The Experts below are selected from a list of 297 Experts worldwide ranked by ideXlab platform

Urs Jenal - One of the best experts on this subject based on the ideXlab platform.

  • Reciprocal growth control by competitive binding of nucleotide second messengers to a metabolic switch in Caulobacter Crescentus
    Nature Microbiology, 2020
    Co-Authors: Viktoriya Shyp, Badri Nath Dubey, Raphael Böhm, Johannes Hartl, Jutta Nesper, Julia A. Vorholt, Sebastian Hiller, Tilman Schirmer, Urs Jenal
    Abstract:

    Bacteria use small signalling molecules such as (p)ppGpp or c-di-GMP to tune their physiology in response to environmental changes. It remains unclear whether these regulatory networks operate independently or whether they interact to optimize bacterial growth and survival. We report that (p)ppGpp and c-di-GMP reciprocally regulate the growth of Caulobacter Crescentus by converging on a single small-molecule-binding protein, SmbA. While c-di-GMP binding inhibits SmbA, (p)ppGpp competes for the same binding site to sustain SmbA activity. We demonstrate that (p)ppGpp specifically promotes Caulobacter growth on glucose, whereas c-di-GMP inhibits glucose consumption. We find that SmbA contributes to this metabolic switch and promotes growth on glucose by quenching the associated redox stress. The identification of an effector protein that acts as a central regulatory hub for two global second messengers opens up future studies on specific crosstalk between small-molecule-based regulatory networks. Crosstalk between small-molecule regulated networks controls growth in Caulobacter Crescentus .

  • tad pili play a dynamic role in Caulobacter Crescentus surface colonization
    Mbio, 2019
    Co-Authors: Matteo Sangermani, Isabelle Hug, Nora Sauter, Thomas Pfohl, Urs Jenal
    Abstract:

    Bacterial surface attachment is mediated by filamentous appendages called pili. Here, we describe the role of Tad pili during surface colonization of Caulobacter Crescentus Using an optical trap and microfluidic controlled flow conditions to mimic natural environments, we demonstrated that Tad pili undergo repeated dynamic cycles of extension and retraction. Within seconds after establishing surface contact, pilus retraction reorients cells into an upright position, promoting walking-like movements against the medium flow. Pilus-mediated positioning of the flagellate pole close to the surface facilitates motor-mediated mechanical sensing and promotes anchoring of the holdfast, an adhesive substance that affords long-term attachment. We present evidence that the second messenger c-di-GMP regulates pilus dynamics during surface encounter in distinct ways, promoting increased activity at intermediate levels and retraction of pili at peak concentrations. We propose a model in which flagellum and Tad pili functionally interact and together impose a ratchet-like mechanism that progressively drives C. Crescentus cells toward permanent surface attachment.IMPORTANCE Bacteria are able to colonize surfaces in environmental, industrial, and medical settings, where they form resilient communities called biofilms. In order to control bacterial surface colonization, microbiologists need to gain a detailed understanding of the processes that bacteria use to live at the liquid-surface interface and that allow them to adhere to and move on surfaces and eventually grow and persist on solid media. To facilitate these processes, bacteria are equipped with adhesive structures such as flagella and pili and with matrix components such as exopolysaccharides. How these cellular organelles are coordinated to optimize surface processes is currently subject to intense investigations. Here we used the model organism Caulobacter Crescentus to demonstrate that polar pili are highly dynamic structures that are functionally interconnected with the flagellar motor to mediate surface sensing, thereby enforcing rapid and permanent surface attachment. These studies provide an entry point for an in-depth molecular analysis of bacterial surface colonization.

  • genetic analysis of a novel pathway for d xylose metabolism in Caulobacter Crescentus
    Journal of Bacteriology, 2007
    Co-Authors: Craig Stephens, Beat Christen, Thomas Fuchs, Vidyodhaya Sundaram, Kelly Watanabe, Urs Jenal
    Abstract:

    Genetic data suggest that the oligotrophic freshwater bacterium Caulobacter Crescentus metabolizes d-xylose through a pathway yielding α-ketoglutarate, comparable to the recently described l-arabinose degradation pathway of Azospirillum brasilense. Enzymes of the C. Crescentus pathway, including an NAD+-dependent xylose dehydrogenase, are encoded in the xylose-inducible xylXABCD operon (CC0823-CC0819).

  • holdfast formation in motile swarmer cells optimizes surface attachment during Caulobacter Crescentus development
    Journal of Bacteriology, 2006
    Co-Authors: Assaf Levi, Urs Jenal
    Abstract:

    The adhesive holdfast is required for irreversible surface anchoring of Caulobacter Crescentus cells. The holdfast is synthesized early during swarmer cell development and, together with pili and a functional flagellum, contributes to optimal attachment during cell differentiation. We present evidence that the timing of holdfast formation in swarmer cells is regulated posttranslationally and is dependent on the diguanylate cyclase PleD.

  • isolation and characterization of a xylose dependent promoter from Caulobacter Crescentus
    Journal of Bacteriology, 1997
    Co-Authors: A C Meisenzahl, Lucy Shapiro, Urs Jenal
    Abstract:

    An inducible promoter is a useful tool for the controlled expression of a given gene. Accordingly, we identified, cloned, and sequenced a chromosomal locus, xylX, from Caulobacter Crescentus which is required for growth on xylose as the sole carbon source and showed that transcription from a single site is dependent on the presence of xylose in the growth medium. P(xylX) promoter activity was determined as a function of the composition of the growth medium both in single copy and on a plasmid using different reporter genes. One hundred micromolar exogenously added xylose was required for maximal induction of P(xylX) in a strain that is unable to metabolize xylose. P(xylX) activity was induced immediately after the addition of xylose and repressed almost completely when xylose was removed from the growth medium. In addition to the strong transcriptional control, the expression of xylX is also regulated on the translational level.

Lucy Shapiro - One of the best experts on this subject based on the ideXlab platform.

  • an intracellular compass spatially coordinates cell cycle modules in Caulobacter Crescentus
    Current Opinion in Microbiology, 2016
    Co-Authors: Keren Lasker, Thomas H Mann, Lucy Shapiro
    Abstract:

    Cellular functions in Bacteria, such as chromosome segregation and cytokinesis, result from cascades of molecular events operating largely as self-contained modules. Regulated timing of these cellular modules stems from global genetic circuits that allow precise temporal activation with respect to cell cycle progression and cell differentiation. Critically, many of these functions occur at defined locations within the cell, and therefore regulators of each module must communicate to remain coordinated in space. In this perspective, we highlight recent discoveries in Caulobacter Crescentus asymmetric cell division to illuminate diverse mechanisms by which a cellular compass, composed of scaffolding and signaling proteins, directs cell cycle modules to their exact cellular addresses.

  • Synchronization of Caulobacter Crescentus for investigation of the bacterial cell cycle.
    Journal of visualized experiments : JoVE, 2015
    Co-Authors: Jared M Schrader, Lucy Shapiro
    Abstract:

    The cell cycle is important for growth, genome replication, and development in all cells. In bacteria, studies of the cell cycle have focused largely on unsynchronized cells making it difficult to order the temporal events required for cell cycle progression, genome replication, and division. Caulobacter Crescentus provides an excellent model system for the bacterial cell cycle whereby cells can be rapidly synchronized in a G0 state by density centrifugation. Cell cycle synchronization experiments have been used to establish the molecular events governing chromosome replication and segregation, to map a genetic regulatory network controlling cell cycle progression, and to identify the establishment of polar signaling complexes required for asymmetric cell division. Here we provide a detailed protocol for the rapid synchronization of Caulobacter NA1000 cells. Synchronization can be performed in a large-scale format for gene expression profiling and western blot assays, as well as a small-scale format for microscopy or FACS assays. The rapid synchronizability and high cell yields of Caulobacter make this organism a powerful model system for studies of the bacterial cell cycle.

  • the coding and noncoding architecture of the Caulobacter Crescentus genome
    PLOS Genetics, 2014
    Co-Authors: Jared M Schrader, Sean Crosson, Harley H Mcadams, Keren Lasker, Bo Zhou, Seth W Childers, Brandon Williams, Tao Long, Jonathan S Weissman, Lucy Shapiro
    Abstract:

    Caulobacter Crescentus undergoes an asymmetric cell division controlled by a genetic circuit that cycles in space and time. We provide a universal strategy for defining the coding potential of bacterial genomes by applying ribosome profiling, RNA-seq, global 5′-RACE, and liquid chromatography coupled with tandem mass spectrometry (LC-MS) data to the 4-megabase C. Crescentus genome. We mapped transcript units at single base-pair resolution using RNA-seq together with global 5′-RACE. Additionally, using ribosome profiling and LC-MS, we mapped translation start sites and coding regions with near complete coverage. We found most start codons lacked corresponding Shine-Dalgarno sites although ribosomes were observed to pause at internal Shine-Dalgarno sites within the coding DNA sequence (CDS). These data suggest a more prevalent use of the Shine-Dalgarno sequence for ribosome pausing rather than translation initiation in C. Crescentus. Overall 19% of the transcribed and translated genomic elements were newly identified or significantly improved by this approach, providing a valuable genomic resource to elucidate the complete C. Crescentus genetic circuitry that controls asymmetric cell division.

  • super resolution imaging of the nucleoid associated protein hu in Caulobacter Crescentus
    Biophysical Journal, 2011
    Co-Authors: Steven F Lee, Lucy Shapiro, Michael A. Thompson, Monica A Schwartz, W. E. Moerner
    Abstract:

    Little is known about the structure and function of most nucleoid-associated proteins (NAPs) in bacteria. One reason for this is that the distribution and structure of the proteins is obfuscated by the diffraction limit in standard wide-field and confocal fluorescence imaging. In particular, the distribution of HU, which is the most abundant NAP, has received little attention. In this study, we investigate the distribution of HU in Caulobacter Crescentus using a combination of super-resolution fluorescence imaging and spatial point statistics. By simply increasing the laser power, single molecules of the fluorescent protein fusion HU2-eYFP can be made to blink on and off to achieve super-resolution imaging with a single excitation source. Through quantification by Ripley's K-test and comparison with Monte Carlo simulations, we find the protein is slightly clustered within a mostly uniform distribution throughout the swarmer and stalked stages of the cell cycle but more highly clustered in predivisional cells. The methods presented in this letter should be of broad applicability in the future study of prokaryotic NAPs.

  • super resolution imaging in live Caulobacter Crescentus cells using photoswitchable eyfp
    Nature Methods, 2008
    Co-Authors: Julie S. Biteen, Lucy Shapiro, Michael A. Thompson, Nicole K Tselentis, Grant R Bowman, W. E. Moerner
    Abstract:

    The commonly used, monomeric EYFP enabled imaging of intracellular protein structures beyond the optical resolution limit ('super-resolution' imaging) in living cells. By combining photoinduced activation of single EYFP fusions and time-lapse imaging, we obtained sub-40 nm resolution images of the filamentous superstructure of the bacterial actin protein MreB in live Caulobacter Crescentus cells. These studies demonstrated that EYFP is a useful emitter for in vivo super-resolution imaging.

Yves V Brun - One of the best experts on this subject based on the ideXlab platform.

  • surface sensing stimulates cellular differentiation in Caulobacter Crescentus
    Proceedings of the National Academy of Sciences of the United States of America, 2020
    Co-Authors: Rhett A Snyder, Courtney K Ellison, Geoffrey B Severin, Gregory B Whitfield, Christopher M Waters, Yves V Brun
    Abstract:

    Cellular differentiation is a fundamental strategy used by cells to generate specialized functions at specific stages of development. The bacterium Caulobacter Crescentus employs a specialized dimorphic life cycle consisting of two differentiated cell types. How environmental cues, including mechanical inputs such as contact with a surface, regulate this cell cycle remain unclear. Here, we find that surface sensing by the physical perturbation of retracting extracellular pilus filaments accelerates cell-cycle progression and cellular differentiation. We show that physical obstruction of dynamic pilus activity by chemical perturbation or by a mutation in the outer-membrane pilus secretin CpaC stimulates early initiation of chromosome replication. In addition, we find that surface contact stimulates cell-cycle progression by demonstrating that surface-stimulated cells initiate early chromosome replication to the same extent as planktonic cells with obstructed pilus activity. Finally, we show that obstruction of pilus retraction stimulates the synthesis of the cell-cycle regulator cyclic diguanylate monophosphate (c-di-GMP) through changes in the activity and localization of two key regulatory histidine kinases that control cell fate and differentiation. Together, these results demonstrate that surface contact and sensing by alterations in pilus activity stimulate C. Crescentus to bypass its developmentally programmed temporal delay in cell differentiation to more quickly adapt to a surface-associated lifestyle.

  • a multiprotein complex anchors adhesive holdfast at the outer membrane of Caulobacter Crescentus
    Journal of Bacteriology, 2019
    Co-Authors: Nina I Sulkowski, Gail G. Hardy, Yves V Brun, Tanmay A M Bharat
    Abstract:

    ABSTRACT Adhesion allows microbes to colonize surfaces and is the first stage in biofilm formation. Stable attachment of the freshwater alphaproteobacterium Caulobacter Crescentus to surfaces requires an adhesive polysaccharide called holdfast, which is synthesized at a specific cell pole and ultimately found at the tip of cylindrical extensions of the cell envelope called stalks. Secretion and anchoring of holdfast to the cell surface are governed by proteins HfsDAB and HfaABD, respectively. The arrangement and organization of these proteins with respect to each other and the cell envelope, and the mechanism by which the holdfast is anchored on cells, are unknown. In this study, we have imaged a series of C. Crescentus mutants using electron cryotomography, revealing the architecture and arrangement of the molecular machinery involved in holdfast anchoring in cells. We found that the holdfast is anchored to cells by a defined complex made up of the HfaABD proteins and that the HfsDAB secretion proteins are essential for proper assembly and localization of the HfaABD anchor. Subtomogram averaging of cell stalk tips showed that the HfaABD complex spans the outer membrane. The anchor protein HfaB is the major component of the anchor complex located on the periplasmic side of the outer membrane, while HfaA and HfaD are located on the cell surface. HfaB is the critical component of the complex, without which no HfaABD complex was observed in cells. These results allow us to propose a working model of holdfast anchoring, laying the groundwork for further structural and cell biological investigations. IMPORTANCE Adhesion and biofilm formation are fundamental processes that accompany bacterial colonization of surfaces, which are of critical importance in many infections. Caulobacter Crescentus biofilm formation proceeds via irreversible adhesion mediated by a polar polysaccharide called holdfast. Mechanistic and structural details of how the holdfast is secreted and anchored on cells are still lacking. Here, we have assigned the location and described the arrangement of the holdfast anchor complex. This work increases our knowledge of the relatively underexplored field of polysaccharide-mediated adhesion by identifying structural elements that anchor polysaccharides to the cell envelope, which is important in a variety of bacterial species.

  • Physiological role of stalk lengthening in Caulobacter Crescentus
    Communicative & integrative biology, 2013
    Co-Authors: Eric A. Klein, Yves V Brun, Susan Schlimpert, Velocity Hughes, Martin Thanbichler, Zemer Gitai
    Abstract:

    The Gram-negative bacterium Caulobacter Crescentus forms a thin polar stalk, which mediates its attachment to solid surfaces. Whereas stalks remain short (1 µm) in nutrient-rich conditions, they lengthen dramatically (up to 30 µm) upon phosphate starvation. A long-standing hypothesis is that the Caulobacter stalk functions as a nutrient scavenging "antenna" that facilitates phosphate uptake and transport to the cell body. The mechanistic details of this model must be revisited, given our recent identification of a protein-mediated diffusion barrier, which prevents the exchange of both membrane and soluble proteins between the stalk extension and the cell body. In this report, we discuss the potential of stalks to facilitate nutrient uptake and propose additional physiological roles for stalk elongation in Caulobacter cells.

  • Getting in the Loop: Regulation of Development in Caulobacter Crescentus
    Microbiology and molecular biology reviews : MMBR, 2010
    Co-Authors: Patrick D. Curtis, Yves V Brun
    Abstract:

    Summary: Caulobacter Crescentus is an aquatic Gram-negative alphaproteobacterium that undergoes multiple changes in cell shape, organelle production, subcellular distribution of proteins, and intracellular signaling throughout its life cycle. Over 40 years of research has been dedicated to this organism and its developmental life cycles. Here we review a portion of many developmental processes, with particular emphasis on how multiple processes are integrated and coordinated both spatially and temporally. While much has been discovered about Caulobacter Crescentus development, areas of potential future research are also highlighted.

  • Complex regulatory pathways coordinate cell-cycle progression and development in Caulobacter Crescentus.
    Advances in Microbial Physiology, 2008
    Co-Authors: Pamela J. B. Brown, Gail G. Hardy, Michael J. Trimble, Yves V Brun
    Abstract:

    Caulobacter Crescentus has become the predominant bacterial model system to study the regulation of cell-cycle progression. Stage-specific processes such as chromosome replication and segregation, and cell division are coordinated with the development of four polar structures: the flagellum, pili, stalk, and holdfast. The production, activation, localization, and proteolysis of specific regulatory proteins at precise times during the cell cycle culminate in the ability of the cell to produce two physiologically distinct daughter cells. We examine the recent advances that have enhanced our understanding of the mechanisms of temporal and spatial regulation that occur during cell-cycle progression.

W. E. Moerner - One of the best experts on this subject based on the ideXlab platform.

  • Spatial organization and dynamics of RNase E and ribosomes in Caulobacter Crescentus.
    Proceedings of the National Academy of Sciences of the United States of America, 2018
    Co-Authors: Camille Bayas, Jared M Schrader, Jiarui Wang, Marissa K. Lee, W. E. Moerner
    Abstract:

    We report the dynamic spatial organization of Caulobacter Crescentus RNase E (RNA degradosome) and ribosomal protein L1 (ribosome) using 3D single-particle tracking and superresolution microscopy. RNase E formed clusters along the central axis of the cell, while weak clusters of ribosomal protein L1 were deployed throughout the cytoplasm. These results contrast with RNase E and ribosome distribution in Escherichia coli, where RNase E colocalizes with the cytoplasmic membrane and ribosomes accumulate in polar nucleoid-free zones. For both RNase E and ribosomes in Caulobacter, we observed a decrease in confinement and clustering upon transcription inhibition and subsequent depletion of nascent RNA, suggesting that RNA substrate availability for processing, degradation, and translation facilitates confinement and clustering. Importantly, RNase E cluster positions correlated with the subcellular location of chromosomal loci of two highly transcribed rRNA genes, suggesting that RNase E’s function in rRNA processing occurs at the site of rRNA synthesis. Thus, components of the RNA degradosome and ribosome assembly are spatiotemporally organized in Caulobacter, with chromosomal readout serving as the template for this organization.

  • Spatial organization and dynamics of RNase E and ribosomes in Caulobacter Crescentus
    2017
    Co-Authors: Camille Bayas, Jared M Schrader, Jiarui Wang, Marissa K. Lee, W. E. Moerner
    Abstract:

    We report the dynamic spatial organization of Caulobacter Crescentus RNase E (RNA degradosome) and ribosomal protein L1 (ribosome) using 3D single particle tracking and super-resolution microscopy. RNase E formed clusters along the central axis of the cell, while weak clusters of ribosomal protein L1 were deployed throughout the cytoplasm. These results contrast with RNase E and ribosome distribution in E. coli , where RNase E co-localizes with the cytoplasmic membrane and ribosomes accumulate in polar nucleoid-free zones. For both RNase E and ribosomes in Caulobacter , we observed a decrease in confinement and clustering upon transcription inhibition and subsequent depletion of nascent RNA, suggesting that RNA substrate availability for processing, degradation, and translation facilitates confinement and clustering. Moreover, RNase E cluster positions correlate with the subcellular location of chromosomal loci of two highly transcribed ribosomal RNA genes, suggesting that RNase E9s function in ribosomal RNA processing occurs at the site of rRNA synthesis. Thus, components of the RNA degradosome and ribosome assembly are spatiotemporally organized in Caulobacter , with chromosomal readout serving as the template for this organization.

  • super resolution imaging of the nucleoid associated protein hu in Caulobacter Crescentus
    Biophysical Journal, 2011
    Co-Authors: Steven F Lee, Lucy Shapiro, Michael A. Thompson, Monica A Schwartz, W. E. Moerner
    Abstract:

    Little is known about the structure and function of most nucleoid-associated proteins (NAPs) in bacteria. One reason for this is that the distribution and structure of the proteins is obfuscated by the diffraction limit in standard wide-field and confocal fluorescence imaging. In particular, the distribution of HU, which is the most abundant NAP, has received little attention. In this study, we investigate the distribution of HU in Caulobacter Crescentus using a combination of super-resolution fluorescence imaging and spatial point statistics. By simply increasing the laser power, single molecules of the fluorescent protein fusion HU2-eYFP can be made to blink on and off to achieve super-resolution imaging with a single excitation source. Through quantification by Ripley's K-test and comparison with Monte Carlo simulations, we find the protein is slightly clustered within a mostly uniform distribution throughout the swarmer and stalked stages of the cell cycle but more highly clustered in predivisional cells. The methods presented in this letter should be of broad applicability in the future study of prokaryotic NAPs.

  • super resolution imaging in live Caulobacter Crescentus cells using photoswitchable eyfp
    Nature Methods, 2008
    Co-Authors: Julie S. Biteen, Lucy Shapiro, Michael A. Thompson, Nicole K Tselentis, Grant R Bowman, W. E. Moerner
    Abstract:

    The commonly used, monomeric EYFP enabled imaging of intracellular protein structures beyond the optical resolution limit ('super-resolution' imaging) in living cells. By combining photoinduced activation of single EYFP fusions and time-lapse imaging, we obtained sub-40 nm resolution images of the filamentous superstructure of the bacterial actin protein MreB in live Caulobacter Crescentus cells. These studies demonstrated that EYFP is a useful emitter for in vivo super-resolution imaging.

Patrick H. Viollier - One of the best experts on this subject based on the ideXlab platform.

  • Growth control switch by a DNA-damage-inducible toxin–antitoxin system in Caulobacter Crescentus
    Nature Microbiology, 2016
    Co-Authors: Clare L. Kirkpatrick, Daniel Martins, Peter Redder, Antonio Frandi, Johann Mignolet, Julien Bortoli Chapalay, Marc Chambon, Gerardo Turcatti, Patrick H. Viollier
    Abstract:

    The HigBA toxin–antitoxin system of Caulobacter Crescentus can act as a switch between promoting and inhibiting bacterial growth, depending on the dosage of HigA antitoxin, HigB toxin and its mRNA target. 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.

  • Complete genome sequence of Caulobacter Crescentus bacteriophage φCbK.
    Journal of virology, 2012
    Co-Authors: Gaël Panis, Christophe Lambert, Patrick H. Viollier
    Abstract:

    φCbK is a B3 morphotype bacteriophage of the Siphoviridae family that infects Caulobacter Crescentus, the preeminent model system for bacterial cell cycle studies. The last 4 decades of research with φCbK as a genetic and cytological tool to study the biology of the host warrant an investigation of the phage genome composition. Herein, we report the complete genome sequence of φCbK and highlight unusual features that emerged from its annotation. The complete genome analysis of the φCbK phage provides new insight into its characteristics and potential interactions with its Caulobacter Crescentus host, setting the stage for future functional studies with φCbK.

  • alternative mechanism for bacteriophage adsorption to the motile bacterium Caulobacter Crescentus
    Proceedings of the National Academy of Sciences of the United States of America, 2011
    Co-Authors: Ricardo C Guerreroferreira, Bert Ely, Patrick H. Viollier, Grant J Jensen, Jeanne S Poindexter, Maria Georgieva, Elizabeth R Wright
    Abstract:

    2D and 3D cryo-electron microscopy, together with adsorption kinetics assays of ϕCb13 and ϕCbK phage-infected Caulobacter Crescentus, provides insight into the mechanisms of infection. ϕCb13 and ϕCbK actively interact with the flagellum and subsequently attach to receptors on the cell pole. We present evidence that the first interaction of the phage with the bacterial flagellum takes place through a filament on the phage head. This contact with the flagellum facilitates concentration of phage particles around the receptor (i.e., the pilus portals) on the bacterial cell surface, thereby increasing the likelihood of infection. Phage head filaments have not been well characterized and their function is described here. Phage head filaments may systematically underlie the initial interactions of phages with their hosts in other systems and possibly represent a widespread mechanism of efficient phage propagation.