Bacteriophage
Bacteriophages are viruses that specifically infect and replicate within bacteria. They consist of a protein coat surrounding genetic material, and they use their tail fibers to attach to and inject their DNA into bacterial cells. This process ultimately leads to the destruction of the host bacterium as new phages are produced.
7 Key excerpts on "Bacteriophage"
eBook - ePub- Jeremy W. Dale, Simon F. Park(Authors)
- 2013(Publication Date)
- Wiley(Publisher)
...4 Genetics of Bacteriophages Bacteriophages (or phages for short) are simply viruses that infect bacteria. They played a central role in the development of molecular biology, especially in our understanding of gene structure and expression, and are also important, in the laboratory and in nature, for providing a way in which genes can be transferred from one bacterium to another. With the development of gene cloning, phages took on an additional role, as vectors for cloned DNA (see Chapter 8). In many of their basic properties, phages are similar to other viruses. They contain either RNA or DNA enclosed in a protein coat. The phage infects by attaching to a specific receptor on the surface of the bacterium, and the nucleic acid enters the cell. Some of the phage genes (the early genes) are expressed almost immediately, using pre-existing host enzymes; in general, these code for proteins required for replication of the phage nucleic acid. A number of copies of the phage nucleic acid are then made, and the expression of the late genes starts: these are mainly those needed for production of the phage particle. The nature of the switch from early to late gene expression varies between different phages. Later in this chapter we will consider some specific examples. The phage particles are then assembled and the cell lyses, liberating a number of phage particles, each of which can then go on to infect another bacterial cell (see Figure 4.1). If a Bacteriophage infects a liquid culture of bacteria, it may result in complete clearing of the culture. On the other hand, if the bacteria are spread on the surface of an agar plate, the phage particles liberated from an individual infected cell will only be able to infect neighbouring bacteria, which will result in localized clearing of the bacterial lawn, referred to as plaques...
eBook - ePub- Alexander McLennan, Andy Bates, Phil Turner, Michael White(Authors)
- 2012(Publication Date)
- Taylor & Francis(Publisher)
...Their genomes can be of RNA or DNA and range in size from around 2.5 to 150 kb. They can have simple lytic life cycles or more complex, tightly regulated life cycles involving integration in the host genome or even transposition (Section E4). Bacteriophages have played an important role in the history of both virology and molecular biology. They have been studied intensively as model viruses and were important tools in the original identification of DNA as the genetic material, the determination of the genetic code, the existence of MRNA, and many more fundamental concepts of molecular biology. Since phages parasitize bacteria, they often have significant sequence similarity to their hosts, and have, therefore, also been used extensively as simple models for various aspects of bacterial molecular biology. Some phages are also used as cloning vectors (Section P2). Lytic and lysogenic infections Some phages replicate extremely quickly: infection, replication, assembly, and release by lysis of the host cell may all occur within 20 minutes. In such cases, replication of the phage genome occurs independently of the bacterial genome. Sometimes, however, replication and release of new virus can occur without lysis of the host cell (e.g. in Bacteriophage M13 infection). Other phages alternate between a lytic phase of infection, with DNA replication in the cytosol, and a lysogenic phase in which the viral genome is integrated into that of its host (e.g. Bacteriophage l). Yet another group of phages replicate while integrated into the host cell genome via a combination of replication and transposition (e.g. Bacteriophage μ, Mu). Bacteriophage M13 Bacteriophage M13 has a small (6.4 kb) single-stranded, positive-sense, circular DNA genome (Figure 1). M13 particles attach specifically to E. coli through a minor coat protein (g3p) located at one end of the particle. Binding of the minor coat protein induces a structural change in the major capsid protein...
eBook - ePub- Phoebe Lostroh(Author)
- 2019(Publication Date)
- Garland Science(Publisher)
...The viral genome and the way that genome interacts with its host cell determines how viruses accomplish gene expression and genome replication. In this chapter, we examine Bacteriophages with three different types of genomes; in Chapters 5 through 10, we will study gene expression and genome replication in viruses that infect eukaryotic cells. Some features of Bacteriophages differ from those of viruses that infect eukaryotes because the host cells handle synthesis and translation of mRNA differently. Consequently, this chapter begins with background discussions of bacterial transcription, mRNA features, and translation. Other features of Bacteriophages are similar to those in viruses that infect eukaryotes; these cases will be pointed out to provide a prelude to the Chapters 5 through 15. Bacteriophages are also everywhere in research in molecular biology both historically and in the present day. For example, introductory biology courses often discuss the research of Hershey and Chase, which helped to show that DNA is the genetic material rather than protein. These experiments involved the use of a double-stranded DNA Bacteriophage with either radioactive protein or DNA; it was the radioactive DNA (not protein) that entered the host cells to direct the production of new offspring phages. In the present day, we often use phage proteins or nucleic acids as research tools. One example is that a common protein overexpression system relies upon a Bacteriophage protein called T7 RNA polymerase. The chapter focuses on specific Bacteriophages that infect the model bacterial host Escherichia coli : T7, λ, φ χ 174, M13, MS2, and Q b. We begin by discussing two phages with dsDNA genomes, which led to many fundamental discoveries in virology. One of them, phage T7, causes exclusively lytic infections, whereas the other, phage λ, causes both lytic and latent infections...
eBook - ePubViruses
Molecular Biology, Host Interactions, and Applications to Biotechnology
- Paula Tennant, Gustavo Fermin, Jerome E. Foster(Authors)
- 2018(Publication Date)
- Academic Press(Publisher)
...Phages possess many features that make them perfect allies of biotechnology: they cause little harm in nonhost organisms and can be easily removed from the human body. They can be used as-they-are in therapies aimed at deterring bacterial infections; their virions are amenable to manipulation for the display of functional peptide motifs of interest (for us, that is) that can be produced in large quantities by amplification in bacteria; even more, some can self-assemble into nanofibrous tissue-like matrix structures. In other cases, their modified genomes have been extremely helpful in increasing our knowledge and in manipulating organisms, while some of their proteins have helped in designing new approaches for the generation of enormous amounts of sequence data (some nanopore sequencing platforms). This section highlights the potential for whole phage or phage-based antibacterial agents, while the section at the end of the chapter addresses the use of phages in the design of novel nanoengineered systems. In some instances, the best way to defeat an enemy is by using a proxy antagonist against the former. Such is the case of using a lytic phage against the bacterium Klebsiella pneumoniae, that causes hospital-acquired urinary tract infections, pneumonia, and soft tissue infections. A recently described lytic virus (φBO1E; Podoviridae) was found to be specific for KPC carbapenemase-producing strains of the K. pneumonia bacterium. This was a very important discovery given the pandemic dissemination of the pathogenic bacterium that not only is ubiquitous, but also shows extensive multidrug resistance profiles. The phage is specific for this multidrug-resistant bacterial strain, it does not lysogenize its host and it is envisioned to be amenable for the development of new agents in the treatment of Klebsiella infections, or for the decolonization of patients afflicted by the bacterium...
eBook - ePub- Ronald G. Labbé, Santos García, Ronald G. Labbé, Santos García(Authors)
- 2013(Publication Date)
- Wiley-Blackwell(Publisher)
...28 Bacteriophage biocontrol Lars Fieseler 1 and Martin J. Loessner 2 1 Zurich University of Applied Sciences, Institute of Food and Beverage Innovation, Wädenswil, Switzerland 2 ETH Zurich, Institute of Food, Nutrition, and Health, Zurich, Switzerland 28.1 Introduction In 1915, when Bacteriophages were discovered, A. F. Twort initially reported on a ‘glassy transformation’ of micrococcus germs. Today, in terms of food safety and biocontrol, sales professionals promote phages as ‘natural born killers’. This is mainly because Bacteriophages feature unique and efficient mechanisms to specifically target and eliminate bacteria. Accordingly, Bacteriophages (literally ‘bacteria-eaters’) are viruses of bacteria. The diversity and abundance of Bacteriophages is striking. Phages have been isolated from many different environments and also from a diverse set of foods. Generally, a particular Bacteriophage can be found in an environment as long as this is also inhabited by the corresponding host bacterium. Conspicuously, most phage isolates (96%) belong to a single taxonomic order of the tailed phages (Caudovirales). According to the International Committee on Taxonomy of Viruses, tailed phages are further separated into three distinct families. All members of the Caudovirales exhibit an icosahedral capsid (the ‘head’), which contains the virus genetic material in a highly condensed form (mostly double-stranded DNA). For further classification of a phage particles, the tail structure is considered. Members of the Podoviridae are characterized by very short tails. In fact, many podoviralisolates appear as capsids that exhibit appendages at a particular capsid vertex only. In contrast, phages of the Myoviridae family have much longer straight and contractile tails. The tails of the Siphoviridae family members are also long, but flexible and cannot be contracted...
eBook - ePub- Boriana Marintcheva(Author)
- 2017(Publication Date)
- Academic Press(Publisher)
...Recent research efforts are exploring the application of reoviruses for control of oil palm pests in South Africa; nudiviruses for control of rhinoceros beetle in Asia, and tetraviruses for control of heliothine moths. There are growing trends to optimize insect virus formulations to improve their UV stability, to increase shelf-life, and to experiment with pheromone-based and gustatory additives. 7.4. Applications of Bacteriophages to Control Agricultural Pests, Food-Borne Diseases, and Food Spoilage Bacteria Issues related to food production, storage, preservation, and safety are always on the forefront of technology development, safety regulations, and economic investments. Food-related diseases are a diverse group and a significant part of them are caused by bacteria susceptible to Bacteriophage infections. In addition, food production and processing are complex endeavors involving many plant and animal organisms and their pests living in a constantly changing environment. Different food products are characterized by a variety of physical and chemical properties directly connected to mechanisms of their processing, consumption, preservation, and storage. As a consequence of the enormous complexity of the field, it is practically not possible to cover its depth and breadth in a fraction of a chapter, thus this section should be considered only a primer to the topic and specialized sources should be sought for a detailed description of the current state of research of phage utilization in food-related industries. Bacteriophage applications toward control of food-borne diseases are on the interface between biocontrol and phage therapy, which is discussed in Chapter 9, dedicated to viruses as therapeutic agents...
eBook - ePubMarine Microbiology
Ecology & Applications
- Colin Munn, Colin B. Munn(Authors)
- 2019(Publication Date)
- CRC Press(Publisher)
...For example, some cyanophages have been shown to infect both Synechococcus and Prochlorococcus and some vibriophages infect several species of Vibrio. If correct, this has significant implications for the possibility of genetic exchange between different organisms and for the role of phages in determining bacterial community structure. Very little is known about the nature of the receptors for phage adsorption to marine bacteria. It is possible that broad host range phages target conserved amino acid sequences of proteins on the cell surface of different bacterial types and that the tail fibers can recognize more than one type of receptor. Recent work suggests that some phages exploit membrane proteins of host cells as a mechanism for entry (see p.237). In most cases, enzymes in the tail or capsid of the phage attack the bacterial cell wall, forming a small pore through which its nucleic acid enters. The phage genetic material then remains in the cytoplasm or is integrated into the host cell genome. In the lytic cycle (Figure 7.5a), this is followed by expression of phage proteins, phage genome replication, and formation of the capsids and other parts of the virion. When assembly is complete, most phages cause lysis of the host cell by producing enzymes that damage the cytoplasmic membrane and hydrolyze the peptidoglycan in the cell wall. Figure 7.5 Possible outcomes of infection of a bacterial cell by a DNA phage. a) In the lytic cycle, viral genes are expressed, DNA is replicated, and host machinery is used to make the components of the virus particles. These self-assemble into mature virions which are released. b) The DNA of temperate phages may be incorporated and replicated with the host genome as a prophage. The host cell is said to be lysogenic because it may be triggered to enter the lytic cycle under certain conditions. c) In pseudolysogeny, the phage genome remains unintegrated for an extended period, usually due to nutrient depletion...
