Publications by authors named "Johann Mignolet"

21 Publications

  • Page 1 of 1

AFM force-clamp spectroscopy captures the nanomechanics of the Tad pilus retraction.

Nanoscale Horiz 2021 06;6(6):489-496

Louvain Institute of Biomolecular Science and Technology, UCLouvain, Croix du Sud, 4-5, bte, L7.07.07, Louvain-la-Neuve B-1348, Belgium.

Motorization of bacterial pili is key to generate traction forces to achieve cellular function. The Tad (or Type IVc) pilus from Caulobacter crescentus is a widespread motorized nanomachine crucial for bacterial survival, evolution and virulence. An unusual bifunctional ATPase motor drives Tad pilus retraction, which helps the bacteria to land on target surfaces. Here, we use a novel platform combining a fluorescence-based screening of piliated bacteria and atomic force microscopy (AFM) force-clamp spectroscopy, to monitor over time (30 s) the nanomechanics and dynamics of the Tad nanofilament retraction under a high constant tension (300 pN). We observe striking transient variations of force and height originating from two phenomena: active pilus retraction and passive hydrophobic interactions between the pilus and the hydrophobic substrate. That the Tad pilus is able to retract under high tensile loading - at a velocity of ∼150 nm s-1 - indicates that this nanomachine is stronger than previously anticipated. Our findings show that pilus retraction and hydrophobic interactions work together to mediate bacterial cell landing and surface adhesion. The motorized pilus retraction actively triggers the cell to approach the substrate. At short distances, passive hydrophobic interactions accelerate the approach phenomenon and promote strong cell-substrate adhesion. This mechanism could provide a strategy to save ATP-based energy by the retraction ATPase. Our force-clamp AFM methodology offers promise to decipher the physics of bacterial nanomotors with high sensitivity and temporal resolution.
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http://dx.doi.org/10.1039/d1nh00158bDOI Listing
June 2021

AFM Unravels the Unique Adhesion Properties of the Type IVc Pilus Nanomachine.

Nano Lett 2021 04 23;21(7):3075-3082. Epub 2021 Mar 23.

Louvain Institute of Biomolecular Science and Technology, UCLouvain, Croix du Sud, 4-5, bte, L7.07.07., B-1348 Louvain-la-Neuve, Belgium.

Bacterial pili are proteinaceous motorized nanomachines that play various functional roles including surface adherence, bacterial motion, and virulence. The surface-contact sensor type IVc (or Tad) pilus is widely distributed in both Gram-positive and Gram-negative bacteria. In , this nanofilament, though crucial for surface colonization, has never been thoroughly investigated at the molecular level. As assembles several surface appendages at specific stages of the cell cycle, we designed a fluorescence-based screen to selectively study single piliated cells and combined it with atomic force microscopy and genetic manipulation to quantify the nanoscale adhesion of the type IVc pilus to hydrophobic substrates. We demonstrate that this nanofilament exhibits high stickiness compared to the canonical type IVa/b pili, resulting mostly from multiple hydrophobic interactions along the fiber length, and that it features nanospring mechanical properties. Our findings may be helpful to better understand the structure-function relationship of bacterial pilus nanomachines.
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http://dx.doi.org/10.1021/acs.nanolett.1c00215DOI Listing
April 2021

AFM in cellular and molecular microbiology.

Cell Microbiol 2021 Jul 22;23(7):e13324. Epub 2021 Mar 22.

Louvain Institute of Biomolecular Science and Technology, Université Catholique de Louvain, Louvain-la-Neuve, Belgium.

The unique capabilities of the atomic force microscope (AFM), including super-resolution imaging, piconewton force-sensitivity, nanomanipulation and ability to work under physiological conditions, have offered exciting avenues for cellular and molecular biology research. AFM imaging has helped unravel the fine architectures of microbial cell envelopes at the nanoscale, and how these are altered by antimicrobial treatment. Nanomechanical measurements have shed new light on the elasticity, tensile strength and turgor pressure of single cells. Single-molecule and single-cell force spectroscopy experiments have revealed the forces and dynamics of receptor-ligand interactions, the nanoscale distribution of receptors on the cell surface and the elasticity and adhesiveness of bacterial pili. Importantly, recent force spectroscopy studies have demonstrated that extremely stable bonds are formed between bacterial adhesins and their cognate ligands, originating from a catch bond behaviour allowing the pathogen to reinforce adhesion under shear or tensile stress. Here, we survey how the versatility of AFM has enabled addressing crucial questions in microbiology, with emphasis on bacterial pathogens. TAKE AWAYS: AFM topographic imaging unravels the ultrastructure of bacterial envelopes. Nanomechanical mapping shows what makes cell envelopes stiff and resistant to drugs. Force spectroscopy characterises the molecular forces in pathogen adhesion. Stretching pili reveals a wealth of mechanical and adhesive responses.
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http://dx.doi.org/10.1111/cmi.13324DOI Listing
July 2021

How Microbes Use Force To Control Adhesion.

J Bacteriol 2020 05 27;202(12). Epub 2020 May 27.

Louvain Institute of Biomolecular Science and Technology, UCLouvain, Louvain-la-Neuve, Belgium

Microbial adhesion and biofilm formation are usually studied using molecular and cellular biology assays, optical and electron microscopy, or laminar flow chamber experiments. Today, atomic force microscopy (AFM) represents a valuable addition to these approaches, enabling the measurement of forces involved in microbial adhesion at the single-molecule level. In this minireview, we discuss recent discoveries made applying state-of-the-art AFM techniques to microbial specimens in order to understand the strength and dynamics of adhesive interactions. These studies shed new light on the molecular mechanisms of adhesion and demonstrate an intimate relationship between force and function in microbial adhesins.
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http://dx.doi.org/10.1128/JB.00125-20DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7253613PMC
May 2020

Molecular dissection of pheromone selectivity in the competence signaling system ComRS of streptococci.

Proc Natl Acad Sci U S A 2020 04 20;117(14):7745-7754. Epub 2020 Mar 20.

Louvain Institute of Biomolecular Science and Technology, Biochemistry and Genetics of Microorganisms, Université catholique de Louvain, B-1348 Louvain-La-Neuve, Belgium;

Competence allows bacteria to internalize exogenous DNA fragments for the acquisition of new phenotypes such as antibiotic resistance or virulence traits. In most streptococci, competence is regulated by ComRS signaling, a system based on the mature ComS pheromone (XIP), which is internalized to activate the (R)RNPP-type ComR sensor by triggering dimerization and DNA binding. Cross-talk analyses demonstrated major differences of selectivity between ComRS systems and raised questions concerning the mechanism of pheromone-sensor recognition and coevolution. Here, we decipher the molecular determinants of selectivity of the closely related ComRS systems from and Despite high similarity, we show that the divergence in ComR-XIP interaction does not allow reciprocal activation. We perform the structural analysis of the ComRS system from Comparison with its ortholog from reveals an activation mechanism based on a toggle switch involving the recruitment of a key loop by the XIP C terminus. Together with a broad mutational analysis, we identify essential residues directly involved in peptide binding. Notably, we generate a ComR mutant that displays a fully reversed selectivity toward the heterologous pheromone with only five point mutations, as well as other ComR variants featuring XIP bispecificity and/or neofunctionalization for hybrid XIP peptides. We also reveal that a single XIP mutation relaxes the strictness of ComR activation, suggesting fast adaptability of molecular communication phenotypes. Overall, this study is paving the way toward the rational design or directed evolution of artificial ComRS systems for a range of biotechnological and biomedical applications.
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http://dx.doi.org/10.1073/pnas.1916085117DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7149491PMC
April 2020

Subtle selectivity in a pheromone sensor triumvirate desynchronizes competence and predation in a human gut commensal.

Elife 2019 08 21;8. Epub 2019 Aug 21.

Biochemistry and Genetics of Microorganisms (BGM), Louvain Institute of Biomolecular Science and Technology, Université catholique de Louvain, Louvain-la-Neuve, Belgium.

Constantly surrounded by kin or alien organisms in nature, eukaryotes and prokaryotes developed various communication systems to coordinate adaptive multi-entity behavior. In complex and overcrowded environments, they require to discriminate relevant signals in a myriad of pheromones to execute appropriate responses. In the human gut commensal , the cytoplasmic Rgg/RNPP regulator ComR couples competence to bacteriocin-mediated predation. Here, we describe a paralogous sensor duo, ScuR and SarF, which circumvents ComR in order to disconnect these two physiological processes. We highlighted the recurring role of Rgg/RNPP in the production of antimicrobials and designed a robust genetic screen to unveil potent/optimized peptide pheromones. Further mutational and biochemical analyses dissected the modifiable selectivity toward their pheromone and operating sequences at the subtle molecular level. Additionally, our results highlight how we might mobilize antimicrobial molecules while silencing competence in endogenous populations of human microflora and temper gut disorders provoked by bacterial pathogens.
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http://dx.doi.org/10.7554/eLife.47139DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6703854PMC
August 2019

Mobilization of Microbiota Commensals and Their Bacteriocins for Therapeutics.

Trends Microbiol 2019 08 12;27(8):690-702. Epub 2019 Apr 12.

Biochemistry and Genetics of Microorganisms (BGM), Louvain Institute of Biomolecular Science and Technology (LIBST), UCLouvain, 1348 Louvain-la-Neuve, Belgium; Syngulon, rue du Bois Saint-Jean 15/1, 4102, Seraing, Belgium. Electronic address:

With the specter of resurgence of pathogens due to the propagation of antibiotic-resistance genes, innovative antimicrobial strategies are needed. In this review, we summarize the beneficial aspects of bacteriocins, a set of miscellaneous peptide-based bacterium killers, compared with classical antibiotics, and emphasize their use in cocktails to curb the emergence of new resistance. We highlight that their prey spectrum, their molecular malleability, and their multiple modes of production might lead to specific and personalized treatments to prevent systemic disorders. Complementarily, we discuss how we might exploit prevailing bacterial commensals, such as Streptococcus salivarius, and deliberately mobilize their bacteriocin arsenal 'on site' to cure multiresistant infections or finely reshape the endogenous microbiota for prophylaxis purposes.
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http://dx.doi.org/10.1016/j.tim.2019.03.007DOI Listing
August 2019

Circuitry Rewiring Directly Couples Competence to Predation in the Gut Dweller Streptococcus salivarius.

Cell Rep 2018 02;22(7):1627-1638

Biochemistry, Biophysics, and Genetics of Microorganisms (BBGM), Institute of Life Sciences, Université catholique de Louvain, 1348 Louvain-la-Neuve, Belgium. Electronic address:

Small distortions in transcriptional networks might lead to drastic phenotypical changes, especially in cellular developmental programs such as competence for natural transformation. Here, we report a pervasive circuitry rewiring for competence and predation interplay in commensal streptococci. Canonically, in streptococci paradigms such as Streptococcus pneumoniae and Streptococcus mutans, the pheromone-based two-component system BlpRH is a central node that orchestrates the production of antimicrobial compounds (bacteriocins) and incorporates signal from the competence activation cascade. However, the human commensal Streptococcus salivarius does not contain a functional BlpRH pair, while the competence signaling system ComRS directly couples bacteriocin production and competence commitment. This network shortcut might underlie an optimal adaptation against microbial competitors and explain the high prevalence of S. salivarius in the human digestive tract. Moreover, the broad spectrum of bacteriocin activity against pathogenic bacteria showcases the commensal and genetically tractable S. salivarius species as a user-friendly model for competence and bacterial predation.
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http://dx.doi.org/10.1016/j.celrep.2018.01.055DOI Listing
February 2018

More than a Tad: spatiotemporal control of Caulobacter pili.

Curr Opin Microbiol 2018 04 21;42:79-86. Epub 2017 Nov 21.

Department of Microbiology and Molecular Medicine, Faculty of Medicine, University of Geneva, Geneva, Switzerland.

The Type IV pilus (T4P) is a powerful and sophisticated bacterial nanomachine involved in numerous cellular processes, including adhesion, DNA uptake and motility. Aside from the well-described subtype T4aP of the Gram-negative genera, including Myxococcus, Pseudomonas and Neisseria, the Tad (tight adherence) pilus secretion system re-shuffles homologous parts from other secretion systems along with uncharacterized components into a new type of protein translocation apparatus. A representative of the Tad apparatus, the Caulobacter crescentus pilus assembly (Cpa) machine is built exclusively at the newborn cell pole once per cell cycle. Recent comprehensive genetic analyses unearthed a myriad of spatiotemporal determinants acting on the Tad/Cpa system, many of which are conserved in other α-proteobacteria, including obligate intracellular pathogens and symbionts.
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http://dx.doi.org/10.1016/j.mib.2017.10.017DOI Listing
April 2018

Modularity and determinants of a (bi-)polarization control system from free-living and obligate intracellular bacteria.

Elife 2016 12 23;5. Epub 2016 Dec 23.

Department Microbiology and Molecular Medicine, Institute of Genetics and Genomics in Geneva, Faculty of Medicine, University of Geneva, Geneva, Switzerland.

Although free-living and obligate intracellular bacteria are both polarized it is unclear whether the underlying polarization mechanisms and effector proteins are conserved. Here we dissect at the cytological, functional and structural level a conserved polarization module from the free living α-proteobacterium and an orthologous system from an obligate intracellular (rickettsial) pathogen. The NMR solution structure of the zinc-finger (ZnR) domain from the bifunctional and bipolar ZitP pilus assembly/motility regulator revealed conserved interaction determinants for PopZ, a bipolar matrix protein that anchors the ParB centromere-binding protein and other regulatory factors at the poles. We show that ZitP regulates cytokinesis and the localization of ParB and PopZ, targeting PopZ independently of the previously known binding sites for its client proteins. Through heterologous localization assays with rickettsial ZitP and PopZ orthologs, we document the shared ancestries, activities and structural determinants of a (bi-)polarization system encoded in free-living and obligate intracellular α-proteobacteria.
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http://dx.doi.org/10.7554/eLife.20640DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5182065PMC
December 2016

Functional dichotomy and distinct nanoscale assemblies of a cell cycle-controlled bipolar zinc-finger regulator.

Elife 2016 12 23;5. Epub 2016 Dec 23.

Microbiology and Molecular Medicine, Institute of Genetics and Genomics in Geneva (iGE3), Faculty of Medicine, University of Geneva, Geneva, Switzerland.

Protein polarization underlies differentiation in metazoans and in bacteria. How symmetric polarization can instate functional asymmetry remains elusive. Here, we show by super-resolution photo-activated localization microscopy and edgetic mutations that the bitopic zinc-finger protein ZitP implements specialized developmental functions - pilus biogenesis and multifactorial swarming motility - while shaping distinct nanoscale (bi)polar architectures in the asymmetric model bacterium . Polar assemblage and accumulation of ZitP and its effector protein CpaM are orchestrated in time and space by conserved components of the cell cycle circuitry that coordinate polar morphogenesis with cell cycle progression, and also act on the master cell cycle regulator CtrA. Thus, this novel class of potentially widespread multifunctional polarity regulators is deeply embedded in the cell cycle circuitry.
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http://dx.doi.org/10.7554/eLife.18647DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5182063PMC
December 2016

Structural Insights into Streptococcal Competence Regulation by the Cell-to-Cell Communication System ComRS.

PLoS Pathog 2016 12 1;12(12):e1005980. Epub 2016 Dec 1.

Institute for Integrative Biology of the Cell (I2BC), CEA, CNRS, Univ. Paris-Sud, Université Paris-Saclay, Gif-sur-Yvette cedex, France.

In Gram-positive bacteria, cell-to-cell communication mainly relies on extracellular signaling peptides, which elicit a response either indirectly, by triggering a two-component phosphorelay, or directly, by binding to cytoplasmic effectors. The latter comprise the RNPP family (Rgg and original regulators Rap, NprR, PrgX and PlcR), whose members regulate important bacterial processes such as sporulation, conjugation, and virulence. RNPP proteins are increasingly considered as interesting targets for the development of new antibacterial agents. These proteins are characterized by a TPR-type peptide-binding domain, and except for Rap proteins, also contain an N-terminal HTH-type DNA-binding domain and display a transcriptional activity. Here, we elucidate the structure-function relationship of the transcription factor ComR, a new member of the RNPP family, which positively controls competence for natural DNA transformation in streptococci. ComR is directly activated by the binding of its associated pheromone XIP, the mature form of the comX/sigX-inducing-peptide ComS. The crystal structure analysis of ComR from Streptococcus thermophilus combined with a mutational analysis and in vivo assays allows us to propose an original molecular mechanism of the ComR regulation mode. XIP-binding induces release of the sequestered HTH domain and ComR dimerization to allow DNA binding. Importantly, we bring evidence that this activation mechanism is conserved and specific to ComR orthologues, demonstrating that ComR is not an Rgg protein as initially proposed, but instead constitutes a new member of the RNPP family. In addition, identification of XIP and ComR residues important for competence activation constitutes a crucial step towards the design of antagonistic strategies to control gene exchanges among streptococci.
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http://dx.doi.org/10.1371/journal.ppat.1005980DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5131891PMC
December 2016

In-phase oscillation of global regulons is orchestrated by a pole-specific organizer.

Proc Natl Acad Sci U S A 2016 11 17;113(44):12550-12555. Epub 2016 Oct 17.

School of Biology, Indian Institute of Science Education and Research Thiruvananthapuram, Thiruvananthapuram 695016, Kerala, India;

Cell fate determination in the asymmetric bacterium Caulobacter crescentus (Caulobacter) is triggered by the localization of the developmental regulator SpmX to the old (stalked) cell pole during the G1→S transition. Although SpmX is required to localize and activate the cell fate-determining kinase DivJ at the stalked pole in Caulobacter, in cousins such as Asticcacaulis, SpmX directs organelle (stalk) positioning and possibly other functions. We define the conserved σ-dependent transcriptional activator TacA as a global regulator in Caulobacter whose activation by phosphorylation is indirectly down-regulated by SpmX. Using a combination of forward genetics and cytological screening, we uncover a previously uncharacterized and polarized component (SpmY) of the TacA phosphorylation control system, and we show that SpmY function and localization are conserved. Thus, SpmX organizes a site-specific, ancestral, and multifunctional regulatory hub integrating the in-phase oscillation of two global transcriptional regulators, CtrA (the master cell cycle transcriptional regulator A) and TacA, that perform important cell cycle functions.
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http://dx.doi.org/10.1073/pnas.1610723113DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5098664PMC
November 2016

Growth control switch by a DNA-damage-inducible toxin-antitoxin system in Caulobacter crescentus.

Nat Microbiol 2016 Feb 22;1:16008. Epub 2016 Feb 22.

Department of Microbiology &Molecular Medicine, Institute of Genetics &Genomics in Geneva (iGE3), Faculty of Medicine/CMU, University of Geneva, Rue Michel-Servet 1, 1211 Genève 4, Switzerland.

Bacterial toxin-antitoxin systems (TASs) are thought to respond to various stresses, often inducing growth-arrested (persistent) sub-populations of cells whose housekeeping functions are inhibited. Many such TASs induce this effect through the translation-dependent RNA cleavage (RNase) activity of their toxins, which are held in check by their cognate antitoxins in the absence of stress. However, it is not always clear whether specific mRNA targets of orthologous RNase toxins are responsible for their phenotypic effect, which has made it difficult to accurately place the multitude of TASs within cellular and adaptive regulatory networks. Here, we show that the TAS HigBA of Caulobacter crescentus can promote and inhibit bacterial growth dependent on the dosage of HigB, a toxin regulated by the DNA damage (SOS) repressor LexA in addition to its antitoxin HigA, and the target selectivity of HigB's mRNA cleavage activity. HigB reduced the expression of an efflux pump that is toxic to a polarity control mutant, cripples the growth of cells lacking LexA, and targets the cell cycle circuitry. Thus, TASs can have outcome switching activity in bacterial adaptive (stress) and systemic (cell cycle) networks.
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http://dx.doi.org/10.1038/nmicrobiol.2016.8DOI Listing
February 2016

Complete Genome Sequence of Streptococcus salivarius HSISS4, a Human Commensal Bacterium Highly Prevalent in the Digestive Tract.

Genome Announc 2016 Feb 4;4(1). Epub 2016 Feb 4.

Institut des Sciences de La Vie, Université catholique de Louvain, Louvain-la-Neuve, Belgium

The human commensal bacterium Streptococcus salivarius plays a major role in the equilibrium of microbial communities of the digestive tract. Here, we report the first complete genome sequence of a Streptococcus salivarius strain isolated from the small intestine, namely, HSISS4. Its circular chromosome comprises 1,903 coding sequences and 2,100,988 nucleotides.
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http://dx.doi.org/10.1128/genomeA.01637-15DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4742683PMC
February 2016

Regulation of competence for natural transformation in streptococci.

Infect Genet Evol 2015 Jul 16;33:343-60. Epub 2014 Sep 16.

Institut des Sciences de la Vie, Université catholique de Louvain, Place Croix du Sud 5, B-1348 Louvain-la-Neuve, Belgium.

Natural DNA transformation is a lateral gene transfer mechanism during which bacteria take up naked DNA from their environment and stably integrate it in their genome. The proteins required for this process are conserved between species and are produced during a specific physiological state known as competence. Although natural transformation drives genome plasticity and adaptability, it is also likely to cause deleterious effects in the chromosome of the recipient bacteria and negatively impact cell growth. The competence window is thus generally tightly regulated in response to species-specific environmental conditions and limited to a proportion of the cell population. In streptococci species, the entry into competence is dictated by the amount of the competence sigma factor σ(X), the master regulator of natural transformation in those species. The Streptococcus genus includes 7 phylogenetic groups that have evolved different regulatory circuits to govern natural transformation. Here, we review the current knowledge on transcriptional and post-transcriptional mechanisms that control the activity of σ(X) at the whole population and the single-cell level, with an emphasis on growth conditions that modulate their activation. Recent findings regarding competence regulation by the ComCDE and ComRS cell-cell signalling pathways and the Clp proteolytic system are specifically highlighted.
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http://dx.doi.org/10.1016/j.meegid.2014.09.010DOI Listing
July 2015

The histidine kinase PdhS controls cell cycle progression of the pathogenic alphaproteobacterium Brucella abortus.

J Bacteriol 2012 Oct 27;194(19):5305-14. Epub 2012 Jul 27.

Microorganisms Biology Research Unit (URBM), University of Namur (FUNDP), Namur, Belgium.

Bacterial differentiation is often associated with the asymmetric localization of regulatory proteins, such as histidine kinases. PdhS is an essential and polarly localized histidine kinase in the pathogenic alphaproteobacterium Brucella abortus. After cell division, PdhS is asymmetrically segregated between the two sibling cells, highlighting a differentiation event. However, the function(s) of PdhS in the B. abortus cell cycle remains unknown. We used an original approach, the pentapeptide scanning mutagenesis method, to generate a thermosensitive allele of pdhS. We report that a B. abortus strain carrying this pdhS allele displays growth arrest and an altered DivK-yellow fluorescent protein (YFP) polar localization at the restrictive temperature. Moreover, the production of a nonphosphorylatable PdhS protein or truncated PdhS proteins leads to dominant-negative effects by generating morphological defects consistent with the inhibition of cell division. In addition, we have used a domain mapping approach combined with yeast two-hybrid and fluorescence microscopy methods to better characterize the unusual PdhS sensory domain. We have identified a fragment of the PdhS sensory domain required for protein-protein interaction (amino acids [aa] 210 to 434), a fragment sufficient for polar localization (aa 1 to 434), and a fragment (aa 527 to 661) whose production in B. abortus correlates with the generation of cell shape alterations. The data support a model in which PdhS acts as an essential regulator of cell cycle progression in B. abortus and contribute to a better understanding of the differentiation program inherited by the two sibling cells.
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http://dx.doi.org/10.1128/JB.00699-12DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3457221PMC
October 2012

A sweet twist gets Bacillus into shape.

Mol Microbiol 2011 Apr 3;80(2):283-5. Epub 2011 Mar 3.

Department of Microbiology and Molecular Medicine, University of Geneva, 1 rue Michel-Servet, 1211 Geneva 4, Switzerland.

A protective organelle that is essential for viability under most conditions, the cell wall is a dynamic structure that is continuously remodelled with the growth of the bacterial cell. Because the cell wall also moulds the bacterium, the mechanisms of cell wall homeostasis can be deciphered using cell shape as a convenient proxy. In this issue of Molecular Microbiology, Foulquier et al. illuminate a connection between cell shape regulation and metabolism in Bacillus subtilis. They find that the putative NAD(P)-binding enzyme YvcK organizes into helical subcellular structures that exert shape control by directing the cell wall biosynthetic enzyme PBP1 along the cell cylinder and to the septum, a function shared with the MreB actin cytoskeleton. Unlike MreB, however, the role of YvcK in cell shape control is manifested only on certain carbon sources, presumably by way of a previously unknown metabolic feed that taps into cell morphogenesis.
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http://dx.doi.org/10.1111/j.1365-2958.2011.07588.xDOI Listing
April 2011

PdhS, an old-pole-localized histidine kinase, recruits the fumarase FumC in Brucella abortus.

J Bacteriol 2010 Jun 9;192(12):3235-9. Epub 2010 Apr 9.

Molecular Biology Research Unit (URBM), University of Namur (FUNDP), 61 rue de Bruxelles, B-5000 Namur, Belgium.

The bacterial pathogen Brucella abortus was recently demonstrated to recruit the essential cytoplasmic histidine kinase PdhS to its old pole. Here, we report identification of the fumarase FumC as a specific partner for the N-terminal "sensing" domain of PdhS, using an ORFeome-based yeast two-hybrid screen. We observed that FumC and PdhS colocalize at the old pole of B. abortus, while the other fumarase FumA is not polarly localized. FumC is not required for PdhS localization, and polar FumC localization is not FumA dependent. FumC homologs are not polarly localized in Sinorhizobium meliloti and Caulobacter crescentus, suggesting that polar recruitment of FumC by PdhS is evolutionarily recent.
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http://dx.doi.org/10.1128/JB.00066-10DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2901695PMC
June 2010

The asymmetric distribution of the essential histidine kinase PdhS indicates a differentiation event in Brucella abortus.

EMBO J 2007 Mar 15;26(5):1444-55. Epub 2007 Feb 15.

Unité de Recherche en Biologie Moléculaire, University of Namur FUNDP, Namur, Belgium.

Many organisms use polar localization of signalling proteins to control developmental events in response to completion of asymmetric cell division. Asymmetric division was recently reported for Brucella abortus, a class III facultative intracellular pathogen generating two sibling cells of slightly different size. Here we characterize PdhS, a cytoplasmic histidine kinase essential for B. abortus viability and homologous to the asymmetrically distributed PleC and DivJ histidine kinases from Caulobacter crescentus. PdhS is localized at the old pole of the large cell, and after division and growth, the small cell acquires PdhS at its old pole. PdhS may therefore be considered as a differentiation marker as it labels the old pole of the large cell. Moreover, PdhS colocalizes with its paired response regulator DivK. Finally, PdhS is able to localize at one pole in other alpha-proteobacteria, suggesting that a polar structure associating PdhS with one pole is conserved in these bacteria. We propose that a differentiation event takes place after the completion of cytokinesis in asymmetrically dividing alpha-proteobacteria. Altogether, these data suggest that prokaryotic differentiation may be much more widespread than expected.
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http://dx.doi.org/10.1038/sj.emboj.7601577DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1817626PMC
March 2007
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