Transcript 噬菌体
Chapter 4. Bacteriophage 噬菌体 •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. Bacteriophage (Phage) Definition - Obligate intracellular parasites that multiply inside bacteria by making use of some or all of the host biosynthetic machinery Significance – Models for animal cell viruses – Gene transfer in bacteria – Medical applications Identification of bacteria - phage typing Treatment and prophylaxsis??? viral common properties smallest，simple structure DNA/RNA病毒的基本特性 parasite in living cell widespread existence 分布广泛 high host –specific parasitism严格的宿主 特异性 Main contents 1 COMPOSITION AND STRUCTURE OF BACTERIOPHAGE 2 PHAGE MULTIPLICATION CYCLE 3 APPLICATION OF BACTERIOPHAGE Requirement Master the interrelation between phage and bacteria Master the following concepts : 1. lysogenic state 2. lysogenic phage (temperate phage) 3.lysogenec bacteria 4.prophage Understand the.size, shape and structure of phage. [Class hour: 1 hours ] 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 Protein: function in infection and protect the nucleic acid Biological properties 生物学性状 Shape and structure Seen by EM :icosahedral 二十面体 – – – – Tadpol蝌蚪形 microsphere微球形 slim rod丝形 head core DNA/RNA tail pipe-like capsid protein coat base plate Antigenicity 抗原性 Resistive 抵抗力 – >Bacteria 75°C 30′ – sensitive to rays filamentous Composition and Structure Composition – Nucleic acid Head/Capsid Genome size Modified bases – Protein Protection Infection Structure (T4) – Size – Head or capsid Contractile Sheath Tail Tail Fibers Base Plate Types of Bacteriophage Lytic or Virulent Phages毒性噬菌体 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. 噬菌体的种类 毒性噬菌体（virulent phage） – 能在宿主菌细胞内复制增殖，产生许多子代噬 菌体，并最终裂解细菌，称为毒性噬菌体 温和噬菌体（temperate phage）/ 溶原性噬菌体（lysogenic phage） – 噬菌体基因与宿主菌染色体整合，不产生子代 噬菌体，但噬菌体DNA能随细菌DNA复制，并 随细菌的分裂而传代 Life Cycle毒性噬菌体复制周期 Adsorption吸附 Penetration穿入 Biological Synthesis生物合成 Maturation and Release成熟和释放 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. 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). Lytic or Virulent Phages毒性噬菌体 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. 噬菌现象 液体培养基 混浊 澄清 固体培养基中，出现噬斑（plaque） 一定体积内的噬斑形成单位数目（pfu） 温和噬菌体 前噬菌体（prophage） 溶原性细菌（lysogenic bacterium） 溶原性（lysogeny） 溶原状态 溶原性周期和溶菌性周期 溶原性转换 Animation summarizing the lysogenic life cycle of a temperate bacteriophage. Lysogenic bacterium PHAGE MULTIPLICATION CYCLE- Life Cycle: Lysogenic or Temperate Phage溶原性 噬菌体或温和 噬菌体 溶原性细菌的溶原性周期和溶菌性周期 Application of Bacteriophage 噬菌体的应用 Used in treatment of bacterial infections细 菌感染的诊断与治疗 Used for the identification of pathogenic bacteria细菌的鉴定与分型 (phage typing噬 菌体型分型) Used in molecular biology分子生物学研究 的重要工具 Medical Applications of Phage “I strongly believe phage could become an effective antibacterial tool” - Carl Merril, Chief of the Laboratory of Biochemical Genetics, National Institute of Mental Health, NIH. “It might be another string on the bow, such that when (conventional antibiotics) fail, here’s something that has a chance of working. But it’s not going to be a panacea” Joshua Lederberg, Sackler Foundation Scholar at The Rockefeller University Reassessment of Medicinal Phage Spurs Companies to Study Therapeutic Uses American Society for Microbiology News 64:620-623, 1998 Medical Applications of Phage Exponential Biotherapies (Rockville, MD) – Vancomycin resistant Enterococcus facium and Streptococcus pneumoniae Phage Therapeutics (Bothell, WA) – Staphylococcus aureus and Staphylococcus epidermidis Intralytix, Inc. (Baltimore, MD) – Salmonella in meat and poultry Biopharm Ltd. (Tblisi, Georgia) – Infections associated with burns University of Idaho – Escherichia coli O157:H7 in cattle Reassessment of Medicinal Phage Spurs Companies to Study Therapeutic Uses. American Society for Microbiology News 64:620-623, 1998. Phages eyed as agents to protect against harmful E. coli. American Society for Microbiology News 65:666-667, 1999. Assay for Lytic Phage Plaque assay噬斑测定 整合在细菌染色体上的噬菌体基因 组称____________。 a.prophage b.virulent phage c.lysogenic bacterium d.lysogeny e.temperate phage