The Transcription Factor VdHapX Controls Iron Homeostasis and Is Crucial for Virulence in the Vascular Pathogen Verticillium dahliae

ABSTRACT Iron homeostasis is essential for full virulence and viability in many pathogenic fungi. Here, we showed that the bZip transcription factor VdHapX functions as a key regulator of iron homeostasis for adaptation to iron-depleted and iron-excess conditions and is required for full virulence in the vascular wilt fungus, Verticillium dahliae. Deletion of VdHapX impaired mycelial growth and conidiation under both iron starvation and iron sufficiency. Furthermore, disruption of VdHapX led to decreased formation of the long-lived survival structures of V. dahliae, known as microsclerotia. Expression of genes involved in iron utilization pathways and siderophore biosynthesis was misregulated in the ΔVdHapX strain under the iron-depleted condition. Additionally, the ΔVdHapX strain exhibited increased sensitivity to high iron concentrations and H2O2, indicating that VdHapX also contributes to iron or H2O2 detoxification. The ΔVdHapX strain showed a strong reduction in virulence on smoke tree seedlings (Cotinus coggygria) and was delayed in its ability to penetrate plant epidermal tissue. IMPORTANCE This study demonstrated that VdHapX is a conserved protein that mediates adaptation to iron starvation and excesses, affects microsclerotium formation, and is crucial for virulence of V. dahliae.

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Transcription Factor ADS-4 Regulates Adaptive Responses and Resistance to Antifungal Azole Stress

Antimicrobial Agents and Chemotherapy ◽

10.1128/aac.00542-15 ◽

2015 ◽

Vol 59 (9) ◽

pp. 5396-5404 ◽

Cited By ~ 9

Author(s):

Kangji Wang ◽

Zhenying Zhang ◽

Xi Chen ◽

Xianyun Sun ◽

Cheng Jin ◽

...

Keyword(s):

Transcription Factor ◽

Efflux Pump ◽

Fungal Infections ◽

Antifungal Drugs ◽

Bzip Transcription Factor ◽

Azole Resistance ◽

Homologous Gene ◽

Adaptive Responses ◽

Transcriptional Responses ◽

Content Type

ABSTRACTAzoles are commonly used as antifungal drugs or pesticides to control fungal infections in medicine and agriculture. Fungi adapt to azole stress by rapidly activating the transcription of a number of genes, and transcriptional increases in some azole-responsive genes can elevate azole resistance. The regulatory mechanisms that control transcriptional responses to azole stress in filamentous fungi are not well understood. This study identified a bZIP transcription factor, ADS-4 (antifungaldrugsensitive-4), as a new regulator of adaptive responses and resistance to antifungal azoles. Transcription ofads-4inNeurospora crassacells increased when they were subjected to ketoconazole treatment, whereas the deletion ofads-4resulted in hypersensitivity to ketoconazole and fluconazole. In contrast, the overexpression ofads-4increased resistance to fluconazole and ketoconazole inN. crassa. Transcriptome sequencing (RNA-seq) analysis, followed by quantitative reverse transcription (qRT)-PCR confirmation, showed that ADS-4 positively regulated the transcriptional responses of at least six genes to ketoconazole stress inN. crassa. The gene products of four ADS-4-regulated genes are known contributors to azole resistance, including the major efflux pump CDR4 (Pdr5p ortholog), an ABC multidrug transporter (NcAbcB), sterol C-22 desaturase (ERG5), and a lipid transporter (NcRTA2) that is involved in calcineurin-mediated azole resistance. Deletion of theads-4-homologous gene Afads-4inAspergillus fumigatuscaused hypersensitivity to itraconazole and ketoconazole, which suggested that ADS-4 is a functionally conserved regulator of adaptive responses to azoles. This study provides important information on a new azole resistance factor that could be targeted by a new range of antifungal pesticides and drugs.

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The Iron Deficiency Response of Corynebacterium glutamicum and a Link to Thiamine Biosynthesis

Applied and Environmental Microbiology ◽

10.1128/aem.00065-20 ◽

2020 ◽

Vol 86 (10) ◽

Cited By ~ 1

Author(s):

Andreas Küberl ◽

Aliye Mengus-Kaya ◽

Tino Polen ◽

Michael Bott

Keyword(s):

Corynebacterium Glutamicum ◽

Iron Homeostasis ◽

Essential Element ◽

Iron Limitation ◽

Thiamine Pyrophosphate ◽

Exponential Growth Phase ◽

Iron Starvation ◽

Content Type ◽

Oxoglutarate Dehydrogenase ◽

Thiamine Biosynthesis

ABSTRACT The response to iron limitation of the Gram-positive soil bacterium Corynebacterium glutamicum was analyzed with respect to secreted metabolites, the transcriptome, and the proteome. During growth in glucose minimal medium, iron limitation caused a shift from lactate to pyruvate as the major secreted organic acid complemented by l-alanine and 2-oxoglutarate. Transcriptome and proteome analyses revealed that a pronounced iron starvation response governed by the transcriptional regulators DtxR and RipA was detectable in the late, but not in the early, exponential-growth phase. A link between iron starvation and thiamine pyrophosphate (TPP) biosynthesis was uncovered by the strong upregulation of thiC. As phosphomethylpyrimidine synthase (ThiC) contains an iron-sulfur cluster, limiting activities of the TPP-dependent pyruvate–2-oxoglutarate dehydrogenase supercomplex probably cause the excretion of pyruvate and 2-oxoglutarate. In line with this explanation, thiamine supplementation could strongly diminish the secretion of these acids. The upregulation of thiC and other genes involved in thiamine biosynthesis and transport is presumably due to TPP riboswitches present at the 5′ end of the corresponding operons. The results obtained in this study provide new insights into iron homeostasis in C. glutamicum and demonstrate that the metabolic consequences of iron limitation can be due to the iron dependency of coenzyme biosynthesis. IMPORTANCE Iron is an essential element for most organisms but causes problems due to poor solubility under oxic conditions and due to toxicity by catalyzing the formation of reactive oxygen species (ROS). Therefore, bacteria have evolved complex regulatory networks for iron homeostasis aiming at a sufficient iron supply while minimizing ROS formation. In our study, the responses of the actinobacterium Corynebacterium glutamicum to iron limitation were analyzed, resulting in a detailed view on the processes involved in iron homeostasis in this model organism. In particular, we provide evidence that iron limitation causes TPP deficiency, presumably due to insufficient activity of the iron-dependent phosphomethylpyrimidine synthase (ThiC). TPP deficiency was deduced from the upregulation of genes controlled by a TPP riboswitch and secretion of metabolites caused by insufficient activity of the TPP-dependent enzymes pyruvate dehydrogenase and 2-oxoglutarate dehydrogenase. To our knowledge, the link between iron starvation and thiamine synthesis has not been elaborated previously.

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Identification of Genes Upregulated by the Transcription Factor Bcr1 That Are Involved in Impermeability, Impenetrability, and Drug Resistance of Candida albicansa/α Biofilms

Eukaryotic Cell ◽

10.1128/ec.00071-13 ◽

2013 ◽

Vol 12 (6) ◽

pp. 875-888 ◽

Cited By ~ 34

Author(s):

Thyagarajan Srikantha ◽

Karla J. Daniels ◽

Claude Pujol ◽

Elena Kim ◽

David R. Soll

Keyword(s):

Drug Resistance ◽

Transcription Factor ◽

Iron Homeostasis ◽

Drug Resistant ◽

Cross Link ◽

Type Locus ◽

Content Type ◽

Number Of Genes ◽

The Difference ◽

Upregulated Genes

ABSTRACTCandida albicansforms two types of biofilm, depending upon the configuration of the mating type locus. Although architecturally similar,a/α biofilms are impermeable, impenetrable, and drug resistant, whereasa/aand α/α biofilms lack these traits. The difference appears to be the result of an alternative matrix. Overexpression ina/acells ofBCR1, a master regulator of thea/α matrix, conferred impermeability, impenetrability, and drug resistance toa/abiofilms. Deletion ofBCR1ina/α cells resulted in the loss of thesea/α-specific biofilm traits. UsingBCR1overexpression ina/acells, we screened 107 genes of interest and identified 8 that were upregulated by Bcr1. When each was overexpressed ina/abiofilms, the threea/α traits were partially conferred, and when each was deleted ina/α cells, the traits were partially lost. Five of the eight genes have been implicated in iron homeostasis, and six encode proteins that are either in the wall or plasma membrane or secreted. All six possess sites for O-linked and N-linked glycosylation that, like glycosylphosphatidylinositol (GPI) anchors, can cross-link to the wall and matrix, suggesting that they may exert a structural role in conferring impermeability, impenetrability, and drug resistance, in addition to their physiological functions. The fact that in a screen of 107 genes, all 8 of the Bcr1-upregulated genes identified play a role in impermeability, impenetrability, and drug resistance suggests that the formation of thea/α matrix is highly complex and involves a larger number of genes than the initial ones identified here.

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Conversion of Norepinephrine to 3,4-Dihdroxymandelic Acid in Escherichia coli Requires the QseBC Quorum-Sensing System and the FeaR Transcription Factor

Journal of Bacteriology ◽

10.1128/jb.00564-17 ◽

2017 ◽

Vol 200 (1) ◽

Cited By ~ 1

Author(s):

Sasikiran Pasupuleti ◽

Nitesh Sule ◽

Michael D. Manson ◽

Arul Jayaraman

Keyword(s):

Escherichia Coli ◽

Transcription Factor ◽

Quorum Sensing ◽

Aromatic Amines ◽

Response Regulator ◽

Content Type ◽

E Coli ◽

Expression Of Genes ◽

K 12 ◽

Cognate Response Regulator

ABSTRACTThe detection of norepinephrine (NE) as a chemoattractant byEscherichia colistrain K-12 requires the combined action of the TynA monoamine oxidase and the FeaB aromatic aldehyde dehydrogenase. The role of these enzymes is to convert NE into 3,4-dihydroxymandelic acid (DHMA), which is a potent chemoattractant sensed by the Tsr chemoreceptor. These two enzymes must be induced by prior exposure to NE, and cells that are exposed to NE for the first time initially show minimal chemotaxis toward it. The induction of TynA and FeaB requires the QseC quorum-sensing histidine kinase, and the signaling cascade requires new protein synthesis. Here, we demonstrate that the cognate response regulator for QseC, the transcription factor QseB, is also required for induction. The related quorum-sensing kinase QseE appears not to be part of the signaling pathway, but its cognate response regulator, QseF, which is also a substrate for phosphotransfer from QseC, plays a nonessential role. The promoter of thefeaRgene, which encodes a transcription factor that has been shown to be essential for the expression oftynAandfeaB, has two predicted QseB-binding sites. One of these sites appears to be in an appropriate position to stimulate transcription from the P1promoter of thefeaRgene. This study unites two well-known pathways: one for expression of genes regulated by catecholamines (QseBC) and one for expression of genes required for metabolism of aromatic amines (FeaR, TynA, and FeaB). This cross talk allowsE. colito convert the host-derived and chemotactically inert NE into the potent bacterial chemoattractant DHMA.IMPORTANCEThe chemotaxis ofE. coliK-12 to norepinephrine (NE) requires the conversion of NE to 3,4-dihydroxymandleic acid (DHMA), and DHMA is both an attractant and inducer of virulence gene expression for a pathogenic enterohemorrhagicE. coli(EHEC) strain. The induction of virulence by DHMA and NE requires QseC. The results described here show that the cognate response regulator for QseC, QseB, is also required for conversion of NE into DHMA. Production of DHMA requires induction of a pathway involved in the metabolism of aromatic amines. Thus, the QseBC sensory system provides a direct link between virulence and chemotaxis, suggesting that chemotaxis to host signaling molecules may require that those molecules are first metabolized by bacterial enzymes to generate the actual chemoattractant.

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Genome-wide identification and analysis of the basic leucine zipper (bZIP) transcription factor gene family in Ustilaginoidea virens

Genome ◽

10.1139/gen-2017-0089 ◽

2017 ◽

Vol 60 (12) ◽

pp. 1051-1059 ◽

Cited By ~ 11

Author(s):

Weixiao Yin ◽

Peng Cui ◽

Wei Wei ◽

Yang Lin ◽

Chaoxi Luo

Keyword(s):

Transcription Factor ◽

Phylogenetic Relationships ◽

Leucine Zipper ◽

Expression Profiles ◽

Pathogenic Fungi ◽

Bzip Transcription Factor ◽

Basic Leucine Zipper ◽

Ustilaginoidea Virens ◽

Infection Period ◽

Genome Wide

The basic leucine zipper (bZIP) transcription factor (TF) family is one of the largest and most diverse TF families widely distributed across the eukaryotes. The bZIP TF family plays an important role in growth, development, and response to abiotic or biotic stresses, which have been well characterized in plants, but not in plant pathogenic fungi. In this study, we performed genome-wide and systematic bioinformatics analysis of bZIP genes in the fungus Ustilaginoidea virens, the causal agent of rice false smut disease. We identified 28 bZIP family members in the U. virens genome by searching for the bZIP domain in predicted genes. The gene structures, motifs, and phylogenetic relationships were analyzed for bZIP genes in U. virens (UvbZIP). Together with bZIP proteins from two other fungi, the bZIP genes can be divided into eight groups according to their phylogenetic relationships. Based on RNA-Seq data, the expression profiles of UvbZIP genes at different infection stages were evaluated. Results showed that 17 UvbZIP genes were up-regulated during the infection period. Furthermore, 11 infection-related UvbZIP genes were investigated under H2O2 stress and the expression level of eight genes were changed, which confirmed their role in stress tolerance and pathogenicity. In summary, our genome-wide systematic characterization and expression analysis of UvbZIP genes provided insight into the molecular function of these genes in U. virens and provides a reference for other pathogens.

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Characterization of the TyrR Regulon in the Rhizobacterium Enterobacter ludwigii UW5 Reveals Overlap with the CpxR Envelope Stress Response

Journal of Bacteriology ◽

10.1128/jb.00313-20 ◽

2020 ◽

Vol 203 (1) ◽

Author(s):

Thomas J. D. Coulson ◽

René M. Malenfant ◽

Cheryl L. Patten

Keyword(s):

Transcription Factor ◽

Stress Response ◽

Acid Synthesis ◽

Plant Interactions ◽

Amino Acid Synthesis ◽

Content Type ◽

E Coli ◽

Expression Of Genes ◽

Envelope Stress ◽

Enterobacter Ludwigii

ABSTRACT The TyrR transcription factor controls the expression of genes for the uptake and biosynthesis of aromatic amino acids in Escherichia coli. In the plant-associated and clinically significant proteobacterium Enterobacter ludwigii UW5, the TyrR orthologue was previously shown to regulate genes that encode enzymes for synthesis of the plant hormone indole-3-acetic acid and for gluconeogenesis, indicating a broader function for the transcription factor. This study aimed to delineate the TyrR regulon of E. ludwigii by comparing the transcriptomes of the wild type and a tyrR deletion strain. In E. ludwigii, TyrR positively or negatively regulates the expression of over 150 genes. TyrR downregulated expression of envelope stress response regulators CpxR and CpxP through interaction with a DNA binding site in the intergenic region between divergently transcribed cpxP and cpxR. Repression of cpxP was alleviated by tyrosine. Methyltransferase gene dmpM, which is possibly involved in antibiotic synthesis, was strongly activated in the presence of tyrosine and phenylalanine by TyrR binding to its promoter region. TyrR also regulated expression of genes for aromatic catabolism and anaerobic respiration. Our findings suggest that the E. ludwigii TyrR regulon has diverged from that of E. coli to include genes for survival in the diverse environments that this bacterium inhabits and illustrate the expansion and plasticity of transcription factor regulons. IMPORTANCE Genome-wide RNA sequencing revealed a broader regulatory role for the TyrR transcription factor in the ecologically versatile bacterium Enterobacter ludwigii beyond that of aromatic amino acid synthesis and transport that constitute the role of the TyrR regulon of E. coli. In E. ludwigii, a plant symbiont and human gut commensal, the TyrR regulon is expanded to include genes that are beneficial for plant interactions and response to stresses. Identification of the genes regulated by TyrR provides insight into the mechanisms by which the bacterium adapts to its environment.

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HapX, an Indispensable bZIP Transcription Factor for Iron Acquisition, Regulates Infection Initiation by Orchestrating Conidial Oleic Acid Homeostasis and Cytomembrane Functionality in Mycopathogen Beauveria bassiana

mSystems ◽

10.1128/msystems.00695-20 ◽

2020 ◽

Vol 5 (5) ◽

Author(s):

Yue-Jin Peng ◽

Jia-Jia Wang ◽

Hai-Yan Lin ◽

Jin-Li Ding ◽

Ming-Guang Feng ◽

...

Keyword(s):

Transcription Factor ◽

Oleic Acid ◽

Fatty Acid ◽

Filamentous Fungi ◽

Beauveria Bassiana ◽

Iron Acquisition ◽

Membrane Integrity ◽

Fatty Acid Desaturase ◽

Bzip Transcription Factor ◽

Content Type

ABSTRACT In pathogenic filamentous fungi, conidial germination not only is fundamental for propagation in the environment but is also a critical step of infection. In the insect mycopathogen Beauveria bassiana, we genetically characterized the role of the basic leucine zipper (bZIP) transcription factor HapX (BbHapX) in conidial nutrient reserves and pathogen-host interaction. Ablation of BbHapX resulted in an almost complete loss of virulence in the topical inoculation and intrahemocoel injection assays. Comparative transcriptomic analysis revealed that BbHapX is required for fatty acid (FA)/lipid metabolism, and biochemical analyses indicated that BbHapX loss caused a significant reduction in conidial FA contents. Exogenous oleic acid could partially or completely restore the impaired phenotypes of the ΔBbHapX mutant, including germination rate, membrane integrity, vegetative growth, and virulence. BbHapX mediates fungal iron acquisition which is not required for desaturation of stearic acid. Additionally, inactivation of the Δ9-fatty acid desaturase gene (BbOle1) generated defects similar to those of the ΔBbHapX mutant; oleic acid also had significant restorative effects on the defective phenotypes of the ΔBbOle1 mutant. A gel retarding assay revealed that BbHapX directly regulated the expression of BbOle1. Lipidomic analyses indicated that both BbHapX and BbOle1 contributed to the homeostasis of phospholipids with nonpolar tails derived from oleic acid; therefore, exogenous phospholipids could significantly restore membrane integrity. These data reveal that the HapX-Ole1 pathway contributes to conidial fatty acid/lipid reserves and that there are important links between the lipid biology and membrane functionality involved in the early stages of infection caused by B. bassiana. IMPORTANCE Conidial maturation and germination are highly coupled physiological processes in filamentous fungi that are critical for the pathogenicity of mycopathogens. Compared to the mechanisms involved in conidial germination, those of conidial reserves during maturation are less understood. The insect-pathogenic fungus Beauveria bassiana, as a representative species of filamentous fungi, is important for applied and fundamental research. In addition to its conserved roles in fungal adaptation to iron status, the bZIP transcription factor HapX acts as a master regulator involved in conidial virulence and regulates fatty acid/lipid metabolism. Further investigation revealed that the Δ9-fatty acid desaturase gene (Ole1) is a direct downstream target of HapX. This study reveals the HapX-Ole1 pathway involved in the fatty acid/lipid accumulation associated with conidial maturation and provides new insights into the startup mechanism of infection caused by spores from pathogenic fungi.

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HYPOXIA-INDUCIBLE FACTOR (HIF): STRUCTURE, FUNCTION AND GENETIC POLYMORPHISM

Hygiene and Sanitation ◽

10.18821/0016-9900-2019-98-7-723-728 ◽

2019 ◽

Vol 98 (7) ◽

pp. 723-728 ◽

Cited By ~ 2

Author(s):

Anna G. Zhukova ◽

A. S. Kazitskaya ◽

T. G. Sazontova ◽

N. N. Mikhailova

Keyword(s):

Transcription Factor ◽

Genetic Polymorphism ◽

Gene Polymorphism ◽

Adaptive Systems ◽

Iron Homeostasis ◽

Hypoxia Inducible Factor ◽

The Body ◽

Adaptive Responses ◽

Related Factors ◽

Expression Of Genes

Introduction. The review presents data on the structure and functions of hypoxia-inducible transcription factor - HIF. In today’s world, a person is constantly exposed to harmful damaging factors, the response of the body to which, depending on the state of adaptive systems leads either to the development of diseases or increase resistance. Important importance in the adaptation of the body to damaging effects belongs to the transcription factor, denoted as a hypoxia-inducible factor (HIF). There were identified more than 100 genes activated by HIF and therefore mediated by this transcription factor affecting the regulation of iron homeostasis, energy metabolism, the balance of Pro - and antioxidants in the cells, the activation of inhibitors of apoptosis and the formation of new blood vessels. The structure of HIF and its isoforms. The data on isoforms of HIF-α and organ-specific features of the distribution of HIF-1α, HIF-2α, and HIF-3α. Increased expression of α-subunits of transcription factor occurs in response to hypoxic effects, both acute and adaptive, psycho-emotional stress, under the action of toxic production-related factors. The increase in the level of HIF-α isoforms provides an expression of genes involved in the implementation of compensatory-adaptive responses to various harmful effects. Genetic polymorphism of the HIF. The data on the HIF-1α gene polymorphism and its association with various diseases are presented. It is shown that the most studied polymorphisms are rs11549465 C > T and rs11549467 T > C identified in the domain of oxygen-dependent degradation of the DNA sequence of the HIF-1α gene. Carriers of the C/T genotype have increased expression of HIF-1α transcription factor for rs11549465 C > T and rs11549467 T > Cpolymorphisms, Association with the risk of coronary heart disease and myocardial infarction is shown. The study of HIF-1α gene polymorphism can be promising for the diagnosis and prognosis of occupationally caused diseases, as well as the development of effective ways of their correction and prevention.

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A Transcriptome Profile Reveals The Regulatory Mechanism of Verticillium Dahliae Against Bacillus

10.21203/rs.3.rs-779813/v1 ◽

2021 ◽

Author(s):

Wenhui Tian ◽

Zhenrui Cheng ◽

Junxia Wang ◽

Fengfeng Cheng ◽

Luping Li ◽

...

Keyword(s):

Verticillium Dahliae ◽

Regulatory Mechanism ◽

Pathogenic Fungi ◽

Oxygen Species ◽

Rna Seq ◽

Transcriptome Profile ◽

Biocontrol Bacteria ◽

Expression Of Genes ◽

Prevention And Treatment

Abstract Background: Verticillium dahliae, the causal agent of Verticillium wilt, is notoriously invasive in many crops and has been involved in numerous epidemics worldwide. Bacillus species, as representatives of biocontrol bacteria, produce a variety of lipopeptides (LPs), which are useful as biofungicides to many pathogenic fungi, including Verticillium dahliae. This study will explore the mechanism of resistance of V. dahliae to Bacillus and biocontrol bacteria.Results: By using in vitro confrontation bioassays, we found that under the stress induced by Bacillus, the spore vitality of V. dahliae with larger colonies was higher, and more abundant microsclerotia were formed. Then, according to the RNA-Seq analysis, the target of rapamycin (TOR) and mitophagy pathways were enriched among the significantly upregulated 542 genes observed in two co-culture groups with different colony sizes. In addition, in the group of V. dahliae with large colonies, the pathways related to cell wall synthesis, microsclerotia formation and the clearance of reactive oxygen species were regulated, and the expression of genes was up-regulated.Conclusion: This study found that the larger colonies of V. dahliae were more resistant to the antagonistic actions of Bacillus and the likelihood of the formation of homeostasis. Therefore, the prevention of Verticillium wilt by Bacillus is more effective than the treatment of an active fungal infection. These transcriptomic insights provide direction for the use of fungicides in the prevention and treatment of diseases such as Verticillium wilt.

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Escherichia coli Free Radical-Based Killing Mechanism Driven by a Unique Combination of Iron Restriction and Certain Antibiotics

Journal of Bacteriology ◽

10.1128/jb.00758-15 ◽

2015 ◽

Vol 197 (23) ◽

pp. 3708-3719 ◽

Cited By ~ 11

Author(s):

Li Ma ◽

Yongjun Gao ◽

Anthony W. Maresso

Keyword(s):

Escherichia Coli ◽

Reactive Oxygen Species ◽

Iron Homeostasis ◽

Reactive Oxygen ◽

Medical Community ◽

Emission Spectrometry ◽

Iron Chelators ◽

Oxygen Species ◽

Iron Starvation ◽

Content Type

ABSTRACTBacterial resistance to antibiotics is precipitating a medical crisis, and new antibacterial strategies are being sought. Hypothesizing that a growth-restricting strategy could be used to enhance the efficacy of antibiotics, we determined the effect of FDA-approved iron chelators and various antibiotic combinations on invasive and multidrug-resistant extraintestinal pathogenicEscherichia coli(ExPEC), the Gram-negative bacterium most frequently isolated from the bloodstreams of hospitalized patients. We report that certain antibiotics used at sublethal concentrations display enhanced growth inhibition and/or killing when combined with the iron chelator deferiprone (DFP). Inductively coupled plasma optical emission spectrometry reveals abnormally high levels of cell-associated iron under these conditions, a response that correlates with an iron starvation response and supraphysiologic levels of reactive oxygen species (ROS). The high ROS level is reversed upon the addition of antioxidants, which restores bacterial growth, suggesting that the cells are inhibited or killed by excessive free radicals. A model is proposed in which peptidoglycan-targeting antibiotics facilitate the entry of lethal levels of iron-complexed DFP into the bacterial cytoplasm, a process that drives the generation of ROS. This new finding suggests that, in addition to restriction of access to iron as a general growth-restricting strategy, targeting of cellular pathways or networks that selectively disrupt normal iron homeostasis can have potent bactericidal outcomes.IMPORTANCEThe prospect that common bacteria will become resistant to all antibiotics is challenging the medical community. In addition to the development of next-generation antibiotics, new bacterial targets that display cytotoxic properties when altered need to be identified. Data presented here demonstrate that combining subinhibitory levels of both iron chelators and certain antibiotics kills pathogenicEscherichia coli. The mechanism of this effect is the production of supraphysiologic levels of reactive oxygen species, likely powered by the excessive import of iron. These findings were consistent for both clinically relevant and no longer clinically used antibiotics and may extend toStaphylococcus aureusas well.

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