Glutathione status and sensitivity to GSH-reacting compounds of Escherichia coli strains deficient in glutathione metabolism and/or catalase activity

Staphylococcus aureus Uses the Bacilliredoxin (BrxAB)/Bacillithiol Disulfide Reductase (YpdA) Redox Pathway to Defend Against Oxidative Stress Under Infections

Staphylococcus aureus is a major human pathogen and has to cope with reactive oxygen and chlorine species (ROS, RCS) during infections. The low molecular weight thiol bacillithiol (BSH) is an important defense mechanism of S. aureus for detoxification of ROS and HOCl stress to maintain the reduced state of the cytoplasm. Under HOCl stress, BSH forms mixed disulfides with proteins, termed as S-bacillithiolations, which are reduced by bacilliredoxins (BrxA and BrxB). The NADPH-dependent flavin disulfide reductase YpdA is phylogenetically associated with the BSH synthesis and BrxA/B enzymes and was recently suggested to function as BSSB reductase (Mikheyeva et al., 2019). Here, we investigated the role of the complete bacilliredoxin BrxAB/BSH/YpdA pathway in S. aureus COL under oxidative stress and macrophage infection conditions in vivo and in biochemical assays in vitro. Using HPLC thiol metabolomics, a strongly enhanced BSSB level and a decreased BSH/BSSB ratio were measured in the S. aureus COL ΔypdA deletion mutant under control and NaOCl stress. Monitoring the oxidation degree (OxD) of the Brx-roGFP2 biosensor revealed that YpdA is required for regeneration of the reduced BSH redox potential (E_BSH) upon recovery from oxidative stress. In addition, the ΔypdA mutant was impaired in H₂O₂ detoxification as measured with the novel H₂O₂-specific Tpx-roGFP2 biosensor. Phenotype analyses further showed that BrxA and YpdA are required for survival under NaOCl and H₂O₂ stress in vitro and inside murine J-774A.1 macrophages in infection assays in vivo. Finally, NADPH-coupled electron transfer assays provide evidence for the function of YpdA in BSSB reduction, which depends on the conserved Cys14 residue. YpdA acts together with BrxA and BSH in de-bacillithiolation of S-bacillithiolated GapDH. In conclusion, our results point to a major role of the BrxA/BSH/YpdA pathway in BSH redox homeostasis in S. aureus during recovery from oxidative stress and under infections.

Probing the ArcA regulon under aerobic/ROS conditions in Salmonella enterica serovar Typhimurium

BACKGROUND

Hydrogen peroxide (H₂O₂) is a reactive oxygen species (ROS), which is part of the oxidative burst encountered upon internalization of Salmonella enterica serovar Typhimurium (S. Typhimurium) by phagocytic cells. It has previously been established that, the ArcAB two-component system plays a critical role in ROS resistance, but the genes regulated by the system remained undetermined to date. We therefore investigated the ArcA regulon in aerobically growing S. Typhimurium before and after exposure to H₂O₂ by querying gene expression and other physiological changes in wild type and ΔarcA strains.

RESULTS

In the ΔarcA strain, expression of 292 genes showed direct or indirect regulation by ArcA in response to H₂O₂, of which 141were also regulated in aerobiosis, but in the opposite direction. Gene set enrichment analysis (GSEA) of the expression data from WT and ΔarcA strains, revealed that, in response to H₂O₂ challenge in aerobically grown cells, ArcA down regulated multiple PEP-PTS and ABC transporters, while up regulating genes involved in glutathione and glycerolipid metabolism and nucleotide transport. Further biochemical analysis guided by GSEA results showed that deletion of arcA during aerobic growth lead to increased reactive oxygen species (ROS) production which was concomitant with an increased NADH/NAD+ ratio. In absence of ArcA under aerobic conditions, H₂O₂ exposure resulted in lower levels of glutathione reductase activity, leading to a decreased GSH (reduced glutathione)/GSSG (oxidized glutathione) ratio.

CONCLUSION

The ArcA regulon was defined in 2 conditions, aerobic growth and the combination of peroxide treatment and aerobic growth in S. Typhimurium. ArcA coordinates a response that involves multiple aspects of the carbon flux through central metabolism, which ultimately modulates the reducing potential of the cell.

Cytoplasmic glutathione redox status determines survival upon exposure to the thiol-oxidant 4,4'-dipyridyl disulfide

Dipyridyl disulfide (DPS) is a highly reactive thiol oxidant that functions as electron acceptor in thiol-disulfide exchange reactions. DPS is very toxic to yeasts, impairing growth at low micromolar concentrations. The genes TRX2 (thioredoxin), SOD1 (superoxide dismutase), GSH1 (gamma-glutamyl-cysteine synthetase) and, particularly, GLR1 (glutathione reductase) are required for survival on DPS. DPS is uniquely thiol-specific, and we found that the cellular mechanisms for DPS detoxification differ substantially from that of the commonly used thiol oxidant diamide. In contrast to this oxidant, the full antioxidant pools of glutathione (GSH) and thioredoxin are required for resistance to DPS. We found that DPS-sensitive mutants display increases in the disulfide form of GSH (GSSG) during DPS exposure that roughly correlate with their more oxidizing GSH redox potential in the cytosol and their degree of DPS sensitivity. DPS seems to induce a specific disulfide stress, where an increase in the cytoplasmic/nuclear GSSG/GSH ratio results in putative DPS target(s) becoming sensitive to DPS.

Glutathione in bacteria

Glutathione metabolism and its role in vital functions of bacterial cells are considered, as well as common features and differences between the functions of glutathione in prokaryotic and eukaryotic cells. Particular attention is given to the recent data for the role of glutathione in bacterial redox-regulation and adaptation to stresses.

Metabolic pathway engineering to enhance aerobic degradation of chlorinated ethenes and to reduce their toxicity by cloning a novel glutathione S-transferase, an evolved toluene o-monooxygenase, and gamma-glutamylcysteine synthetase

Aerobic, co-metabolic bioremediation of trichloroethylene (TCE), cis-1,2-dichloroethylene (cis-DCE) and other chlorinated ethenes with monooxygenase-expressing microorganisms is limited by the toxic epoxides produced as intermediates. A recombinant Escherichia coli strain less sensitive to the toxic effects of cis-DCE, TCE and trans-1,2-dichloroethylene (trans-DCE) degradation has been created by engineering a novel pathway consisting of eight genes including a DNA-shuffled toluene ortho-monooxygenase from Burkholderia cepacia G4 (TOM-Green), a newly discovered glutathione S-transferase (GST) from RhodococcusAD45 (IsoILR1), found to have activity towards epoxypropane and cis-DCE epoxide, and an overexpressed E. coli mutant gamma-glutamylcysteine synthetase (GSHI*). Along with IsoILR1, another new RhodococcusAD45 GST, IsoILR2, was cloned that lacks activity towards cis-DCE epoxide and differs from IsoILR1 by nine amino acids. The recombinant strain in which TOM-Green and IsoILR1 were co-expressed on separate plasmids degraded 1.9-fold more cis-DCE compared with a strain that lacked IsoILR1. In the presence of IsoILR1 and TOM-Green, the addition of GSH1* resulted in a sevenfold increase in the intracellular GSH concentration and a 3.5-fold improvement in the cis-DCE degradation rate based on chloride released (2.1 +/- 0.1 versus 0.6 +/- 0.1 nmol min(-1) mg(-1) protein at 540 microM), a 1.8-fold improvement in the trans-DCE degradation rate (1.29 +/- 0.03 versus 0.71 +/- 0.04 nmol x min(-1) mg(-1) protein at 345 microM) and a 1.7-fold improvement in the TCE degradation rate (6.8 +/- 0.24 versus 4.1 +/- 0.16 nmol x min(-1) mg(-1) protein at 339 microM). For cis-DCE degradation with TOM-Green (based on substrate depletion), V(max) was 27 nmol x min(-1) mg(-1) protein with both IsoILR1 and GSHI* expressed compared with V(max) = 10 nmol x min(-1) mg(-1) protein for the GST(-)GSHI*(-) strain. In addition, cells expressing IsoILR1 and GSHI* grew 78% faster in rich medium than a strain lacking these two heterologous genes.

Role of glutathione metabolism of Treponema denticola in bacterial growth and virulence expression

Hydrogen sulfide (H(2)S) is a major metabolic end product detected in deep periodontal pockets that is produced by resident periodontopathic microbiota associated with the progression of periodontitis. Treponema denticola, a member of the subgingival biofilm at disease sites, produces cystalysin, an enzyme that catabolizes cysteine, releasing H(2)S. The metabolic pathway leading to H(2)S formation in periodontal pockets has not been determined. We used a variety of thiol compounds as substrates for T. denticola to produce H(2)S. Our results indicate that glutathione, a readily available thiol source in periodontal pockets, is a suitable substrate for H(2)S production by this microorganism. In addition to H(2)S, glutamate, glycine, ammonia, and pyruvate were metabolic end products of metabolism of glutathione. Cysteinyl glycine (Cys-Gly) was also catabolized by the bacteria, yielding glycine, H(2)S, ammonia, and pyruvate. However, purified cystalysin could not catalyze glutathione and Cys-Gly degradation in vitro. Moreover, the enzymatic activity(ies) in T. denticola responsible for glutathione breakdown was inactivated by trypsin or proteinase K, by heating (56 degrees C) and freezing (-20 degrees C), by sonication, and by exposure to N alpha-p-tosyl-L-lysine chloromethyl ketone (TLCK). These treatments had no effect on degradation of cysteine by the purified enzyme. In this study we delineated an enzymatic pathway for glutathione metabolism in the oral spirochete T. denticola; our results suggest that glutathione metabolism plays a role in bacterial nutrition and potential virulence expression.

Escherichia coli gamma-glutamylcysteine synthetase. Two active site metal ions affect substrate and inhibitor binding

Gamma-glutamylcysteine synthetase (gamma-GCS, glutamate-cysteine ligase), which catalyzes the first and rate-limiting step in glutathione biosynthesis, is present in many prokaryotes and in virtually all eukaryotes. Although all eukaryotic gamma-GCS isoforms examined to date are rapidly inhibited by buthionine sulfoximine (BSO), most reports indicate that bacterial gamma-GCS is resistant to BSO. We have confirmed the latter finding with Escherichia coli gamma-GCS under standard assay conditions, showing both decreased initial binding affinity for BSO and a reduced rate of BSO-mediated inactivation compared with mammalian isoforms. We also find that substitution of Mn2+ for Mg2+ in assay mixtures increases both the initial binding affinity of BSO and the rate at which BSO causes mechanism-based inactivation. Similarly, the specificity of E. coli gamma-GCS for its amino acid substrates is broadened in the presence of Mn2+, and the rate of reaction for some very poor substrates is improved. These results suggest that divalent metal ions have a role in amino acid binding to E. coli gamma-GCS. Electron paramagnetic resonance (EPR) studies carried out with Mn2+ show that E. coli gamma-GCS binds two divalent metal ions; Kd values for Mn2+ are 1.1 microm and 82 microm, respectively. Binding of l-glutamate or l-BSO to the two Mn2+/gamma-GCS species produces additional upfield and downfield X-band EPR hyperfine lines at 45 G intervals, a result indicating that the two Mn2+ are spin-coupled and thus apparently separated by 5 A or less in the active site. Additional EPR studies in which Cu2+ replaced Mg2+ or Mn2+ suggest that Cu2+ is bound by one N and three O ligands in the gamma-GCS active site. The results are discussed in the context of the catalytic mechanism of gamma-GCS and its relationship to the more fully characterized glutamine synthetase reaction.

Roles of the glutathione- and thioredoxin-dependent reduction systems in the Escherichia coli and saccharomyces cerevisiae responses to oxidative stress

The glutathione- and thioredoxin-dependent reduction systems are responsible for maintaining the reduced environment of the Escherichia coli and Saccharomyces cerevisiae cytosol. Here we examine the roles of these two cellular reduction systems in the bacterial and yeast defenses against oxidative stress. The transcription of a subset of the genes encoding glutathione biosynthetic enzymes, glutathione reductases, glutaredoxins, thioredoxins, and thioredoxin reductases, as well as glutathione- and thioredoxin-dependent peroxidases is clearly induced by oxidative stress in both organisms. However, only some strains carrying mutations in single genes are hypersensitive to oxidants. This is due, in part, to the redundant effects of the gene products and the overlap between the two reduction systems. The construction of strains carrying mutations in multiple genes is helping to elucidate the different roles of glutathione and thioredoxin, and studies with such strains have recently revealed that these two reduction systems modulate the activities of the E. coli OxyR and SoxR and the S. cerevisiae Yap1p transcriptional regulators of the adaptive responses to oxidative stress.

The levels of ribonucleotide reductase, thioredoxin, glutaredoxin 1, and GSH are balanced in Escherichia coli K12

The dithiol forms of thioredoxin and glutaredoxin are hydrogen donors for ribonucleotide reductase. We have determined the intracellular levels of ribonucleotide reductase (RRase), thioredoxin (Trx), glutaredoxin 1 (Grx1), and glutathione (GSH) and the glutathione redox status in new Escherichia coli K12 strains lacking thioredoxin (trxA-), glutaredoxin 1 (grxA-), and/or GSH (gshA-) or overproducing Trx or Grx1 from multicopy plasmids. We propose a regulatory network in which RRase levels are balanced with those of Trx, Grx1, and GSH so that deficiency or overproduction of one component would promote the opposite effect on the others to maintain a balanced supply of deoxyribonucleotides. GSH deficiency strongly increased both Grx1 levels and RRase activity, even more than Trx deficiency. Double gshA-trxA- bacteria were viable, whereas additional deficiency in lipoate synthesis (gshA-trxA-lipA-) caused the inability to grow in minimal medium plates supplemented with acetate plus succinate instead of lipoic acid. Thus, lipoate might be the only substitute of GSH for glutaredoxin reduction in gshA-trxA- cells, although the extremely high Grx1 content (55-fold) of these bacteria suggests that electron transfer from lipoate might be an inefficient reduction mechanism of glutaredoxins. Moreover, the enhanced Grx1 level of gshA-trxA- cells could obviate the need for a large increase in RRase activity, in contrast to grxA-trxA- double mutant cells. Impairment of the sulfate assimilation pathway, leading to very low GSH concentrations, and an oxidized glutathione redox state might explain the inability of grxA-trxA- cells to grow in minimal medium. Restoration of nearly normal levels of both GSH content and redox status cure the growth defect.

Rapid determination of glutathione status in fish liver using high-performance liquid chromatography and electrochemical detection

A rapid and sensitive method for the detection of reduced (GSH), oxidised (GSSG) and protein-bound (PSSG) glutathione in fish liver, using reversed-phase HPLC with electrochemical detection has been developed. Separation was carried out isocratically at room temperature using 0.020 M sodium phosphate, pH 2.7 as mobile phase. A series dual-channel electrochemical detector was used for the simultaneous determination of GSH and GSSG. PSSG was determined after reduction by 1,4-dithiothreitol. The detection limits found for a 3:1 signal-to-noise ratio were 16.2 and 8.1 pmol for GSH and GSSG, respectively. The results obtained demonstrate that this method could be useful for measurement of the glutathione redox status in fish liver and are consistent with those reported for other fish. The method has been applied to follow the oxidative stress induced in vivo by copper(II) ions in the gilthead seabream fish (Sparus aurata). At longer times after copper(II) injection, the glutathione redox status of the exposed fish returned to a more reduced state, suggesting the existence of adaptive processes.

Induction of the alkylation-inducible aidB gene of Escherichia coli by cytoplasmic acidification and N-ethylmaleimide

We have studied the effects of changes in intracellular pH and the influence of thiol reagents on the induction of the DNA damage-inducible genes of Escherichia coli, aidB, alkA, and alkB. Under aerobic conditions in the absence of alkylating agents aidB, but not alkA or alkB, was induced by an acidification of cytoplasm or by treatment with the sulfhydryl reagent N-ethylmaleimide. Alkaline shift and thiosalicyclic acid did not affect the induction of aidB and alkB. The induction of alkA increased under the alkaline shift but not in the case of treatment with reducing agents. Compared with the aidB gene, a component of the SOS system, the sulA (sfiA) gene, responded to changes in cytoplasmic pH and in the level of intracellular thiols in an opposite way. SulA induction was observed under alkaline shift and after treatment with thiosalicylic acid.

Acidification of Escherichia coli and Salmonella typhimurium cytoplasm reduces the mutagenic effect of N-methyl-N'-nitro-N-nitrosoguanidine

Preliminary acidification of the cytoplasm of E. coli cells growing at pH 6.9 by adding to the medium 50 mM of sodium acetate or propionate reduced the mutagenic effect of N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) to almost the spontaneous level. In experiments with S. typhimurium the protective effects of cytoplasm acidification against the mutagenic effect of MNNG was observed at pH 5.5 and was absent at a medium pH of 6.9. Alkalinization of the cytoplasm by adding 80 mM of methylamine to the growth medium at pH 8.1 did not modify the effect of MNNG on the cells of E. coli and S. typhimurium. Alkalinization of the cytoplasm of E. coli B/r and K12 was followed by a reduction of the intracellular non-protein SH group level by 25 and 50%, respectively. It is supposed that the protective effect of acidification may be due to a decline in the productivity of mutagenically more active intermediates of MNNG when the pH is reduced and the associated fall of the level of intracellular non-protein thiols occurs. The above situation may serve as a model for studying the effects of MNNG and other alkylating agents on cells differing in physiological status.

Peptostreptococcus micros has a uniquely high capacity to form hydrogen sulfide from glutathione

There are high amounts of hydrogen sulfide in deep periodontal pockets. This volatile sulfur compound may be formed from L-cysteine, but only low levels of this amino acid can be expected to be present in periodontal pockets. Glutathione, L-gamma-glutamyl-L-cysteinylglycine, is in high concentration in most tissue cells, and this tripeptide may be more readily available as a source of hydrogen sulfide formation in the pockets. The ability of 37 different species of oral bacteria to utilize glutathione in hydrogen sulfide formation was studied. Of these species, only 2 species of Peptostreptococcus and 5 species of Fusobacterium formed high amounts of hydrogen sulfide from glutathione within 24 h. Since the initial rate of hydrogen sulfide formation was more than 5 times higher in Peptostreptococcus micros than in any of the other bacterial species, the kinetics of sulfide formation from glutathione by P. micros was further elucidated. The formation of sulfide followed quite closely hyperbolic Michaelis-Menten kinetics. The maximal initial rate of sulfide formation (Vmax) was 163 +/- 2 nmol sulfide per minute per milligram of cellular protein. Half maximal initial rate (Km) was obtained at 7.4 +/- 0.8 microM glutathione. The initial rate of sulfide formation from L-cysteine was much slower and was almost proportional to L-cysteine concentration. This difference in kinetics of sulfide formation between glutathione and L-cysteine strongly suggested that glutathione was actively transported into the cell, whereas the transport of L-cysteine was more or less controlled by diffusion. The sulfide formation from the dipeptide L-cysteinylglycine also followed quite closely hyperbolic Michaelis-Menten kinetics.(ABSTRACT TRUNCATED AT 250 WORDS)

Physiological functions of hydroperoxidases in Rhodobacter capsulatus

Rhodobacter capsulatus J1 has two hydroperoxidases: a catalase-peroxidase and a peroxidase. A mutant strain, AH18, that had no catalase-peroxidase was isolated. The growth rate under aerobic and photosynthetic conditions, respiration, superoxide dismutase and peroxidase activities, and pigment content of the mutant were similar to those of the wild type. AH18 was more susceptible to killing and to inhibition of nitrogenase by H2O2 but not by molecular oxygen. The incidences of spontaneous mutations were similar in both strains. Viable counts in aerobic but not anaerobic cultures of AH18 started to decline as soon as the cultures reached the stationary phase, and the rate of cell death was much higher in AH18 than in the wild type. It is inferred that the peroxidase provides protection against H2O2 in log-phase cells and that the catalase-peroxidase provides protection under the oxidative conditions that prevail in aging cultures. This protective function might be related to the dual activity of the latter as a catalase and a peroxidase or to its capacity to oxidize NADH, NADPH, and cytochrome c.

Bacterial genes involved in response to near-ultraviolet radiation

A model of the possible pathways of activities following NUV treatment was presented in Section I and in Fig. 1. Some of the components are firmly established, some are speculative, and many are difficult to evaluate because of insufficient experimental information. Perhaps the most relevant experiments, especially concerning ozone depletion, would be to determine the mutational specificity of NUV. By selecting lacI mutants after exposing cells to NUV, and sequencing the bases of this gene, this is now feasible. There are some problems, however. The mutation frequency is normally so low that it might be difficult to distinguish NUV mutants from spontaneous mutants. However, by irradiating cells having a uvrA or uvrB mutation, the frequency of mutation above background can be increased considerably. There remains the problem as to what fraction of the observed mutations results from oxidative damage. Some of this could be clarified by comparing mutation spectra of cells treated with NUV and cells subjected to excess oxidative damage and determining what fraction results from other avenues of lesion formation in DNA. Different species of reactive oxygen could cause different kinds of DNA lesions, and, fortunately, use of appropriate mutants should allow us to sort out any differences in specificity of lesions. Also, by appropriate manipulation of quantities of endogenous photosensitizers, it might be possible to sort out the specific mutations that are caused by photodynamic action. Another avenue of research is to explore the pathways by which NUV lesions are repaired, and whether such repair is error prone or error free. Again, the use of mutants such as xthA, uvr, and polA should assist in our understanding of the specificity of the mutational events. There are now a number of examples of global control mechanisms whereby cells abruptly shift their protein synthesis pattern under environmental stress. It is important to understand whether NUV stress results in induction of one or more of the known regulatory genes, or whether another regulon might be involved. One particular aspect of regulation that remains unsolved is the role of the katF gene, which is known to regulate the xthA and katE, but it may also regulate other genes as well. A number of striking physiological events occur even at very low fluences of NUV irradiation of cells. In part, this may be related to regulon induction. However, some of these events are in need of special exploration, such as changes at the membrane level.(ABSTRACT TRUNCATED AT 400 WORDS)

Study of the causes of direct-acting mutagenicity in coffee and tea using the Ara test in Salmonella typhimurium

The mutagenic activities of 6 of the chemicals identified in coffee solutions were assayed with the Salmonella Ara test, under experimental conditions optimized for coffee mutagenicity. Caffeine was the only non-mutagenic compound. Among the other 5 chemicals, hydrogen peroxide was the strongest mutagen and chlorogenic acid the weakest; methylglyoxal, glyoxal and caffeic acid exhibited intermediate mutagenicities. The minimal mutagenic doses of these components correlated negatively with their relative concentrations in coffee. It was concluded that chlorogenic acid, caffeic acid, glyoxal and methylglyoxal cannot contribute alone to the mutagenicity of coffee in the Ara test, since their minimal mutagenic concentrations were much higher than their respective levels in the coffee samples assayed. By contrast, 40-60% of the mutagenic activity in coffee and also in tea could be attributed to their H2O2 contents. Catalase abolished more than 95% of the mutagenic activity of coffee, as detected by the Ara test. A similar sensitivity to catalase has been reported by other authors in relation to the coffee mutagenicity identified by the Salmonella His test. Nevertheless, the results presented in this paper suggest that the Ara forward and the His reverse mutation tests are sensitive to the mutagenicity of different constituents in coffee solutions. We propose that the His test, sensitive at high coffee doses, mainly recognizes the mutagenicity of methylglyoxal, whilst the Ara test, sensitive at low coffee doses, mainly detects the mutagenic activity of hydrogen peroxide. The data reported also suggest that the direct-acting mutagenicity(ies) detected by the Ara test in tea solutions is (are) based on similar, if not identical, mechanisms.