# | Rank | Similarity | Title + Abs. | Year | PMID |
|---|---|---|---|---|---|
| 0 | 1 | 2 | 3 | 4 | 5 |
| 547 | 0 | 0.9883 | Dual role of OhrR as a repressor and an activator in response to organic hydroperoxides in Streptomyces coelicolor. Organic hydroperoxide resistance in bacteria is achieved primarily through reducing oxidized membrane lipids. The soil-inhabiting aerobic bacterium Streptomyces coelicolor contains three paralogous genes for organic hydroperoxide resistance: ohrA, ohrB, and ohrC. The ohrA gene is transcribed divergently from ohrR, which encodes a putative regulator of MarR family. Both the ohrA and ohrR genes were induced highly by various organic hydroperoxides. The ohrA gene was induced through removal of repression by OhrR, whereas the ohrR gene was induced through activation by OhrR. Reduced OhrR bound to the ohrA-ohrR intergenic region, which contains a central (primary) and two adjacent (secondary) inverted-repeat motifs that overlap with promoter elements. Organic peroxide decreased the binding affinity of OhrR for the primary site, with a concomitant decrease in cooperative binding to the adjacent secondary sites. The single cysteine C28 in OhrR was involved in sensing oxidants, as determined by substitution mutagenesis. The C28S mutant of OhrR bound to the intergenic region without any change in binding affinity in response to organic peroxides. These results lead us to propose a model for the dual action of OhrR as a repressor and an activator in S. coelicolor. Under reduced conditions, OhrR binds cooperatively to the intergenic region, repressing transcription from both genes. Upon oxidation, the binding affinity of OhrR decreases, with a concomitant loss of cooperative binding, which allows RNA polymerase to bind to both the ohrA and ohrR promoters. The loosely bound oxidized OhrR can further activate transcription from the ohrR promoter. | 2007 | 17586628 |
| 549 | 1 | 0.9878 | Extracytoplasmic function sigma factor σ(D) confers resistance to environmental stress by enhancing mycolate synthesis and modifying peptidoglycan structures in Corynebacterium glutamicum. Mycolates are α-branched, β-hydroxylated, long-chain fatty acid specifically synthesized in bacteria in the suborder Corynebacterineae of the phylum Actinobacteria. They form an outer membrane, which functions as a permeability barrier and confers pathogenic mycobacteria to resistance to antibiotics. Although the mycolate biosynthetic pathway has been intensively studied, knowledge of transcriptional regulation of genes involved in this pathway is limited. Here, we report that the extracytoplasmic function sigma factor σ(D) is a key regulator of the mycolate synthetic genes in Corynebacterium glutamicum in the suborder. Chromatin immunoprecipitation with microarray analysis detected σ(D) -binding regions in the genome, establishing a consensus promoter sequence for σ(D) recognition. The σ(D) regulon comprised acyl-CoA carboxylase subunits, acyl-AMP ligase, polyketide synthase and mycolyltransferases; they were involved in mycolate synthesis. Indeed, deletion or overexpression of sigD encoding σ(D) modified the extractable mycolate amount. Immediately downstream of sigD, rsdA encoded anti-σ(D) and was under the control of a σ(D) -dependent promoter. Another σ(D) regulon member, l,d-transpeptidase, conferred lysozyme resistance. Thus, σ(D) modifies peptidoglycan cross-linking and enhances mycolate synthesis to provide resistance to environmental stress. | 2018 | 29148103 |
| 581 | 2 | 0.9869 | Inorganic polyphosphates and heavy metal resistance in microorganisms. The mechanisms of heavy metal resistance in microbial cells involve multiple pathways. They include the formation of complexes with specific proteins and other compounds, the excretion from the cells via plasma membrane transporters in case of procaryotes, and the compartmentalization of toxic ions in vacuoles, cell wall and other organelles in case of eukaryotes. The relationship between heavy metal tolerance and inorganic polyphosphate metabolism was demonstrated both in prokaryotic and eukaryotic microorganisms. Polyphosphates, being polyanions, are involved in detoxification of heavy metals through complex formation and compartmentalization. The bacteria and fungi cultivated in the presence of some heavy metal cations contain the enhanced levels of polyphosphate. In bacteria, polyphosphate sequesters heavy metals; some of metal cations stimulate an exopolyphosphatase activity, which releases phosphate from polyphosphates, and MeHPO(4)(-) ions are then transported out of the cells. In fungi, the overcoming of heavy metal stresses is associated with the accumulation of polyphosphates in cytoplasmic inclusions, vacuoles and cell wall and the formation of cation/polyphosphate complexes. The effects of knockout mutations and overexpression of the genes encoding polyphosphate-metabolizing enzymes on heavy metal resistance are discussed. | 2018 | 30151754 |
| 579 | 3 | 0.9868 | Control of expression of a periplasmic nickel efflux pump by periplasmic nickel concentrations. There is accumulating evidence that transenvelope efflux pumps of the resistance, nodulation, cell division protein family (RND) are excreting toxic substances from the periplasm across the outer membrane directly to the outside. This would mean that resistance of Gram-negative bacteria to organic toxins and heavy metals is in fact a two-step process: one set of resistance factors control the concentration of a toxic substance in the periplasm, another one that in the cytoplasm. Efficient periplasmic detoxification requires periplasmic toxin sensing and transduction of this signal into the cytoplasm to control expression of the periplasmic detoxification system. Such a signal transduction system was analyzed using the Cnr nickel resistance system from Cupriavidus (Wautersia, Ralstonia, Alcaligenes) metallidurans strain CH34. Resistance is based on nickel efflux mediated by the CnrCBA efflux pump encoded by the cnrYHXCBAT metal resistance determinant. The products of the three genes cnrYXH transcriptionally regulate expression of cnr. CnrY and CnrX are membrane-bound proteins probably functioning as anti sigma factors while CnrH is a cnr-specific extracytoplasmic functions (ECF) sigma factors. Experimental data provided here indicate a signal transduction chain leading from nickel in the periplasm to transcription initiation at the cnr promoters cnrYp and cnrCp, which control synthesis of the nickel efflux pump CnrCBA. | 2005 | 16158236 |
| 609 | 4 | 0.9868 | A metazoan ortholog of SpoT hydrolyzes ppGpp and functions in starvation responses. In nutrient-starved bacteria, RelA and SpoT proteins have key roles in reducing cell growth and overcoming stresses. Here we identify functional SpoT orthologs in metazoa (named Mesh1, encoded by HDDC3 in human and Q9VAM9 in Drosophila melanogaster) and reveal their structures and functions. Like the bacterial enzyme, Mesh1 proteins contain an active site for ppGpp hydrolysis and a conserved His-Asp-box motif for Mn(2+) binding. Consistent with these structural data, Mesh1 efficiently catalyzes hydrolysis of guanosine 3',5'-diphosphate (ppGpp) both in vitro and in vivo. Mesh1 also suppresses SpoT-deficient lethality and RelA-induced delayed cell growth in bacteria. Notably, deletion of Mesh1 (Q9VAM9) in Drosophila induces retarded body growth and impaired starvation resistance. Microarray analyses reveal that the amino acid-starved Mesh1 null mutant has highly downregulated DNA and protein synthesis-related genes and upregulated stress-responsible genes. These data suggest that metazoan SpoT orthologs have an evolutionarily conserved function in starvation responses. | 2010 | 20818390 |
| 556 | 5 | 0.9868 | An ArsR/SmtB family member regulates arsenic resistance genes unusually arranged in Thermus thermophilus HB27. Arsenic resistance is commonly clustered in ars operons in bacteria; main ars operon components encode an arsenate reductase, a membrane extrusion protein, and an As-sensitive transcription factor. In the As-resistant thermophile Thermus thermophilus HB27, genes encoding homologues of these proteins are interspersed in the chromosome. In this article, we show that two adjacent genes, TtsmtB, encoding an ArsR/SmtB transcriptional repressor and, TTC0354, encoding a Zn(2+) /Cd(2+) -dependent membrane ATPase are involved in As resistance; differently from characterized ars operons, the two genes are transcribed from dedicated promoters upstream of their respective genes, whose expression is differentially regulated at transcriptional level. Mutants defective in TtsmtB or TTC0354 are more sensitive to As than the wild type, proving their role in arsenic resistance. Recombinant dimeric TtSmtB binds in vitro to both promoters, but its binding capability decreases upon interaction with arsenate and, less efficiently, with arsenite. In vivo and in vitro experiments also demonstrate that the arsenate reductase (TtArsC) is subjected to regulation by TtSmtB. We propose a model for the regulation of As resistance in T. thermophilus in which TtSmtB is the arsenate sensor responsible for the induction of TtArsC which generates arsenite exported by TTC0354 efflux protein to detoxify cells. | 2017 | 28696001 |
| 546 | 6 | 0.9867 | Resistance to organic hydroperoxides requires ohr and ohrR genes in Sinorhizobium meliloti. BACKGROUND: Sinorhizobium meliloti is a symbiotic nitrogen-fixing bacterium that elicits nodules on roots of host plants Medicago sativa. During nodule formation bacteria have to withstand oxygen radicals produced by the plant. Resistance to H2O2 and superoxides has been extensively studied in S. meliloti. In contrast resistance to organic peroxides has not been investigated while S. meliloti genome encodes putative organic peroxidases. Organic peroxides are produced by plants and are highly toxic. The resistance to these oxygen radicals has been studied in various bacteria but never in plant nodulating bacteria. RESULTS: In this study we report the characterisation of organic hydroperoxide resistance gene ohr and its regulator ohrR in S. meliloti. The inactivation of ohr affects resistance to cumene and ter-butyl hydroperoxides but not to hydrogen peroxide or menadione in vitro. The expression of ohr and ohrR genes is specifically induced by organic peroxides. OhrR binds to the intergenic region between the divergent genes ohr and ohrR. Two binding sites were characterised. Binding to the operator is prevented by OhrR oxidation that promotes OhrR dimerisation. The inactivation of ohr did not affect symbiosis and nitrogen fixation, suggesting that redundant enzymatic activity exists in this strain. Both ohr and ohrR are expressed in nodules suggesting that they play a role during nitrogen fixation. CONCLUSIONS: This report demonstrates the significant role Ohr and OhrR proteins play in bacterial stress resistance against organic peroxides in S. meliloti. The ohr and ohrR genes are expressed in nodule-inhabiting bacteroids suggesting a role during nodulation. | 2011 | 21569462 |
| 583 | 7 | 0.9866 | MarR family proteins sense sulfane sulfur in bacteria. Members of the multiple antibiotic resistance regulator (MarR) protein family are ubiquitous in bacteria and play critical roles in regulating cellular metabolism and antibiotic resistance. MarR family proteins function as repressors, and their interactions with modulators induce the expression of controlled genes. The previously characterized modulators are insufficient to explain the activities of certain MarR family proteins. However, recently, several MarR family proteins have been reported to sense sulfane sulfur, including zero-valent sulfur, persulfide (R-SSH), and polysulfide (R-SnH, n ≥ 2). Sulfane sulfur is a common cellular component in bacteria whose levels vary during bacterial growth. The changing levels of sulfane sulfur affect the expression of many MarR-controlled genes. Sulfane sulfur reacts with the cysteine thiols of MarR family proteins, causing the formation of protein thiol persulfide, disulfide bonds, and other modifications. Several MarR family proteins that respond to reactive oxygen species (ROS) also sense sulfane sulfur, as both sulfane sulfur and ROS induce the formation of disulfide bonds. This review focused on MarR family proteins that sense sulfane sulfur. However, the sensing mechanisms reviewed here may also apply to other proteins that detect sulfane sulfur, which is emerging as a modulator of gene regulation. | 2024 | 38948149 |
| 726 | 8 | 0.9866 | Regulation of antimicrobial resistance by extracytoplasmic function (ECF) sigma factors. Extracytoplasmic function (ECF) sigma factors are a subfamily of σ(70) sigma factors that activate genes involved in stress-response functions. In many bacteria, ECF sigma factors regulate resistance to antimicrobial compounds. This review will summarize the ECF sigma factors that regulate antimicrobial resistance in model organisms and clinically relevant pathogens. | 2017 | 28153747 |
| 577 | 9 | 0.9865 | The SIR2 gene family, conserved from bacteria to humans, functions in silencing, cell cycle progression, and chromosome stability. Genomic silencing is a fundamental mechanism of transcriptional regulation, yet little is known about conserved mechanisms of silencing. We report here the discovery of four Saccharomyces cerevisiae homologs of the SIR2 silencing gene (HSTs), as well as conservation of this gene family from bacteria to mammals. At least three HST genes can function in silencing; HST1 overexpression restores transcriptional silencing to a sir2 mutant and hst3 hst4 double mutants are defective in telomeric silencing. In addition, HST3 and HST4 together contribute to proper cell cycle progression, radiation resistance, and genomic stability, establishing new connections between silencing and these fundamental cellular processes. | 1995 | 7498786 |
| 607 | 10 | 0.9863 | A novel copper-sensing two-component system for inducing Dsb gene expression in bacteria. In nature, bacteria must sense copper and tightly regulate gene expression to evade copper toxicity. Here, we identify a new copper-responsive two-component system named DsbRS in the important human pathogen Pseudomonas aeruginosa; in this system, DsbS is a sensor histidine kinase, and DsbR, its cognate response regulator, directly induces the transcription of genes involved in protein disulfide bond formation (Dsb) (i.e., the dsbDEG operon and dsbB). In the absence of copper, DsbS acts as a phosphatase toward DsbR, thus blocking the transcription of Dsb genes. In the presence of copper, the metal ion directly binds to the sensor domain of DsbS, and the Cys82 residue plays a critical role in this process. The copper-binding behavior appears to inhibit the phosphatase activity of DsbS, leading to the activation of DsbR. The copper resistance of the dsbRS knock-out mutant is restored by the ectopic expression of the dsbDEG operon, which is a DsbRS major target. Strikingly, cognates of the dsbRS-dsbDEG pair are widely distributed across eubacteria. In addition, a DsbR-binding site, which contains the consensus sequence 5'-TTA-N(8)-TTAA-3', is detected in the promoter region of dsbDEG homologs in these species. These findings suggest that the regulation of Dsb genes by DsbRS represents a novel mechanism by which bacterial cells cope with copper stress. | 2022 | 36546013 |
| 514 | 11 | 0.9862 | The organoarsenical biocycle and the primordial antibiotic methylarsenite. Arsenic is the most pervasive environmental toxic substance. As a consequence of its ubiquity, nearly every organism has genes for resistance to inorganic arsenic. In bacteria these genes are found largely in bacterial arsenic resistance (ars) operons. Recently a parallel pathway for synthesis and degradation of methylated arsenicals has been identified. The arsM gene product encodes the ArsM (AS3MT in animals) As(iii) S-adenosylmethionine methyltransferase that methylates inorganic trivalent arsenite in three sequential steps to methylarsenite MAs(iii), dimethylarsenite (DMAs(iii) and trimethylarsenite (TMAs(iii)). MAs(iii) is considerably more toxic than As(iii), and we have proposed that MAs(iii) was a primordial antibiotic. Under aerobic conditions these products are oxidized to nontoxic pentavalent arsenicals, so that methylation became a detoxifying pathway after the atmosphere became oxidizing. Other microbes have acquired the ability to regenerate MAs(v) by reduction, transforming it again into toxic MAs(iii). Under this environmental pressure, MAs(iii) resistances evolved, including the arsI, arsH and arsP genes. ArsI is a C-As bond lyase that demethylates MAs(iii) back to less toxic As(iii). ArsH re-oxidizes MAs(iii) to MAs(v). ArsP actively extrudes MAs(iii) from cells. These proteins confer resistance to this primitive antibiotic. This oscillation between MAs(iii) synthesis and detoxification is an essential component of the arsenic biogeocycle. | 2016 | 27730229 |
| 124 | 12 | 0.9860 | A bacterial view of the periodic table: genes and proteins for toxic inorganic ions. Essentially all bacteria have genes for toxic metal ion resistances and these include those for Ag+, AsO2-, AsO4(3-), Cd2+ Co2+, CrO4(2-), Cu2+, Hg2+, Ni2+, Pb2+, TeO3(2-), Tl+ and Zn2+. The largest group of resistance systems functions by energy-dependent efflux of toxic ions. Fewer involve enzymatic transformations (oxidation, reduction, methylation, and demethylation) or metal-binding proteins (for example, metallothionein SmtA, chaperone CopZ and periplasmic silver binding protein SilE). Some of the efflux resistance systems are ATPases and others are chemiosmotic ion/proton exchangers. For example, Cd2+-efflux pumps of bacteria are either inner membrane P-type ATPases or three polypeptide RND chemiosmotic complexes consisting of an inner membrane pump, a periplasmic-bridging protein and an outer membrane channel. In addition to the best studied three-polypeptide chemiosmotic system, Czc (Cd2+, Zn2+, and Co2), others are known that efflux Ag+, Cu+, Ni2+, and Zn2+. Resistance to inorganic mercury, Hg2+ (and to organomercurials, such as CH3Hg+ and phenylmercury) involve a series of metal-binding and membrane transport proteins as well as the enzymes mercuric reductase and organomercurial lyase, which overall convert more toxic to less toxic forms. Arsenic resistance and metabolizing systems occur in three patterns, the widely-found ars operon that is present in most bacterial genomes and many plasmids, the more recently recognized arr genes for the periplasmic arsenate reductase that functions in anaerobic respiration as a terminal electron acceptor, and the aso genes for the periplasmic arsenite oxidase that functions as an initial electron donor in aerobic resistance to arsenite. | 2005 | 16133099 |
| 588 | 13 | 0.9860 | Enhanced aphid detoxification when confronted by a host with elevated ROS production. Reactive oxygen species (ROS) plays an important role in plant defense responses against bacteria, fungi and insect pests. Most recently, we have demonstrated that loss of Arabidopsis thaliana BOTRYTIS-INDUCED KINASE1 (BIK1) function releases its suppression of aphid-induced H2O2 production and cell death, rendering the bik1 mutant more resistant to green peach aphid (Myzus persicae) than wild-type plants. However, little is known regarding how ROS-related gene expression is correlated with bik1-mediated resistance to aphids, or whether these aphids biochemically respond to the oxidative stress. Here, we show that the bik1 mutant exhibited elevated basal expression of ROS-generating and -responsive genes, but not ROS-metabolizing genes. Conversely, we detected enhanced detoxification enzymatic activities in aphids reared on bik1 plants compared to those on wild-type plants, suggesting that aphids counter the oxidative stress associated with bik1 through elevated metabolic resistance. | 2015 | 25932782 |
| 587 | 14 | 0.9859 | The Nramp (Slc11) proteins regulate development, resistance to pathogenic bacteria and iron homeostasis in Dictyostelium discoideum. The Dictyostelium discoideum genome harbors two genes encoding members of the Nramp superfamily, which is conserved from bacteria (MntH proteins) to humans (Slc11 proteins). Nramps are proton-driven metal ion transporters with a preference for iron and manganese. Acquisition of these metal cations is vital for all cells, as they act as redox cofactors and regulate key cellular processes, such as DNA synthesis, electron transport, energy metabolism and oxidative stress. Dictyostelium Nramp1 (Slc11a1), like its mammalian ortholog, mediates resistance to infection by invasive bacteria. We have extended the analysis to the nramp2 gene, by generating single and double nramp1/nramp2 knockout mutants and cells expressing GFP fusion proteins. In contrast to Nramp1, which is recruited to phagosomes and macropinosomes, the Nramp2 protein is localized exclusively in the membrane of the contractile vacuole, a vesicular tubular network regulating cellular osmolarity. Both proteins colocalize with the V-H(+)-ATPase, which can provide the electrogenic force for vectorial transport. Like nramp1, nramp2 gene disruption affects resistance to Legionella pneumophila. Disrupting both genes additionally leads to defects in development, with strong delay in cell aggregation, formation of large streams and multi-tipped aggregates. Single and double mutants display differential sensitivity to cell growth under conditions of iron overload or depletion. The data favor the hypothesis that Nramp1 and Nramp2, under control of the V-H(+)-ATPase, synergistically regulate iron homeostasis, with the contractile vacuole possibly acting as a store for metal cations. | 2013 | 22992462 |
| 544 | 15 | 0.9859 | Organic Hydroperoxide Induces Prodigiosin Biosynthesis in Serratia sp. ATCC 39006 in an OhrR-Dependent Manner. The biosynthesis of prodigiosin in the model prodigiosin-producing strain, Serratia sp. ATCC 39006, is significantly influenced by environmental and cellular signals. However, a comprehensive regulatory mechanism for this process has not been well established. In the present study, we demonstrate that organic hydroperoxide activates prodigiosin biosynthesis in an OhrR-dependent manner. Specifically, the MarR-family transcriptional repressor OhrR (Ser39006_RS05455) binds to its operator located far upstream of the promoter region of the prodigiosin biosynthesis operon (319 to 286 nucleotides [nt] upstream of the transcription start site) and negatively regulates the expression of prodigiosin biosynthesis genes. Organic hydroperoxide disassociates the binding between OhrR and its operator, thereby promoting the prodigiosin production. Moreover, OhrR modulates the resistance of Serratia sp. ATCC 39006 to organic hydroperoxide by regulating the transcription of its own gene and the downstream cotranscribed ohr gene. These results demonstrate that OhrR is a pleiotropic repressor that modulates the prodigiosin production and the resistance of Serratia sp. ATCC 39006 to organic hydroperoxide stress. IMPORTANCE Bacteria naturally encounter various environmental and cellular stresses. Organic hydroperoxides generated from the oxidation of polyunsaturated fatty acids are widely distributed and usually cause lethal oxidative stress by damaging cellular components. OhrR is known as a regulator that modulates the resistance of bacteria to organic hydroperoxide stress. In the current study, organic hydroperoxide disassociates OhrR from the promoter of prodigiosin biosynthesis gene cluster, thus promoting transcription of pigA to -O genes. In this model, organic hydroperoxide acts as an inducer of prodigiosin synthesis in Serratia sp. ATCC 39006. These results improve our understanding of the regulatory network of prodigiosin synthesis and serve as an example for identifying the cross talk between the stress responses and the regulation of secondary metabolism. | 2022 | 35044847 |
| 594 | 16 | 0.9859 | Challenging Xanthomonas campestris with low levels of arsenic mediates cross-protection against oxidant killing. Xanthomonas encounters highly toxic reactive oxygen species (ROS) from many sources, such as those generated by plants against invading bacteria, other soil bacteria and from aerobic respiration. Thus, conditions that alter intracellular ROS levels such as exposure to toxic metalloids would have profound effects on bacterial physiology. Here, we report that exposure of Xanthomonas campestris pv. phaseoli (Xp) to low levels of arsenic induces physiological cross-protection against killing by H(2)O(2) and organic hydroperoxide but not a superoxide generator. Cross-protection against H(2)O(2) and organic hydroperoxide toxicity was due to increased expression of genes encoding major peroxide-metabolizing enzymes such as alkyl hydroperoxide reductase (AhpC), catalase (KatA) and organic hydroperoxide resistance protein (Ohr). Arsenic-induced protection against H(2)O(2) and organic hydroperoxide requires the peroxide stress response regulators, OxyR and OhrR, respectively. Moreover, analyses of double mutants of the major H(2)O(2) and organic hyproperoxide-scavenging enzymes, Xp ahpC katA and Xp ahpC ohr, respectively, suggested the existence of unidentified OxyR- and OhrR-regulated genes that are involved in arsenic-induced resistance to H(2)O(2) and organic hyproperoxide killing in Xp. These arsenic-induced physiological alterations could play an important role in bacterial survival both in the soil environment and during plant-pathogen interactions. | 2006 | 16907748 |
| 8425 | 17 | 0.9857 | Carotenoid biosynthesis in extremophilic Deinococcus-Thermus bacteria. Bacteria from the phylum Deinococcus-Thermus are known for their resistance to extreme stresses including radiation, oxidation, desiccation and high temperature. Cultured Deinococcus-Thermus bacteria are usually red or yellow pigmented because of their ability to synthesize carotenoids. Unique carotenoids found in these bacteria include deinoxanthin from Deinococcus radiodurans and thermozeaxanthins from Thermus thermophilus. Investigations of carotenogenesis will help to understand cellular stress resistance of Deinococcus-Thermus bacteria. Here, we discuss the recent progress toward identifying carotenoids, carotenoid biosynthetic enzymes and pathways in some species of Deinococcus-Thermus extremophiles. In addition, we also discuss the roles of carotenoids in these extreme bacteria. | 2010 | 20832321 |
| 510 | 18 | 0.9857 | ArsZ from Ensifer adhaerens ST2 is a novel methylarsenite oxidase. Trivalent methylarsenite [MAs(III)] produced by biomethylation is more toxic than inorganic arsenite [As(III)]. Hence, MAs(III) has been proposed to be a primordial antibiotic. Other bacteria evolved mechanisms to detoxify MAs(III). In this study, the molecular mechanisms of MAs(III) resistance of Ensifer adhaerens ST2 were investigated. In the chromosome of E. adhaerens ST2 is a gene encoding a protein of unknown function. Here, we show that this gene, designated arsZ, encodes a novel MAs(III) oxidase that confers resistance by oxidizing highly toxic MAs(III) to relatively nontoxic MAs(V). Two other genes, arsRK, are adjacent to arsZ but are divergently encoded in the opposite direction. Heterologous expression of arsZ in Escherichia coli confers resistance to MAs(III) but not to As(III). Purified ArsZ catalyses thioredoxin- and NAPD(+) -dependent oxidation of MAs(III). Mutational analysis of ArsZ suggests that Cys59 and Cys123 are involved in the oxidation of MAs(III). Expression of arsZ, arsR and arsK genes is induced by MAs(III) and As(III) and is likely controlled by the ArsR transcriptional repressor. These results demonstrate that ArsZ is a novel MAs(III) oxidase that contributes to E. adhaerens tolerance to environmental organoarsenicals. The arsZRK operon is widely present in bacteria within the Rhizobiaceae family. | 2022 | 35355385 |
| 543 | 19 | 0.9856 | OxyR2 Modulates OxyR1 Activity and Vibrio cholerae Oxidative Stress Response. Bacteria have developed capacities to deal with different stresses and adapt to different environmental niches. The human pathogen Vibrio cholerae, the causative agent of the severe diarrheal disease cholera, utilizes the transcriptional regulator OxyR to activate genes related to oxidative stress resistance, including peroxiredoxin PrxA, in response to hydrogen peroxide. In this study, we identified another OxyR homolog in V. cholerae, which we named OxyR2, and we renamed the previous OxyR OxyR1. We found that OxyR2 is required to activate its divergently transcribed gene ahpC, encoding an alkylhydroperoxide reductase, independently of H(2)O(2) A conserved cysteine residue in OxyR2 is critical for this function. Mutation of either oxyR2 or ahpC rendered V. cholerae more resistant to H(2)O(2) RNA sequencing analyses indicated that OxyR1-activated oxidative stress-resistant genes were highly expressed in oxyR2 mutants even in the absence of H(2)O(2) Further genetic analyses suggest that OxyR2-activated AhpC modulates OxyR1 activity by maintaining low intracellular concentrations of H(2)O(2) Furthermore, we showed that ΔoxyR2 and ΔahpC mutants were less fit when anaerobically grown bacteria were exposed to low levels of H(2)O(2) or incubated in seawater. These results suggest that OxyR2 and AhpC play important roles in the V. cholerae oxidative stress response. | 2017 | 28138024 |