Transcript 第4章 噬菌体
Chapter 4 bacteriophage Bacteriophages ( phages ) are obligate intracellular parasites that multiply inside bacteria by making use of some or all of the host biosynthetic machinery . They are viruses that infect bacteria. Composition of Bacteriophage Nucleic acid: either DNA or RNA but not both ds DNA, ss RNA, ss DNA unusual or modified bases encode 3-5 gene products to over 100 gene products Protein: function in infection and protect the nucleic acid Structure of Bacteriophage different sizes and shapes icosahedral 二十面体 filamentous Capsid DNA Contractile Sheath Head Tail Tail Fibers Base Plate Types of Bacteriophage Lytic or Virulent Phages 毒性噬菌体 Lysogenic or Temperate Phage 溶原性噬菌体或温和噬菌体 Lytic or Virulent Phages Definition: Lytic or virulent phages are phages which can only multiply in bacteria and kill the cell by lysis at the end of the life cycle. Life Cycle Adsorption吸附 Penetration穿入 Biological Synthesis生物合成 Maturation and Release成熟和释放 Adsorption吸附 Penetration穿入 Biological Synthesis生物合成 Maturation and Release成熟和释放 Bacteriophage binding to and injecting their DNA into a bacterial cell bacteriophage after contraction of sheath normal bacteriophage Assay for Lytic Phage Plaque assay噬斑测定 Lytic phage are enumerated by a plaque assay. A plaque is a clear area which results from the lysis of bacteria. Each plaque arises from a single infectious phage. The infectious particle that gives rise to a plaque is called a pfu (plaque forming unit). Lysogenic or Temperate Phage 溶原性噬菌体或温和噬菌体 Lysogenic or temperate phages are those that can either multiply via the lytic cycle or enter a quiescent state in the cell. In this quiescent state most of the phage genes are not transcribed; the phage genome exists in a repressed state. The phage DNA in this repressed state is called a prophage because it is not a phage but it has the potential to produce phage. In most cases the phage DNA actually integrates into the host chromosome and is replicated along with the host chromosome and passed on to the daughter cells. The cell harboring a prophage is termed a lysogenic bacterium. Lysogenic bacterium Induction Animation summarizing the lysogenic life cycle of a temperate bacteriophage. 溶原性细菌的溶原性周期和溶菌性周期 lysogenic conversion 溶原性转换 When a cell becomes lysogenized, occasionally extra genes carried by the phage get expressed in the cell. These genes can change the properties of the bacterial cell. This process is called lysogenic conversion. Application of Bacteriophage Used in treatment of bacterial infections Used for the identification of pathogenic bacteria (phage typing 噬菌体型分型) Used in molecular biology