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Communications Biology Oct 2022Surface attachment of bacteria is the first step of biofilm formation and is often mediated and coordinated by the extracellular appendages, flagellum and pili. The...
Surface attachment of bacteria is the first step of biofilm formation and is often mediated and coordinated by the extracellular appendages, flagellum and pili. The model organism Caulobacter crescentus undergoes an asymmetric division cycle, giving rise to a motile "swarmer cell" and a sessile "stalked cell", which is attached to the surface. In the highly polarized predivisional cell, pili and flagellum, which are assembled at the pole opposite the stalk, are both activated before and during the process of cell separation. We explored the interplay of flagellum and active pili by growing predivisional cells on colloidal beads, creating a bacteria-on-a-bead system. Using this set-up, we were able to simultaneously visualize the bacterial motility and analyze the dynamics of the flagellum and pili during cell separation. The observed activities of flagellum and pili at the new cell pole of the predivisional cell result in a cooperating interplay of the appendages during approaching and attaching to a surface. Even in presence of a functioning flagellum, pili are capable of surface attachment and keeping the cell in position. Moreover, while flagellar rotation decreases the average attachment time of a single pilus, it increases the overall attachment rate of pili in a synergetic manner.
Topics: Caulobacter crescentus; Cell Separation; Fimbriae, Bacterial; Flagella; Hydrodynamics
PubMed: 36241769
DOI: 10.1038/s42003-022-04026-z -
MBio Jan 2021Microorganisms that degrade cellulose utilize extracellular reactions that yield free by-products which can promote interactions with noncellulolytic organisms. We...
Microorganisms that degrade cellulose utilize extracellular reactions that yield free by-products which can promote interactions with noncellulolytic organisms. We hypothesized that these interactions determine the ecological and physiological traits governing the fate of cellulosic carbon (C) in soil. We performed comparative genomics with genome bins from a shotgun metagenomic-stable isotope probing experiment to characterize the attributes of cellulolytic and noncellulolytic taxa accessing C from cellulose. We hypothesized that cellulolytic taxa would exhibit competitive traits that limit access, while noncellulolytic taxa would display greater metabolic dependency, such as signatures of adaptive gene loss. We tested our hypotheses by evaluating genomic traits indicative of competitive exclusion or metabolic dependency, such as antibiotic production, growth rate, surface attachment, biomass degrading potential, and auxotrophy. The most C-enriched taxa were cellulolytic () and (), which exhibited a strategy of self-sufficiency (prototrophy), rapid growth, and competitive exclusion via antibiotic production. Auxotrophy was more prevalent in cellulolytic than in cellulolytic , demonstrating differences in dependency among cellulose degraders. Noncellulolytic taxa that accessed C from cellulose (, , and ) were also more dependent, as indicated by patterns of auxotrophy and C labeling (i.e., partial labeling or labeling at later stages). Major C-labeled cellulolytic microbes (e.g., , and ) possessed adaptations for surface colonization (e.g., gliding motility, hyphae, attachment structures) signifying the importance of surface ecology in decomposing particulate organic matter. Our results demonstrated that access to cellulosic C was accompanied by ecological trade-offs characterized by differing degrees of metabolic dependency and competitive exclusion. Our study reveals the ecogenomic traits of microorganisms participating in the cellulose economy of soil. We identified three major categories of participants in this economy: (i) independent primary degraders, (ii) interdependent primary degraders, and (iii) secondary consumers (mutualists, opportunists, and parasites). Trade-offs between independent primary degraders, whose adaptations favor antagonism and competitive exclusion, and interdependent and secondary degraders, whose adaptations favor complex interspecies interactions, are expected to affect the fate of microbially processed carbon in soil. Our findings provide useful insights into the ecological relationships that govern one of the planet's most abundant resources of organic carbon. Furthermore, we demonstrate a novel gradient-resolved approach for stable isotope probing, which provides a cultivation-independent, genome-centric perspective into soil microbial processes.
Topics: Actinobacteria; Actinomycetales; Agriculture; Alphaproteobacteria; Bacteria; Biomass; Caulobacteraceae; Cellulose; Chaetomium; Gammaproteobacteria; Metagenome; Metagenomics; Phylogeny; Proteobacteria; RNA, Ribosomal, 16S; Soil; Soil Microbiology; Symbiosis
PubMed: 33402535
DOI: 10.1128/mBio.03099-20 -
Cold Spring Harbor Symposia on... 2009The bacterial cell has less internal structure and genetic complexity than cells of eukaryotic organisms, yet it is a highly organized system that uses both temporal and... (Review)
Review
The bacterial cell has less internal structure and genetic complexity than cells of eukaryotic organisms, yet it is a highly organized system that uses both temporal and spatial cues to drive its cell cycle. Key insights into bacterial regulatory programs that orchestrate cell cycle progression have come from studies of Caulobacter crescentus, a bacterium that divides asymmetrically. Three global regulatory proteins cycle out of phase with one another and drive cell cycle progression by directly controlling the expression of 200 cell-cycle-regulated genes. Exploration of this system provided insights into the evolution of regulatory circuits and the plasticity of circuit structure. The temporal expression of the modular subsystems that implement the cell cycle and asymmetric cell division is also coordinated by differential DNA methylation, regulated proteolysis, and phosphorylation signaling cascades. This control system structure has parallels to eukaryotic cell cycle control architecture. Remarkably, the transcriptional circuitry is dependent on three-dimensional dynamic deployment of key regulatory and signaling proteins. In addition, dynamically localized DNA-binding proteins ensure that DNA segregation is coupled to the timing and cellular position of the cytokinetic ring. Comparison to other organisms reveals conservation of cell cycle regulatory logic, even if regulatory proteins, themselves, are not conserved.
Topics: Bacteria; Bacterial Proteins; Biological Evolution; Caulobacter crescentus; Cell Cycle; Chromosomes, Bacterial; DNA, Bacterial; DNA-Binding Proteins; Models, Biological; Transcription Factors
PubMed: 19687139
DOI: 10.1101/sqb.2009.74.005 -
FEBS Letters Dec 2009Understanding of the cell cycle control logic in Caulobacter has progressed to the point where we now have an integrated view of the operation of an entire bacterial... (Review)
Review
Understanding of the cell cycle control logic in Caulobacter has progressed to the point where we now have an integrated view of the operation of an entire bacterial cell cycle system functioning as a state machine. Oscillating levels of a few temporally-controlled master regulator proteins in a cyclical circuit drive cell cycle progression. To a striking degree, the cell cycle regulation is a whole cell phenomenon. Phospho-signaling proteins and proteases dynamically deployed to specific locations on the cell wall are vital. An essential phospho-signaling system integral to the cell cycle circuitry is central to accomplishing asymmetric cell division.
Topics: Bacterial Proteins; Caulobacter crescentus; Cell Cycle; Cell Division; DNA Methylation; DNA-Binding Proteins; Gene Expression Regulation, Bacterial; Phosphoproteins; Signal Transduction; Transcription Factors
PubMed: 19766635
DOI: 10.1016/j.febslet.2009.09.030 -
Microbiology and Molecular Biology... Mar 2010Caulobacter crescentus is an aquatic Gram-negative alphaproteobacterium that undergoes multiple changes in cell shape, organelle production, subcellular distribution of... (Review)
Review
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.
Topics: Bacterial Proteins; Biological Evolution; Caulobacter crescentus; Cell Cycle; DNA Replication; DNA, Bacterial; Gene Expression Regulation, Bacterial
PubMed: 20197497
DOI: 10.1128/MMBR.00040-09 -
Molecular Microbiology Jul 2010Cell division in Gram-negative bacteria involves the co-ordinated invagination of the three cell envelope layers to form two new daughter cell poles. This complex... (Review)
Review
Cell division in Gram-negative bacteria involves the co-ordinated invagination of the three cell envelope layers to form two new daughter cell poles. This complex process starts with the polymerization of the tubulin-like protein FtsZ into a Z-ring at mid-cell, which drives cytokinesis and recruits numerous other proteins to the division site. These proteins are involved in Z-ring constriction, inner- and outer-membrane invagination, peptidoglycan remodelling and daughter cell separation. Three papers in this issue of Molecular Microbiology, from the teams of Lucy Shapiro, Martin Thanbichler and Christine Jacobs-Wagner, describe a novel protein, called DipM for Division Involved Protein with LysM domains, that is required for cell division in Caulobacter crescentus. DipM localizes to the mid-cell during cell division, where it is necessary for the hydrolysis of the septal peptidoglycan to remodel the cell wall. Loss of DipM results in severe defects in cell envelope constriction, which is deleterious under fast-growth conditions. State-of-the-art microscopy experiments reveal that the peptidoglycan is thicker and that the cell wall is incorrectly organized in DipM-depleted cells compared with wild-type cells, demonstrating that DipM is essential for reorganizing the cell wall at the division site, for envelope invagination and cell separation in Caulobacter.
Topics: Bacterial Proteins; Caulobacter crescentus; Cell Cycle Proteins; Cell Division; Endopeptidases; Gene Deletion; Hydrolysis; Microscopy; Peptidoglycan
PubMed: 20497501
DOI: 10.1111/j.1365-2958.2010.07225.x -
Journal of Bacteriology Sep 2019OmpA-like proteins are involved in the stabilization of the outer membrane, resistance to osmotic stress, and pathogenesis. In , OmpA2 forms a physiologically relevant...
OmpA-like proteins are involved in the stabilization of the outer membrane, resistance to osmotic stress, and pathogenesis. In , OmpA2 forms a physiologically relevant concentration gradient that forms by an uncharacterized mechanism, in which the gradient orientation depends on the position of the gene locus. This suggests that OmpA2 is synthesized and translocated to the periplasm close to the position of the gene and that the gradient forms by diffusion of the protein from this point. To further understand how the OmpA2 gradient is established, we determined the localization and mobility of the full protein and of its two structural domains. We show that OmpA2 does not diffuse and that both domains are required for gradient formation. The C-terminal domain binds tightly to the cell wall and the immobility of the full protein depends on the binding of this domain to the peptidoglycan; in contrast, the N-terminal membrane β-barrel diffuses slowly. Our results support a model in which once OmpA2 is translocated to the periplasm, the N-terminal membrane β-barrel is required for an initial fast restriction of diffusion until the position of the protein is stabilized by the binding of the C-terminal domain to the cell wall. The implications of these results on outer membrane protein diffusion and organization are discussed. Protein concentration gradients play a relevant role in the organization of the bacterial cell. The protein OmpA2 forms an outer membrane polar concentration gradient. To understand the molecular mechanism that determines the formation of this gradient, we characterized the mobility and localization of the full protein and of its two structural domains an integral outer membrane β-barrel and a periplasmic peptidoglycan binding domain. Each domain has a different role in the formation of the OmpA2 gradient, which occurs in two steps. We also show that the OmpA2 outer membrane β-barrel can diffuse, which is in contrast to what has been reported previously for several integral outer membrane proteins in , suggesting a different organization of the outer membrane proteins.
Topics: Bacterial Outer Membrane; Bacterial Outer Membrane Proteins; Caulobacter crescentus; Diffusion; Gene Expression Regulation, Bacterial; Protein Folding
PubMed: 31209077
DOI: 10.1128/JB.00177-19 -
Current Opinion in Biotechnology Aug 2007A major breakthrough in understanding the bacterial cell cycle is the discovery that bacteria exhibit a high degree of intracellular organization. Chromosomal loci and... (Review)
Review
A major breakthrough in understanding the bacterial cell cycle is the discovery that bacteria exhibit a high degree of intracellular organization. Chromosomal loci and many protein complexes are positioned at particular subcellular sites. In this review, we examine recently discovered control mechanisms that make use of dynamically localized protein complexes to orchestrate the Caulobacter crescentus cell cycle. Protein localization, notably of signal transduction proteins, chromosome partition proteins, and proteases, serves to coordinate cell division with chromosome replication and cell differentiation. The developmental fate of daughter cells is decided before completion of cytokinesis, via the early establishment of cell polarity by the distribution of activated signaling proteins, bacterial cytoskeleton, and landmark proteins.
Topics: Bacterial Proteins; Caulobacter; Cell Cycle; Gene Expression Regulation, Bacterial; Models, Biological; Signal Transduction
PubMed: 17709236
DOI: 10.1016/j.copbio.2007.07.007 -
FEMS Microbiology Reviews Jan 2015Recent data indicate that cell cycle transcription in many alpha-Proteobacteria is executed by at least three conserved functional modules in which pairs of antagonistic... (Review)
Review
Recent data indicate that cell cycle transcription in many alpha-Proteobacteria is executed by at least three conserved functional modules in which pairs of antagonistic regulators act jointly, rather than in isolation, to control transcription in S-, G2- or G1-phase. Inactivation of module components often results in pleiotropic defects, ranging from cell death and impaired cell division to fairly benign deficiencies in motility. Expression of module components can follow systemic (cell cycle) or external (nutritional/cell density) cues and may be implemented by auto-regulation, ancillary regulators or other (unknown) mechanisms. Here, we highlight the recent progress in understanding the molecular events and the genetic relationships of the module components in environmental, pathogenic and/or symbiotic alpha-proteobacterial genera. Additionally, we take advantage of the recent genome-wide transcriptional analyses performed in the model alpha-Proteobacterium Caulobacter crescentus to illustrate the complexity of the interactions of the global regulators at selected cell cycle-regulated promoters and we detail the consequences of (mis-)expression when the regulators are absent. This review thus provides the first detailed mechanistic framework for understanding orthologous operational principles acting on cell cycle-regulated promoters in other alpha-Proteobacteria.
Topics: Alphaproteobacteria; Caulobacter crescentus; Cell Cycle Checkpoints; Gene Expression Regulation, Bacterial; Promoter Regions, Genetic
PubMed: 25793963
DOI: 10.1093/femsre/fuu002 -
Sub-cellular Biochemistry 2017Caulobacter crescentus, an aquatic Gram-negative α-proteobacterium, is dimorphic, as a result of asymmetric cell divisions that give rise to a free-swimming swarmer... (Review)
Review
Caulobacter crescentus, an aquatic Gram-negative α-proteobacterium, is dimorphic, as a result of asymmetric cell divisions that give rise to a free-swimming swarmer daughter cell and a stationary stalked daughter. Cell polarity of vibrioid C. crescentus cells is marked by the presence of a stalk at one end in the stationary form and a polar flagellum in the motile form. Progression through the cell cycle and execution of the associated morphogenetic events are tightly controlled through regulation of the abundance and activity of key proteins. In synergy with the regulation of protein abundance or activity, cytoskeletal elements are key contributors to cell cycle progression through spatial regulation of developmental processes. These include: polarity establishment and maintenance, DNA segregation, cytokinesis, and cell elongation. Cytoskeletal proteins in C. crescentus are additionally required to maintain its rod shape, curvature, and pole morphology. In this chapter, we explore the mechanisms through which cytoskeletal proteins in C. crescentus orchestrate developmental processes by acting as scaffolds for protein recruitment, generating force, and/or restricting or directing the motion of molecular machines. We discuss each cytoskeletal element in turn, beginning with those important for organization of molecules at the cell poles and chromosome segregation, then cytokinesis, and finally cell shape.
Topics: Bacterial Proteins; Caulobacter crescentus; Cell Cycle; Cell Shape; Cytoskeletal Proteins
PubMed: 28500524
DOI: 10.1007/978-3-319-53047-5_4