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The Biochemical Journal Jul 2019Bacterial capsules have evolved to be at the forefront of the cell envelope, making them an essential element of bacterial biology. Efforts to understand the (Mtb)... (Review)
Review
Bacterial capsules have evolved to be at the forefront of the cell envelope, making them an essential element of bacterial biology. Efforts to understand the (Mtb) capsule began more than 60 years ago, but the relatively recent development of mycobacterial genetics combined with improved chemical and immunological tools have revealed a more refined view of capsule molecular composition. A glycogen-like α-glucan is the major constituent of the capsule, with lower amounts of arabinomannan and mannan, proteins and lipids. The major Mtb capsular components mediate interactions with phagocytes that favor bacterial survival. Vaccination approaches targeting the mycobacterial capsule have proven successful in controlling bacterial replication. Although the Mtb capsule is composed of polysaccharides of relatively low complexity, the concept of antigenic variability associated with this structure has been suggested by some studies. Understanding how Mtb shapes its envelope during its life cycle is key to developing anti-infective strategies targeting this structure at the host-pathogen interface.
Topics: Bacterial Capsules; Humans; Lipids; Mycobacterium tuberculosis; Polysaccharides, Bacterial; Tuberculosis Vaccines
PubMed: 31320388
DOI: 10.1042/BCJ20190324 -
Annual Review of Microbiology Sep 2020Polysaccharides are dominant features of most bacterial surfaces and are displayed in different formats. Many bacteria produce abundant long-chain capsular... (Review)
Review
Polysaccharides are dominant features of most bacterial surfaces and are displayed in different formats. Many bacteria produce abundant long-chain capsular polysaccharides, which can maintain a strong association and form a capsule structure enveloping the cell and/or take the form of exopolysaccharides that are mostly secreted into the immediate environment. These polymers afford the producing bacteria protection from a wide range of physical, chemical, and biological stresses, support biofilms, and play critical roles in interactions between bacteria and their immediate environments. Their biological and physical properties also drive a variety of industrial and biomedical applications. Despite the immense variation in capsular polysaccharide and exopolysaccharide structures, patterns are evident in strategies used for their assembly and export. This review describes recent advances in understanding those strategies, based on a wealth of biochemical investigations of select prototypes, supported by complementary insight from expanding structural biology initiatives. This provides a framework to identify and distinguish new systems emanating from genomic studies.
Topics: Bacteria; Bacterial Capsules; Bacterial Outer Membrane Proteins; Bacterial Physiological Phenomena; Biofilms; Biological Transport; Escherichia coli Proteins; Genomics; Polysaccharides; Polysaccharides, Bacterial
PubMed: 32680453
DOI: 10.1146/annurev-micro-011420-075607 -
Microbiology Spectrum Mar 2019The polysaccharide capsule of is the dominant surface structure of the organism and plays a critical role in virulence, principally by interfering with host... (Review)
Review
The polysaccharide capsule of is the dominant surface structure of the organism and plays a critical role in virulence, principally by interfering with host opsonophagocytic clearance mechanisms. The capsule is the target of current pneumococcal vaccines, but there are 98 currently recognised polysaccharide serotypes and protection is strictly serotype-specific. Widespread use of these vaccines is driving changes in serotype prevalence in both carriage and disease. This chapter summarises current knowledge on the role of the capsule and its regulation in pathogenesis, the mechanisms of capsule synthesis, the genetic basis for serotype differences, and provides insights into how so many structurally distinct capsular serotypes have evolved. Such knowledge will inform ongoing refinement of pneumococcal vaccination strategies.
Topics: Animals; Bacterial Capsules; Humans; Pneumococcal Vaccines; Polysaccharides, Bacterial; Streptococcus pneumoniae
PubMed: 30977464
DOI: 10.1128/microbiolspec.GPP3-0019-2018 -
Current Protocols in Microbiology Nov 2009Bacterial capsules are composed of high-molecular-weight polysaccharides and/or polypeptides, and are associated with virulence and biofilm formation. Unfortunately,...
Bacterial capsules are composed of high-molecular-weight polysaccharides and/or polypeptides, and are associated with virulence and biofilm formation. Unfortunately, capsules do not stain well with crystal violet, methylene blue, or other simple stains. This unit describes two methods of capsule staining. The first is a wet-mount method using india ink; the capsule is visualized as a refractile zone surrounding a cell. The second is a direct-staining dry-mount method that precipitates copper sulfate and leaves the capsule as a pale blue zone. Both methods are easily performed within approximately 5 min.
Topics: Bacteria; Bacterial Capsules; Bacterial Typing Techniques; Coloring Agents; Staining and Labeling
PubMed: 19885936
DOI: 10.1002/9780471729259.mca03is15 -
PLoS Biology Jul 2021The horizontal transfer of mobile DNA is one of the signature moves of bacterial evolution, but the specific rules that govern this transfer remain elusive. In this PLOS...
The horizontal transfer of mobile DNA is one of the signature moves of bacterial evolution, but the specific rules that govern this transfer remain elusive. In this PLOS Biology issue, Haudiquet and colleagues revealed that the interactions between mobile genetic elements and the bacterial capsule shape the horizontal flow of DNA in an important bacterial pathogen.
Topics: Bacteria; Bacterial Capsules; Gene Transfer, Horizontal
PubMed: 34228713
DOI: 10.1371/journal.pbio.3001308 -
Current Opinion in Microbiology Apr 2020For ∼30 years, two distinct groups of clinical isolates of Klebsiella pneumoniae have been recognized. Classical strains (cKp) are typically isolated from patients... (Review)
Review
For ∼30 years, two distinct groups of clinical isolates of Klebsiella pneumoniae have been recognized. Classical strains (cKp) are typically isolated from patients with some degree of immunocompromise and are not virulent in mouse models of infection whereas hypervirulent strains (hvKp) are associated with community acquired invasive infections and are highly virulent in mouse models of infection. Hyperproduction of capsule and a hypermucoviscous colony phenotype have been strongly associated with the hypervirulence of hvKp strains. Recent studies have begun to elucidate the relationship between capsule gene expression, hypermucoviscosity and hypervirulence. Additionally, genes associated with hyperproduction of capsule and hypermucoviscosity in hvKp strains have been identified in a few cKp isolates. However, it is not clear how the acquisition of these genes impacts the virulence of cKp isolates. A better understanding of the potential risks of these strains is particularly important given that many of them are resistant to multiple antibiotics, including carbapenems.
Topics: Animals; Bacterial Capsules; Bacterial Proteins; Gene Expression Regulation, Bacterial; Genes, Bacterial; Humans; Klebsiella Infections; Klebsiella pneumoniae; Mice; Mutation; Virulence; Virulence Factors
PubMed: 32062153
DOI: 10.1016/j.mib.2020.01.006 -
Microbiology and Molecular Biology... Sep 2016Klebsiella pneumoniae causes a wide range of infections, including pneumonias, urinary tract infections, bacteremias, and liver abscesses. Historically, K. pneumoniae... (Review)
Review
Klebsiella pneumoniae causes a wide range of infections, including pneumonias, urinary tract infections, bacteremias, and liver abscesses. Historically, K. pneumoniae has caused serious infection primarily in immunocompromised individuals, but the recent emergence and spread of hypervirulent strains have broadened the number of people susceptible to infections to include those who are healthy and immunosufficient. Furthermore, K. pneumoniae strains have become increasingly resistant to antibiotics, rendering infection by these strains very challenging to treat. The emergence of hypervirulent and antibiotic-resistant strains has driven a number of recent studies. Work has described the worldwide spread of one drug-resistant strain and a host defense axis, interleukin-17 (IL-17), that is important for controlling infection. Four factors, capsule, lipopolysaccharide, fimbriae, and siderophores, have been well studied and are important for virulence in at least one infection model. Several other factors have been less well characterized but are also important in at least one infection model. However, there is a significant amount of heterogeneity in K. pneumoniae strains, and not every factor plays the same critical role in all virulent Klebsiella strains. Recent studies have identified additional K. pneumoniae virulence factors and led to more insights about factors important for the growth of this pathogen at a variety of tissue sites. Many of these genes encode proteins that function in metabolism and the regulation of transcription. However, much work is left to be done in characterizing these newly discovered factors, understanding how infections differ between healthy and immunocompromised patients, and identifying attractive bacterial or host targets for treating these infections.
Topics: Anti-Bacterial Agents; Bacterial Capsules; Bacterial Outer Membrane Proteins; Drug Resistance, Multiple, Bacterial; Fimbriae, Bacterial; Humans; Immunocompromised Host; Klebsiella Infections; Klebsiella pneumoniae; Lipopolysaccharides; Siderophores; Virulence Factors
PubMed: 27307579
DOI: 10.1128/MMBR.00078-15 -
Proceedings. Biological Sciences Mar 2021The fitness cost associated with the production of bacterial capsules is considered to be offset by the protection provided by these extracellular structures against...
The fitness cost associated with the production of bacterial capsules is considered to be offset by the protection provided by these extracellular structures against biotic aggressions or abiotic stress. However, it is unknown if the capsule contributes to fitness in the absence of these. Here, we explored conditions favouring the maintenance of the capsule in where the capsule is known to be a major virulence factor. Using short-term experimental evolution on different strains, we showed that small environmental variations have a strong impact on the maintenance of the capsule. Capsule inactivation is frequent in nutrient-rich, but scarce in nutrient-poor media. Competitions between wild-type and capsule mutants in nine different strains confirmed that the capsule is costly in nutrient-rich media. Surprisingly, these results also showed that the presence of a capsule provides a clear fitness advantage in nutrient-poor conditions by increasing both growth rates and population yields. The comparative analyses of the wild-type and capsule mutants reveal complex interactions between the environment, genetic background and serotype even in relation to traits known to be relevant during pathogenesis. In conclusion, our data suggest there are novel roles for bacterial capsules yet to be discovered and further supports the notion that the capsule's role in virulence may be a by-product of its contribution to bacterial adaptation outside the host.
Topics: Bacterial Capsules; Klebsiella; Klebsiella pneumoniae; Nutrients; Virulence
PubMed: 33653142
DOI: 10.1098/rspb.2020.2876 -
Journal of the American Chemical Society Jan 2024Great effort has been made to encapsulate or coat living mammalian cells for a variety of applications ranging from diabetes treatment to three-dimensional printing....
Great effort has been made to encapsulate or coat living mammalian cells for a variety of applications ranging from diabetes treatment to three-dimensional printing. However, no study has reported the synthesis of a biomimetic bacterial capsule to display high-affinity aptamers on the cell surface for enhanced cell recognition. Therefore, we synthesized an ultrathin alginate-polylysine coating to display aptamers on the surface of living cells with natural killer (NK) cells as a model. The results show that this coating-mediated aptamer display is more stable than direct cholesterol insertion into the lipid bilayer. The half-life of the aptamer on the cell surface can be increased from less than 1.5 to over 20 h. NK cells coated with the biomimetic bacterial capsule exhibit a high efficiency in recognizing and killing target cells. Therefore, this work has demonstrated a promising cell coating method for the display of aptamers for enhanced cell recognition.
Topics: Animals; Aptamers, Nucleotide; Bacterial Capsules; Biomimetics; Cell Membrane; SELEX Aptamer Technique; Mammals
PubMed: 38153404
DOI: 10.1021/jacs.3c11208 -
Critical Reviews in Microbiology Sep 2016Neisseria meningitidis, a devastating pathogen exclusive to humans, expresses capsular polysaccharides that are the major meningococcal virulence determinants and the... (Review)
Review
Neisseria meningitidis, a devastating pathogen exclusive to humans, expresses capsular polysaccharides that are the major meningococcal virulence determinants and the basis for successful meningococcal vaccines. With rare exceptions, the expression of capsule (serogroups A, B, C, W, X, Y) is required for systemic invasive meningococcal disease. Changes in capsule expression or structure (e.g. hypo- or hyper-encapsulation, capsule "switching", acetylation) can influence immunologic diagnostic assays or lead to immune escape. The loss or down-regulation of capsule is also critical in meningococcal biology facilitating meningococcal attachment, microcolony formation and the carriage state at human mucosal surfaces. Encapsulated meningococci contain a cps locus with promoters located in an intergenic region between the biosynthesis and the conserved capsule transport operons. The cps intergenic region is transcriptionally regulated (and thus the amount of capsule expressed) by IS element insertion, by a two-component system, MisR/MisS and through sequence changes that result in post-transcriptional RNA thermoregulation. Reversible on-off phase variation of capsule expression is controlled by slipped strand mispairing of homo-polymeric tracts and by precise insertion and excision of IS elements (e.g. IS1301) in the biosynthesis operon. Capsule structure can be altered by phase-variable expression of capsular polymer modification enzymes or "switched" through transformation and homologous recombination of different polymerases. Understanding the complex regulation of meningococcal capsule has important implications for meningococcal biology, pathogenesis, diagnostics, current and future vaccine development and vaccine strategies.
Topics: Animals; Bacterial Capsules; Bacterial Proteins; Gene Expression Regulation, Bacterial; Humans; Meningococcal Infections; Neisseria meningitidis
PubMed: 26089023
DOI: 10.3109/1040841X.2015.1022507