity of 2.56 µW (m2 s)-1 (absorbed doses were 3.8 mGy for the radiation of 15 min and 7.2 mGy-for 30 min) on Escherichia coli M-17 and Pseudomonas aeruginosa GRP3 wild type cells. The changes of bacterial, growth, survival, morphology, and membrane activity had been studied after γ irradiation. Verified microbiological (specific growth rate, lag phase duration, colony-forming units (CFU) number, and light microscopy digital image analysis), biochemical (ATPase activity of bacterial membrane vesicles), and biophysical (H+ fluxes throughout cytoplasmic membrane of bacteria) methods were used for assessment of radiation implications on bacteria. It was shown that growth specific rate, lag phase duration and CFU number of these bacteria were lowered after irradiation, and average cell surface area was decreased too. Moreover ion fluxes of bacteria were changed: for P. aeruginosa they were decreased and for E. coli-increased. The N,N'-dicyclohexylcarbodiimide (DCCD) sensitive fluxes were also changed which were indicative for the membrane-associated F0F1-ATPase enzyme. ATPase activity of irradiated membrane vesicles was decreased for P. aeruginosa and stimulated for E. coli. Furthermore, DCCD sensitive ATPase activity was also changed. The results obtained suggest that these bacteria especially, P. aeruginosa are sensitive to γ radiation and might be used for developing new monitoring methods for estimating environmental changes after γ irradiation.

pH and a mixed carbon-substrate spectrum influence FocA- and FocB-dependent, formate-driven H2 production in Escherichia coli.

Escherichia coli encodes two formate channels, FocA and FocB, that either export formate or import it for further disproportionation by the formate hydrogenlyase (FHL) complex to H2 and CO2. We show that FocA/B appear to change their substrate-translocation direction depending on pH and electron donor. When cells were grown on glucose and glycerol at pH 7.5, formate accumulated in focB or focA-focB mutants when glucose or formate was used as electron donor because H2 production increased ∼2- and ∼1.5-fold, respectively. Moreover, addition of external formate to the growth medium increased H2 production in a focA-focB mutant. This indicates that in the wild type, formate is preferentially exported at pH 7.5 and that another FocA/B-independent uptake system exists. At pH 6.5 and 5.5, the formate channel mutants showed reduced H2 production, suggesting that formate is usually imported by them to produce H2 at acidic pH. Addition of formate to the growth medium increased H2 production at these pHs. Notably, glycerol failed to act as an effective electron donor for formate production. Taken together, our results suggest that regulation of formate translocation direction by FocA/FocB channels is important for maintaining internal pH and proton motive force by modulating H2 production.

Comparative Analysis of UV Irradiation Effects on Escherichia coli and Pseudomonas aeruginosa Bacterial Cells Utilizing Biological and Computational Approaches.

Microorganisms have a large number of tools to withstand different, and sometimes strong, environmental stresses, including irradiation, but this ability should be further evaluated for certain applications. Growth inhibition and morphological alterations of Escherichia coli M-17 and Pseudomonas aeruginosa GRP3 wild-type cells caused by UV-A irradiation have been detected in the present study. Comparative analysis was carried out using well-established microbiological methods (determination of specific growth rate, growth lag phase duration, and colony-forming unit number-CFU) and computational approaches, employing light microscopy and digital image analysis to evaluate bacterial cell morphology. Decreases in the specific growth rate, prolonged lag-phases, and lowered CFUs were observed after 5 and 10 min of UV irradiation (approx. 40 Gy) compared to the control (nonirradiated) cells. Accordingly, two computational parameters-the average bacterial cell surface area and the bacterial cell perimeter (i.e., of the 2D projection of bacterial cells in microscopy image)-were reduced. The ratio of bacterial cell surface area (S) to the square of the perimeter (p (2) ) was reduced after 5 min of irradiation, but after 10 min of irradiation the studied bacterial cells became flat cylinders. The revealed findings are concluded to be highly useful in developing new, rapid analysis methods to monitor environmental and UV irradiation effects on bacteria and to detect bacterial cell morphology alterations.

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.

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.

K+ uptake by fermenting Escherichia coli cells: pH dependent mode of the TrkA system operating.

Escherichia coli accumulates K+ by means of multiple transport systems, of which TrkA is the most prominent at neutral and alkaline pH while Kup is major at acidic pH. In the present study, K+ uptake was observed with cells grown under fermentative conditions at an initial pH of 9.0 and 7.3 (the medium pH decreased to 8.4 and 6.8, respectively, during the mid-logarithmic growth phase), washed with distilled water and resuspended in a K+ containing medium at pH 7.5 in the presence of glucose. The kinetics for this K+ uptake and the amount of K+ accumulated by the wild type and mutants having a functional TrkA or Kup could confirm that K+ uptake by E. coli grown either at pH 9.0 or pH 7.3 occurs mainly through TrkA. The following results distinguish pH dependent mode of TrkA operating: (1) K+ uptake was inhibited by DCCD in cells grown either at pH 9.0 or pH 7.3, although the stoichiometry of K+ influx to DCCD-inhibited H+ efflux for bacteria grown at pH 9.0 varied with external K+ concentration, but remained constant for cells grown at pH 7.3; (2) K+ uptake was observed with an atpD mutant grown at pH 9.0 but not at pH 7.3; (3) The DCCD-inhibited H+ efflux was increased 8-fold less by 5 mM K+ added into a K+ free medium for bacteria grown at pH 9.0 than that for cells grown at pH 7.3; (4) the DCCD-inhibited ATPase activity of membrane vesicles from bacteria grown at pH 9.0 was reduced a little in the presence of 100 mM K+, but stimulated more than 2.4-fold at pH 7.3.

Relationship of the Escherichia coli TrkA system of potassium ion uptake with the F0F1-ATPase under growth conditions without anaerobic or aerobic respiration.

K+ uptake by the Escherichia coli TrkA system is unusual in that it requires both ATP and deltamuH+; a relation with H+ circulation through the membrane is therefore suggested. The relationship of this system with the F0F1-ATPase was studied in intact cells grown under different conditions. A significant increase of the N,N'-dicyclohexylcarbodiimide(DCCD)-inhibited H+ efflux through the F0F1 by 5 mM K+, but not by Na+ added into the potassium-free medium was revealed only in fermenting wild-type or parent cells, that were grown under anaerobic conditions without anaerobic or aerobic respiration and with the production of H2. Such an increase disappeared in the deltaunc or the trkA mutants that have altered F0F1 or defective TrkA, respectively. This finding indicates a closed relationship between TrkA and F0F1, with these transport systems being associated in a single mechanism that functions as an ATP-driven H(+)-K(+)-exchanging pump. A DCCD-inhibited H(+)-L(+)-exchange through these systems with the fixed stoichiometry of H+ and K+ fluxes (2H+/K+) and a higher K+ gradient between the cytoplasm and the external medium were also found in these bacteria. They were not observed in cells cultured under anaerobic conditions in the presence of nitrate or under aerobic conditions with respiration and without production of H2. The role of anaerobic or aerobic respiration as a determinant of the relationship of the TrkA with the F0F1 is postulated. Moreover, an increase of DCCD-inhibited H+ efflux by added K+, as well as the characteristics of DCCD-sensitive H(+)-K(+)-exchange found in a parent strain, were lost in the arcA mutant with a defective Arc system, suggesting a repression of enzymes in respiratory pathways. In addition, K+ influx in the latest mutant was not markedly changed by valinomycin or with temperature. The arcA gene product or the Arc system is proposed to be implicated in the regulation of the relationship between TrkA and F0F1.

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.