head of the department: Prof. Häußler

Recent Submissions

  • Regulation of Flagellum Biosynthesis in Response to Cell Envelope Stress in Serovar Typhimurium.

    Spöring, Imke; Felgner, Sebastian; Preuße, Matthias; Eckweiler, Denitsa; Rohde, Manfred; Häussler, Susanne; Weiss, Siegfried; Erhardt, Marc (2018-05-01)
    Flagellum-driven motility of serovar Typhimurium facilitates host colonization. However, the large extracellular flagellum is also a prime target for the immune system. As consequence, expression of flagella is bistable within a population of , resulting in flagellated and nonflagellated subpopulations. This allows the bacteria to maximize fitness in hostile environments. The degenerate EAL domain protein RflP (formerly YdiV) is responsible for the bistable expression of flagella by directing the flagellar master regulatory complex FlhDC with respect to proteolytic degradation. Information concerning the environmental cues controlling expression of and thus about the bistable flagellar biosynthesis remains ambiguous. Here, we demonstrated that RflP responds to cell envelope stress and alterations of outer membrane integrity. Lipopolysaccharide (LPS) truncation mutants of Typhimurium exhibited increasing motility defects due to downregulation of flagellar gene expression. Transposon mutagenesis and genetic profiling revealed that σ (RpoE) and Rcs phosphorelay-dependent cell envelope stress response systems sense modifications of the lipopolysaccaride, low pH, and activity of the complement system. This subsequently results in activation of RflP expression and degradation of FlhDC via ClpXP. We speculate that the presence of diverse hostile environments inside the host might result in cell envelope damage and would thus trigger the repression of resource-costly and immunogenic flagellum biosynthesis via activation of the cell envelope stress response. Pathogenic bacteria such as Typhimurium sense and adapt to a multitude of changing and stressful environments during host infection. At the initial stage of gastrointestinal colonization, uses flagellum-mediated motility to reach preferred sites of infection. However, the flagellum also constitutes a prime target for the host's immune response. Accordingly, the pathogen needs to determine the spatiotemporal stage of infection and control flagellar biosynthesis in a robust manner. We found that uses signals from cell envelope stress-sensing systems to turn off production of flagella. We speculate that downregulation of flagellum synthesis after cell envelope damage in hostile environments aids survival of during late stages of infection and provides a means to escape recognition by the immune system.
  • Inoculation density and nutrient level determine the formation of mushroom-shaped structures in Pseudomonas aeruginosa biofilms.

    Ghanbari, Azadeh; Dehghany, Jaber; Schwebs, Timo; Müsken, Mathias; Häussler, Susanne; Meyer-Hermann, Michael; BRICS, Braunschweiger Zentrum für Systembiologie, Rebenring 56, 38106 Braunschweig, Germany. (2016-09-09)
    Pseudomonas aeruginosa often colonises immunocompromised patients and the lungs of cystic fibrosis patients. It exhibits resistance to many antibiotics by forming biofilms, which makes it hard to eliminate. P. aeruginosa biofilms form mushroom-shaped structures under certain circumstances. Bacterial motility and the environment affect the eventual mushroom morphology. This study provides an agent-based model for the bacterial dynamics and interactions influencing bacterial biofilm shape. Cell motility in the model relies on recently published experimental data. Our simulations show colony formation by immotile cells. Motile cells escape from a single colony by nutrient chemotaxis and hence no mushroom shape develops. A high number density of non-motile colonies leads to migration of motile cells onto the top of the colonies and formation of mushroom-shaped structures. This model proposes that the formation of mushroom-shaped structures can be predicted by parameters at the time of bacteria inoculation. Depending on nutrient levels and the initial number density of stalks, mushroom-shaped structures only form in a restricted regime. This opens the possibility of early manipulation of spatial pattern formation in bacterial colonies, using environmental factors.
  • The Anaerobically Induced sRNA PaiI Affects Denitrification in Pseudomonas aeruginosa PA14.

    Tata, Muralidhar; Amman, Fabian; Pawar, Vinay; Wolfinger, Michael T; Weiss, Siegfried; Häussler, Susanne; Bläsi, Udo; Helmholtz-Zentrum für Infektionsforschung GmbH, Inhoffenstr. 7, 38124 Braunschweig, Germany. (2017)
    Pseudomonas aeruginosa is an opportunistic pathogen that can thrive by anaerobic respiration in the lungs of cystic fibrosis patients using nitrate as terminal electron acceptor. Here, we report the identification and characterization of the small RNA PaiI in the P. aeruginosa strain 14 (PA14). PaiI is anaerobically induced in the presence of nitrate and depends on the two-component system NarXL. Our studies revealed that PaiI is required for efficient denitrification affecting the conversion of nitrite to nitric oxide. In the absence of PaiI anaerobic growth was impaired on glucose, which can be reconciled with a decreased uptake of the carbon source under these conditions. The importance of PaiI for anaerobic growth is further underlined by the observation that a paiI deletion mutant was impaired in growth in murine tumors.
  • Towards individualized diagnostics of biofilm-associated infections: a case study.

    Müsken, Mathias; Klimmek, Kathi; Sauer-Heilborn, Annette; Donnert, Monique; Sedlacek, Ludwig; Suerbaum, Sebastian; Häussler, Susanne; H-Zentrum für Infektionsforschung GmbH, Inhoffenstr.7, 38124 Braunschweig, Germany. (2017)
    Organized within biofilm communities, bacteria exhibit resistance towards a broad spectrum of antibiotics. Thus, one might argue that bacteria isolated from biofilm-associated chronic infections should be subjected to resistance profiling under biofilm growth conditions. Various test systems have been developed to determine the biofilm-associated resistance; however, it is not clear to what extent the in vitro results reflect the situation in vivo, and whether the biofilm-resistance profile should guide clinicians in their treatment choice. To address this issue, we used confocal microscopy in combination with live/dead staining, and profiled biofilm-associated resistance of a large number (>130) of clinical Pseudomonas aeruginosa isolates from overall 15 cystic fibrosis patients. Our results demonstrate that in addition to a general non-responsiveness of bacteria when grown under biofilm conditions, there is an isolate-specific and antibiotic-specific biofilm-resistance profile. This individual resistance profile is independent on the structural properties of the biofilms. Furthermore, biofilm resistance is not linked to the resistance profile under planktonic growth conditions, or a mucoid, or small colony morphology of the tested isolates. Instead, it seems that individual biofilm structures evolve during biofilm-associated growth and are shaped by environment-specific cues. In conclusion, our results demonstrate that biofilm resistance profiles are isolate specific and cannot be deduced from commonly studied phenotypes. Further clinical studies will have to show the added value of biofilm-resistance profiling. Individualized diagnosis of biofilm resistance might lead to more rational recommendations for antimicrobial therapy and, thus, increased effectiveness of the treatment of chronically infected patients.
  • Tumour-targeting bacteria-based cancer therapies for increased specificity and improved outcome.

    Felgner, Sebastian; Pawar, Vinay; Kocijancic, Dino; Erhardt, Marc; Weiss, Siegfried; Helmholtz Centre for infection research, Inhoffenstr. 7, 38124 Braunschweig, Germany. (2017-08-03)
  • Use of Single-Frequency Impedance Spectroscopy to Characterize the Growth Dynamics of Biofilm Formation in Pseudomonas aeruginosa.

    van Duuren, Jozef B J H; Müsken, Mathias; Karge, Bianka; Tomasch, Jürgen; Wittmann, Christoph; Häussler, Susanne; Brönstrup, Mark (2017-07-12)
    Impedance spectroscopy has been applied in prokaryotic and eukaryotic cytometry as a label-free method for the investigation of adherent cells. In this paper, its use for characterizing the growth dynamics of P. aeruginosa biofilms is described and compared to crystal violet staining and confocal microscopy. The method allows monitoring the growth of biofilm-forming P. aeruginosa in a continuous and label-free manner over a period of 72 h in a 96 well plate format. Impedance curves obtained for P. aeruginosa PA14 wild type and mutant strains with a transposon insertion in pqsA and pelA genes exhibited distinct phases. We propose that the slope of the declining curve following a maximum at ca. 35-40 h is a measure of biofilm formation. Transplant experiments with P. aeruginosa biofilms and paraffin suggest that the impedance also reflects pellicle formation at the liquid-air interface, a barely considered contributor to impedance. Finally, the impairment of biofilm formation upon treatment of cultures with L-arginine and with ciprofloxacin, tobramycin and meropenem was studied by single frequency impedance spectroscopy. We suggest that these findings qualify impedance spectroscopy as an additional technique to characterize biofilm formation and its modulation by small molecule drugs.
  • Cross-regulation by CrcZ RNA controls anoxic biofilm formation in Pseudomonas aeruginosa.

    Pusic, Petra; Tata, Muralidhar; Wolfinger, Michael T; Sonnleitner, Elisabeth; Häussler, Susanne; Bläsi, Udo; Helmholtz Centre for infection research, Inhoffenstr. 7, 38124 Braunschweig, Germany. (2016-12-21)
    Pseudomonas aeruginosa (PA) can thrive in anaerobic biofilms in the lungs of cystic fibrosis (CF) patients. Here, we show that CrcZ is the most abundant PA14 RNA bound to the global regulator Hfq in anoxic biofilms grown in cystic fibrosis sputum medium. Hfq was crucial for anoxic biofilm formation. This observation complied with an RNAseq based transcriptome analysis and follow up studies that implicated Hfq in regulation of a central step preceding denitrification. CrcZ is known to act as a decoy that sequesters Hfq during relief of carbon catabolite repression, which in turn alleviates Hfq-mediated translational repression of catabolic genes. We therefore inferred that CrcZ indirectly impacts on biofilm formation by competing for Hfq. This hypothesis was supported by the findings that over-production of CrcZ mirrored the biofilm phenotype of the hfq deletion mutant, and that deletion of the crcZ gene augmented biofilm formation. To our knowledge, this is the first example where competition for Hfq by CrcZ cross-regulates an Hfq-dependent physiological process unrelated to carbon metabolism.
  • An oral multispecies biofilm model for high content screening applications.

    Kommerein, Nadine; Stumpp, Sascha N; Müsken, Mathias; Ehlert, Nina; Winkel, Andreas; Häussler, Susanne; Behrens, Peter; Buettner, Falk F R; Stiesch, Meike; Helmholtz Centre for infection research, Inhoffenstr.7, 38124 Braunschweig, Germany. (2017)
    Peri-implantitis caused by multispecies biofilms is a major complication in dental implant treatment. The bacterial infection surrounding dental implants can lead to bone loss and, in turn, to implant failure. A promising strategy to prevent these common complications is the development of implant surfaces that inhibit biofilm development. A reproducible and easy-to-use biofilm model as a test system for large scale screening of new implant surfaces with putative antibacterial potency is therefore of major importance. In the present study, we developed a highly reproducible in vitro four-species biofilm model consisting of the highly relevant oral bacterial species Streptococcus oralis, Actinomyces naeslundii, Veillonella dispar and Porphyromonas gingivalis. The application of live/dead staining, quantitative real time PCR (qRT-PCR), scanning electron microscopy (SEM) and urea-NaCl fluorescence in situ hybridization (urea-NaCl-FISH) revealed that the four-species biofilm community is robust in terms of biovolume, live/dead distribution and individual species distribution over time. The biofilm community is dominated by S. oralis, followed by V. dispar, A. naeslundii and P. gingivalis. The percentage distribution in this model closely reflects the situation in early native plaques and is therefore well suited as an in vitro model test system. Furthermore, despite its nearly native composition, the multispecies model does not depend on nutrient additives, such as native human saliva or serum, and is an inexpensive, easy to handle and highly reproducible alternative to the available model systems. The 96-well plate format enables high content screening for optimized implant surfaces impeding biofilm formation or the testing of multiple antimicrobial treatment strategies to fight multispecies biofilm infections, both exemplary proven in the manuscript.
  • Unravelling post-transcriptional PrmC-dependent regulatory mechanisms in Pseudomonas aeruginosa.

    Krueger, Jonas; Pohl, Sarah; Preusse, Matthias; Kordes, Adrian; Rugen, Nils; Schniederjans, Monika; Pich, Andreas; Häussler, Susanne; Twincore, Zentrum für experimentelle und klinische Infektionsforschung GmbH, Feodor-Lynen Str. 7, 30625 Hannover, Germany. (2016-10)
    Transcriptional regulation has a central role in cellular adaptation processes and is well investigated. In contrast, the importance of the post-transcriptional regulation on these processes is less well defined. The technological advancements have been critical to precisely quantify protein and mRNA level changes and hold promise to provide more insights into how post-transcriptional regulation determines phenotypes. In Pseudomonas aeruginosa the methyltransferase PrmC methylates peptide chain release factors to facilitate translation termination. Loss of PrmC activity abolishes anaerobic growth and leads to reduced production of quorum sensing-associated virulence factors. Here, by applying SILAC technology in combination with mRNA-sequencing, they provide evidence that the P. aeruginosa phenotype can be attributed to a change in protein to mRNA ratios of selected protein groups. The UAG-dependent translation termination was more dependent on PrmC activity than the UAA- and UGA-dependent translation termination. Additionally, a bias toward UAG stop codons in global transcriptional regulators was found. The finding that this bias in stop codon usage determines the P. aeruginosa phenotype is unexpected and adds complexity to regulatory circuits. Via modulation of PrmC activity the bacterial cell can cross-regulate targets independently of transcriptional signals, a process with an underestimated impact on the bacterial phenotype.
  • Identification of a Pseudomonas aeruginosa PAO1 DNA Methyltransferase, Its Targets, and Physiological Roles.

    Doberenz, Sebastian; Eckweiler, Denitsa; Reichert, Olga; Jensen, Vanessa; Bunk, Boyke; Spröer, Cathrin; Kordes, Adrian; Frangipani, Emanuela; Luong, Khai; Korlach, Jonas; Heeb, Stephan; Overmann, Jörg; Kaever, Volkhard; Häussler, Susanne; Helmholtz Centre for infection research, Inhoffenstr. 7, 38124 Braunschweig, Germany. (2017-02-21)
    DNA methylation is widespread among prokaryotes, and most DNA methylation reactions are catalyzed by adenine DNA methyltransferases, which are part of restriction-modification (R-M) systems. R-M systems are known for their role in the defense against foreign DNA; however, DNA methyltransferases also play functional roles in gene regulation. In this study, we used single-molecule real-time (SMRT) sequencing to uncover the genome-wide DNA methylation pattern in the opportunistic pathogen Pseudomonas aeruginosa PAO1. We identified a conserved sequence motif targeted by an adenine methyltransferase of a type I R-M system and quantified the presence of N(6)-methyladenine using liquid chromatography-tandem mass spectrometry (LC-MS/MS). Changes in the PAO1 methylation status were dependent on growth conditions and affected P. aeruginosa pathogenicity in a Galleria mellonella infection model. Furthermore, we found that methylated motifs in promoter regions led to shifts in sense and antisense gene expression, emphasizing the role of enzymatic DNA methylation as an epigenetic control of phenotypic traits in P. aeruginosa Since the DNA methylation enzymes are not encoded in the core genome, our findings illustrate how the acquisition of accessory genes can shape the global P. aeruginosa transcriptome and thus may facilitate adaptation to new and challenging habitats.IMPORTANCE With the introduction of advanced technologies, epigenetic regulation by DNA methyltransferases in bacteria has become a subject of intense studies. Here we identified an adenosine DNA methyltransferase in the opportunistic pathogen Pseudomonas aeruginosa PAO1, which is responsible for DNA methylation of a conserved sequence motif. The methylation level of all target sequences throughout the PAO1 genome was approximated to be in the range of 65 to 85% and was dependent on growth conditions. Inactivation of the methyltransferase revealed an attenuated-virulence phenotype in the Galleria mellonella infection model. Furthermore, differential expression of more than 90 genes was detected, including the small regulatory RNA prrF1, which contributes to a global iron-sparing response via the repression of a set of gene targets. Our finding of a methylation-dependent repression of the antisense transcript of the prrF1 small regulatory RNA significantly expands our understanding of the regulatory mechanisms underlying active DNA methylation in bacteria.
  • Evaluation of a microarray-hybridization based method applicable for discovery of single nucleotide polymorphisms (SNPs) in the Pseudomonas aeruginosa genome

    Dötsch, Andreas; Pommerenke, Claudia; Bredenbruch, Florian; Geffers, Robert; Häussler, Susanne (2009-01-19)
    Abstract Background Whole genome sequencing techniques have added a new dimension to studies on bacterial adaptation, evolution and diversity in chronic infections. By using this powerful approach it was demonstrated that Pseudomonas aeruginosa undergoes intense genetic adaptation processes, crucial in the development of persistent disease. The challenge ahead is to identify universal infection relevant adaptive bacterial traits as potential targets for the development of alternative treatment strategies. Results We developed a microarray-based method applicable for discovery of single nucleotide polymorphisms (SNPs) in P. aeruginosa as an easy and economical alternative to whole genome sequencing. About 50% of all SNPs theoretically covered by the array could be detected in a comparative hybridization of PAO1 and PA14 genomes at high specificity (> 0.996). Variations larger than SNPs were detected at much higher sensitivities, reaching nearly 100% for genetic differences affecting multiple consecutive probe oligonucleotides. The detailed comparison of the in silico alignment with experimental hybridization data lead to the identification of various factors influencing sensitivity and specificity in SNP detection and to the identification of strain specific features such as a large deletion within the PA4684 and PA4685 genes in the Washington Genome Center PAO1. Conclusion The application of the genome array as a tool to identify adaptive mutations, to depict genome organizations, and to identify global regulons by the "ChIP-on-chip" technique will expand our knowledge on P. aeruginosa adaptation, evolution and regulatory mechanisms of persistence on a global scale and thus advance the development of effective therapies to overcome persistent disease.
  • Deep transcriptome profiling of clinical Klebsiella pneumoniae isolates reveals strain and sequence type-specific adaptation.

    Bruchmann, Sebastian; Muthukumarasamy, Uthayakumar; Pohl, Sarah; Preusse, Matthias; Bielecka, Agata; Nicolai, Tanja; Hamann, Isabell; Hillert, Roger; Kola, Axel; Gastmeier, Petra; Eckweiler, Denitsa; Häussler, Susanne; Helmholtz Centre for infection research, Inhoffenstr. 7, 38124 Braunschweig, Germany. (2015-11)
    Health-care-associated infections by multi-drug-resistant bacteria constitute one of the greatest challenges to modern medicine. Bacterial pathogens devise various mechanisms to withstand the activity of a wide range of antimicrobial compounds, among which the acquisition of carbapenemases is one of the most concerning. In Klebsiella pneumoniae, the dissemination of the K. pneumoniae carbapenemase is tightly connected to the global spread of certain clonal lineages. Although antibiotic resistance is a key driver for the global distribution of epidemic high-risk clones, there seem to be other adaptive traits that may explain their success. Here, we exploited the power of deep transcriptome profiling (RNA-seq) to shed light on the transcriptomic landscape of 37 clinical K. pneumoniae isolates of diverse phylogenetic origins. We identified a large set of 3346 genes which was expressed in all isolates. While the core-transcriptome profiles varied substantially between groups of different sequence types, they were more homogenous among isolates of the same sequence type. We furthermore linked the detailed information on differentially expressed genes with the clinically relevant phenotypes of biofilm formation and bacterial virulence. This allowed for the identification of a diminished expression of biofilm-specific genes within the low biofilm producing ST258 isolates as a sequence type-specific trait.
  • RNASeq Based Transcriptional Profiling of Pseudomonas aeruginosa PA14 after Short- and Long-Term Anoxic Cultivation in Synthetic Cystic Fibrosis Sputum Medium.

    Tata, Muralidhar; Wolfinger, Michael T; Amman, Fabian; Roschanski, Nicole; Dötsch, Andreas; Sonnleitner, Elisabeth; Häussler, Susanne; Bläsi, Udo; Helmholtz Centre for infection research (HZI), Inhoffenstraße 7, 38124 Braunschweig, Germany. (2016)
    The opportunistic human pathogen Pseudomonas aeruginosa can thrive under microaerophilic to anaerobic conditions in the lungs of cystic fibrosis patients. RNASeq based comparative RNA profiling of the clinical isolate PA14 cultured in synthetic cystic fibrosis medium was performed after planktonic growth (OD600 = 2.0; P), 30 min after shift to anaerobiosis (A-30) and after anaerobic biofilm growth for 96h (B-96) with the aim to reveal differentially regulated functions impacting on sustained anoxic biofilm formation as well as on tolerance towards different antibiotics. Most notably, functions involved in sulfur metabolism were found to be up-regulated in B-96 cells when compared to A-30 cells. Based on the transcriptome studies a set of transposon mutants were screened, which revealed novel functions involved in anoxic biofilm growth.In addition, these studies revealed a decreased and an increased abundance of the oprD and the mexCD-oprJ operon transcripts, respectively, in B-96 cells, which may explain their increased tolerance towards meropenem and to antibiotics that are expelled by the MexCD-OprD efflux pump. The OprI protein has been implicated as a target for cationic antimicrobial peptides, such as SMAP-29. The transcriptome and subsequent Northern-blot analyses showed that the abundance of the oprI transcript encoding the OprI protein is strongly decreased in B-96 cells. However, follow up studies revealed that the susceptibility of a constructed PA14ΔoprI mutant towards SMAP-29 was indistinguishable from the parental wild-type strain, which questions OprI as a target for this antimicrobial peptide in strain PA14.
  • Evolutionary conservation of essential and highly expressed genes in Pseudomonas aeruginosa.

    Dötsch, Andreas; Klawonn, Frank; Jarek, Michael; Scharfe, Maren; Blöcker, Helmut; Häussler, Susanne; Helmholtz Centre for infection research, Inhoffenstr. 7, D-38124 Braunschweig, Germany. (2010)
    The constant increase in development and spread of bacterial resistance to antibiotics poses a serious threat to human health. New sequencing technologies are now on the horizon that will yield massive increases in our capacity for DNA sequencing and will revolutionize the drug discovery process. Since essential genes are promising novel antibiotic targets, the prediction of gene essentiality based on genomic information has become a major focus.
  • Very high-density lipoprotein and vitellin as carriers of novel biliverdins IXα with a farnesyl side-chain presumably derived from heme A in Spodoptera littoralis.

    Kayser, Hartmut; Nimtz, Manfred; Ringler, Philippe; Müller, Shirley A; Helmholtz Centre for infection research, Inhoffenstr. 7, D-38124 Braunschweig, Germany. (2016-01)
    Bilins in complex with specific proteins play key roles in many forms of life. Biliproteins have also been isolated from insects; however, structural details are rare and possible functions largely unknown. Recently, we identified a high-molecular weight biliprotein from a moth, Cerura vinula, as an arylphorin-type hexameric storage protein linked to a novel farnesyl biliverdin IXα; its unusual structure suggests formation by cleavage of mitochondrial heme A. In the present study of another moth, Spodoptera littoralis, we isolated two different biliproteins. These proteins were identified as a very high-density lipoprotein (VHDL) and as vitellin, respectively, by mass spectrometric sequencing. Both proteins are associated with three different farnesyl biliverdins IXα: the one bilin isolated from C. vinula and two new structurally closely related bilins, supposed to be intermediates of heme A degradation. The different bilin composition of the two biliproteins suggests that the presumed oxidations at the farnesyl side-chain take place mainly during egg development. The egg bilins are supposedly transferred from hemolymph VHDL to vitellin in the female. Both biliproteins show strong induced circular dichroism activity compatible with a predominance of the M-conformation of the bilins. This conformation is opposite to that of the arylphorin-type biliprotein from C. vinula. Electron microscopy of the VHDL-type biliprotein from S. littoralis provided a preliminary view of its structure as a homodimer and confirmed the biochemically determined molecular mass of ∼350 kDa. Further, images of S. littoralis hexamerins revealed a 2 × 3 construction identical to that known from the hexamerin from C. vinula.
  • Application of Synthetic Peptide Arrays To Uncover Cyclic Di-GMP Binding Motifs

    Düvel, Juliane; Bense, Sarina; Möller, Stefan; Bertinetti, Daniela; Schwede, Frank; Morr, Michael; Eckweiler, Denitsa; Genieser, Hans-Gottfried; Jänsch, Lothar; Herberg, Friedrich W.; Frank, Ronald; Häussler, Susanne; Helmholtz Centre for infection research, Inhoffenstr. 7, D-38124 Braunschweig, Germany. (2016-01-01)
    ABSTRACT High levels of the universal bacterial second messenger cyclic di-GMP (c-di-GMP) promote the establishment of surface-attached growth in many bacteria. Not only can c-di-GMP bind to nucleic acids and directly control gene expression, but it also binds to a diverse array of proteins of specialized functions and orchestrates their activity. Since its development in the early 1990s, the synthetic peptide array technique has become a powerful tool for high-throughput approaches and was successfully applied to investigate the binding specificity of protein-ligand interactions. In this study, we used peptide arrays to uncover the c-di-GMP binding site of a Pseudomonas aeruginosa protein (PA3740) that was isolated in a chemical proteomics approach. PA3740 was shown to bind c-di-GMP with a high affinity, and peptide arrays uncovered LKKALKKQTNLR to be a putative c-di-GMP binding motif. Most interestingly, different from the previously identified c-di-GMP binding motif of the PilZ domain (RXXXR) or the I site of diguanylate cyclases (RXXD), two leucine residues and a glutamine residue and not the charged amino acids provided the key residues of the binding sequence. Those three amino acids are highly conserved across PA3740 homologs, and their singular exchange to alanine reduced c-di-GMP binding within the full-length protein. IMPORTANCE In many bacterial pathogens the universal bacterial second messenger c-di-GMP governs the switch from the planktonic, motile mode of growth to the sessile, biofilm mode of growth. Bacteria adapt their intracellular c-di-GMP levels to a variety of environmental challenges. Several classes of c-di-GMP binding proteins have been structurally characterized, and diverse c-di-GMP binding domains have been identified. Nevertheless, for several c-di-GMP receptors, the binding motif remains to be determined. Here we show that the use of a synthetic peptide array allowed the identification of a c-di-GMP binding motif of a putative c-di-GMP receptor protein in the opportunistic pathogen P. aeruginosa . The application of synthetic peptide arrays will facilitate the search for additional c-di-GMP receptor proteins and aid in the characterization of c-di-GMP binding motifs.
  • The Pseudomonas aeruginosa Transcriptional Landscape Is Shaped by Environmental Heterogeneity and Genetic Variation.

    Dötsch, Andreas; Schniederjans, Monika; Khaledi, Ariane; Hornischer, Klaus; Schulz, Sebastian; Bielecka, Agata; Eckweiler, Denitsa; Pohl, Sarah; Häussler, Susanne; Helmholtz Centre for infection research, Inhoffenstr. 7, D-38124 Braunschweig, Germany. (2015)
    Phenotypic variability among bacteria depends on gene expression in response to different environments, and it also reflects differences in genomic structure. In this study, we analyzed transcriptome sequencing (RNA-seq) profiles of 151 Pseudomonas aeruginosa clinical isolates under standard laboratory conditions and of one P. aeruginosa type strain under 14 different environmental conditions. Our approach allowed dissection of the impact of the genetic background versus environmental cues on P. aeruginosa gene expression profiles and revealed that phenotypic variation was larger in response to changing environments than between genomically different isolates. We demonstrate that mutations within the global regulator LasR affect more than one trait (pleiotropy) and that the interaction between mutations (epistasis) shapes the P. aeruginosa phenotypic plasticity landscape. Because of pleiotropic and epistatic effects, average genotype and phenotype measures appeared to be uncorrelated in P. aeruginosa.
  • Cross talk between the response regulators PhoB and TctD allows for the integration of diverse environmental signals in Pseudomonas aeruginosa.

    Bielecki, Piotr; Jensen, Vanessa; Schulze, Wiebke; Gödeke, Julia; Strehmel, Janine; Eckweiler, Denitsa; Nicolai, Tanja; Bielecka, Agata; Wille, Thorsten; Gerlach, Roman G; Häussler, Susanne; HZI-Helmholzzentrum für Infektionsforschung (2015-07-27)
    Two-component systems (TCS) serve as stimulus-response coupling mechanisms to allow organisms to adapt to a variety of environmental conditions. The opportunistic pathogen Pseudomonas aeruginosa encodes for more than 100 TCS components. To avoid unwanted cross-talk, signaling cascades are very specific, with one sensor talking to its cognate response regulator (RR). However, cross-regulation may provide means to integrate different environmental stimuli into a harmonized output response. By applying a split luciferase complementation assay, we identified a functional interaction of two RRs of the OmpR/PhoB subfamily, namely PhoB and TctD in P. aeruginosa. Transcriptional profiling, ChIP-seq analysis and a global motif scan uncovered the regulons of the two RRs as well as a quadripartite binding motif in six promoter regions. Phosphate limitation resulted in PhoB-dependent expression of the downstream genes, whereas the presence of TctD counteracted this activation. Thus, the integration of two important environmental signals e.g. phosphate availability and the carbon source are achieved by a titration of the relative amounts of two phosphorylated RRs that inversely regulate a common subset of genes. In conclusion, our results on the PhoB and TctD mediated two-component signal transduction pathways exemplify how P. aeruginosa may exploit cross-regulation to adapt bacterial behavior to complex environments.
  • In Vivo Efficacy of Antimicrobials against Biofilm-Producing Pseudomonas aeruginosa.

    Pawar, Vinay; Komor, Uliana; Kasnitz, Nadine; Bielecki, Piotr; Pils, Marina C; Gocht, Benjamin; Moter, Annette; Rohde, Manfred; Weiss, Siegfried; Häussler, Susanne; Molecular Bacteriology, Twincore, Centre for Clinical and Experimental Infection Research, Hannover, Germany. (2015-08)
    Patients suffering from cystic fibrosis (CF) are commonly affected by chronic Pseudomonas aeruginosa biofilm infections. This is the main cause for the high disease severity. In this study, we demonstrate that P. aeruginosa is able to efficiently colonize murine solid tumors after intravenous injection and to form biofilms in this tissue. Biofilm formation was evident by electron microscopy. Such structures could not be observed with transposon mutants, which were defective in biofilm formation. Comparative transcriptional profiling of P. aeruginosa indicated physiological similarity of the bacteria in the murine tumor model and the CF lung. The efficacy of currently available antibiotics for treatment of P. aeruginosa-infected CF lungs, such as ciprofloxacin, colistin, and tobramycin, could be tested in the tumor model. We found that clinically recommended doses of these antibiotics were unable to eliminate wild-type P. aeruginosa PA14 while being effective against biofilm-defective mutants. However, colistin-tobramycin combination therapy significantly reduced the number of P. aeruginosa PA14 cells in tumors at lower concentrations. Hence, we present a versatile experimental system that is providing a platform to test approved and newly developed antibiofilm compounds.
  • Constitutive production of c-di-GMP is associated with mutations in a variant of Pseudomonas aeruginosa with altered membrane composition.

    Blanka, Andrea; Düvel, Juliane; Dötsch, Andreas; Klinkert, Birgit; Abraham, Wolf-Rainer; Kaever, Volkhard; Ritter, Christiane; Narberhaus, Franz; Häussler, Susanne; Institute for Molecular Bacteriology, TWINCORE,30625 Hannover, Germany. (2015)
    Most bacteria can form multicellular communities called biofilms on biotic and abiotic surfaces. This multicellular response to surface contact correlates with an increased resistance to various adverse environmental conditions, including those encountered during infections of the human host and exposure to antimicrobial compounds. Biofilm formation occurs when freely swimming (planktonic) cells encounter a surface, which stimulates the chemosensory-like, surface-sensing system Wsp and leads to generation of the intracellular second messenger 3',5'-cyclic-di-guanosine monophosphate (c-di-GMP). We identified adaptive mutations in a clinical small colony variant (SCV) of Pseudomonas aeruginosa and correlated their presence with self-aggregating growth behavior and an enhanced capacity to form biofilms. We present evidence that a point mutation in the 5' untranslated region of the accBC gene cluster, which encodes components of an enzyme responsible for fatty acid biosynthesis, was responsible for a stabilized mRNA structure that resulted in reduced translational efficiency and an increase in the proportion of short-chain fatty acids in the plasma membrane. We propose a model in which these changes in P. aeruginosa serve as a signal for the Wsp system to constitutively produce increased amounts of c-di-GMP and thus play a role in the regulation of adhesion-stimulated bacterial responses.

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