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. 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

3 APPLICATION OF BACTERIOPHAGE 2 PHAGE MULTIPLICATION CYCLE 1 COMPOSITION AND STRUCTURE OF BACTERIOPHAGE Main contents

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 : 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 Genome size Modified bases –Protein ProtectionInfection Structure (T 4 ) –Size –Head or capsid –Tail Tail Tail Fibers Base Plate Head/Capsid Contractile Sheath

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 ） 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 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: 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: , 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: , Phages eyed as agents to protect against harmful E. coli. American Society for Microbiology News 65: , 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