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Berlin Brandenburg

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  • 1
    Language: English
    In: Science (New York, N.Y.), 08 March 2013, Vol.339(6124), pp.1210-3
    Description: Recent observations have suggested that classic antibiotics kill bacteria by stimulating the formation of reactive oxygen species (ROS). If true, this notion might guide new strategies to improve antibiotic efficacy. In this study, the model was directly tested. Contrary to the hypothesis, antibiotic treatment did not accelerate the formation of hydrogen peroxide in Escherichia coli and did not elevate intracellular free iron, an essential reactant for the production of lethal damage. Lethality persisted in the absence of oxygen, and DNA repair mutants were not hypersensitive, undermining the idea that toxicity arose from oxidative DNA lesions. We conclude that these antibiotic exposures did not produce ROS and that lethality more likely resulted from the direct inhibition of cell-wall assembly, protein synthesis, and DNA replication.
    Keywords: Anti-Bacterial Agents -- Pharmacology ; Drug Resistance, Bacterial -- Physiology ; Escherichia Coli -- Drug Effects
    ISSN: 00368075
    E-ISSN: 1095-9203
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  • 2
    Language: English
    In: Proceedings of the National Academy of Sciences of the United States of America, 29 March 2011, Vol.108(13), pp.5402-7
    Description: H(2)O(2) is commonly generated in biological habitats by environmental chemistry and by cellular immune responses. H(2)O(2) penetrates cells, disrupts metabolism, and blocks growth; it therefore is of interest to identify the major cellular molecules that H(2)O(2) damages and the strategies by which cells protect themselves from it. We used a strain of Escherichia coli that lacks catalases and peroxidases to impose protracted low-grade H(2)O(2) stress. Physiological analysis indicated that the pentose-phosphate pathway, in particular, was poisoned by submicromolar intracellular H(2)O(2). Assays determined that ribulose-5-phosphate 3-epimerase (Rpe) was specifically inactivated. In vitro studies demonstrated that Rpe employs a ferrous iron atom as a solvent-exposed cofactor and that H(2)O(2) rapidly oxidizes this metal in a Fenton reaction. The oxidized iron is released immediately, causing a loss of activity. Most Rpe proteins could be reactivated by remetallation; however, a small fraction of proteins were irreversibly damaged by each oxidation cycle, and so repeated cycles of oxidation and remetallation progressively led to permanent inactivation of the entire Rpe pool. Manganese import and iron sequestration are key elements of the H(2)O(2) stress response, and we found that manganese can activate Rpe in vitro in place of iron, converting the enzyme to a form that is unaffected by H(2)O(2). Indeed, the provision of manganese to H(2)O(2)-stressed cells protected Rpe and enabled the pentose-phosphate pathway to retain function. These data indicate that mononuclear iron enzymes can be primary targets of H(2)O(2) stress and that cells adapt by shifting from iron- to manganese-centered metabolism.
    Keywords: Carbohydrate Epimerases -- Metabolism ; Escherichia Coli -- Enzymology ; Hydrogen Peroxide -- Metabolism ; Iron -- Metabolism ; Manganese -- Metabolism ; Oxidants -- Metabolism
    ISSN: 00278424
    E-ISSN: 1091-6490
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  • 3
    Language: English
    In: Current Opinion in Microbiology, April 2015, Vol.24, pp.124-131
    Description: Microorganisms are vulnerable to elevated levels of intracellular reactive oxygen species (ROS). This situation has led to proposals that many natural stresses might be toxic specifically because they accelerate endogenous ROS formation. Such a mechanism has been convincingly demonstrated for redox-cycling compounds. However, the evidence is much weaker for most other stressors. The hypothesis that clinical antibiotics generate lethal ROS stress has attracted much attention, and the author discusses some aspects of evidence that support or oppose this idea. Importantly, even if all cellular electron flow were somehow diverted to ROS formation, the resultant doses of H O and O would more likely be bacteriostatic than bacteriocidal unless key defense mechanisms were simultaneously blocked.
    Keywords: Biology
    ISSN: 1369-5274
    E-ISSN: 1879-0364
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  • 4
    Language: English
    In: Proceedings of the National Academy of Sciences of the United States of America, 15 August 2017, Vol.114(33), pp.E6922-E6931
    Description: Microbial cytochrome peroxidases (Ccp) have been studied for 75 years, but their physiological roles are unclear. Ccps are located in the periplasms of bacteria and the mitochondrial intermembrane spaces of fungi. In this study, Ccp is demonstrated to be a significant degrader of hydrogen peroxide in anoxic Intriguingly, transcription requires both the presence of HO and the absence of O Experiments show that Ccp lacks enough activity to shield the cytoplasm from exogenous HO However, it receives electrons from the quinone pool, and its flux rate approximates flow to other anaerobic electron acceptors. Indeed, Ccp enabled to grow on a nonfermentable carbon source when HO was supplied. behaved similarly. This role rationalizes repression in oxic environments. We speculate that micromolar HO is created both biologically and abiotically at natural oxic/anoxic interfaces. The OxyR response appears to exploit this HO as a terminal oxidant while simultaneously defending the cell against its toxicity.
    Keywords: Oxyr ; Anaerobic Respiration ; Oxidative Stress ; Cytochrome-C Peroxidase -- Metabolism ; Escherichia Coli -- Metabolism ; Escherichia Coli Proteins -- Metabolism ; Hydrogen Peroxide -- Metabolism ; Oxidoreductases -- Metabolism
    ISSN: 00278424
    E-ISSN: 1091-6490
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  • 5
    Language: English
    In: Journal of Bacteriology, Oct, 2013, Vol.195(19-20), p.4569(11)
    Description: When Escherichia coli grows on conventional substrates, it continuously generates 10 to 15 micro M/s intracellular (H.sub.2)(O.sub.2) through the accidental autoxidation of redox enzymes. Dosimetric analyses indicate that scavenging enzymes barely keep this (H.sub.2)(O.sub.2) below toxic levels. Therefore, it seemed potentially problematic that E. coli can synthesize a catabolic phenylethylamine oxidase that stoichiometrically generates (H.sub.2)(O.sub.2). This study was undertaken to understand how E. coli tolerates the oxidative stress that must ensue. Measurements indicated that phenylethylamine-fed cells generate (H.sub.2)(O.sub.2) at 30 times the rate of glucose-fed cells. Two tolerance mechanisms were identified. First, in enclosed laboratory cultures, growth on phenylethylamine triggered induction of the OxyR (H.sub.2)(O.sub.2) stress response. Null mutants (delta oxyR) that could not induce that response were unable to grow. This is the first demonstration that OxyR plays a role in protecting cells against endogenous (H.sub.2)(O.sub.2). The critical element of the OxyR response was the induction of (H.sub.2)(O.sub.2) scavenging enzymes, since mutants that lacked NADH peroxidase (Ahp) grew poorly, and those that additionally lacked catalase did not grow at all. Other OxyR-controlled genes were expendable. Second, phenylethylamine oxidase is an unusual catabolic enzyme in that it is localized in the periplasm. Calculations showed that when cells grow in an open environment, virtually all of the oxidase-generated (H.sub.2)(O.sub.2) will diffuse across the outer membrane and be lost to the external world, rather than enter the cytoplasm where (H.sub.2)(O.sub.2)-sensitive enzymes are located. In this respect, the periplasmic compartmentalization of phenylethylamine oxidase serves the same purpose as the peroxisomal compartmentalization of oxidases in eukaryotic cells.
    Keywords: Escherichia Coli -- Research ; Escherichia Coli -- Physiological Aspects ; Hydrogen Peroxide -- Influence ; Phenethylamines -- Research
    ISSN: 0021-9193
    Source: Cengage Learning, Inc.
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  • 6
    Language: English
    In: Proceedings of the National Academy of Sciences of the United States of America, 03 April 2018, Vol.115(14), pp.E3266-E3275
    Description: It has been unclear whether superoxide and/or hydrogen peroxide play important roles in the phenomenon of obligate anaerobiosis. This question was explored using , a major fermentative bacterium in the human gastrointestinal tract. Aeration inactivated two enzyme families-[4Fe-4S] dehydratases and nonredox mononuclear iron enzymes-whose homologs, in contrast, remain active in aerobic Inactivation-rate measurements of one such enzyme, fumarase, showed that it is no more intrinsically sensitive to oxidants than is an fumarase. Indeed, when the enzymes were expressed in , they no longer could tolerate aeration; conversely, the enzymes maintained full activity when expressed in aerobic Thus, the aerobic inactivation of the enzymes is a feature of their intracellular environment rather than of the enzymes themselves. possesses superoxide dismutase and peroxidases, and it can repair damaged enzymes. However, measurements confirmed that the rate of reactive oxygen species production inside aerated is far higher than in Analysis of the damaged enzymes recovered from aerated suggested that they had been inactivated by superoxide rather than by hydrogen peroxide. Accordingly, overproduction of superoxide dismutase substantially protected the enzymes from aeration. We conclude that when this anaerobe encounters oxygen, its internal superoxide levels rise high enough to inactivate key catabolic and biosynthetic enzymes. Superoxide thus comprises a major element of the oxygen sensitivity of this anaerobe. The extent to which molecular oxygen exerts additional direct effects remains to be determined.
    Keywords: Bacteroides ; Obligate Anaerobiosis ; Oxidative Stress ; Reactive Oxygen Species ; Bacterial Proteins -- Metabolism ; Bacteroides Thetaiotaomicron -- Metabolism ; Escherichia Coli -- Metabolism ; Oxygen -- Metabolism ; Superoxides -- Metabolism
    ISSN: 00278424
    E-ISSN: 1091-6490
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  • 7
    Language: English
    In: Journal of the American Chemical Society, 18 May 2011, Vol.133(19), pp.7571-6
    Description: Rapid identification of both species and even specific strains of human pathogenic bacteria grown on standard agar has been achieved from the volatiles they produce using a disposable colorimetric sensor array in a Petri dish imaged with an inexpensive scanner. All 10 strains of bacteria tested, including Enterococcus faecalis and Staphylococcus aureus and their antibiotic-resistant forms, were identified with 98.8% accuracy within 10 h, a clinically important time frame. Furthermore, the colorimetric sensor arrays also proved useful as a simple research tool for the study of bacterial metabolism and as an easy method for the optimization of bacterial production of fine chemicals or other fermentation processes.
    Keywords: Disposable Equipment ; Microarray Analysis ; Bacteria -- Chemistry ; Bacterial Typing Techniques -- Methods ; Colorimetry -- Methods
    ISSN: 00027863
    E-ISSN: 1520-5126
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  • 8
    Language: English
    In: The Journal of Bacteriology, 2011, Vol. 193(9), p.2186
    Description: Hydrogen peroxide ([H.sub.2][O.sub.2]) is commonly formed in microbial habitats by either chemical oxidation processes or host defense responses. [H.sub.2][O.sub.2] can penetrate membranes and damage key intracellular biomolecules, including DNA and iron-dependent enzymes. Bacteria defend themselves against this [H.sub.2][O.sub.2] by inducing a regulon that engages multiple defensive strategies. A previous microarray study suggested that yaaA, an uncharacterized gene found in many bacteria, was induced by [H.sub.2][O.sub.2] in Escherichia coli as part of its OxyR regulon. Here we confirm that yaaA is a key element of the stress response to [H.sub.2][O.sub.2]. In a catalase/peroxidase-deficient ([Hpx.sup.-]) background, yaaA deletion mutants grew poorly, filamented extensively, and lost substantial viability when they wer and the growth defect of the yaaA deletion in a recombination-deficient (recA56) background indicated that yaaA mutants accumulated high levels of DNA damage. The growth defect of yaaA mutants could be suppressed by either the addition of iron chelators or mutations that slowed iron import, indicating that the DNA damage was caused by the Fenton reaction. Spin-trapping experiments confirmed that [Hpx.sup.-] yaaA cells had a higher hydroxyl radical ([HO.sup.*]) level. Electron paramagnetic resonance spectroscopy analysis showed that the proximate cause was an unusually high level of intracellular unincorporated iron. These results demonstrate that during periods of [H.sub.2][O.sub.2] stress the induction of YaaA is a critical device to suppress intracellular iron levels; it thereby attenuates the Fenton reaction and the DNA damage that would otherwise result. The molecular mechanism of YaaA action remains unknown. doi: 10.1128/JB.00001-11
    Keywords: Escherichia Coli -- Genetic Aspects ; Hydrogen Peroxide -- Genetic Aspects ; Hydrogen Peroxide -- Chemical Properties ; Toxicity -- Control ; Proteins -- Physiological Aspects ; Bacterial Genetics -- Research ; Genomics -- Research;
    ISSN: 0021-9193
    ISSN: 00219193
    E-ISSN: 10985530
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  • 9
    In: Molecular Microbiology, December 2013, Vol.90(6), pp.1356-1371
    Description: Obligate anaerobes are periodically exposed to oxygen, and it has been conjectured that on such occasions their low‐potential biochemistry will predispose them to rapid formation. We sought to identify scavenging enzymes that might protect the anaerobe from the that would be formed. Genetic analysis of eight candidate enzymes revealed that four of these scavenge  : rubrerythrins 1 and 2, , and catalase E. The rubrerythrins served as key peroxidases under anoxic conditions. However, they quickly lost activity upon aeration, and and catalase were induced to compensate. The is an peroxidase that effectively degraded low micromolar levels of , while the catalytic cycle of catalase enabled it to quickly degrade higher concentrations that might arise from exogenous sources. Using a non‐scavenging mutant we verified that endogenous formation was much higher in aerated than in . Indeed, the stress response to was induced when was aerated, and in that circumstance this response was necessary to forestall cell death. Thus aeration is a serious threat for this obligate anaerobe, and to cope it employs a set of defences that includes a repertoire of complementary scavenging enzymes.
    Keywords: Hydrogen Peroxide -- Analysis ; Enzymes -- Analysis ; Bacteria -- Analysis ; Consortia -- Analysis ; Enzymology -- Analysis;
    ISSN: 0950-382X
    E-ISSN: 1365-2958
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  • 10
    Language: English
    In: Molecular microbiology, April 2011, Vol.80(2), pp.319-34
    Description: The genome of Escherichia coli encodes two class I ribonucleotide reductases. The first, NrdAB, is a well-studied iron-dependent enzyme that is essential for aerobic growth. The second, NrdEF, is not functional under routine conditions, and its role is obscure. Recent studies demonstrated that NrdEF can be activated in vitro by manganese as well as iron. Since iron enzymes are potential targets for hydrogen peroxide, and since the nrdHIEF operon is induced during H(2) O(2) stress, we hypothesized that H(2) O(2) might inactivate NrdAB and that NrdEF might be induced to compensate. This idea was tested using E. coli mutants that are chronically stressed by H(2) O(2) . Contrary to expectation, NrdAB remained active. Its resistance to H(2) O(2) depended upon YfaE, which helps to activate NrdB. The induction of NrdEF during H(2) O(2) stress was mediated by the inactivation of Fur, an iron-dependent repressor. This regulatory arrangement implied that NrdEF has a physiological role during periods of iron starvation. Indeed, NrdEF supported cell replication in iron-depleted cells. Iron bound to NrdF when it was expressed in iron-rich cells, but NrdEF was functional only in cells that were both iron-depleted and manganese-rich. Thus NrdEF supports DNA replication when iron is unavailable to activate the housekeeping NrdAB enzyme.
    Keywords: Bacterial Proteins -- Metabolism ; DNA -- Biosynthesis ; Escherichia Coli -- Enzymology ; Escherichia Coli Proteins -- Metabolism ; Iron -- Metabolism ; Manganese -- Metabolism ; Ribonucleotide Reductases -- Metabolism
    ISSN: 0950382X
    E-ISSN: 1365-2958
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