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  • 1
    Language: English
    In: Proceedings of the National Academy of Sciences of the United States of America, 23 March 2010, Vol.107(12), pp.5599-604
    Description: Protein localization mechanisms dictate the functional and structural specialization of cells. Of the four polar surface organelles featured by the dimorphic bacterium Caulobacter crescentus, the stalk, a cylindrical extension of all cell envelope layers, is the least well characterized at the molecular level. Here we apply a powerful experimental scheme that integrates genetics with high-throughput localization to discover StpX, an uncharacterized bitopic membrane protein that modulates stalk elongation and is sequestered to the stalk. In stalkless mutants StpX is dispersed. Two populations of StpX were discernible within the stalk with different mobilities: an immobile one near the stalk base and a mobile one near the stalk tip. Molecular anatomy provides evidence that (i) the StpX transmembrane domain enables access to the stalk organelle, (ii) the N-terminal periplasmic domain mediates retention in the stalk, and (iii) the C-terminal cytoplasmic domain enhances diffusion within the stalk. Moreover, the accumulation of StpX and an N-terminally truncated isoform is differentially coordinated with the cell cycle. Thus, at the submicron scale the localization and the mobility of a protein are precisely regulated in space and time and are important for the correct organization of a subcellular compartment or organelle such as the stalk.
    Keywords: Bacterial Proteins -- Metabolism ; Caulobacter Crescentus -- Metabolism ; Cell Surface Extensions -- Metabolism ; Membrane Proteins -- Metabolism
    ISSN: 00278424
    E-ISSN: 1091-6490
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  • 2
    In: Nature, 2014, Vol.506(7489), p.489
    Description: What mechanisms underlie the transitions responsible for the diverse shapes observed in the living world? Although bacteria exhibit a myriad of morphologies (1), the mechanisms responsible for the evolution of bacterial cell shape are not understood. We investigated morphological diversity in a group of bacteria that synthesize an appendage-like extension of the cell envelope called the stalk (2,3). The location and number of stalks varies among species, as exemplified by three distinct subcellular positions of stalks within a rod-shaped cell body: polar in the genus Caulobacter and subpolar or bilateral in the genus Asticcacaulis (4). Here we show that a developmental regulator of Caulobacter crescentus, SpmX (5), is co-opted in the genus Asticcacaulis to specify stalk synthesis either at the subpolar or bilateral positions. We also show that stepwise evolution of a specific region of SpmX led to the gain of a new function and localization of this protein, which drove the sequential transition in stalk positioning. Our results indicate that changes in protein function, co-option and modularity are key elements in the evolution of bacterial morphology. Therefore, similar evolutionary principles of morphological transitions apply to both single-celled prokaryotes and multicellular eukaryotes.
    Keywords: Evolution (Biology) – Research ; Bacteria – Physiological Aspects ; Morphology (Biology) – Research;
    ISSN: 0028-0836
    E-ISSN: 14764687
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  • 3
    Language: English
    In: Current Biology, 02 February 2015, Vol.25(3), pp.R113-R115
    Description: Mechanosensing of surfaces in bacteria is a process that often uses obstruction of flagellum rotation to trigger behaviors such as adhesion and surface-associated movement. In a recent publication, the PilY1 protein of has been implicated as a novel mechanosensor that stimulates virulence in response to surface attachment. Mechanosensing of surfaces in bacteria is a process that often uses obstruction of flagellum rotation to trigger behaviors such as adhesion and surface-associated movement. In a recent publication, the PilY1 protein of has been implicated as a novel mechanosensor that stimulates virulence in response to surface attachment.
    Keywords: Biology
    ISSN: 0960-9822
    E-ISSN: 1879-0445
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  • 4
    Language: English
    In: Proceedings of the National Academy of Sciences of the United States, Jan 31, 2012, Vol.109(5), p.1697(5)
    Description: Elongation of many rod-shaped bacteria occurs by peptidoglycan synthesis at discrete foci along the sidewall of the cells. However, within the Rhizobiales, there are many budding bacteria, in which new cell growth is constrained to a specific region. The phylogeny of the Rhizobiales indicates that this mode of zonal growth may be ancestral. We demonstrate that the rod-shaped bacterium Agrobacterium tumefaciens grows unidirectionally from the new pole generated after cell division and has an atypical peptidoglycan composition. Polar growth occurs under ali conditions tested, including when cells are attached to a plant root and under conditions that induce virulence. Finally, we show that polar growth also occurs in the closely related bacteria Sinorhizobium meliloti, Brucella abortus, and Ochrobactrum anthropi. We find that unipolar growth is an ancestral and conserved trait among the Rhizobiales, which includes important mutualists and pathogens of plants and animals. cell wall morphogenesis | cell elongation-division cycle doi: 10.1073/pnas.1114476109
    Keywords: Proteobacteria -- Physiological Aspects ; Proteobacteria -- Growth ; Peptidoglycans -- Physiological Aspects ; Morphology (Biology) -- Research
    ISSN: 0027-8424
    Source: Cengage Learning, Inc.
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  • 5
    Language: English
    In: Journal of bacteriology, September 2011, Vol.193(17), pp.4567-8
    Description: The Alphaproteobacteria comprise morphologically diverse bacteria, including many species of stalked bacteria. Here we announce the genome sequences of eight alphaproteobacteria, including the first genome sequences of species belonging to the genera Asticcacaulis, Hirschia, Hyphomicrobium, and Rhodomicrobium.
    Keywords: Genome, Bacterial ; Alphaproteobacteria -- Classification
    ISSN: 00219193
    E-ISSN: 1098-5530
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  • 6
    In: Molecular Microbiology, July 2013, Vol.89(2), pp.350-371
    Description: Subcellular protein localization is thought to promote protein–protein interaction by increasing the effective concentration and enabling spatial co‐ordination and proper segregation of proteins. We found that protein overexpression allowed the assembly of a productive polysaccharide biosynthesis‐export‐anchoring complex in the absence of polar localization in . Polar localization of the holdfast export protein, , depends on the presence of the other export proteins, and , and on the polar scaffold protein . The holdfast deficiency of and mutants is suppressed by the overexpression of export proteins. Restored holdfasts are randomly positioned and colocalize with a holdfast anchor protein in these strains, indicating that functional complexes can form at non‐polar sites. Therefore, overexpression of export proteins surpasses a concentration threshold necessary for holdfast synthesis. Restoration of holdfast synthesis at non‐polar sites reduces surface adhesion, consistent with the need to spatially co‐ordinate the holdfast synthesis machinery with the flagellum and pili. These strains lack the cell‐specific segregation of the holdfast, resulting in the presence of holdfasts in motile daughter cells. Our results highlight the fact that multiple facets of subcellular localization can be coupled to improve the phenotypic outcome of a protein assembly.
    Keywords: Polysaccharides -- Physiological Aspects ; Proteins -- Physiological Aspects;
    ISSN: 0950-382X
    E-ISSN: 1365-2958
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  • 7
    In: Molecular Microbiology, August 2014, Vol.93(4), pp.713-735
    Description: The cell cycle of is controlled by a complex signalling network that co‐ordinates events. Genome sequencing has revealed many cell cycle genes are conserved in other lphaproteobacteria, but it is not clear to what extent their function is conserved. As many cell cycle regulatory genes are essential in , the essential genes of two lphaproteobacteria, (hizobiales) and (aulobacterales), were elucidated to identify changes in cell cycle protein function over different phylogenetic distances as demonstrated by changes in essentiality. The results show the majority of conserved essential genes are involved in critical cell cycle processes. Changes in component essentiality reflect major changes in lifestyle, such as divisome components in resulting from that organism's different growth pattern. Larger variability of essentiality was observed in cell cycle regulators, suggesting regulatory mechanisms are more customizable than the processes they regulate. Examples include variability in the essentiality of and spatial cell cycle regulators, and non‐essentiality of the highly conserved and usually essential methyltransferase . These results show that while essential cell functions are conserved across varying genetic distance, much of a given organism's essential gene pool is specific to that organism.
    Keywords: Genes ; Cell Cycle ; Genomics;
    ISSN: 0950-382X
    E-ISSN: 1365-2958
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  • 8
    Language: English
    In: Journal of Physical Chemistry B, Sept 12, 2013, Vol.117(36), p.10492-10503
    Description: To colonize surfaces, the bacterium Caulobacter crescentus employs a polar polysaccharide, the holdfast, located at the end of a thin, long stalk protruding from the cell body. Unlike many other bacteria which adhere through an extended extracellular polymeric network, the holdfast footprint area is tens of thousands times smaller than that of the total bacterium cross-sectional surface, making for some very demanding adhesion requirements. At present, the mechanism of holdfast adhesion remains poorly understood. We explore it here along three lines of investigation: (a) the impact of environmental conditions on holdfast binding affinity, (b) adhesion kinetics by dynamic force spectroscopy, and (c) kinetic modeling of the attachment process to interpret the observed time-dependence of the adhesion force at short and long time scales. A picture emerged in which discrete molecular units called adhesins are responsible for initial holdfast adhesion, by acting in a cooperative manner.
    Keywords: Caulobacter -- Research ; Caulobacter -- Physiological Aspects ; Polysaccharides -- Research ; Spectroscopy -- Usage
    ISSN: 1520-6106
    E-ISSN: 15205207
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  • 9
    In: Molecular Microbiology, May 2013, Vol.88(3), pp.486-500
    Description: Bacterial exopolysaccharide synthesis is a prevalent and indispensible activity in many biological processes, including surface adhesion and biofilm formation. In , surface attachment and subsequent biofilm growth depend on the ability to synthesize an adhesive polar polysaccharide known as the holdfast. In this work, we show that polar polysaccharide synthesis is a conserved phenomenon among lphaproteobacterial species closely related to . Among them, mutagenesis of showed that disruption of the gene, which encodes a putative polysaccharide deacetylase, leads to accumulation of holdfast in the culture supernatant. Examination of the deletion mutant in revealed that this strain synthesizes holdfast; however, like the   mutant, the holdfasts are shed into the medium and have decreased adhesiveness and cohesiveness. Site‐directed mutagenesis at the predicted catalytic site of   phenocopied the mutant and abolished the esterase activity of . In contrast, overexpression of increased cell adherence without increasing holdfast synthesis. We conclude that the polysaccharide deacetylase activity of is required for the adhesive and cohesive properties of the holdfast, as well as for the anchoring of the holdfast to the cell envelope.
    Keywords: Microbial Polysaccharides -- Analysis;
    ISSN: 0950-382X
    E-ISSN: 1365-2958
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  • 10
    Language: English
    In: Journal of Bacteriology, 02/01/2018, Vol.200(3)
    Description: Sinorhizobium meliloti is a soil-dwelling alphaproteobacterium that engages in a nitrogen-fixing root nodule symbiosis with leguminous plants. Cell surface polysaccharides are important both for adapting to stresses in the soil and for the development of an effective symbiotic interaction. Among the polysaccharides characterized to date, the acidic exopolysaccharides I (EPS-I; succinoglycan) and II (EPS-II; galactoglucan) are particularly important for protection from abiotic stresses, biofilm formation, root colonization, and infection of plant roots. Previous genetic screens discovered mutants with impaired EPS production, allowing the delineation of EPS biosynthetic pathways. Here we report on a genetic screen to isolate mutants with mucoid colonial morphologies that suggest EPS overproduction. Screening with Tn5 -110, which allows the recovery of both null and upregulation mutants, yielded 47 mucoid mutants, most of which overproduce EPS-I; among the 30 unique genes and intergenic regions identified, 14 have not been associated with EPS production previously. We identified a new protein-coding gene, emmD, which may be involved in the regulation of EPS-I production as part of the EmmABC threecomponent regulatory circuit. We also identified a mutant defective in EPS-I production, motility, and symbiosis, where Tn5 -110 was not responsible for the mutant phenotypes; these phenotypes result from a missense mutation in rpoA corresponding to the domain of the RNA polymerase alpha subunit known to interact with transcription regulators. IMPORTANCE The alphaproteobacterium Sinorhizobium meliloti converts dinitrogen to ammonium while inhabiting specialized plant organs termed root nodules. The transformation of S. meliloti from a free-living soil bacterium to a nitrogen-fixing plant symbiont is a complex developmental process requiring close interaction between the two partners. As the interface between the bacterium and its environment, the S. meliloti cell surface plays a critical role in adaptation to varied soil environments and in interaction with plant hosts. We isolated and characterized S. meliloti mutants with increased production of exopolysaccharides, key cell surface components. Our diverse set of mutants suggests roles for exopolysaccharide production in growth, metabolism, cell division, envelope homeostasis, biofilm formation, stress response, motility, and symbiosis.
    Keywords: Sinorhizobium Meliloti ; Bacteria ; Polymers ; Symbiosis ; Stress Response ; Nitrogen ; Polysaccharides ; Colonization ; Mutants ; Ammonium ; Genes ; Metabolism ; Ammonium ; Regulators ; Biofilms ; Transcription ; Soil Microorganisms ; Homeostasis ; Transformation ; Saccharides ; Cell Division ; Cell Surface ; DNA-Directed RNA Polymerase ; Organs ; Symbiosis ; Symbiosis ; Symbiosis ; Cell Division ; Colonization ; Exopolysaccharides ; Polysaccharides ; Missense Mutation ; Nodules ; Biofilms ; Soil Stresses ; Sinorhizobium Meliloti ; Plant Roots ; Gene Expression ; Biofilms ; Homeostasis ; Metabolism ; Nitrogen Fixation ; Genetic Screening ; Polymerase ; Nodules ; Leguminous Plants ; Soils ; Ribonucleic Acid–RNA ; Cellular Stress Response;
    ISSN: 0021-9193
    E-ISSN: 1098-5530
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