Effect of the thiol-oxidizing agent diamide on the growth of Escherichia coli

Redox-mediated Biomolecular information transfer in single electrogenetic biological cells

Electronic communication in natural systems makes use, inter alia, of molecular transmission, where electron transfer occurs within networks of redox reactions, which play a vital role in many physiological systems. In view of the limited understanding of redox signaling, we developed an approach and an electrochemical-optical lab-on-a-chip to observe cellular responses in localized redox environments. The developed fluidic micro-system uses electrogenetic bacteria in which a cellular response is activated to electrically and chemically induced stimulations. Specifically, controlled environments for the cells are created by using microelectrodes to generate spatiotemporal redox gradients. The in-situ cellular responses at both single-cell and population levels are monitored by optical microscopy. The elicited electrogenetic fluorescence intensities after 210 min in response to electrochemical and chemical activation were 1.3 × 108±0.30 × 108 arbitrary units (A.U.) and 1.2 × 108±0.30 × 108 A.U. per cell population, respectively, and 1.05 ± 0.01 A.U. and 1.05 ± 0.01 A.U. per-cell, respectively. We demonstrated that redox molecules' mass transfer between the electrode and cells - and not the applied electrical field - activated the electrogenetic cells. Specifically, we found an oriented amplified electrogenetic response on the charged electrodes' downstream side, which was determined by the location of the stimulating electrodes and the flow profile. We then focused on the cellular responses and observed distinct subpopulations that were attributed to electrochemical rather than chemical stimulation, with the distance between the cells and the stimulating electrode being the main determinant. These observations provide a comprehensive understanding of the mechanisms by which diffusible redox mediators serve as electron shuttles, imposing context and activating electrogenetic responses.

Ribonucleases control distinct traits of Pseudomonas putida lifestyle

The role of archetypal ribonucleases (RNases) in the physiology and stress endurance of the soil bacterium and metabolic engineering platform Pseudomonas putida KT2440 has been inspected. To this end, variants of this strain lacking each of the most important RNases were constructed. Each mutant lacked either one exoribonuclease (PNPase, RNase R) or one endoribonuclease (RNase E, RNase III, RNase G). The global physiological and metabolic costs of the absence of each of these enzymes were then analysed in terms of growth, motility and morphology. The effects of different oxidative chemicals that mimic the stresses endured by this microorganism in its natural habitats were studied as well. The results highlighted that each ribonuclease is specifically related with different traits of the environmental lifestyle that distinctively characterizes this microorganism. Interestingly, the physiological responses of P. putida to the absence of each enzyme diverged significantly from those known previously in Escherichia coli. This exposed not only species-specific regulatory functions for otherwise known RNase activities but also expanded the panoply of post-transcriptional adaptation devices that P. putida can make use of for facing hostile environments.

Neutralizing the detrimental effect of glutathione on precious metal catalysts

We report our efforts to enable transition-metal catalysis in the presence of cellular debris, notably Escherichia coli cell free extracts and cell lysates. This challenging goal is hampered by the presence of thiols, mainly present in the form of glutathione (GSH), which poison precious metal catalysts. To overcome this, we evaluated a selection of oxidizing agents and electrophiles toward their potential to neutralize the detrimental effect of GSH on a Ir-based transfer hydrogenation catalyst. While the bare catalyst was severely inhibited by cellular debris, embedding the organometallic moiety within a host protein led to promising results in the presence of some neutralizing agents. In view of its complementary to natural enzymes, the asymmetric imine reductase based on the incorporation of a biotinylated iridium pianostool complex within streptavidin (Sav) isoforms was selected as a model reaction. Compared to purified protein samples, we show that pretreatment of cell free extracts and cell lysates containing Sav mutants with diamide affords up to >100 TON's and only a modest erosion of enantioselectivity.

The metabolic cost of flagellar motion in Pseudomonas putida KT2440

Although the flagellar machinery of environmental bacteria endows cells with a phenomenal survival device, it also consumes much of the metabolic currency necessary for fuelling such a vigorous nano-motor. The physiological cost of flagella-related functions of the soil bacterium Pseudomonas putida KT2440 was examined and quantified through the deletion of a ≈ 70 kb DNA segment of the genome (≈ 1.1%), which includes relevant structural and regulatory genes in this micro-organism. The resulting strain lacked the protruding polar cords that define flagella in the wild-type P. putida strain and was unable of any swimming motility while showing a significant change in surface hydrophobicity. However, these deficiencies were otherwise concomitant with clear physiological advantages: rapid adaptation of the deleted strain to both glycolytic and gluconeogenic carbon sources, increased energy charge and, most remarkably, improved tolerance to oxidative stress, reflecting an increased NADPH/NADP(+) ratio. These qualities improve the endurance of non-flagellated cells to the metabolic fatigue associated with rapid growth in rich medium. Thus, flagellar motility represents the archetypal tradeoff involved in acquiring environmental advantages at the cost of a considerable metabolic burden.

The Entner-Doudoroff pathway empowers Pseudomonas putida KT2440 with a high tolerance to oxidative stress

Glucose catabolism of Pseudomonas putida is carried out exclusively through the Entner-Doudoroff (ED) pathway due to the absence of 6-phosphofructokinase. In order to activate the Embden-Meyerhof-Parnas (EMP) route we transferred the pfkA gene from Escherichia coli to a P. putida wild-type strain as well as to an eda mutant, i.e. lacking 2-keto-3-deoxy-6-phosphogluconate aldolase. PfkA(E. coli) failed to redirect the carbon flow from the ED route towards the EMP pathway, suggesting that ED was essential for sugar catabolism. The presence of PfkA(E. coli) was detrimental for growth, which could be traced to the reduction of ATP and NAD(P)H pools along with alteration of the NAD(P)H/NADP(+) ratio. Pseudomonas putida cells carrying PfkA(E. coli) became highly sensitive to diamide and hydrogen peroxide, the response to which is very demanding of NADPH. The inhibitory effect of PfkA(E. coli) could in part be relieved by methionine, the synthesis of which relies much on NADPH. These results expose the role of the ED pathway for generating the redox currency (NADPH) that is required for counteracting oxidative stress. It is thus likely that environmental bacteria that favour the ED pathway over the EMP pathway do so in order to gear their aerobic metabolism to endure oxidative-related insults.

Accumulation of deoxynivalenol and its 15-acetylated form is significantly modulated by oxidative stress in liquid cultures of Fusarium graminearum

Liquid cultures of Fusarium graminearum were supplemented with H2O2 or other oxidative compounds. The accumulation kinetics of the resulting trichothecenes were monitored. At non-lethal concentrations, the H2O2 treatments modulated toxin accumulation, dependent on the method of supplementation. When H2O2 was added at the same time as the inoculation, higher levels of toxins accumulated 30 days later. Conversely, adding H2O2 2 or 7 days after inoculation had little effect. When H2O2 was added daily over the course of the culture, the accumulation of trichothecenes was rapidly and strongly enhanced. The fungus may adapt to oxidative stress when the first exposure to H2O2 occurs at the beginning of the culture course. The highest toxin levels were measured when the H2O2 was added daily. The importance of the first hours of culture was confirmed: pre-treating conidia with H2O2 does not affect their germination kinetics but leads to a reduction in the yield of trichothecenes 40 days later. The H2O2 regulation of this trichothecene accumulation may be specific, as paraquat, another pro-oxidant compound, inhibits their production. Since H2O2 is a major component of the oxidative burst occurring in pathogen/host interactions, these data support the theory that trichothecenes may act as virulence factors.

Band 3 tyr-phosphorylation in normal and glucose-6-phospate dehydrogenase-deficient human erythrocytes

Haemolysis is usually episodic in glucose-6-phosphate dehydrogenase (G6PD) deficiency, often triggered by a period of oxidative stress. In the present work, we investigate a possible biochemical mechanism underlying the enhanced susceptibility of G6PD deficient red blood cells (RBC) to oxidative stress. We analysed eight male subjects with Mediterranean glucose-6P-dehydrogenase deficiency (G6PDd), class II, for their ability in phosphorylating erythrocyte membrane band 3 following oxidative and osmotic stress. Our findings show that this sensitivity is connected to an early membrane band 3 Tyr-phosphorylation in the presence of diamide. However, since both Syk, and Lyn kinases, and SHP-2 phosphatase, mostly implicated in the band 3 P-Tyr level regulation, are alike in content and activity in normal and patient erythrocytes, an alteration in the membrane organization is likely the cause of the anomalous response to the oxidant. We report, in fact, that hypertonic-induced morphological change in G6PDd erythrocyte induces a higher membrane band 3 Tyr-phosphorylation, suggesting a pre-existing membrane alteration, likely due to the chronic lowering of the redox systems in patients. We also report that 1-chloro-2,4-dinitrobenzene-pre-treatment of normal red cells can alter the normal protein-protein and protein-membrane interaction under hypertonic rather than oxidative stress, thus partially resembling the response in patients, and that RBC may utilize a wider range of redox defence, under oxidative conditions, including, but not exclusively, NADPH and glutathione. On the whole, these results would encourage a different approach to the evaluation of the effects of pharmacological administration to patients, giving more attention to the possible drug-induced membrane alteration evidenced by the abnormal band 3 Tyr-phosphorylation.

Identification and characterization of a diamide sensitive mutant of Mycobacterium smegmatis

A mutant, T7, highly sensitive to oxidative stress as caused by diamide was isolated from a Mycobacterium smegmatis mc(2)155 transposon mutant library. While wild-type M. smegmatis is able to grow well on solid media supplemented with 10 mM diamide, T7 is only able to grow on solid media containing up to 1 mM diamide. This mutant is also sensitive to other thiol modifying agents such as iodoacetamide and chlorodinitrobenzene. By sequencing the genomic DNA flanking the transposon, T7 was found to be mutated in the region upstream of the homolog of M. tuberculosis Rv0274 open reading frame. Sequence analysis revealed that Rv0274 is a member of a superfamily of metalloenzymes comprising enzymes such as extradiol dioxygenases, glyoxalases, and fosfomycin resistant glutathione transferases. Cloning and epichromosomal expression of M. tuberculosis Rv0274 in the mutant resulted in complementation of the sensitivity to diamide.

The role of the thioredoxin and glutaredoxin pathways in reducing protein disulfide bonds in the Escherichia coli cytoplasm

In Escherichia coli, two pathways use NADPH to reduce disulfide bonds that form in some cytoplasmic enzymes during catalysis: the thioredoxin system, which consists of thioredoxin reductase and thioredoxin, and the glutaredoxin system, composed of glutathione reductase, glutathione, and three glutaredoxins. These systems may also reduce disulfide bonds which form spontaneously in cytoplasmic proteins when E. coli is grown aerobically. We have investigated the role of both systems in determining the thiol-disulfide balance in the cytoplasm by determining the ability of protein disulfide bonds to form in mutants missing components of these systems. We find that both the thioredoxin and glutaredoxin systems contribute to reducing disulfide bonds in cytoplasmic proteins. In addition, these systems can partially substitute for each other in vivo since double mutants missing parts of both systems generally allow substantially more disulfide bond formation than mutants missing components of just one system. Some of these double mutants were found to require the addition of a disulfide reductant to the medium to grow well aerobically. Thus, E. coli requires either a functional thioredoxin or glutaredoxin system to reduce disulfide bonds which appear after each catalytic cycle in the essential enzyme ribonucleotide reductase and perhaps to reduce non-native disulfide bonds in cytoplasmic proteins. Our results suggest the existence of a novel thioredoxin in E. coli.

Glutathione content and growth in A549 human lung carcinoma cells

The relationship between glutathione content and cell growth was investigated in A549 human lung carcinoma cells. A decreased cellular glutathione content was achieved by exposing the cells to L-buthionine-SR-sulfoximine (BSO). It also occurred in these cells as they approached their plateau phase of growth. During exponential growth, a lower initial glutathione content correlated with a longer lag phase in subcultured cells. Further, depletion of cellular glutathione by BSO inhibited cell growth. This inhibition became apparent 36 h after the addition of BSO. These observations raise the possibility that a critical concentration of GSH may be required for optimal growth of A549 human lung carcinoma cells.

AppppA and related adenylylated nucleotides are synthesized as a consequence of oxidation stress

AppppA , ApppGpp , AppppG , ApppG , and ApppA rapidly accumulate to high levels in Salmonella typhimurium following exposure to a variety of oxidizing agents, but not to a variety of other stresses. Among the agents inducing these adenylylated nucleotides are 1-chloro-2,4-dinitrobenzene, diamide, hydrogen peroxide, t-butyl hydroperoxide, N-ethyl maleimide, iodoacetamide, cadmium chloride, and a variety of quinones. Some of these oxidizing agents cause preferential synthesis of specific adenylylated nucleotides, e.g., N-ethyl maleimide induces ApppA and menadione induces ApppGpp . Our data, as well as other evidence in the literature, strongly suggest that oxidation stress is coupled to adenylylated nucleotide synthesis by aminoacyl-tRNA synthetases. Although adenylylated nucleotides are made by tRNA synthetases in vitro, their synthesis in vivo is not a simple consequence of inhibition of synthetase activity. Compounds that inhibit normal charging by aminoacyl-tRNA synthetases do not result in the synthesis of adenylylated nucleotides, nor do mutations in tRNA synthetase structural genes or tRNA structural, modifying, or processing genes. We propose that the family of adenylylated nucleotides are alarmones signaling the onset of oxidation stress, and that particular ones may be alarmones for specific oxidative stresses, e.g., ApppGpp for oxidative damage to amino acid biosynthesis.

The effect of oxidant stress on diamide-treated human granulocytes

The role of sulfhydryls in the protection of human polymorphonuclear neutrophils against extracellular oxidant attack was investigated by simultaneously exposing polymorphonuclear neutrophils to the thiol-oxidizing agent diamide and the oxidant-generating system xanthine-xanthine oxidase. Neither diamide nor the oxidants generated by the xanthine-xanthine oxidase system alone impaired the burst in chemiluminescence, hexose monophosphate shunt activity or formate oxidation normally seen during polymorphonuclear neutrophil phagocytosis. Incubation of the polymorphonuclear neutrophils simultaneously with diamide and xanthine-xanthine oxidase markedly impaired polymorphonuclear neutrophil phagocytosis, hexose monophosphate shunt activity, chemiluminescence and formate oxidation. Although the polymorphonuclear neutrophils exposed to diamide and xanthine-xanthine oxidase did not respond to a variety of phagocytizable stimuli, trypan blue exclusion was normal and hexose monophosphate shunt activity could be stimulated by diamide. The damaging effect of the diamide xanthine-xamthine oxidase system could be blocked by the addition of superoxide dismutase or catalase, but not by hydroxyl radical or singlet oxygen scavengers. We hypothesize that an unidentified population of thiols may play a role in protecting the polymorphonuclear neutrophil from endogenously derived oxidants.

Role of glutathione in reversing the deleterious effects of a thiol-oxidizing agent in Escherichia coli

Diamide was found to be much less specific for the oxidation of glutathione in vivo in Escherichia coli than had been previously assumed. In vivo, only a slight alteration of the ratio of reduced to oxidized glutathione was found, whereas a significant amount of glutathione was found in the form of mixed disulfide with proteins. This latter occurrence was postulated as being responsible for the bacteriostatic effect of diamide.

Isolation of an Escherichia coli mutant deficient in glutathione synthesis

A mutant of Escherichia coli that contains essentially no detectable glutathione has been isolated. The mutant contains a very low level of the enzyme glutathione synthetase and accumulates lambda-glutamyl cysteine at a concentration approximately equal to the level of glutathione found in its parent. No significant differences in growth were observed between the mutant and its parent. However, the activity of at least one enzyme was found to be affected by the absence of glutathione; the specific activity of the B1 subunit of ribonucleoside diphosphate reductase was greatly reduced. The possibility that the decreased B1 activity is due to a mutation in the structural gene coding for B1 or its regulatory gene could be eliminated. This suggests that one role of glutathione in the cell is to maintain at least this one protein in an active state. We propose the designation gshB for the gene coding for glutathione synthetase.

[Glutathione (author's transl)]

Glutathione plays an important role in biology and medicine. Most cells of plants and animals contain high concentrations of reduced glutathione and a much smaller amount of oxidised glutathione. GSH is important for several metabolic functions of live cells, e.g. the protection of oxidative stress by peroxides, mediation of enzyme reactions, regulation of metabolic events, transport of amino acids across cell membranes via the gamma-glutamyl cycle, elimination of foreign compounds by GSH-conjugation, release of neurotransmitter substances. Irreversible perturbations of the glutathione metabolism may be the reason for severe clinical symptoms of hemolytic anemia or, perhaps, of central nervous disease.

Substituted diazenes: effect on the growth of enterobacteria and possible use as selective agents for isolation of pseudomonads

Incorporation of various diazenes into Trypticase soy media appeared selectively to permit the growth of pseudomonads while inhibiting the growth of a variety of enterobacteria. One of these diazenes, diamide (diazenedicarboxylic acid bisdimethylamide), was shown to be bactericidal for pure cultures of Escherichia coli, Proteus sp., and Salmonella enteritidis and to cause a 1- to 2-hr delay in the growth of Pseudomonas aeruginosa. When mixtures of these four organisms were inoculated into Trypticase soy broth or Trypticase soy agar (TSA) containing diamide, P. aeruginosa grew in overnight cultures. TSA containing diamide was also used successfully to isolate pseudomonads from soil, clinical urine specimens, fish, ground beef, ground pork, and ground veal.

The inhibition of ribonucleic acid synthesis by the thiol-oxidizing agent, diamide, in Escherichia coli

The thiol-oxidizing agent, diamide, has been used to convert glutathione to glutathione disulfide within the cells of a stringent strain of Escherichia coli (CP 78), leading to a cessation of 14C-leucine incorporation (protein synthesis) and 3H-uracil incorporation (RNA synthesis). Parallel experiments with an isogenic relaxed strain (CP 79) gave similar results, providing evidence that glutathione is closely linked to RNA synthesis indepently of the link previously shown to protein synthesis.