Scanning Electron Microscopy
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Earth's Icy Biosphere
- Authors: John C. Priscu, Brent C. Christner
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Source: Microbial Diversity and Bioprospecting , pp 130-145
Publication Date :
January 2004
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Abstract:
Studies of Earthly ice-bound microbes are relevant to the evolution and persistence of life on extraterrestrial bodies. Great diversity of icy environments make up Earth's cold biosphere. This chapter describes research conducted in laboratories on the newly discovered life associated with permanent Antarctic lake ice, glaciers and ice sheets (polar and temperate), and sub-glacial Antarctic lakes. Molecular-based approaches to microbial ecology yield data that measure the natural evolutionary relationships between microorganisms. The chapter illustrates the phylogenetic relatedness, based on 16S rDNA identity, between bacteria recovered in the laboratories and by others from Antarctica and permanently cold nonpolar locales. As indicated, these psychrophilic and psychrotrophic isolates originate from locations ranging from aquatic and marine ecosystems to terrestrial soils and glacial ice, with little in common between these environments except that all are permanently cold or frozen. Such information, coupled with a dedicated effort to further investigate microbial diversity within the planet's frozen realms, will provide the perspective necessary to understand the evolution and ecological impacts of microbial ecosystems residing within Earth's icy biosphere.
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Methodological Approaches to Analysis of Adhesins and Adhesion
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Source: Bacterial Adhesion to Animal Cells and Tissues , pp 19-42
Publication Date :
January 2003
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Abstract:
The study of mechanisms of adhesion vary from simple methods providing limited information to more complex methods that are difficult to perform and analyze but provide more meaningful information. This chapter discusses some of the most important methods and emphasizes the types of knowledge gained from the use of a specific method. Bacteria that exhibit increased hydrophobicity, as determined by the contact angle technique, are more readily engulfed by phagocytes, consistent with the notion that hydrophobicity is important in adhesion. Adhesion to microspheres can be determined by light microscopy, among many other techniques (enzyme-linked immunosorbent assay (ELISA) and use of radiolabeled bacteria). Hemagglutination reactions have been responsible for the initial identification of many lectin adhesins and were important in the characterization of adhesin-saccharide specificities, through the use of carbohydrate inhibitors of the reactions. In approaching important subjects such as affinity, the chapter mentions two basic types of experiments that can be performed. The usefulness of the kinetic approach is extended when experimental variables are manipulated. Methods have been developed to easily differentiate between extracellularly bound and internalized bacteria. One of simplest tests to determine whether an adhesin is expressed in vivo during a natural infection is to assay for antibodies against the adhesin in patient sera. Another relatively easy assay is to screen isolates from an infection for mRNA for an adhesin by reverse transcription-PCR.
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Conjugation and Genetic Exchange in Enterococci
- Authors: Don B. Clewell, Gary M. Dunny
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Source: The Enterococci , pp 265-300
Publication Date :
January 2002
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Abstract:
The medical importance of the enterococci is closely related to the propensity of these organisms to participate in the horizontal transfer of determinants for antibiotic resistance and virulence. Conjugative plasmids in enterococci tend to fall into two main groups. Members of one group encode recognition of recipient-produced peptide pheromones that initiate the mating process; the others do not make use of such signals. The pheromone-responding plasmids usually transfer efficiently in broth (liquid) matings, whereas the others transfer relatively poorly under these conditions. An exception is pMGl, a resistance plasmid in Enterococcus faecium that transfers well in broth despite the apparent absence of a pheromone system. Those plasmids that make use of sex pheromones (e.g., pADl and pCFlO) thus far appear to exhibit a narrow host range—primarily Enterococcus faecalis and closely related species-although information on this point is very limited. A partial list of pheromone-responding plasmids is presented in this chapter. The formation of mating aggregates relates to the induction of a protein "aggregation substance" (AS), which appears extensively over the donor surface and binds to "enterococcal binding substance" (EBS) on the recipient surface. Conjugative transposons are particularly common in enterococci and streptococci and play an important role in the dissemination of antibiotic resistance in these organisms. It is likely that the enterococci play a significant role as a hardy facultative reservoir of genetic information available to a variety of other genera.
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Infections of the Female Genital Tract
- Author: P. Joan Chesney
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Source: Infections Associated with Indwelling Medical Devices, Third Edition , pp 265-286
Publication Date :
January 2000
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Over the last quarter of a century, the use of intrauterine devices (lUDs) and tampons by millions of women worldwide has introduced four previously rare and unrecognized infections. The morbidity and mortality associated with toxic shock syndrome (TSS), spontaneous septic midtrimester abortion, pelvic actinomycosis, and lUD-associated pelvic inflammatory disease (PID) have been significant. These events have focused badly needed attention on the composition of these devices and pathogenesis of these infections. Initial insertion of the IUD is associated with bacterial colonization of the normally sterile uterine cavity. The sterile-foreignbody- induced inflammation may persist in both the endometrium and the endosalpinx, as demonstrated by histopathology and the presence of neutrophils and macrophages in uterine washes. The upper genital tract is normally sterile since the cervix provides an effective physical and chemical barrier to bacteria. The closed internal os, resistant squamous epithelium, and bacteriostatic endocervical mucus maintain the barrier. A recent prospective controlled study confirmed that infectious complications of IUDs are more frequent if the threads lead from the uterine cavity to the vagina than if they are contained within the uterine cavity. As for many other postoperative cases of TSS, most of these cases may have been secondary to wound infections.
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Colonization of Medical Devices by Coagulase-Negative Staphylococci
- Authors: Friedrich Götz, Georg Peters
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Source: Infections Associated with Indwelling Medical Devices, Third Edition , pp 55-88
Publication Date :
January 2000
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In 1981, intravenous catheters infected with staphylococci by perfusion were investigated by scanning electron microscopy (SEM) to demonstrate the mode of adhesion. Bacterial cells, primarily those of staphylococci, followed by Acinetobacter calcoaceticus and Pseudomonas aeruginosa, were shown to be attached to the inner surface of the catheter. The thickest bacterial layers were found in catheters infected by coagulase-negative staphylococci (CoNS). Right heart flow-directed catheters removed from 18 critically ill patients after an average of 2.6 days after insertion were covered by a bacterial biofilm. In a neonatal intensive care unit, CoNS caused the majority of the nosocomial bacteremias. A study of arterial and central venous catheters removed from patients after 1 to 14 days revealed an extensive biofilm on all 42 arterial and 26 central venous catheters. By using special biofilm culture recovery methods, it was shown that 81% of the catheters were colonized by bacteria growing in slime-enclosed biofilms. It was speculated that the colonization represents a nidus for infection and bacteremia in these patients. Staphylococci also produced biofilm on polyvinyl chloride (PVC) endotracheal tubes used in neonates. Adherence of staphylococci to various intravascular catheter materials was investigated; these materials were composed of silicone elastomer, thermoplastic polyurethane, and polyurethane coated with Hydromer, a coating that absorbs water and provides a hydrophilic sheath around the catheter. Production of slime is necessary for Staphylococcus epidermidis colonization and is also observed with many other pathogens, including S. aureus.
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Pathogenesis of Vascular Catheter Infection
- Author: Robert J. Sherertz
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Source: Infections Associated with Indwelling Medical Devices, Third Edition , pp 111-125
Publication Date :
January 2000
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The pathogenesis of vascular catheter infections has recently been extensively reviewed. This chapter summarizes existing understandings and presents details of new work published on vascular catheter infections since the recent reviews. Many factors have been shown to affect the risk of catheters becoming infected. These include the unique abilities of certain organisms, Staphylococcus epidermidis, Staphylococcus aureus, and Candida albicans, to cause catheter-related infections. Molecular typing studies increasingly are improving our understanding of the pathogenesis of S. epidermidis/CoNS catheter-related infection. Recent studies with isogenic S. epidermidis mutants increasingly suggest that production of a polysaccharide adhesin is crucial to the pathogenesis of foreign-body infection. This polysaccharide, first named PS/A, was initially described as a virulence factor in association with work examining the pathogenesis of endocarditis. Two additional findings of relevance to the pathogenesis of endocarditis and possibly vascular catheter infections are that binding to platelets facilitates endocarditis and S. aureus strains causing endocarditis are much more likely to be resistant to platelet microbicidal proteins. The pathogenesis of catheter-related thrombosis has been studied in greater depth in recent years. With peripheral catheters, ultrasonographic imaging has shown that early thrombus formation (<24 h after insertion) occurs near the site of insertion, whereas later thrombus formation (>24 h after insertion) occurs near the catheter tip. Recent in vitro studies have shown that surface manipulations of polyurethane can lead to differences in protein and platelet deposition with associated differences in bacterial adherence.
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The Role of Siderophores in Iron Oxide Dissolution
- Author: Larry E. Hersman
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Source: Environmental Microbe-Metal Interactions , pp 145-157
Publication Date :
January 2000
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For over 50 years microbiologists have been aware of a class of compounds, produced by microorganisms, called siderophores. This chapter examines the type of Iron(Fe) to which siderophores bind and the location where they do so. The assumption in the literature has been that the purpose of siderophores is to supply Fe to the cell-so often stated that this quote is rarely referenced. Even though the dissolution of Fe oxides has been reviewed extensively in the literature, it is worthwhile to briefly review dissolution mechanisms, since they apply to the potential involvement of siderophores. In a study, Fe release and siderophore production by Azotobacter vinelandii (a gram-negative, asymbiotic nitrogen-fixing soil bacterium with an absolute requirement for Fe) was investigated by using several Fe oxide minerals as sources of Fe. Undoubtedly, siderophores are used by microorganisms to acquire Fe and are produced by microorganisms in response to a limited availability of Fe. These two observations are supported by hundreds of publications in the open literature. However, the results discussed in the chapter suggest that siderophores may not be entirely responsible for Fe oxide dissolution, that the role that siderophores play in the dissolution of Fe oxides remains unclear, and thus that the microbial dissolution of Fe oxides merits further investigation.
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Dissimilatory Reduction of Selenate and Arsenate in Nature
- Authors: Ronald S. Oremland, John Stolz
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Source: Environmental Microbe-Metal Interactions , pp 199-224
Publication Date :
January 2000
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Abstract:
This chapter discusses the biogeochemical reduction of selenate (Se(VI)) and arsenate (As(V)) when they enter anoxic environments and are used as electron acceptors for the oxidation of organic matter. These reductions are of a dissimilative nature and support the anaerobic growth of selected bacteria which conserve energy from this process. The chapter summarizes what is known about the bacteria's taxonomy, physiology, and biochemistry. Reduction to the solid, relatively unreactive Se(0) represents a mechanism for the removal of toxic Se(VI) and Se(IV) from natural waters. The environmental ramifications of these issues are also discussed in the chapter. The number of bacterial species known to respire selenate and arsenate continues to increase. The biological reduction of selenate and arsenate occurs for a number of reasons. In general, these are assimilation, regulation of reducing equivalents, detoxification, and dissimilation. Each is discussed in detail in the chapter. The realization that arsenate and selenate are indeed suitable electron acceptors and are readily available in both natural and contaminated environments suggests that even more unrelated species will be discovered. The initial biochemical studies also suggest that there may be different pathways for selenate and arsenate reduction, with specific terminal reductases and cytochromes.
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Biofilms and Device-Related Infections
- Authors: J. William Costerton, Philip S. Stewart
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Source: Persistent Bacterial Infections , pp 423-439
Publication Date :
January 2000
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Abstract:
The study of bacterial biofilms is more advanced in the engineering field than in the medical field, but the simple realization that biofilms are involved in chronic infections opens the way for a massive transfer of valuable information from the engineering realm to the medical realm and for its application to the treatment of infectious diseases. Pseudomonas aeruginosa first came to the attention of biofilm microbiologists because it predominates in cold alpine streams and grows predominantly (99.99%) in biofilms in this natural habitat. The Center for Biofilm Engineering (CBE) has established the fact that most biofilms assume this microcolony and water channel structure, including all biofilms formed by the few grampositive species examined to date, and the most significant consequence of this new observation is that we must now explain how these elaborate structures are established and maintained. If we try to imagine the bacterial survival strategies that would have been effective in the earliest stages of the development of life on this planet, growth in stationary biofilms that were protected from unfavorable conditions would prevent bacteria from being swept into acid or boiling downstream pools and from surges of threatening water from upstream sources. The role of host defenses in controlling biofilm infections is discussed in the chapter. There is a growing conviction that antibiotics are losing their ability to control bacterial infections because the bacteria have mobilized all of their survival strategies in the face of this frontal attack.
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Diverse Roles of Agrobacterium Ti Plasmid-Borne Genes in the Formation and Colonization of Plant Tumors
- Authors: Stephen C. Winans, Virginia Kalogeraki, Santina Jafri, Reiko Akakura, Qi Xia
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Source: Pathogenicity Islands and Other Mobile Virulence Elements , pp 289-307
Publication Date :
January 1999
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Abstract:
This chapter describes the various steps in plant colonization, including binding of the bacteria to host cells, recognition of diffusible host-released chemical signals, and processing and transfer of oncogenic DNA (T-DNA). It includes a discussion on the utilization of tumor-released compounds called opines and on the horizontal transfer of the Ti plasmid. Species of Agrobacterium have been classified primarily by their phytopathogenic properties, which are largely due to differences in plasmid content. With respect to chromosomally encoded properties, A. rubi and A. vitis are well-defined separate taxa whereas A. tumefaciens, A. radiobacter, and A. rhizogenes are not. The most thoroughly studied A. tumefaciens strains contain either octopine-type or nopaline-type Ti plasmids. Virtually all genes found on Ti plasmids play direct or indirect roles in some aspect of crown gall tumorigenesis or tumor colonization. VirD4 is absolutely required for transfer and pilus formation. Some members of the vir regulon are not essential for tumorigenesis and may play other roles in pathogenesis. Since Ti plasmids encode both TraI and TraR, each conjugal donor takes a census of other donors rather than of recipients. It is a challenge even to speculate about the adaptive value of such a system. The observation that two opines regulate conjugation in opposite ways is equally perplexing.
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Pfiesteria piscicida and Human Health
- Authors: David W. Oldach, Lynn M. Grattan, J. Glenn Morris
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Source: Emerging Infections 3 , pp 135-151
Publication Date :
January 1999
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Abstract:
Presumptive exposure to toxins produced by Pfiesteria piscicida, a small dinoflagellate found in mid-Atlantic estuarine waters, emerged as the cause of a novel human health syndrome of impaired cognition associated with skin rash, headache, gastrointestinal symptoms, and respiratory complaints following fish-kill events in Maryland's Chesapeake Bay in 1997. Dinoflagellates meet their nutritional needs either by photosynthesis (autotrophy), phagocytosis of food sources (heterotrophy), or combinations of these strategies (mixotrophy). Blooms of populations of these and other organisms that affect environmental quality and, at times, human health are often considered collectively under the general topic of harmful algal bloom (HAB). Toxin production by marine and estuarine dinoflagellates is responsible for four human health syndromes. Many fish collected during Pfiesteria-related fish-kill events display aberrant swimming behavior and have diffuse epithelial injury, with hemorrhage and necrosis. No consistent or unexpected abnormalities were found on physical examination. As outlined in this chapter, much remains to be learned about the organism, its presumed toxins, the environmental conditions which promote toxin expression, and the mechanisms by which these toxins might cause disease in humans. At the same time, there is an increasing convergence of data which support the idea of a link between exposure to toxins produced by this and related dinoflagellates and the occurrence of illness in humans.
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Biochemistry
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Source: Cryptococcus neoformans , pp 71-114
Publication Date :
January 1998
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This chapter surveys the available information on Cryptococcus neoformans biochemistry. The C. neoformans capsule is important for virulence and, as a result, the capsular polysaccharide has been studied extensively. Glucuronoxylomannan (GXM), galactoxylomannan (GalXM), and mannoprotein (MP), the three major components of the C. neoformans capsular exopolysaccharides, can each elicit antibody responses, but only the MP component elicits cell-mediated immunity as measured by delayed-type hypersensitivity reaction. The immune response to C. neoformans polysaccharide antigens is discussed. The detection and analysis of capsular polysaccharides in tissue remain dependent upon serological assays. Many assays have been described for the measurement of cryptococcal capsular polysaccharides based on the use of antibody reagents. Electron microscopy of the process of cell wall digestion with snail gut enzymes shows that protoplast-spheroplast formation is a two-stage process. First, the enzymes induce a hole in the equatorial region of the cell wall, through which the protoplast-spheroplast emerges from a cell wall “ ghost”. Second, continued digestion of the cell wall leads to the disappearance of these structures. The biochemistry of melanin and the assembly of melanin on the cell wall remain poorly understood. Melanogenesis is interesting because of its association with virulence and because it is a potential target for antifungal drug design. Mouse passage of environmental C. neoformans isolates produced isolates with higher amphotericin B and fluconazole MICs, suggesting that sterols and antifungal drug resistance could be altered by mammalian infection without a need for exposure to antifungal drugs.
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Murine Colonic Hyperplasia
- Author: David В. Schauer
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Source: Molecular Genetics of Bacterial Pathogenesis , pp 197-208
Publication Date :
January 1994
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Despite the low incidence of clinical cases, transmissible murine colonic hyperplasia is of interest to microbiologists and gastroenterologists alike because of the unusual pathogenesis of the disease. Koch’s postulates have also been fulfilled with Citrobacter freundii biotype 4280, which produces transmissible murine colonic hyperplasia when pure cultures are inoculated into either conventional or germ free mice. The transient hyperplastic state which is induced by C. freundii biotype 4280 has a profound effect on the cytokinetics of the mucosal epithelial cells in the large bowel. These changes also serve to increase the susceptibility of the colonic epithelial cells to the carcinogenic effect of 1,2-dimethylhydrazine (DMH). The cytokinetics of the hyperplastic mucosa in transmissible murine colonic hyperplasia have been characterized by autoradiography of histological sections labeled with [3H]thymidine. The role of eaeA in the pathogenesis of transmissible murine colonic hyperplasia has been examined by the construction of an isogenic mutant of C. freundii biotype 4280. The molecular basis of transmissible murine colonic hyperplasia remains enigmatic. Characteristic histopathological lesions are produced by C. freundii biotype 4280 in the mucosa of the large bowel of laboratory mice prior to the onset of gross hyperplasia. At least one common, indigenous organism has the ability to cause histopathological changes in enterocytes at the site of bacterial adherence which are reminiscent of AE lesions. It seems likely that a better understanding of the molecular pathogenesis of transmissible murine colonic hyperplasia will also bring a better understanding of the role of bacteria in proliferative bowel disease.
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Holistic Perspective on the Escherichia coli Hemolysin
- Author: Rodney A. Welch
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Source: Molecular Genetics of Bacterial Pathogenesis , pp 351-364
Publication Date :
January 1994
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This chapter reviews the knowledge of the prototype of the RTX family of pore-forming toxins, the Escherichia coli hemolysin, and proposes that new efforts be made to study the significance and roles of the exotoxins, together with those of endotoxins, as an integrated synergistic system of multiple virulence factors. The fundamental approach taken by biochemists and cell biologists interested in understanding the role in pathogenesis of a bacterial virulence factor such as an exoprotein has been to purify the exoprotein and observe its activity on different substrates, cells, and hosts. The RTX-associated diseases include pertussis, juvenile periodontitis, pneumonia, urinary tract infections, and wound infections. The epidemiological evidence for an association between RTX toxin production and isolates that cause disease is strong for all of the organisms except E. colii, Morganella morganii, and Proteus vulgaris. The solubilization of hemolysin aggregates by a chaotropic agent such as urea causes an increase in the specific lytic activity of the hemolysin. The erythrocytes transform into echinocytes, in which gross cytoskeletal or membrane irregularities result in rounding of the cell and the formation of multiple teardrop-shaped projections from the cell surface. The cellular transformation is similar to that caused by the treatment of erthrocytes by a calcium ionophore. The motivation for covering the older literature in the chapter is to stimulate thought, experimentation, and discussion about the significance of the ever-present lipopolysaccharide (LPS) molecules on the structure and activity of the E. coli hemolysin.
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Yops of the Pathogenic Yersinia spp.
- Author: James B. Bliska
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Source: Molecular Genetics of Bacterial Pathogenesis , pp 365-381
Publication Date :
January 1994
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During their interaction with host cells, the pathogenic Yersinia spp. export a set of proteins known as the Yersinia outer membrane proteins, or Yops. This chapter reviews the work that led to the discovery of the Yops and discusses recent progress made in understanding the expression and function of these proteins. Bacterial infection of the lungs results in pneumonic plague, a form of the disease that is transmissible by aerosolization and that is often fatal. Yersinia enterocolitica is responsible for a variety of human illnesses ranging in severity from mild gastroenteritis to acute terminal ileitis. Various rodents, farm animals, and birds are the normal reservoirs for Y. pseudotuberculosis. The product of yscC shares significant homology with PulD, a protein required for the export of pullulanase by Klebsiella pneumoniae. A number of additional polypeptides (later to be identified as the Yops) were detected in sucrose gradient-purified outer membranes from pYV-containing Y. enterocolitica and Yersinia pseudotuberculosis grown under LCR conditions. The ability of Yersinia strains to induce rounding and detachment of cultured mammalian cells has been referred to as "cytotoxicity". A partial cytotoxic activity is reconstituted if these protein preparations are introduced into HeLa cells by the use of glass carrier beads. This indicates that YopE must enter the cytoplasm of the host cell to be active. Signal transduction is critically involved in a number of cellular host responses to microbial infection.
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Ribosomal Structure and Genetics
- Author: Tina M. Henkin
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Source: Bacillus subtilis and Other Gram-Positive Bacteria , pp 669-682
Publication Date :
January 1993
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This chapter summarizes the current knowledge about Bacillus ribosomes and translation factors. Much of the information concerning Bacillus ribosome structure and function has been obtained from work with Bacillus stearothermophilus, while most of the genetic analysis has been carried out with B. subtilis. Available information about ribosome structure and genetics in other gram-positive systems are also summarized in this chapter. B. subtilis contains 10 rRNA operons.The sequences of the rrnB and rrnO operons have been determined; they show an organizational pattern identical to that of the E. coli rRNA operons, containing genes for 16S, 23S, and 5S rRNA in that order. Ribosomal-protein gene characterization was initiated by the isolation and mapping of mutations conferring resistance to antibiotics that were known to target the translational machinery. A number of mutants that have alterations in components of the translational apparatus and exhibit defects in sporulation have been identified. These include mutants with altered sensitivity to antibiotics that act on the ribosome and temperature-sensitive mutants that result in spore-minus or spore-conditional phenotypes. In E. coli, sequences in the promoter regions of genes sensitive to the stringent response have been identified, and it has been proposed that (p)ppGpp acts directly as an effector in modulating promoter recognition by RNA polymerase. Expression of a fusion of the B. subtilis rrnO promoter to lacZ was repressed by induction of the stringent response by the addition of serine hydroxamate in wild-type strains but not in a relA-minus mutant.
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Morphogenesis of Bacteriophage ϕ29
- Authors: Dwight Anderson, Bernard Reilly
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Source: Bacillus subtilis and Other Gram-Positive Bacteria , pp 859-867
Publication Date :
January 1993
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Bacteriophages are very useful models for studying the protein-derived principles of form determination in virus assembly. Bacteriophage models cannot be ignored because of the assembly of the virus tail at the prohead portal vertex or connector, the entry point of double-stranded DNA. Bacteriophage ø29 of Bacillus subtilis, illustrated in the family portrait with bacteriophage T2 of Escherichia coli, features simplicity, efficient in vitro assembly, and advanced genetic and biochemical characterizations. This chapter emphasizes ø29 structure and the mechanisms of prohead assembly and DNA packaging, the major thrusts of current ø29 research in Minneapolis. The basic problem of ø29 morphogenesis is the mechanism by which a prolate shell of particular dimensions is assembled from subunits that are also capable of being assembled into incorrect structures. Mutants of asporogenous B. subtilis that cannot assemble ø29 (vam) were selected by the use of antibodies that reacted more strongly with the free connectors than with the portal vertex of proheads or phage. Bacteriophage DNA-packaging machines seem to have in common two packaging proteins and a connector with sixfold symmetry. Restriction enzyme digestion of DNA molecules extracted from DNase I-treated proheads shows that DNA-gp3 packaging is oriented with respect to the physical map. A gyrase action would be needed to generate supercoiled DNA for packaging.