654 research outputs found
Skin and bones: the bacterial cytoskeleton, cell wall, and cell morphogenesis
The bacterial world is full of varying cell shapes and sizes, and individual species perpetuate a defined morphology generation after generation. We review recent findings and ideas about how bacteria use the cytoskeleton and other strategies to regulate cell growth in time and space to produce different shapes and sizes
A Self-Associating Protein Critical for Chromosome Attachment, Division, and Polar Organization in Caulobacter
Cell polarization is an integral part of many unrelated bacterial processes. How intrinsic cell polarization is achieved is poorly understood. Here, we provide evidence that Caulobacter crescentus uses a multimeric pole-organizing factor (PopZ) that serves as a hub to concurrently achieve several polarizing functions. During chromosome segregation, polar PopZ captures the ParB•ori complex and thereby anchors sister chromosomes at opposite poles. This step is essential for stabilizing bipolar gradients of a cell division inhibitor and setting up division near midcell. PopZ also affects polar stalk morphogenesis and mediates the polar localization of the morphogenetic and cell cycle signaling proteins CckA and DivJ. Polar accumulation of PopZ, which is central to its polarizing activity, can be achieved independently of division and does not appear to be dictated by the pole curvature. Instead, evidence suggests that localization of PopZ largely relies on PopZ multimerization in chromosome-free regions, consistent with a self-organizing mechanism
Mutations in the Lipopolysaccharide Biosynthesis Pathway Interfere with Crescentin-Mediated Cell Curvature in Caulobacter crescentus
Bacterial cell morphogenesis requires coordination among multiple cellular systems, including the bacterial
cytoskeleton and the cell wall. In the vibrioid bacterium Caulobacter crescentus, the intermediate filament-like
protein crescentin forms a cell envelope-associated cytoskeletal structure that controls cell wall growth to
generate cell curvature. We undertook a genetic screen to find other cellular components important for cell
curvature. Here we report that deletion of a gene (wbqL) involved in the lipopolysaccharide (LPS) biosynthesis
pathway abolishes cell curvature. Loss of WbqL function leads to the accumulation of an aberrant Opolysaccharide
species and to the release of the S layer in the culture medium. Epistasis and microscopy
experiments show that neither S-layer nor O-polysaccharide production is required for curved cell morphology
per se but that production of the altered O-polysaccharide species abolishes cell curvature by apparently
interfering with the ability of the crescentin structure to associate with the cell envelope. Our data suggest that
perturbations in a cellular pathway that is itself fully dispensable for cell curvature can cause a disruption of
cell morphogenesis, highlighting the delicate harmony among unrelated cellular systems. Using the wbqL
mutant, we also show that the normal assembly and growth properties of the crescentin structure are
independent of its association with the cell envelope. However, this envelope association is important for
facilitating the local disruption of the stable crescentin structure at the division site during cytokinesis
Cytokinesis Monitoring during Development Rapid Pole-to-Pole Shuttling of a Signaling Protein by Localized Kinase and Phosphatase in Caulobacter
AbstractFor successful generation of different cell types by asymmetric cell division, cell differentiation should be initiated only after completion of division. Here, we describe a control mechanism by which Caulobacter couples the initiation of a developmental program to the completion of cytokinesis. Genetic evidence indicates that localization of the signaling protein DivK at the flagellated pole prevents premature initiation of development. Photobleaching and FRET experiments show that polar localization of DivK is dynamic with rapid pole-to-pole shuttling of diffusible DivK generated by the localized activities of PleC phosphatase and DivJ kinase at opposite poles. This shuttling is interrupted upon completion of cytokinesis by the segregation of PleC and DivJ to different daughter cells, resulting in disruption of DivK localization at the flagellated pole and subsequent initiation of development in the flagellated progeny. Thus, dynamic polar localization of a diffusible protein provides a control mechanism that monitors cytokinesis to regulate development
The Bacterial Cytoplasm Has Glass-like Properties and Is Fluidized by Metabolic Activity
SummaryThe physical nature of the bacterial cytoplasm is poorly understood even though it determines cytoplasmic dynamics and hence cellular physiology and behavior. Through single-particle tracking of protein filaments, plasmids, storage granules, and foreign particles of different sizes, we find that the bacterial cytoplasm displays properties that are characteristic of glass-forming liquids and changes from liquid-like to solid-like in a component size-dependent fashion. As a result, the motion of cytoplasmic components becomes disproportionally constrained with increasing size. Remarkably, cellular metabolism fluidizes the cytoplasm, allowing larger components to escape their local environment and explore larger regions of the cytoplasm. Consequently, cytoplasmic fluidity and dynamics dramatically change as cells shift between metabolically active and dormant states in response to fluctuating environments. Our findings provide insight into bacterial dormancy and have broad implications to our understanding of bacterial physiology, as the glassy behavior of the cytoplasm impacts all intracellular processes involving large components
G1-arrested newborn cells are the predominant infectious form of the pathogen Brucella abortus
Several intracellular pathogens, such as Brucella abortus, display a biphasic infection process starting with a non-proliferative stage of unclear nature. Here, we study the cell cycle of B. abortus at the single-cell level, in culture and during infection of HeLa cells and macrophages. The localization of segregation and replication loci of the two bacterial chromosomes indicates that, immediately after being engulfed by host-cell endocytic vacuoles, most bacterial cells are newborn. These bacterial cells do not initiate DNA replication for the next 4 to 6 h, indicating a G1 arrest. Moreover, growth is completely stopped during that time, reflecting a global cell cycle block. Growth and DNA replication resume later, although bacteria still reside within endosomal-like compartments. We hypothesize that the predominance of G1-arrested bacteria in the infectious population, and the bacterial cell cycle arrest following internalization, may constitute a widespread strategy among intracellular pathogens to colonize new proliferation niches
Spatiotemporal control of PopZ localization through cell cycle–coupled multimerization
Ultra-High Resolution 3D Imaging of Whole Cells.
Fluorescence nanoscopy, or super-resolution microscopy, has become an important tool in cell biological research. However, because of its usually inferior resolution in the depth direction (50-80 nm) and rapidly deteriorating resolution in thick samples, its practical biological application has been effectively limited to two dimensions and thin samples. Here, we present the development of whole-cell 4Pi single-molecule switching nanoscopy (W-4PiSMSN), an optical nanoscope that allows imaging of three-dimensional (3D) structures at 10- to 20-nm resolution throughout entire mammalian cells. We demonstrate the wide applicability of W-4PiSMSN across diverse research fields by imaging complex molecular architectures ranging from bacteriophages to nuclear pores, cilia, and synaptonemal complexes in large 3D cellular volumes
A Modular BAM Complex in the Outer Membrane of the α-Proteobacterium Caulobacter crescentus
Mitochondria are organelles derived from an intracellular α-proteobacterium. The biogenesis of mitochondria relies on the assembly of β-barrel proteins into the mitochondrial outer membrane, a process inherited from the bacterial ancestor. Caulobacter crescentus is an α-proteobacterium, and the BAM (β-barrel assembly machinery) complex was purified and characterized from this model organism. Like the mitochondrial sorting and assembly machinery complex, we find the BAM complex to be modular in nature. A ∼150 kDa core BAM complex containing BamA, BamB, BamD, and BamE associates with additional modules in the outer membrane. One of these modules, Pal, is a lipoprotein that provides a means for anchorage to the peptidoglycan layer of the cell wall. We suggest the modular design of the BAM complex facilitates access to substrates from the protein translocase in the inner membrane
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