scholarly journals Histidine Kinase Two-Component Response Regulator Proteins Regulate Reproductive Development, Virulence, and Stress Responses of the Fungal Cereal Pathogens Cochliobolus heterostrophus and Gibberella zeae

2010 ◽  
Vol 9 (12) ◽  
pp. 1867-1880 ◽  
Author(s):  
Shinichi Oide ◽  
Jinyuan Liu ◽  
Sung-Hwan Yun ◽  
Dongliang Wu ◽  
Alex Michev ◽  
...  
Keyword(s):  
Stress Responses ◽  
Histidine Kinase ◽  
Response Regulator ◽  
Gibberella Zeae ◽  
Cochliobolus Heterostrophus ◽  
Wild Type ◽  
Content Type ◽  
Major Mechanism ◽  
Asexual Spore ◽  
Mutant Phenotypes

ABSTRACT Histidine kinase (HK) phosphorelay signaling is a major mechanism by which fungi sense their environment. The maize pathogen Cochliobolus heterostrophus has 21 HK genes, 4 candidate response regulator (RR) genes (SSK1, SKN7, RIM15, REC1), and 1 gene (HPT1) encoding a histidine phosphotransfer domain protein. Because most HKs are expected to signal through RRs, these were chosen for deletion. Except for pigment and slight growth alterations for rim15 mutants, no measurable altered phenotypes were detected in rim15 or rec1 mutants. Ssk1p is required for virulence and affects fertility and proper timing of sexual development of heterothallic C. heterostrophus. Pseudothecia from crosses involving ssk1 mutants ooze masses of single ascospores, and tetrads cannot be found. Wild-type pseudothecia do not ooze. Ssk1p represses asexual spore proliferation during the sexual phase, and lack of it dampens asexual spore proliferation during vegetative growth, compared to that of the wild type. ssk1 mutants are heavily pigmented. Mutants lacking Skn7p do not display any of the above phenotypes; however, both ssk1 and skn7 mutants are hypersensitive to oxidative and osmotic stresses and ssk1 skn7 mutants are more exaggerated in their spore-type balance phenotype and more sensitive to stress than single mutants. ssk1 mutant phenotypes largely overlap hog1 mutant phenotypes, and in both types of mutant, the Hog1 target gene, MST1, is not induced. ssk1 and hog1 mutants were examined in the homothallic cereal pathogen Gibberella zeae, and pathogenic and reproductive phases of development regulated by Ssk1 and Hog1 were found to mirror, but also vary from, those of C. heterostrophus.

scholarly journals Nisin Resistance of Listeria monocytogenes Is Increased by Exposure to Salt Stress and Is Mediated via LiaR

2013 ◽  
Vol 79 (18) ◽  
pp. 5682-5688 ◽  
Author(s):  
Teresa M. Bergholz ◽  
Silin Tang ◽  
Martin Wiedmann ◽  
Kathryn J. Boor
Keyword(s):  
Salt Stress ◽  
Listeria Monocytogenes ◽  
Safety Concern ◽  
Response Regulator ◽  
Brain Heart Infusion ◽  
Control Measures ◽  
Protective Effects ◽  
Wild Type ◽  
Content Type ◽  
Type Strains

ABSTRACTGrowth ofListeria monocytogeneson refrigerated, ready-to-eat food is a significant food safety concern. Natural antimicrobials, such as nisin, can be used to control this pathogen on food, but little is known about how other food-related stresses may impact how the pathogen responds to these compounds. Prior work demonstrated that exposure ofL. monocytogenesto salt stress at 7°C led to increased expression of genes involved in nisin resistance, including the response regulatorliaR. We hypothesized that exposure to salt stress would increase subsequent resistance to nisin and that LiaR would contribute to increased nisin resistance. Isogenic deletion mutations inliaRwere constructed in 7 strains ofL. monocytogenes, and strains were exposed to 6% NaCl in brain heart infusion broth and then tested for resistance to nisin (2 mg/ml Nisaplin) at 7°C. For the wild-type strains, exposure to salt significantly increased subsequent nisin resistance (P< 0.0001) over innate levels of resistance. Compared to the salt-induced nisin resistance of wild-type strains, ΔliaRstrains were significantly more sensitive to nisin (P< 0.001), indicating that induction of LiaFSR led to cross-protection ofL. monocytogenesagainst subsequent inactivation by nisin. Transcript levels of LiaR-regulated genes were induced by salt stress, and lmo1746 andtelAwere found to contribute to LiaR-mediated salt-induced nisin resistance. These data suggest that environmental stresses similar to those on foods can influence the resistance ofL. monocytogenesto antimicrobials such as nisin, and potential cross-protective effects should be considered when selecting and applying control measures for this pathogen on ready-to-eat foods.

scholarly journals Changes to Its Peptidoglycan-Remodeling Enzyme Repertoire Modulate β-Lactam Resistance in Pseudomonas aeruginosa

2013 ◽  
Vol 57 (7) ◽  
pp. 3078-3084 ◽  
Author(s):  
Joseph F. Cavallari ◽  
Ryan P. Lamers ◽  
Edie M. Scheurwater ◽  
Andrea L. Matos ◽  
Lori L. Burrows
Keyword(s):  
Pseudomonas Aeruginosa ◽  
Penicillin Binding Protein ◽  
Wild Type ◽  
Content Type ◽  
Lytic Transglycosylases ◽  
Phenotypic Screen ◽  
Simultaneous Activation ◽  
Mutant Phenotypes ◽  
High Level ◽  
Hospital Acquired

ABSTRACTPseudomonas aeruginosais a leading cause of hospital-acquired infections and is resistant to many antibiotics. Among its primary mechanisms of resistance is expression of a chromosomally encoded AmpC β-lactamase that inactivates β-lactams. The mechanisms leading to AmpC expression inP. aeruginosaremain incompletely understood but are intricately linked to cell wall metabolism. To better understand the roles of peptidoglycan-active enzymes in AmpC expression—and consequent β-lactam resistance—a phenotypic screen ofP. aeruginosamutants lacking such enzymes was performed. Mutants lacking one of four lytic transglycosylases (LTs) or the nonessential penicillin-binding protein PBP4 (dacB) had altered β-lactam resistance.mltFandsltmutants with reduced β-lactam resistance were designated WIMPs (wall-impaired mutant phenotypes), while highly resistantdacB,sltB1, andmltBmutants were designated HARMs (high-level AmpC resistant mutants). Double mutants lackingdacBandsltB1had extreme piperacillin resistance (>256 μg/ml) compared to either of the single knockouts (64 μg/ml for adacBmutant and 12 μg/ml for ansltB1mutant). Inactivation ofampCreverted these mutants to wild-type susceptibility, confirming that AmpC expression underlies resistance.dacBmutants had constitutively elevated AmpC expression, but the LT mutants had wild-type levels of AmpC in the absence of antibiotic exposure. These data suggest that there are at least two different pathways leading to AmpC expression inP. aeruginosaand that their simultaneous activation leads to extreme β-lactam resistance.

scholarly journals Carbon Storage Regulator A Contributes to the Virulence of Haemophilus ducreyi in Humans by Multiple Mechanisms

2012 ◽  
Vol 81 (2) ◽  
pp. 608-617 ◽  
Author(s):  
Dharanesh Gangaiah ◽  
Wei Li ◽  
Kate R. Fortney ◽  
Diane M. Janowicz ◽  
Sheila Ellinger ◽  
...  
Keyword(s):  
Oxidative Stress ◽  
Stationary Phase ◽  
Carbon Storage ◽  
Stress Responses ◽  
Haemophilus Ducreyi ◽  
Content Type ◽  
Enhanced Sensitivity ◽  
Significant Survival ◽  
Carbon Storage Regulator ◽  
Mutant Phenotypes

ABSTRACTThe carbon storage regulator A (CsrA) controls a wide variety of bacterial processes, including metabolism, adherence, stress responses, and virulence.Haemophilus ducreyi, the causative agent of chancroid, harbors a homolog ofcsrA. Here, we generated an unmarked, in-frame deletion mutant ofcsrAto assess its contribution toH. ducreyipathogenesis. In human inoculation experiments, thecsrAmutant was partially attenuated for pustule formation compared to its parent. Deletion ofcsrAresulted in decreased adherence ofH. ducreyito human foreskin fibroblasts (HFF); Flp1 and Flp2, the determinants ofH. ducreyiadherence to HFF cells, were downregulated in thecsrAmutant. Compared to its parent, thecsrAmutant had a significantly reduced ability to tolerate oxidative stress and heat shock. The enhanced sensitivity of the mutant to oxidative stress was more pronounced in bacteria grown to stationary phase compared to that in bacteria grown to mid-log phase. ThecsrAmutant also had a significant survival defect within human macrophages when the bacteria were grown to stationary phase but not to mid-log phase. Complementation intranspartially or fully restored the mutant phenotypes. These data suggest that CsrA contributes to virulence by multiple mechanisms and that these contributions may be more profound in bacterial cell populations that are not rapidly dividing in the human host.

scholarly journals The Hybrid Histidine Kinase Hk1 Is Part of a Two-Component System That Is Essential for Survival of Borrelia burgdorferi in Feeding Ixodes scapularis Ticks

2011 ◽  
Vol 79 (8) ◽  
pp. 3117-3130 ◽  
Author(s):  
Melissa J. Caimano ◽  
Melisha R. Kenedy ◽  
Toru Kairu ◽  
Daniel C. Desrosiers ◽  
Michael Harman ◽  
...  
Keyword(s):  
Borrelia Burgdorferi ◽  
Histidine Kinase ◽  
Ixodes Scapularis ◽  
Response Regulator ◽  
Content Type ◽  
Diguanylate Cyclases ◽  
Two Component ◽  
Tick Transmission ◽  
Two Component Systems ◽  
Hybrid Histidine Kinase

ABSTRACTTwo-component systems (TCS) are principal mechanisms by which bacteria adapt to their surroundings.Borrelia burgdorferiencodes only two TCS. One is comprised of a histidine kinase, Hk2, and the response regulator Rrp2. While the contribution of Hk2 remains unclear, Rrp2 is part of a regulatory pathway involving the spirochete's alternate sigma factors, RpoN and RpoS. Genes within the Rrp2/RpoN/RpoS regulon function to promote tick transmission and early infection. The other TCS consists of a hybrid histidine kinase, Hk1, and the response regulator Rrp1. Hk1 is composed of two periplasmic sensor domains (D1 and D2), followed by conserved cytoplasmic histidine kinase core, REC, and Hpt domains. In addition to its REC domain, Rrp1 contains a GGDEF motif characteristic of diguanylate cyclases. To investigate the role of Hk1 during the enzootic cycle, we inactivated this gene in two virulent backgrounds. Extensive characterization of the resulting mutants revealed a dramatic phenotype whereby Hk1-deficient spirochetes are virulent in mice and able to migrate out of the bite site during feeding but are killed within the midgut following acquisition. We hypothesize that the phosphorelay between Hk1 and Rrp1 is initiated by the binding of feeding-specific ligand(s) to Hk1 sensor domain D1 and/or D2. Once activated, Rrp1 directs the synthesis of cyclic dimeric GMP (c-di-GMP), which, in turn, modulates the expression and/or activity of gene products required for survival within feeding ticks. In contrast to the Rrp2/RpoN/RpoS pathway, which is active only within feeding nymphs, the Hk1/Rrp1 TCS is essential for survival during both larval and nymphal blood meals.

scholarly journals The Two-Component Signal Transduction System VxrAB Positively Regulates Vibrio cholerae Biofilm Formation

2017 ◽  
Vol 199 (18) ◽  
Author(s):  
Jennifer K. Teschler ◽  
Andrew T. Cheng ◽  
Fitnat H. Yildiz
Keyword(s):  
Signal Transduction ◽  
Vibrio Cholerae ◽  
Histidine Kinase ◽  
Biofilm Formation ◽  
Pathogenic Bacteria ◽  
Response Regulator ◽  
Systematic Analysis ◽  
Content Type ◽  
Two Component ◽  
Two Component Signal Transduction

ABSTRACT Two-component signal transduction systems (TCSs), typically composed of a sensor histidine kinase (HK) and a response regulator (RR), are the primary mechanism by which pathogenic bacteria sense and respond to extracellular signals. The pathogenic bacterium Vibrio cholerae is no exception and harbors 52 RR genes. Using in-frame deletion mutants of each RR gene, we performed a systematic analysis of their role in V. cholerae biofilm formation. We determined that 7 RRs impacted the expression of an essential biofilm gene and found that the recently characterized RR, VxrB, regulates the expression of key structural and regulatory biofilm genes in V. cholerae. vxrB is part of a 5-gene operon, which contains the cognate HK vxrA and three genes of unknown function. Strains carrying ΔvxrA and ΔvxrB mutations are deficient in biofilm formation, while the ΔvxrC mutation enhances biofilm formation. The overexpression of VxrB led to a decrease in motility. We also observed a small but reproducible effect of the absence of VxrB on the levels of cyclic di-GMP (c-di-GMP). Our work reveals a new function for the Vxr TCS as a regulator of biofilm formation and suggests that this regulation may act through key biofilm regulators and the modulation of cellular c-di-GMP levels. IMPORTANCE Biofilms play an important role in the Vibrio cholerae life cycle, providing protection from environmental stresses and contributing to the transmission of V. cholerae to the human host. V. cholerae can utilize two-component systems (TCS), composed of a histidine kinase (HK) and a response regulator (RR), to regulate biofilm formation in response to external cues. We performed a systematic analysis of V. cholerae RRs and identified a new regulator of biofilm formation, VxrB. We demonstrated that the VxrAB TCS is essential for robust biofilm formation and that this system may regulate biofilm formation via its regulation of key biofilm regulators and cyclic di-GMP levels. This research furthers our understanding of the role that TCSs play in the regulation of V. cholerae biofilm formation.

scholarly journals The Atypical Response Regulator AtvR Is a New Player in Pseudomonas aeruginosa Response to Hypoxia and Virulence

2017 ◽  
Vol 85 (8) ◽  
Author(s):  
Gilberto Hideo Kaihami ◽  
Leandro Carvalho Dantas Breda ◽  
José Roberto Fogaça de Almeida ◽  
Thays de Oliveira Pereira ◽  
Gianlucca Gonçalves Nicastro ◽  
...  
Keyword(s):  
Pseudomonas Aeruginosa ◽  
Type Strain ◽  
Wild Type Strain ◽  
Environmental Changes ◽  
Response Regulator ◽  
Classical Pathway ◽  
Wild Type ◽  
Macrophage Infection ◽  
Content Type ◽  
Successful Infection

ABSTRACT Two-component systems are widespread in bacteria, allowing adaptation to environmental changes. The classical pathway is composed of a histidine kinase that phosphorylates an aspartate residue in the cognate response regulator (RR). RRs lacking the phosphorylatable aspartate also occur, but their function and contribution during host-pathogen interactions are poorly characterized. AtvR (PA14_26570) is the only atypical response regulator with a DNA-binding domain in the opportunistic pathogen Pseudomonas aeruginosa. Macrophage infection with the atvR mutant strain resulted in higher levels of tumor necrosis factor alpha secretion as well as increased bacterial clearance compared to those for macrophages infected with the wild-type strain. In an acute pneumonia model, mice infected with the atvR mutant presented increased amounts of proinflammatory cytokines, increased neutrophil recruitment to the lungs, reductions in bacterial burdens, and higher survival rates in comparison with the findings for mice infected with the wild-type strain. Further, several genes involved in hypoxia/anoxia adaptation were upregulated upon atvR overexpression, as seen by high-throughput transcriptome sequencing (RNA-Seq) analysis. In addition, atvR was more expressed in hypoxia in the presence of nitrate and required for full expression of nitrate reductase genes, promoting bacterial growth under this condition. Thus, AtvR would be crucial for successful infection, aiding P. aeruginosa survival under conditions of low oxygen tension in the host. Taken together, our data demonstrate that the atypical response regulator AtvR is part of the repertoire of transcriptional regulators involved in the lifestyle switch from aerobic to anaerobic conditions. This finding increases the complexity of regulation of one of the central metabolic pathways that contributes to Pseudomonas ubiquity and versatility.

scholarly journals Distinct and Combined Roles of the MAP Kinases of Cochliobolus heterostrophus in Virulence and Stress Responses

2008 ◽  
Vol 21 (6) ◽  
pp. 769-780 ◽  
Author(s):  
Aeid Igbaria ◽  
Sophie Lev ◽  
Mark S. Rose ◽  
Bee Na Lee ◽  
Ruthi Hadar ◽  
...  
Keyword(s):  
Stress Responses ◽  
Map Kinases ◽  
Cochliobolus Heterostrophus ◽  
Wild Type ◽  
Necrotrophic Pathogen ◽  
Disease Symptoms ◽  
Monosaccharide Transporter ◽  
Maize Leaves ◽  
Mitogen Activated Protein ◽  
Corn Leaf Blight

Pathogenicity mitogen-activated protein kinases (MAPKs), related to yeast FUS3/KSS1, are essential for virulence in fungi, including Cochliobolus heterostrophus, a necrotrophic pathogen causing Southern corn leaf blight. We compared the phenotypes of mutants in three MAPK genes: HOG1, MPS1, and CHK1. The chk1 and mps1 mutants show autolytic appearance, light pigmentation, and dramatic reduction in virulence and conidiation. Similarity of mps1 and chk1 mutants is reflected by coregulation by these two MAPKs of several genes. Unlike chk1, mps1 mutants are female-fertile and form normal-looking appressoria. HOG1 mediates resistance to hyperosmotic and, to a lesser extent, oxidative stress, and is required for stress upregulation of glycerol-3-phosphate phosphatase, transaldolase, and a monosaccharide transporter. Hog1, but not Mps1 or Chk1, was rapidly phosphorylated in response to increased osmolarity. The hog1 mutants have smaller appressoria and cause decreased disease symptoms on maize leaves. Surprisingly, loss of MPS1 in a wild-type or hog1 background improved resistance to some stresses. All three MAPKs contribute to the regulation of central developmental functions under normal and stress conditions, and full virulence cannot be achieved without appropriate input from all three pathways.

scholarly journals LuxS-Mediated Signaling in Streptococcus mutans Is Involved in Regulation of Acid and Oxidative Stress Tolerance and Biofilm Formation

2004 ◽  
Vol 186 (9) ◽  
pp. 2682-2691 ◽  
Author(s):  
Zezhang T. Wen ◽  
Robert A. Burne
Keyword(s):  
Streptococcus Mutans ◽  
Response Regulator ◽  
Regulatory Protein ◽  
Protein A ◽  
Signal Recognition Particle ◽  
Northern Hybridization ◽  
Wild Type ◽  
Increased Sensitivity ◽  
Mutant Phenotypes ◽  
Almost All

ABSTRACT LuxS-mediated quorum sensing has recently been shown to regulate important physiologic functions and virulence in a variety of bacteria. In this study, the role of luxS of Streptococcus mutans in the regulation of traits crucial to pathogenesis was investigated. Reporter gene fusions showed that inactivation of luxS resulted in a down-regulation of fructanase, a demonstrated virulence determinant, by more than 50%. The LuxS-deficient strain (TW26) showed increased sensitivity to acid killing but could still undergo acid adaptation. Northern hybridization revealed that the expression of RecA, SmnA (AP endonuclease), and Nth (endonuclease) were down-regulated in TW26, especially in early-exponential-phase cells. Other down-regulated genes included ffh (a signal recognition particle subunit) and brpA (biofilm regulatory protein A). Interestingly, the luxS mutant showed an increase in survival rate in the presence of hydrogen peroxide (58.8 mM). The luxS mutant formed less biofilm on hydroxylapatite disks, especially when grown in biofilm medium with sucrose, and the mutant biofilms appeared loose and hive-like, whereas the biofilms of the wild type were smooth and confluent. The mutant phenotypes were complemented by exposure to supernatants from wild-type cultures. Two loci, smu486 and smu487, were identified and predicted to encode a histidine kinase and a response regulator. The phenotypes of the smu486 smu487 mutant were, in almost all cases, similar to those of the luxS mutant, although our results suggest that this is not due to AI-2 signal transduction via Smu486 and Smu487. This study demonstrates that luxS-dependent signaling plays critical roles in modulating key virulence properties of S. mutans.

scholarly journals Usp14 is required for spermatogenesis and ubiquitin stress responses in Drosophila melanogaster

2019 ◽  
Author(s):  
Levente Kovács ◽  
Ágota Nagy ◽  
Margit Pál ◽  
Peter Deák
Keyword(s):  
Male Sterility ◽  
Stress Responses ◽  
Expression Patterns ◽  
Loss Of Function ◽  
Wild Type ◽  
Cellular Processes ◽  
Protein Conjugates ◽  
Covalently Linked ◽  
Mutant Phenotypes

ABSTRACTDeubiquitinating (DUB) enzymes free covalently linked ubiquitins from ubiquitin-ubiquitin and ubiquitin-protein conjugates, and thereby maintain the equilibrium between free and conjugated ubiquitins and regulate ubiquitin-mediated cellular processes. The present genetic analyses of mutant phenotypes demonstrate that loss of Usp14 function results in male sterility, with defects in spermatid individualization and reduced testicular free monoubiquitin levels. These phenotypes were rescued by germline specific overexpression of wild type Usp14. Synergistic genetic interactions with Ubi-p63E and cycloheximide sensitivity suggest that ubiquitin shortage is a primary cause of male sterility. In addition, Usp14 is predominantly expressed in testes in Drosophila, and differential expression patterns may be causative of testis-specific loss of function Usp14 phenotypes. Collectively, these results suggest a major role of Usp14 in maintaining normal steady state free monoubiquitin levels during the later stages of Drosophila spermatogenesis.

scholarly journals Serratia marcescensarn, a PhoP-Regulated Locus Necessary for Polymyxin B Resistance

2014 ◽  
Vol 58 (9) ◽  
pp. 5181-5190 ◽  
Author(s):  
Quei Yen Lin ◽  
Yi-Lin Tsai ◽  
Ming-Che Liu ◽  
Wei-Cheng Lin ◽  
Po-Ren Hsueh ◽  
...  
Keyword(s):  
Type Strain ◽  
Wild Type Strain ◽  
Response Regulator ◽  
Challenge Test ◽  
Polymyxin B ◽  
Resistant Bacteria ◽  
Wild Type ◽  
Mobility Shift ◽  
Content Type ◽  
In The Wild

ABSTRACTPolymyxins, which are increasingly being used to treat infections caused by multidrug-resistant bacteria, perform poorly againstSerratia marcescens. To investigate the underlying mechanisms, Tn5mutagenesis was performed and two mutants exhibiting increased polymyxin B (PB) susceptibility were isolated. The mutants were found to have Tn5inserted into thearnBandarnCgenes. In other bacteria,arnBandarnCbelong to the seven-genearnoperon, which is involved in lipopolysaccharide (LPS) modification. LPSs ofarnmutants had greater PB-binding abilities than that of wild-type LPS. Further, we identified PhoP, a bacterial two-component response regulator, as a regulator of PB susceptibility inS. marcescens. By the reporter assay, we found PB- and low-Mg2+-induced expression ofphoPandarnin the wild-type strain but not in thephoPmutant. Complementation of thephoPmutant with the full-lengthphoPgene restored the PB MIC and induction by PB and low Mg2+levels, as in the wild type. An electrophoretic mobility shift assay (EMSA) further demonstrated that PhoP bound directly to thearnpromoter. The PB challenge test confirmed that pretreatment with PB and low Mg2+levels protectedS. marcescensfrom a PB challenge in the wild-type strain but not in thephoPmutant. Real-time reverse transcriptase-PCR also indicated that PB serves as a signal to regulate expression ofugd, a gene required for LPS modification, inS. marcescensthrough a PhoP-dependent pathway. Finally, we found that PB-resistant clinical isolates displayed greater expression ofarnAupon exposure to PB than did susceptible isolates. This is the first report to describe the role ofS. marcescensarnin PB resistance and its modulation by PB and Mg2+through the PhoP protein.

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