Bacteriophage

3 Key excerpts on "Bacteriophage"

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  eBook - ePub

  Snyder and Champness Molecular Genetics of Bacteria

  • Tina M. Henkin, Joseph E. Peters(Authors)
  • 2020(Publication Date)
  • ASM Press

    (Publisher)

  10 protein-coding sequence, the descendants of different phage in the population express different fusion peptides on their surfaces. Some of them (shown in orange) express a peptide that happens to bind to the target, while most (shown in red) express peptides that do not bind. When this mixture of phage is exposed to the target and the target is washed, those expressing a peptide that binds are preferentially retained, and more of the others are washed away. The retained phage can then be eluted from the target and propagated. This process is repeated multiple times to further enrich for the phage that specifically bind to the target.

  Phage Therapy

  The increase in global antibiotic resistance has led to a need for development of new antimicrobial therapies. One possible strategy is the use of phage to target specific disease organisms without causing harm to the general microbial population in and on our bodies. Phage therapy was investigated at some level many years ago, and interest in this concept has increased in recent years (see Abedon et al. , Suggested Reading). Further understanding of phage biology and phage-host interactions will be crucial to the success of this approach.

  Summary

  1. Viruses that infect bacteria are called Bacteriophages, or phages for short. The plural of phage is also phage if they are all the same type, while phages refers to more than one type.
  2. The developmental cycle of a phage that leads to production of new phage particles is called the lytic cycle. Many phages utilize a complex program of gene expression to increase the efficiency of the developmental cycle.
  3. The products of phage regulatory genes regulate the expression of other phage genes during development. One or more regulatory genes at each stage of development turns on the genes in the following stage and turns off the genes in the preceding stage, creating a regulatory cascade. In this way, all the information for the stepwise development of the phage can be preprogrammed into the phage DNA.
  4. Phage T7 encodes an RNA polymerase that specifically recognizes the promoters for the late genes of the phage. Phage N4 encodes two RNA polymerases, one that is encapsulated in the phage head with the DNA and another that transcribes the middle genes. Only the late genes are transcribed by the host RNA polymerase.
  5. Phage SPO1 uses the host RNA polymerase to transcribe its early genes, which include a gene for a new sigma factor, gp28. This sigma factor directs transcription of the middle genes, which include two genes that encode proteins that serve as a “split” sigma factor; these proteins work together to direct RNA polymerase to transcribe the late genes.

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  Marine 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

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  Sustainable Approaches to Controlling Plant Pathogenic Bacteria

  • V. Rajesh Kannan, Kubilay Kurtulus Bastas(Authors)
  • 2015(Publication Date)
  • CRC Press

    (Publisher)

  Vibrio cholera (the causative agent of cholera); at that time, the disease was one of the deadliest threats faced by humans (Abedon et al., 2011). In 1915, Fredric Twort hypothesized that this antibacterial activity could be due to the virus (phage) itself, but did not pursue this line of thought. Felix D’Herelle, who discovered Bacteriophages in 1917 (Hermoso et al., 2007), proposed that the phenomenon was caused by viruses capable of parasitizing bacteria and used a combination of the words “phagein” (Greek for “to eat”) and “bacteria” to name them. In 1925, D’Herelle’s report on the treatment of plague by anti-plague phage drew attention to the use of Bacteriophages in disease control (phage therapy) (D’Herelle et al., 1927). Phages were first applied therapeutically in the treatment of infectious staphylococcal skin disease in humans, which was first identified in 1921 by Richard Bruynoghe and Joseph Maisin. Several similarly promising studies, such as those by D’Herelle and others (Sulakvelidze et al., 2001), were encouraged by these early results. The concept of phage therapy in Western countries was abandoned after the emergence of antibiotics in 1940, but the practice continued in the Soviet Union and is still used in Russia today. The phage therapy concept also fell out of favor in Western countries because of the unreliable and inconsistent results of many phage therapy trials (Haq et al., 2012). When complete understanding of phage biology was obtained, the concept was generally accepted; to date, it has been used successfully in humans, animals, and plants.

  After D’Herelle’s discovery, phages were proposed as an agent for the control of plant diseases and were evaluated for the control of bacterial diseases in plants (Moore, 1926). Phage therapy has been found to be an effective tool for the control of several phytopathogenic bacteria, including Xanthomonas spp. (bacterial spot of peach) (Ceverolo, 1973), Pseudomonas spp. (bacterial blotch of mushroom) (Kim et al., 2011), Erwinia spp. (fire blight of apple and pear) (Nagy et al., 2012), Pantoea spp. (Stewart’s wilt of corn) (Thomas, 1935), Ralsotnia spp. (bacterial wilt of tobacco) (Fujiwara et al., 2011), Streptomyces spp. (common scab) (Goyer, 2005), Dickeya spp. (blackleg disease of potato) (Adriaenssens et al., 2012), and Pectobacterium

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