Type II Secretion System
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The Mosaic Type IV Secretion Systems
- Author: Peter J. Christie
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Citation: Christie P. 2016. The Mosaic Type IV Secretion Systems, EcoSal Plus 2016; doi:10.1128/ecosalplus.ESP-0020-2015
- DOI 10.1128/ecosalplus.ESP-0020-2015
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Abstract:
Escherichia coli and other Gram-negative and -positive bacteria employ type IV secretion systems (T4SSs) to translocate DNA and protein substrates, generally by contact-dependent mechanisms, to other cells. The T4SSs functionally encompass two major subfamilies, the conjugation systems and the effector translocators. The conjugation systems are responsible for interbacterial transfer of antibiotic resistance genes, virulence determinants, and genes encoding other traits of potential benefit to the bacterial host. The effector translocators are used by many Gram-negative pathogens for delivery of potentially hundreds of virulence proteins termed effectors to eukaryotic cells during infection. In E. coli and other species of Enterobacteriaceae, T4SSs identified to date function exclusively in conjugative DNA transfer. In these species, the plasmid-encoded systems can be classified as the P, F, and I types. The P-type systems are the simplest in terms of subunit composition and architecture, and members of this subfamily share features in common with the paradigmatic Agrobacterium tumefaciens VirB/VirD4 T4SS. This review will summarize our current knowledge of the E. coli systems and the A. tumefaciens P-type system, with emphasis on the structural diversity of the T4SSs. Ancestral P-, F-, and I-type systems were adapted throughout evolution to yield the extant effector translocators, and information about well-characterized effector translocators also is included to further illustrate the adaptive and mosaic nature of these highly versatile machines.
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Multifaceted Functions of NOD-Like Receptor Proteins in Myeloid Cells at the Intersection of Innate and Adaptive Immunity
- Authors: Thomas A. Kufer, Giulia Nigro, Philippe J. Sansonetti
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Citation: Kufer T, Nigro G, Sansonetti P. 2016. Multifaceted functions of nod-like receptor proteins in myeloid cells at the intersection of innate and adaptive immunity. 4(4): doi:10.1128/microbiolspec.MCHD-0021-2015
- DOI 10.1128/microbiolspec.MCHD-0021-2015
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NOD-like receptor (NLR) proteins, as much as Toll-like receptor proteins, play a major role in modulating myeloid cells in their immune functions. There is still, however, limited knowledge on the expression and function of several of the mammalian NLR proteins in myeloid lineages. Still, the function of pyrin domain-containing NLR proteins and NLRC4/NAIP as inflammasome components that drive interleukin-1β (IL-1β) and IL-18 maturation and secretion upon pathogen stimulation is well established. NOD1, NOD2, NLRP3, and NLRC4/NAIP act as bona fide pattern recognition receptors (PRRs) that sense microbe-associated molecular patterns (MAMPs) but also react to endogenous danger-associated molecular patterns (DAMPs). Ultimately, activation of these receptors achieves macrophage activation and maturation of dendritic cells to drive antigen-specific adaptive immune responses. Upon infection, sensing of invading pathogens and likely of DAMPs that are released in response to tissue injury is a process that involves multiple PRRs in both myeloid and epithelial cells, and these act in concert to design tailored, pathogen-adapted immune responses by induction of different cytokine profiles, giving rise to appropriate lymphocyte polarization.
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Metabolism and Pathogenicity of Pseudomonas aeruginosa Infections in the Lungs of Individuals with Cystic Fibrosis
- Authors: Gregory C. Palmer, Marvin Whiteley
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Citation: Palmer G, Whiteley M. 2015. Metabolism and pathogenicity of pseudomonas aeruginosa infections in the lungs of individuals with cystic fibrosis. 3(4): doi:10.1128/microbiolspec.MBP-0003-2014
- DOI 10.1128/microbiolspec.MBP-0003-2014
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Individuals with the genetic disease cystic fibrosis (CF) accumulate mucus or sputum in their lungs. This sputum is a potent growth substrate for a range of potential pathogens, and the opportunistic bacterium Pseudomonas aeruginosa is generally most difficult of these to eradicate. As a result, P. aeruginosa infections are frequently maintained in the CF lung throughout life, and are the leading cause of death for these individuals. While great effort has been expended to better understand and treat these devastating infections, only recently have researchers begun to rigorously examine the roles played by specific nutrients in CF sputum to cue P. aeruginosa pathogenicity. This chapter summarizes the current state of knowledge regarding how P. aeruginosa metabolism in CF sputum affects initiation and maintenance of these infections. It contains an overview of CF lung disease and the mechanisms of P. aeruginosa pathogenicity. Several model systems used to study these infections are described with emphasis on the challenge of replicating the chronic infections observed in humans with CF. Nutrients present in CF sputum are surveyed, and the impacts of these nutrients on the infection are discussed. The chapter concludes by addressing the future of this line of research including the use of next-generation technologies and the potential for metabolism-based therapeutics.
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Genotypic Changes in Enterohemorrhagic Escherichia coli During Human Infection
- Authors: Alexander Mellmann, Martina Bielaszewska, Helge Karch
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Source: Genome Plasticity and Infectious Diseases , pp 16-26
Publication Date :
January 2012
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The chapter begins with an overview of epidemiology and clinical pathogenesis of Enterohemorrhagic Escherichia coli (EHEC). EHEC causes diarrhea, bloody diarrhea, and hemolytic-uremic syndrome (HUS). The major virulence factor of EHEC responsible for the microvascular endothelial injury is Shiga toxin (Stx). In additon to Stx, several other potential virulence determinants have been identified in EHEC. Next, the chapter focuses on genomes of EHEC. The lability of horizontally acquired genomic elements, such as pathogenicity islands, and especially of bacteriophages, increases the possibility of genomic alterations during human infections. Most EHEC strains possess one or more large plasmids. To investigate genetic changes of EHEC in patients with HUS, consecutive stool samples from such patients was analyzed by detecting stx and eae genes and by using a cytotoxicity assay to detect free Stx. Further, the chapter talks about interserotype differences in conversion of EHEC to EHEC-LST, and consequences of in vivo genetic changes in EHEC. To identify both EHEC and EHEC-LST in stool samples, detection of stx must be complemented by detection of stx-independent target(s) which are common to both pathotypes. Genetic changes in EHEC during infection might influence clinical outcome and have impacts on diagnosis, epidemiology, and evolution. For clinicians, awareness of a potential conversion of the pathotype of the infecting EHEC during infection is essential in making decisions about correct management of the patients and appropriate therapies.
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Genome Plasticity in Legionella pneumophila and Legionella longbeachae: Impact on Host Cell Exploitation
- Authors: L. Gomez Valero, C. Rusniok, C. Buchrieser
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Source: Genome Plasticity and Infectious Diseases , pp 58-83
Publication Date :
January 2012
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This chapter starts with a description of the general characteristics of the genome sequences of Legionella pneumophila and Legionella longbeachae. It then highlights the characteristic features and common traits of the two main human-pathogenic Legionella species. Emphasis is given to putative virulence and Legionella life cycle-related functions. In the second part, the focus is on the comparison of these genome sequences, in order to learn about the plasticity of the Legionella genomes and the possible mechanisms involved. In the third part, the possible evolution of the identified virulence factors are analyzed and discussed. Finally, future perspectives in Legionella genomics are presented. L. longbeachae NSW 150 encodes four T4SS, a rather exceptional number and L. longbeachae D-4968 encodes two T4SS. The authors found that IcmE/DotG of L. longbeachae (1,525 amino acids) is 477 amino acids larger than that of L. pneumophila (1,048 amino acids). Most of the T4SS are located on regions of genome plasticity; some even show plasticity on the gene/protein level, as shown above for DotG. The authors undertook a phylogenetic analysis for the L. longbeachae protein Llo2643, which contains PPR repeats, a protein family typically present in plants. In the last few years, genome analyses, as well as comparative and functional genomics, have demonstrated that genome plasticity plays a major role in differences in host cell exploitation and niche adaptation of Legionella.
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Impacts of Fecal Bacteria on Human and Animal Health—Pathogens and Virulence Genes
- Author: Timothy J. Johnson
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Source: The Fecal Bacteria , pp 135-164
Publication Date :
January 2011
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The presence of pathogens in our food and water supplies represents a significant risk to human and animal health. This chapter focuses on the most commonly occurring human pathogens of Enterobacteriaceae, such as Citrobacter, Enterobacter, Escherichia, Klebsiella, Proteus, Salmonella, Shigella, and Yersinia spp. Of these, special attention is given to pathogenic E. coli, which is the most diverse and studied member of Enterobacteriaceae. The types of disease caused by E. coli are grossly classified as either intestinal or extraintestinal. Six pathotypes of intestinal pathogenic E. coli are recognized, each with virulence factors making them distinct. Extraintestinal pathogenic E. coli, or ExPEC, is a broad group of pathogens that colonize the extraintestinal compartment of animal and human hosts, resulting in such diverse conditions as urinary tract infection, meningitis, peritonitis, and septicemia. Enterohemorrhagic E. coli (EHEC; sometimes referred to as Shiga toxin-producing E. coli, or STEC, or members thereof ) are another diarrheal pathotype, well known for their ability to cause diarrhea, hemorrhagic colitis (HC), and hemolytic uremic syndrome (HUS). This chapter focuses on the pathogens and virulence genes of the Salmonella serovars implicated in foodborne gastroenteritis. It also focuses on the virulence genes of these pathogens with regard to genomic content. Already underway, the postgenomic era will lead to a better understanding of the importance of these genomic traits as they pertain to infection within humans.
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Insights from Genomic Studies of the Foodborne and Waterborne Pathogen Escherichia coli O157:H7
- Authors: Victor P. J. Gannon, Chad R. Laing, Yongxiang Zhang
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Source: Genomes of Foodborne and Waterborne Pathogens , pp 1-21
Publication Date :
January 2011
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In this chapter, the knowledge of the genome of E. coli O157:H7 may be used in the control of serious foodborne pathogen, E. coli strains are associated with gastrointestinal and extraintestinal illness. The E. coli O157:H7 genome provides us with information about the evolution and emergence of pathogen and the diversity that exists within populations of E. coli O157:H7. Most of E. coli prophage are defective and cannot form infectious phage. This chapter provides a brief review of subtyping methods used to characterize E. coli O157:H7 strains. Differences in biochemical utilization can be used to distinguish large categories of E. coli strain. Following the generation of cDNA from the bacteria’s mRNA using the enzyme reverse transcriptase, the level of gene expression is inferred from the intensity of the label signal from gene-specific microarray spots following hybridization. This procedure is the foundation of the new science of transcriptomics. Typically, quantitative PCR assays are also carried out on selected genes to measure mRNA levels to verify the significant changes in expression of genes observed in microarray-based transcriptomics studies. It is also evident that our understanding of E. coli O157:H7 gene regulatory systems will be enhanced through genomic sciences. E. coli O157:H7 and other bacterial pathogens have evolved through the acquisition of gene clusters borne on plasmids, bacteriophages, and genomic islands. Finally, with the arrival of the genomics revolution researchers are able to examine the "pan-genome" of the species and specific groups within species such as enterohemorrhagic E. coli(EHEC) and E. coli O157:H7.
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Shigella Genomes: a Tale of Convergent Evolution and Specialization through IS Expansion and Genome Reduction
- Authors: Jian Yang, Vartul Sangal, Qi Jin, Jun Yu
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Source: Genomes of Foodborne and Waterborne Pathogens , pp 23-39
Publication Date :
January 2011
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Although all Shigella species share similar pathogenic properties, each species exhibits peculiar epidemiological characteristics. S. dysenteriae, S. flexneri, and S. boydii are most common in developing countries, whereas S. sonnei is more prevalent in developed countries. A remarkable difference between Shigella and E. coli genomes is the presence of pseudogenes in the former. The second remarkable feature of the Shigella genome is the presence of enormous copies of IS elements, which are likely the cause of genomic rearrangements, including deletions, inversions, and translocations that may effectively disrupt the colinearity among different Shigella genomes. After the acquisition of the ancestral forms of the virulence plasmid by Shigella/enteroinvasive E. coli (EIEC), genome reduction by inactivation of the pathway-specific antivirulence loci (AVL) is vital for adaptation in the cytosolic niche. Similar to obligate pathogens, reduced selection pressure might have played an important role in Shigella genome reduction, which may have further accelerated terminal evolution and resulted in the increased host specificity. Numerous genes responsible for cell motility cell envelope, carbohydrate transport, and metabolism that are present in E. coli were frequently lost in Shigella. A combination of various strategies using the basic information provided by genomic research will be helpful in efficient control and prevention of Shigella infections.
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The Streptococcus-Veillonella Community: How Genome Sequencing Aids Our Understanding of Interspecies Interaction
- Authors: Fengxia Qi, Joseph J. Ferretti
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Source: Oral Microbial Communities , pp 357-370
Publication Date :
January 2011
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This chapter integrates unpublished data with the published reports on the synergism between veillonellae and streptococci. It speculates on how the genome sequence of veillonellae will help one understand its biology and potential role in the pathogenicity of the dental biofilm community. It was discovered that hydrogen peroxide (H2O2) resistance in Streptococcus mutans was increased 100 to 1,000-fold over monospecies culture in cocultures with Veillonella sp. strain PK1910. This chapter focuses on some important findings from the Veillonella sp. strain PK1910 genome. In the 1964 description of Veillonellasp. by Rogosa, the species V. alcalescens was distinguished from V. parvula by the ability to decompose H2O2. In the 1982 revision of the species, the former subspecies in V. alcalescens were classified as three species: V. ratti, V. criceti, and V. dispar. Veillonella species are among the most prevalent early colonizers of oral biofilm. In-depth investigations on the mechanism of interactions of veillonellae with other oral microbial species will contribute significantly to one's overall understanding of the ecology of oral biofilms in the human host. Different from a metagenomics approach, metatranscriptomics focuses on community member functions at a particular time under a particular condition.
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Shiga Toxin-Producing Escherichia Coli
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Source: Population Genetics of Bacteria , pp 199-223
Publication Date :
January 2011
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This chapter discusses the emergence and impact of shiga toxin-producing Escherichia coli (STEC) in human disease, the biology of the Shiga toxins (Stx) family, and approaches to diagnosis, treatment, and prevention of infection with STEC. The occurrence of the seminal STEC outbreaks highlighted the need to implement laboratory methods to readily detect E. coli O157:H7. Although early characterization of STEC strains was made possible by Whittam’s multilocus enzyme electrophoresis (MLEE) method, genetic techniques now allow comparison of strains at the nucleotide level. The current model of the predominant pathway by which Stx intoxicates sensitive cells is as follows: (i) the B pentamer of holotoxin binds to Gb3 within lipid rafts; (ii) the entire receptor-holotoxin complex is endocytosed; (iii) the complex moves by retrograde transport to the Golgi and then to the endoplasmic reticulum; and (iv) the A1 subunit is released into the cytoplasm, where it targets the ribosome. Although transduction of stx genes into E. coli via bacteriophages was crucial to the emergence of STEC, the biology of these toxin-converting phages also contributes significantly to the degree of toxin expression and hence the virulence exhibited by STEC. Although the pathogenicity of various STEC strains that synthesize different types of Stx2 cannot be compared directly because the strains are not isogenic, the authors have found that an O91 strain that produces Stx2 is not virulent in the streptomycin-treated mouse model for STEC infection, whereas O91 strains that produce Stx2d-activatable are highly virulent in those mice.
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Molecular Evolution of Enterohemorrhagic Escherichia coli and Application to Epidemiology
- Authors: Galeb S. Abu-Ali, A. Cody Springman, Lindsey M. Ouellette, Lukas Wick, Weihong Qi, Sivapriya Kalisan Vanaja, Teresa M. Bergholz, David W. Lacher, Seth T. Walk, Jillian A. Tietjen, Hans Steinsland, James T. Riordan, Shannon D. Manning
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Source: Population Genetics of Bacteria , pp 287-302
Publication Date :
January 2011
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Tom Whittam's pioneering research into the structure of Escherichia coli populations not only advanced the field of microbial evolution and genetics, but it also provided a contextual framework for investigating variation in the epidemiology and virulence of bacterial populations. This chapter highlights the work of his laboratory involving the use of various population genetic strategies for characterizing E. coli pathotypes, particularly enterohemorrhagic E. coli (EHEC) O157:H7, while focusing on contributions to epidemiology and public health. To determine whether specific genotypes are associated with human enteric disease, multilocus enzyme electrophoresis (MLEE) was used to examine 1,300 E. coli strains representing 16 serotypes, including EHEC O157:H7 from patients with hemorrhagic colitis and hemolytic uremic syndrome (HUS). Similar to MLEE and multilocus sequence typing (MLST) data, systematic analysis of single nucleotide polymorphisms (SNPs) is amenable to both population genetic and phylogenetic analyses. SNPs data can also be used to examine epidemiological associations between bacterial genotypes and clinical disease. By using the SNP genotyping phylogeny as a framework, it is possible to investigate virulence gene diversity, allelic variation, and gene expression differences among genotypes to identify bacterial genomic determinants of colonization, pathogenesis, and transmissibility. The chapter describes differences in stress resistance properties among clades, nonrandom distribution of stx variants, variation in adherence to epithelial cells, and differential expression among shared genes.
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Biogenesis and Membrane Targeting of Lipoproteins
- Authors: Shin-Ichiro Narita, and Hajime Tokuda
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Citation: Narita S, Tokuda H. 2010. Biogenesis and Membrane Targeting of Lipoproteins, EcoSal Plus 2010; doi:10.1128/ecosalplus.4.3.7
- DOI 10.1128/ecosalplus.4.3.7
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Bacterial lipoproteins represent a unique class of membrane proteins, which are anchored to membranes through triacyl chains attached to the amino-terminal cysteine. They are involved in various functions localized in cell envelope. Escherichia coli possesses more than 90 species of lipoproteins, most of which are localized in the outer membrane, with others being in the inner membrane. All lipoproteins are synthesized in the cytoplasm with an N-terminal signal peptide, translocated across the inner membrane by the Sec translocon to the periplasmic surface of the inner membrane, and converted to mature lipoproteins through sequential reactions catalyzed by three lipoprotein-processing enzymes: Lgt, LspA, and Lnt. The sorting of lipoproteins to the outer membrane requires a system comprising five Lol proteins. An ATP-binding cassette transporter, LolCDE, initiates the sorting by mediating the detachment of lipoproteins from the inner membrane. Formation of the LolA-lipoprotein complex is coupled to this LolCDE-dependent release reaction. LolA accommodates the amino-terminal acyl chain of lipoproteins in its hydrophobic cavity, thereby generating a hydrophilic complex that can traverse the periplasmic space by diffusion. Lipoproteins are then transferred to LolB on the outer membrane and anchored to the inner leaflet of the outer membrane by the action of LolB. In contrast, since LolCDE does not recognize lipoproteins possessing Asp at position +2, these lipoproteins remain anchored to the inner membrane. Genes for Lol proteins are widely conserved among gram-negative bacteria, and Lol-mediated outer membrane targeting of lipoproteins is considered to be the general lipoprotein localization mechanism.
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Strain Improvement of Escherichia coli To Enhance Recombinant Protein Production
- Authors: Michael E. Pyne, Karan S. Sukhija, C. Perry Chou
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Source: Manual of Industrial Microbiology and Biotechnology, Third Edition , pp 273-286
Publication Date :
January 2010
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Typically, the biotechnological basis for strain improvement to enhance recombinant protein production relies on the permanent implementation of desirable traits into the production strain to stimulate both cell growth and functional expression of the target gene during the cultivation. This chapter reviews the major technical issues associated with Escherichia coli strain engineering to enhance recombinant protein production and directs the reader to protocols appropriate for specific applications. Theoretically, strategies based on enhancing the limiting step can lead to an overall improvement in recombinant protein production. Stationary-phase genes encode proteins that may lead to a reduction in cellular and metabolic activity, which can negatively affect recombinant protein production, and as such, these genes are targets for strain improvement. The recently commercialized recombineering protocol from Gene Bridges, also based on λ Redmediated recombination, allows versatile chromosomal engineering, including gene disruption, deletion, insertion, point mutation, modification, and even promoter fine-tuning, and can serve as a versatile manipulation tool for strain improvement and even optimization. The general guidelines for strain improvement are (i) to ensure the genetic stability of the host/vector system, (ii) to maximize the synthesis fluxes for all the gene expression steps (i.e., transcription, translation, and posttranslational processing steps), (iii) to ensure the flux balance of these protein synthesis steps, (iv) to stabilize all the expression intermediates and final products, and (v) to minimize the physiological impact associated with high-level gene expression and high-cell density cultivation.
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Legionella pneumophila, a Pathogen of Amoebae and Macrophages
- Authors: Michele S. Swanson, Andrew Bryan
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Source: Phagocyte-Pathogen Interactions , pp 393-403
Publication Date :
January 2009
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Most Legionella species, including Legionella pneumophila, are aquatic microbes; other species thrive in soil. There, the microbe naturally infects amoebae and protozoa, but, when given the opportunity, L. pneumophila can infect human alveolar macrophages and cause the severe pneumonia Legionnaires’ disease. In particular, the phagosomal transporter protein A (PhtA) enables intracellular bacteria to acquire threonine from macrophages and amoebae, whereas PhtJ behaves as a valine transporter, and PhtC and PhtD are critical for thymidine assimilation. In some manner, the secreted proteins promote growth of L. pneumophila in amoebae, macrophages derived from human peripheral blood, and the lungs of A/J mice, as judged by comparing the yield of type II secretion-competent L. pneumophila with corresponding mutants. The prevailing concept holds that, to replicate in macrophages, L. pneumophila intercepts vesicular traffic from the secretory pathway. For example, in the absence of RalF or SidM, L. pneumophila nevertheless replicates efficiently in amoebae and macrophages. Moreover, when compared with restrictive C57Bl/6 mouse macrophages, permissive A/J naip5 macrophages that are subjected to amino acid starvation exhibit markedly slower maturation of autophagosomes. In the absence of SdhA, L. pneumophila induces mitochondrial damage, caspase activation, and cell death of A/J mouse macrophages, and the intracellular mutant bacteria cannot replicate. Like SdhA, SidH contributes to L. pneumophila growth in mouse macrophages, but not human monocytic cells or D. discoideum. After ingestion by macrophages, L. pneumophila encounters multiple arms of the innate immune system.
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Quorum Sensing in the Soft-Rot Erwinias
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Source: Chemical Communication among Bacteria , pp 185-199
Publication Date :
January 2008
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One of the first bacterial species for which N-acylhomoserine lactone (AHL) quorum sensing (QS) was described was Erwinia carotovora. Since then, QS has been well studied in the soft-rot erwinias, where, as described in this chapter, QS plays a key role in the regulation of secreted plant cell wall-degrading enzymes (PCWDEs) production and hence in virulence. In certain strains, a well-defined AHL QS system also controls production of β-lactam antibiotic, carbapenem. In addition, it must be emphasized that QS is only one of many regulatory inputs into virulence factor production in Erwinia. The majority of the key secreted virulence factors of E. carotovora and E. chrysanthemi, including multiple Pels, Peh, Cel, and Svx, are secreted by a type II secretion system known as the Out system. There have been two reports describing the existence of AHL QS in E. amylovora. First, production of a single AHL, most likely 3-oxo-C6-HSL, was described for several Italian strains of E. amylovora; for one strain, production of AHL was observed in planta. Second, AHL activity was detected in the culture supernatant of a Swiss strain of E. amylovora. Both reports describe the detection and partial sequencing of pairs of convergent luxIR homologues, named eamIR.
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Signal Trafficking with Bacterial Outer Membrane Vesicles
- Authors: Lauren Mashburn-Warren, Marvin Whiteley
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Source: Chemical Communication among Bacteria , pp 333-344
Publication Date :
January 2008
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The gram-negative bacterium Pseudomonas aeruginosa is a ubiquitous opportunistic pathogen that causes infection in immunocompromised individuals, including those with the heritable disease cystic fibrosis (CF). Quorum sensing (QS) has been proposed to be important for colonization of the CF lung, and virulence studies indicate that inactivation of QS in P. aeruginosa significantly reduces virulence in mammalian, plant, and insect models. Pseudomonas quinolone signal (PQS) biosynthesis proceeds through a head-to- head condensation of anthranilic acid and β-keto-decanoic acid to form the immediate precursor of PQS, 2-heptyl-4-quinolone (HHQ). This chapter focuses on membrane vesicles (MVs), including their potential use as trafficking vehicles for a variety of cargo, including cell-cell signals. To be utilized as trafficking vehicles, MVs must (i) have the ability to deliver their cargo to other cells and (ii) possess physiologically relevant cargo, necessitating transfer between cells. MVs isolated from P. aeruginosa have significant antimicrobial activity, particularly against gram-positive bacteria. This antimicrobial activity is multifaceted, including both small molecule and protein components. Recent studies using thin sectioning and transmission electron microscopy revealed that MVs were consistently present in the biofilm EPS matrix.
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Fimbriae: Classification and Biochemistry
- Authors: David G. Thanassi, Sean-Paul Nuccio, Stephane Shu Kin So, and Andreas J. Bäumler
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Citation: Thanassi D, Nuccio S, Shu Kin So S, Bäumler A. 2007. Fimbriae: Classification and Biochemistry, EcoSal Plus 2007; doi:10.1128/ecosalplus.2.4.2.1
- DOI 10.1128/ecosalplus.2.4.2.1
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Proteinaceous, nonflagellar surface appendages constitute a variety of structures, including those known variably as fimbriae or pili. Constructed by distinct assembly pathways resulting in diverse morphologies, fimbriae have been described to mediate functions including adhesion, motility, and DNA transfer. As these structures can represent major diversifying elements among Escherichia and Salmonella isolates, multiple fimbrial classification schemes have been proposed and a number of mechanistic insights into fimbrial assembly and function have been made. Herein we describe the classifications and biochemistry of fimbriae assembled by the chaperone/usher, curli, and type IV pathways.
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Understanding the Model and the Menace: a Postgenomic View of Escherichia coli
- Authors: Roy R. Chaudhuri, Gavin H. Thomas
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Source: Bacterial Pathogenomics , pp 21-48
Publication Date :
January 2007
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This chapter discusses the insights into pathogenicity and the wider processes of Escherichia coli genome evolution that have resulted from the sequencing of the E. coli K-12 genome, and, more recently, those from a number of pathogenic E. coli strains, including several from the related “genus” Shigella. It also discusses the available resources for E. coli genomics and the progress that has been made in recent years toward a complete understanding of E. coli biology. Genes that are acquired by horizontal transfer subsequently undergo a process of amelioration as their base composition becomes acclimatized to the new host. Programs such as BLAST can be used to identify unexpected similarities between genes in phylogenetically distinct species, although it should be noted that BLAST results do not necessarily correspond to those from more robust phylogenetic analyses. Interestingly, strains classified as group B2 are rarely found as human commensals, and the group includes many strains with extraintestinal pathogenic E. coli (ExPEC) virulence determinants. As with enterohemorrhagic E. coli (EHEC) O157:H7, Shigella flexneri serotype 2a was an obvious target for whole-genome sequencing because of its importance as a pathogen. The processes of E. coli genome evolution are clear from the genome sequences already available.
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Genomic Analysis of Plant Pathogenic Bacteria
- Authors: Gail M. Preston, David S. Guttman, Ian Toth
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Source: Bacterial Pathogenomics , pp 392-418
Publication Date :
January 2007
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This chapter provides an overview of how genome sequence data are changing our understanding of the mechanisms and evolution of plant pathogenesis, and discusses the opportunities and challenges genome data present for future research. The majority of plant pathogenic bacteria contain large numbers of genomic islands, and it is clear that in many cases they play an essential role in disease. Genes encoding the P. syringae phytotoxins coronatine and syringomycin reside on PIs, as do their recently discovered counterparts in E. carotovora subsp. atroseptica SCR1043. Pathogenicity and virulence factors have received the greatest focus in the genomic analysis of plant pathogens. Protein secretion systems are essential for pathogenesis in most plant pathogenic bacteria and have been extensively studied, particularly in proteobacterial pathogens. The phytohormones indole-3-acetic acid (IAA or auxin) is produced by many phytopathogenic bacteria. IAA production has been shown to contribute to in planta and epiphytic growth, virulence, and the regulation of syringomycin in P. syringae. Genome analyses of plant pathogens have highlighted three aspects of physiological adaptation to life on plants: specialization, innovation, and flexibility. A largely uninvestigated element in understanding the content and function of plant pathogen genomes, particularly the genomes of facultative plant pathogens, rests on understanding what plant pathogenic bacteria do when not causing disease.
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INDEX
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Source: Bacterial Pathogenomics
Publication Date :
January 2007
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No descriptions available.
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