[The antioxidant characteristics of medicinal plant extracts from Western Siberia].

An antioxidant activity of the water-alcohol extracts of leaves of ten herbs from Western Siberia was studied. In vivo the capability of extracts to protect cells of Escherichia coli against the bacteriostatic action of H2O2 and the influence of the extracts on the expression of the antioxidant gene katG coding catalase-hydroperoxidase I were investigated. In vitro the radical-binding activity with DPhPG (1,1-diphenyl-2-picrylhydrazyl radical), the chelating capability with ferrozine, and total composition of flavonoids and tannins were determined. The extracts of Filipendula stepposa and Limonium gmelinii were characterized by the highest antioxidant activity. According to data, the test extracts could have an antioxidant effect on bacteria in different ways at once including the direct inhibition of ROS (reactive oxygen species), iron ion chelation and antioxidant gene induction.

[The role of thiol redox systems in the peroxide stress response of Escherichia coli].

The effect of mutations in the genes encoding glutathione, glutaredoxin, thioredoxin, and thioredoxin reductase on the response of growing Escherichia coli to oxidative stress was studied. The gshA mutants defective in glutathione synthesis had the lowest resistance to high doses of H2O2, whereas the trxB mutants defective in thioredoxin reductase synthesis had the highest resistance to this oxidant, exceeding that of the parent strain. Among the studied mutants, the trxB cells demonstrated the highest basic levels of catalase activity and intracellular glutathione; they were able to rapidly reach the normal GSH level after oxidative stress. At the same time, these bacteria showed high frequency of induced mutations. The expression of the katG and sulA genes suggests that, having different sensitivity to high oxidant concentrations, the studied mutants differ primarily in their ability to induce the antioxidant genes of the OxyR and SOS regulons.

[The role of antioxidant systems in the response of Escherichia coli to acetamidophenol and some antibiotics].

The role of glutathione and other antioxidant systems in the response of Escherichia coli to acetamidophenol (paracetamol), rifampicin, and chloramphenicol was studied. The exposure of aerobically growing E. coli cells to acetamidophenol diminished the intracellular level of glutathione by 40% and the reduced-to-oxidized glutathione ratio in the cells by 50%, while it enhanced the expression of the antioxidant genes soxS and sodA by 2.7 and 1.8 times, respectively. Glutathione-deficient cells were more susceptible to acetamidophenol than were normal cells. All this suggests that acetamidophenol induces a mild oxidative stress in E. coli cells. The oxidative stress induced by rifampicin was still less pronounced, whereas chloramphenicol-treated E.coli cells exhibited no signs of oxidative stress at all.

[The status and the role of glutathione under disturbed ionic balance and pH homeostasis in Escherichia coli]. / Status i rol' glutationa pri narushenii ionnogo balansa i pH gomeostaza u Escherichia coli.

The study of glutathione status in aerobically grown Escherichia coli cultures showed that the total intracellular glutathione (GSHin + GSSGin) level falls by 63% in response to a rapid downshift in the extracellular pH from 6.5 to 5.5. The incubation of E. coli cells in the presence of 50 mM acetate or 10 micrograms/ml gramicidin S decreased the total intracellular glutathione level by 50 and 25%, respectively. The fall in the total intracellular glutathione level was accompanied by a significant decrease in the (GSHin:GSSGin) ratio. The most profound effect on the extracellular glutathione level was exerted by gramicidin S, which augmented the total glutathione level by 1.8 times and the (GSHout:GSSGout) ratio by 2.1 times. The gramicidin S treatment and acetate stress inhibited the growth of mutant E. coli cells defective in glutathione synthesis 5 and 2 times more severely than the growth of the parent cells. The pH downshift and the exposure of E. coli cells to gramicidin S and 50 mM acetate enhanced the expression of the sodA gene coding for superoxide dismutase SodA.

[Role of the antioxidant system in response of Escherichia coli bacteria to cold stress]. / Rol' antioksidantnykh sistem v otklike bakterii Escherichia coli na kholodovo stress.

The response of aerobically grown Escherichia coli cells to the cold shock induced by the rapid lowering of growth temperature from 37 to 20 degrees C was found to be basically the same as the oxidative stress response. The enhanced sensitivity of cells deficient in two superoxide dismutases, Mn-SOD and Fe-SOD, and the increased expression of the Mn-SOD gene, sodA, in response to cold stress were interpreted as both oxidative and cold stresses are due to a rise in the intracellular level of superoxide anion. The long-term cultivation of E. coli at 20 degrees C was also accompanied by the typical oxidative stress response reactions--an enhanced expression of the Mn-SOD and catalase HPI genes and a decrease in the intracellular level of reduced glutathione (GSH) and in the GSH/GSSG ratio.

[The role of antioxidant systems in response of bacteria Escherichia coli to heat shock]. / Rol' antioksidantnykh sistem v otklike bakterii Escherichia coil na teplovoi shok.

Shifting the temperature from 30 to 45 degrees C in an aerobic Escherichia coli culture inhibited the expression of the antioxidant genes katG, katE, sodA, and gor. The expression was evaluated by measuring beta-galactosidase activity in E. coli strains that contained fusions of the antioxidant gene promoters with the lacZ operon. Heat shock inhibited catalase and glutathione reductase, lowered the intracellular level of glutathione, and increased its extracellular level. It also suppressed the growth of mutants deficient in the katG-encoded catalase HPI, whereas the sensitivity of the wild-type and sodA sodB mutant cells to heat shock was almost the same. In the E. coli culture adapted to growth at 42 degrees C, the content of both intracellular and extracellular glutathione was two times higher than in the culture grown at 30 degrees C. The temperature-adapted cells grown aerobically at 42 degrees C showed an increased ability to express the fused katG-lacZ genes.

[Effect of pH on cea gene expression in cells irradiated with UV-light and unirradiated Escherichia coli cells]. / Vliianie pH na ékspressiiu gena cea u obluchennykh UF-svetom i neobluchennykh kletok Escherichia coli.

The effect of pH on the expression of the cea gene encoding colicin EI in Escherichia coli was investigated by measuring the beta-galactosidase activity in the UV-irradiated growing cells carrying the cea-lacZ fusion. Maximum activity was observed at pH 7, and inhibition of expression was observed at pH 6 and pH 8. Treatment of the irradiated cells with 50-mM acetate increased inhibition at pH 6.0-7.5. No correlation between cea expression and the rate of cell growth was observed at different pH levels. Preliminary treatment with acetate at pH 7 reduced the expression of the recA gene, which participates in the regulation of the cea gene to 33% in irradiated cells and to 25% in nonirradiated cells.

[Hydrogen peroxide modulates intracellular levels of thiols and potassium in Escherichia coli cells]. / Perekis' vodoroda moduliruet vnutrikletochnye urovni tiolov i kaliia v kletkakh Escherichia coli.

Exposure of growing Escherichia coli K12 cells to 2.0-11.0 mM H2O2 resulted in an increase in the intracellular level of low-molecular-weight thiols (LMWT), whereas exposure to 25 mM H2O2 resulted in its decrease. An inverse correlation between levels of LMWT and potassium was revealed. The treatment of E. coli delta oxyR cells, which are incapable of the adaptive response to H2O2, with 10 mM H2O2 caused a decrease in the LMWT level. In E. coli oxyR2 cells, which constitutively express oxyR-controlled proteins, the same treatment caused a 20% increase in the LMWT level. In response to treatment with the oxidant, delta oxyR mutants lost two times more potassium than wild-type cells (oxyR+). A time course study of the levels of LMWT and potassium in mutants with an affected katG gene, which encodes the HPI catalase and is under the control of oxyR, showed that oxyR may regulate LMWT and potassium levels indirectly, through the regulation of catalase activity. A relationship between catalase activity and the LMWT level was revealed in hydrogen peroxide-treated E. coli cells.

[Change in the level of SH-compounds in Escherichia coli and Bacillus subtilis cultures during transition to the stationary phase]. / Izmenenie kolichestva SH-soedinenii v kul'turakh Escherichia coli i Bacillus subtilis pri perekhode v statsionarnuiu fazu.

The redox potential "jump" recorded earlier for aerobic Escherichia coli and Bacillus subtilis cultures passing to the stationary phase was shown to result from a rise in the content of SH-compounds in the medium and on the cell surface. The effect was absent from anaerobic cultures as well as aerobic E. coli cells treated with the protonophore CICCP. Apparently, the elevated content of SH-compounds outside the cell upon starvation is part of the process which leads to a shift in the ratio between low-molecular-mass thiols and disulfides (towards disulfides inside the cell and towards thiols outside the cell) and is associated with a drop in the intracellular pH. Therefore, the entire metabolism of the cell can change as a result of reactions with the SH-groups of functionally significant compounds when the cell enters the stationary phase upon starvation.

[Changes in the redox potential and the number of accessible sulfhydryl groups in Escherichia coli and Bacillus subtilis cultures during transient processes]. / Izmeneniia redoks-potentsiala i kolichestva dostupnykh SH-grupp v kul'turakh Escherichia coli i Bacillus subtilis pri perekhodnykh protsessakh.

It was shown that changes in the redox potential can be due to the influence of compounds which alter the intracellular pH (acetate or propionate, protonophore carbonyl-cyanide-m-chlorophenyl hydrazone, permeate cation TPP+). A correlation was found between the redox potential changes and the number of SH-groups in the medium and on cell surface. It was shown also that the previously reported redox potential shifts during the transition of E. coli and B. subtilis cultures to the stationary phase under glucose or ammonium exhaustion are due to the increase in the number of SH-groups in the medium and on cell surface. A hypothesis is put forward, according to which the changes in intracellular pH play a trigger role, whereas those in the thiol: disulfide ratio inside and outside the cells are thought to amplify regulatory signals.

[Effect of the activity of primary proton pumps on the growth of Escherichia coli in the presence of acetate]. / Vliianie aktivnosti pervichnykh protonnykh pomp na rost Escherichia coli v prisutstvii atsetata.

Escherichia coli batch cultures were grown under aerobic and anaerobic conditions on glucose with the substrate addition at pH 7.0. The cultures accumulated acetate in the medium at concentrations sufficient to inhibit the growth. This inhibitory effect of acetate was mediated apparently via its action on the intracellular pH. The inhibition of E. coli growth by acetate increased when the redox proton pump was switched off in the course of transition from aerobiosis to anaerobiosis and when the regulation of K+ fluxes was disordered in the presence of valinomycin. H+-ATPase was not essentially involved in maintaining the high rate of E. coli growth in the presence of acetate under aerobic conditions. If the activity of H+-ATPase was inhibited under anaerobic conditions at pH 7.0, the growth ceased after the dissipation of ionic gradients on the membrane. When CCCP was added under aerobic conditions, the growth did not stop at once if the medium had a pH of 7.6, but ceased immediately at pHout 7.0 in the glucose-salt medium.

[Effect of acetate on the growth of Escherichia coli during aerobiosis and anaerobiosis]. / Vliianie atsetata na rost Escherichia coli v aérobnykh i anaérobnykh usloviiakh.

The dynamics of acetate accumulation was studied in Escherichia coli K-12 batch cultures with a substrate addition. At pH 7.0, the growth stopped at 150 mmoles of acetate per litre of the medium under the aerobic conditions or at 35 mmoles of acetate per litre of the medium under the anaerobic conditions. Experiments with extraneous addition of acetate suggest that acetic acid plays a key role in inhibiting the growth of E. coli by acid metabolites. The authors propose a hypothetical mechanism to account for the inhibiting action of acetate.

[Dynamics of the redox potential in a fed-batch culture of E. coli]. / Dinamika redoks-potentsiala v kul'ture E. coli v rezhime periodicheskogo kul'tivirovaniia.

Dynamics of Eh, pH, pO2 and optical density in E. coli cultures under glucose and ammonium exhaustion were studied. It has been shown that changes in the redox potential accompanying the exhaustion of these substances in aerobic cultures are the leaps by their character and reflect the physiological state of cells and changes in the structure of cell surface. A relationship between the changes in the redox potential and in the electrochemical potential of H ions (delta mu H) is suggested.

[Batch cultures of Escherichia coli with added substrate under various aeration conditions]. / Periodicheskie kul'tury Escherichia coli s dobavleniem substrata pri razlichnykh usloviiakh aératsii.

The growth parameters (Xmax, Y, mu) of Escherichia coli batch cultures were studied when a substrate was added under different aeration conditions. If the pH was not adjusted, the bacterial growth stopped at pH 4.5 under the aerobic conditions or at pH 5.8 under the anaerobic conditions. When the pH 7.0 was constantly maintained, the accumulation of acid products in the aerobic culture was 3 times as high as in the anaerobic culture by the time the growth ceased. The anaerobic culture resumed its growth upon aeration. A hypothesis is proposed to explain the data.

[Changes in redox potentials during transitional processes in pure and mixed cultures of Escherichia coli and Serratia marcescens]. / Izmenenie redoks-potentsiala pri perekhodnykh protsessakh v chistykh i smeshannykh kul'turakh Escherichia coli i Serratia marcescens.

There were studied transitional processes accompanying the beginning of growth under glucose addition and stopping of growth under glucose exhaustion in pure and mixed aerobic cultures of Escherichia coli and Serratia marcescens. Continued record of Eh, pH, and CO2 showed that these processes sharply differ from each other in their character in pure and mixed cultures, it is particularly related to the changes of the redox potential. There is no characteristic change in the redox potential in pure culture of E. coli at growth termination in the case when S. marcescens cells are present in the culture.

[Changes in the redox potential and pO2 in heat shock to Escherichia coli]. / Izmeneniia redoksi-potentsiala i pO2 pri teplovom shoke Escherichia coli.

When the growing culture of Escherichia coli was subjected to a temperature above 37 degrees C, the pO2 fell abruptly at 42 degrees C; a reversible decrease in the redox potential (ROP) down to the range of negative values was detected if the growth ceased at 46 degrees C. The drop in the ROP took from 6 to 10 min, with the maximal deviation of 42.5 mV. Such changes in the pO2 and ROP were not caused by a heat shock in the stationary cultures. The change in the ROP was not due to a change in the pH and pO2 of the medium. The authors believe that the effect should be attributed to an elimination of the ionic gradients and the electrochemical gradient delta muH+.