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

Antibacterial Properties of Copper Oxide Nanoparticles (Review)

The use of metal and metal oxide nanoparticles is frequently regarded as a potential solution to the issue of bacterial antibiotic resistance. Among the proposed range of nanoparticles with antibacterial properties, copper oxide nanoparticles are of particular interest. Although the antibacterial properties of copper have been known for a considerable period of time, studies on the effects of copper oxide nanomaterials with respect to biological systems have attracted considerable attention in recent years. This review presents a summary of the antibacterial properties of copper oxide nanoparticles, the mechanisms by which the antibacterial effect is realized, and the key reported methods of modifying these nanoparticles to improve their antibacterial activity. A comparative analysis of the effectiveness of these nanoparticles is presented depending on the type of microorganism, the shape of the nanoparticles, and the Gram classification of bacteria based on data from published sources. In addition, the review addresses the biological activities of copper oxide nanoparticles, including their antifungal and cytotoxic properties, as well as their "antioxidant" activity. According to the conducted analysis of the literature data, it can be concluded that copper oxide nanoparticles have a significant bacteriostatic potential with respect to a wide range of microorganisms and, in some cases, contribute to the inhibition of fungal growth. At the same time, the sensitivity of Gram-positive bacteria to the effect of copper oxide nanoparticles was often higher than that of Gram-negative bacteria.

Sodium transport and redox regulation in Saccharomyces cerevisiae under osmotic stress depending on oxygen availability

This study explores the molecular mechanisms behind the differential responses of Saccharomyces cerevisiae industrial strains (ATCC 9804 and ATCC 13007) to osmotic stress. We observed that, in contrast to ATCC 9804 strain, sodium flux in ATCC 13,007 is not N, N'-dicyclohexylcarbodiimide (DCCD)-sensitive under osmotic stress, suggesting a distinct ion homeostasis mechanism. Under aerobic conditions, osmotic stress increased reduced SH groups by 45% in ATCC 9804 and 34% in ATCC 13,007. In contrast, under microaerophilic conditions, both strains experienced a 50% reduction in thiol groups. Notably, ATCC 13,007 exhibited a 1.5-fold increase in catalase (CAT) activity under aerobic stress compared to standard conditions, while ATCC 9804 showed enhanced CAT activity due to SH group binding. Additionally, superoxide dismutase (SOD) activity was doubled during aerobic growth in both strains, with ATCC 13,007 showing a 1.5-fold higher SOD activity under osmotic stress. The results demonstrate that S. cerevisiae adapts to osmotic stress differently under aerobic and microaerophilic conditions, with aerobic conditions promoting Pma-Ena-Trk interplay, reduced thiol levels and increased catalase activity, while microaerophilic conditions demonstrate Pma-Nha-Trk interplay and shifts redox balance towards oxidized thiol groups and enhance superoxide dismutase activity. Understanding these mechanisms can aid in developing stress-resistant yeast strains for industrial applications.

A molecular dynamics study of protein denaturation induced by sulfonate-based surfactants

Microsecond timescale explicit-solvent atomistic simulations were carried out to investigate how anionic surfactants modulate protein structure and dynamics. We found that lysozyme undergoes near-complete denaturation at the high concentration (> 0.1 M) of sodium pentadecyl sulfonate (SPDS), while only partial denaturation occurs at the concentration slightly below 0.1 M. In large part, protein denaturation is structurally manifested by disappearance of helical segments and loss of tertiary interactions. The computational prediction of the extent of burial of cysteine residues was experimentally validated by measuring the accessibility of the respective sulfhydryl groups. Overall, our work indicates an interesting synergy between electrostatic and hydrophobic contributions to lysozyme's denaturation process by anionic surfactants. In fact, first disulfide bridges and hydrogen bonds from protein surface to SPDS head groups loosen the protein globule followed by fuller denaturation via insertion of the surfactant's hydrophobic tails into the protein core.

Cupric ion in combination with hydrogen peroxide and hydroxylamine applied to inactivation of different microorganisms

The microbial inactivation by cupric ion (Cu(II)) in combination with hydrogen peroxide (H₂O₂) and hydroxylamine (HA) was investigated for twelve different microorganisms (five Gram-negative bacteria, three Gram-positive bacteria, and four bacteriophages). The inactivation efficacy, protein oxidation, and RNA (or DNA) damage were monitored during and after treatment by Cu(II), Cu(II)/HA, Cu(II)/H₂O₂ and Cu(II)/HA/H₂O₂. The rate of microbial inactivation by the (combined) microbicides generally increased in the order of Cu(II) < Cu(II)/H₂O₂ < Cu(II)/HA < Cu(II)/HA/H₂O₂; Cu(II)/HA/H₂O₂ resulted in 0.18-0.31, 0.10-0.18, and 0.55-3.83 log inactivation/min for Gram-negative bacteria, Gram-positive bacteria, and bacteriophages, respectively. The degrees of protein oxidation and RNA (or DNA) damage increased in the order of Cu(II) < Cu(II)/HA < Cu(II)/H₂O₂ < Cu(II)/HA/H₂O₂. In particular, Cu(II)/HA/H₂O₂ led to exceptionally fast inactivation of the viruses. Gram-positive bacteria tended to show higher resistance to microbicides than other microbial species. The microbicidal effects of the combined microbicides on the target microorganisms were explained by the roles of Cu(I) and Cu(III) generated by the redox reactions of Cu(II) with H₂O₂, HA, and oxygen. Major findings of this study indicate that Cu(II)-based combined microbicides are promising disinfectants for different waters contaminated by pathogenic microorganisms.

Enhanced Inactivation of Escherichia coli and MS2 Coliphage by Cupric Ion in the Presence of Hydroxylamine: Dual Microbicidal Effects

The inactivation of Escherichia coli and MS2 coliphage by Cu(II) is found to be significantly enhanced in the presence of hydroxylamine (HA). The addition of a small amount of HA (i.e., 5-20 μM) increased the inactivation efficacies of E. coli and MS2 coliphage by 5- to 100-fold, depending on the conditions. Dual effects were anticipated to enhance the biocidal activity of Cu(II) by the addition of HA, viz. (i) the accelerated reduction of Cu(II) into Cu(I) (a stronger biocide) and (ii) the production of reactive oxidants from the reaction of Cu(I) with dissolved oxygen (evidenced by the oxidative transformation of methanol into formaldehyde). Deaeration enhanced the inactivation of E. coli but slightly decreased the inactivation efficacy of MS2 coliphage. The addition of 10 μM hydrogen peroxide (H2O2) greatly enhanced the MS2 inactivation, whereas the same concentration of H2O2 did not significantly affect the inactivation efficacy of E. coli Observations collectively indicate that different biocidal actions lead to the inactivation of E. coli and MS2 coliphage. The toxicity of Cu(I) is dominantly responsible for the E. coli inactivation. However, for the MS2 coliphage inactivation, the oxidative damage induced by reactive oxidants is as important as the effect of Cu(I).

Effects of various heavy metal nanoparticles on Enterococcus hirae and Escherichia coli growth and proton-coupled membrane transport

BACKGROUND

Due to bacterial resistance to antibiotics there is a need for new antimicrobial agents. In this respect nanoparticles can be used as they have expressed antibacterial activity simultaneously being more reactive compared to their bulk material. The action of zinc (II), titanium (IV), copper (II) and (I) oxides thin films with nanostructured surface and silver nanoscale particles on Enterococcus hirae and Escherichia coli growth and membrane activity was studied by using microbiological, potentiometric and spectrophotometric methods.

RESULTS

It was revealed that sapphire base plates with deposited ZnO, TiO2, CuO and Cu2O nanoparticles had no effects neither on E. hirae nor E. coli growth both on agar plates and in liquid medium. Concentrated Ag nanoparticles colloid solution markedly affected bacterial growth which was expressed by changing growth properties. E. hirae was able to grow only at <1:200 dilutions of Ag nanoparticles while E. coli grew even at 1:10 dilution. At the same time Ag nanoparticles directly affected membranes, as the FOF1-ATPase activity and H(+)-coupled transport was changed either (E. coli were less susceptible to nanoparticles compared to E. hirae). Ag nanoparticles increased H(+) and K(+) transport even in the presence of N,N'-dicyclohexylcarbodiimide (DCCD), inhibitor of FOF1. The stoichiometry of DCCD-inhibited ion fluxes was disturbed.

CONCLUSIONS

These results point out to distinguishing antibacterial effects of Ag nanoparticles on different bacteria; the difference between effects can be explained by peculiarities in bacterial membrane structure and properties. H(+)-K(+)-exchange disturbance by Ag nanoparticles might be involved in antibacterial effects on E. hirae. The role of FOF1 in antibacterial action of Ag nanoparticles was shown using atpD mutant lacked β subunit in F1.

Cu(II), Fe(III) and Mn(II) combinations as environmental stress factors have distinguishing effects on Enterococcus hirae

Pollution by various heavy metals as environmental stress factors might affect bacteria. It was established that iron (Fe(III)), manganese (Mn(II)) and copper (Cu(II)) ion combinations caused effects on Enterococcus hirae that differed from the sum of the effects when the metals were added separately. It was shown that the Cu2+-Fe3+ combination decreased the growth and ATPase activity of membrane vesicles of wild-type E. hirae ATCC9790 and atpD mutant (with defective FoF1-ATPase) MS116. Addition of Mn2+-Fe3+ combinations within the same concentration range had no effects on growth compared to control (without heavy metals). ATPase activity was increased in the presence of Mn2+-Fe3+, while together with 0.2 mmol/L N,N'-dicyclohexylcarbodiimide (DCCD), ATPase activity was decreased compared to control (when only 0.2 mmol/L DCCD was present). These results indicate that heavy metals ion combinations probably affect the FOF1-ATPase, leading to conformational changes. Moreover the action may be direct or be mediated by environment redox potential. The effects observed when Fe3+ was added separately disappeared in both cases, which might be a result of competing processes between Fe3+ and other heavy metals. These findings are novel and improve the understanding of heavy metals ions effects on bacteria, and could be applied for regulation of stress response patterns in the environment.

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.

Mechanism of copper surface toxicity in Escherichia coli O157:H7 and Salmonella involves immediate membrane depolarization followed by slower rate of DNA destruction which differs from that observed for Gram-positive bacteria

We have reported previously that copper I and II ionic species, and superoxide but not Fenton reaction generated hydroxyl radicals, are important in the killing mechanism of pathogenic enterococci on copper surfaces. In this new work we determined if the mechanism was the same in non-pathogenic ancestral (K12) and laboratory (DH5α) strains, and a pathogenic strain (O157), of Escherichia coli. The pathogenic strain exhibited prolonged survival on stainless steel surfaces compared with the other E. coli strains but all died within 10 min on copper surfaces using a 'dry' inoculum protocol (with approximately 10(7)  cfu cm(-2) ) to mimic dry touch contamination. We observed immediate cytoplasmic membrane depolarization, not seen with enterococci or methicillin resistant Staphylococcus aureus, and loss of outer membrane integrity, inhibition of respiration and in situ generation of reactive oxygen species on copper and copper alloy surfaces that did not occur on stainless steel. Chelation of copper (I) and (II) ionic species still had the most significant impact on bacterial survival but protection by d-mannitol suggests hydroxyl radicals are involved in the killing mechanism. We also observed a much slower rate of DNA destruction on copper surfaces compared with previous results for enterococci. This may be due to protection of the nucleic acid by the periplasm and the extensive cell aggregation that we observed on copper surfaces. Similar results were obtained for Salmonella species but partial quenching by d-mannitol suggests radicals other than hydroxyl may be involved. The results indicate that copper biocidal surfaces are effective for Gram-positive and Gram-negative bacteria but bacterial morphology affects the mechanism of toxicity. These surfaces could not only help to prevent infection spread but also prevent horizontal gene transmission which is responsible for the evolution of virulent toxin producing and antibiotic resistant bacteria.

Fe(III) and Fe(II) ions different effects on Enterococcus hirae cell growth and membrane-associated ATPase activity

Enterococcus hirae is able to grow under anaerobic conditions during glucose fermentation (pH 8.0) which is accompanied by acidification of the medium and drop in its oxidation-reduction potential (E(h)) from positive values to negative ones (down to ∼-200 mV). In this study, iron (III) ions (Fe(3+)) have been shown to affect bacterial growth in a concentration-dependent manner (within the range of 0.05-2 mM) by decreasing lag phase duration and increasing specific growth rate. While iron(II) ions (Fe(2+)) had opposite effects which were reflected by suppressing bacterial growth. These ions also affected the changes in E(h) values during bacterial growth. It was revealed that ATPase activity with and without N,N'-dicyclohexylcarbodiimide (DCCD), an inhibitor of the F(0)F(1)-ATPase, increased in the presence of even low Fe(3+) concentration (0.05 mM) but decreased in the presence of Fe(2+). It was established that Fe(3+) and Fe(2+) both significantly inhibited the proton-potassium exchange of bacteria, but stronger effects were in the case of Fe(2+) with DCCD. Such results were observed with both wild-type ATCC9790 and atpD mutant (with defective F(0)F(1)) MS116 strains but they were different with Fe(3+) and Fe(2+). It is suggested that the effects of Fe(3+) might be due to interaction of these ions with F(0)F(1) or there might be a Fe(3+)-dependent ATPase different from F(0)F(1) in these bacteria that is active even in the presence of DCCD. Fe(2+) inhibits E. hirae cell growth probably by strong effect on E(h) leading to changes in F(0)F(1) and decreasing its activity.

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.

The effects of copper (II) ions on Enterococcus hirae cell growth and the proton-translocating FoF1 ATPase activity

Enterococcus hirae grow well under anaerobic conditions at alkaline pH (pH 8.0) producing acids by glucose fermentation. Bacterial growth was shown to be accompanied by decrease of redox potential from positive values (approximately +35 mV) to negative ones (approximately -220 mV). An oxidizer copper (II) ions (Cu(2+)) affected bacterial growth in a concentration-dependent manner (within the range of 0.05 mM to 1 mM) increasing lag phase duration and decreasing specific growth rate. These effects were observed with the wild-type strain ATCC9790 and the atpD mutant strain MS116 (with absent beta subunit of F(1) of the F(o)F(1) ATPase) both. Also ATPase activity and proton-potassium ions exchange were assessed with and without N,N'-dicyclohexylcarbodiimide (DCCD), inhibitor of the F(o)F(1) ATPase. In both cases (DCCD +/-), even low Cu(2+) concentrations had noticeable effect on ATPase activity, but with less visible concentration-dependent manner. Changes in the number of accessible SH-groups were observed with E. hirae ATCC9790 and MS116 membrane vesicles. In both strains Cu(2+) markedly decreased the number of SH-groups in the presence of K(+) ions. The addition of ATP increased the amount of accessible SH-groups in ATCC9790 and decreased this number in MS116; Cu(2+) blocked ATP-installed increase in SH-groups number in ATCC9790. H(+)-K(+)-exchange of bacteria was markedly inhibited by Cu(2+), but stronger effects were detected together with DCCD. Moreover, discrimination between Cu(2+) and other bivalent cation--Ni(2+) was shown. It is suggested that Cu(2+) ions inhibit E. hirae cell growth by direct affect on the F(o)F(1) ATPase leading to conformational changes in this protein complex and decrease in its activity.

Genetic analysis of activation of the Vibrio cholerae Cpx pathway

The Cpx two-component system is thought to mediate envelope stress responses in many gram-negative bacteria and has been implicated in the pathogenicity of several enteric pathogens. While cues that activate the Escherichia coli Cpx system have been identified, the nature of the molecular signals that stimulate this pathway is not well understood. Here, we investigated stimuli that trigger this system in Vibrio cholerae, a facultative pathogen that adapts to various niches during its life cycle. In contrast to E. coli, there was no basal activity of the V. cholerae Cpx pathway under standard laboratory conditions. Furthermore, several known stimuli of the E. coli pathway did not induce expression of this system in V. cholerae. There were no defects in intestinal growth in V. cholerae cpx mutants, arguing against the idea that this pathway promotes V. cholerae adaptation to conditions in the mammalian host. We discovered that chloride ions activate the V. cholerae Cpx pathway, raising the possibility that this signal transduction system provides a means for V. cholerae to sense and respond to alterations in salinity. We used a genetic approach to screen for mutants in which the Cpx pathway is activated. We found that mutations in genes whose products are required for periplasmic disulfide bond isomerization result in activation of the Cpx pathway, suggesting that periplasmic accumulation of proteins with aberrant disulfide bonds triggers the V. cholerae Cpx pathway.