rokaryotes(原核生物.ppt

Wang Guohui CHAPTER 2 Microorganisms in the Environment Chaper 2 Microorganisms in the Environment Wang Guohui CHAPTER 2 Microorganisms in the Environment 2.1Viruses 2.2 Bacteria 2.3 Fungi 2.4 Algae 2.5 Protozoa Outline Wang Guohui CHAPTER 2 Microorganisms in the Environment In environmental microbiology, we categorize （分类）microbes as prokaryotes（原核生物） or eukaryotes（真核生物） (Table 2.1). Wang Guohui CHAPTER 2 Microorganisms in the Environment Wang Guohui CHAPTER 2 Microorganisms in the Environment Viruses are significant because of their ability to infect other living organisms and cause disease. Bacteria can also cause infections but are very important in other areas of environmental microbiology including biochemical transformations that affect nutrient（营养） cycling, bioremediation（生物修复）, waste disposal. The fungi are involved in these activities Effect of Microorganism Wang Guohui CHAPTER 2 Microorganisms in the Environment Algae affect surface water quality and can also produce microbial toxins, but their overall impact in the environmental microbiology arena(领域) is not as significant as that of the bacteria and fungi. Protozoa are also key players in surface environments as grazers of bacteria, helping to maintain a steady ecological balance. Wang Guohui CHAPTER 2 Microorganisms in the Environment 2.1 VIRUSES 2.1.1 Concepts 2.1.2 General Properties of Viruses 2.1.3 Structure 2.1.4 General Morphology 2.1.5 General Features of Virus Reproduction 2.1.6 Quantification of Bacterial Virus(phage) by Plaque Assay 2.1.7 Indigenous Virus Populations in the Environment Outline Wang Guohui CHAPTER 2 Microorganisms in the Environment FIGURE 2.2 Comparative sizes of selected bacteria, viruses, and nucleic acids. Wang Guohui CHAPTER 2 Microorganisms in the Environment 2.1.1 Concepts Viruses are simple, acellular（非细胞） entities consisting of one or more molecules of either DNA or RNA enclosed in a coat of protein. They are reproduced only within living cells and are obligately (专一性) intracellular parasites Viruses are classified on the bases of their nucleic acids characteristics, capsid symmetry, the presence or absence of an envelop, their host and other properties. Wang Guohui CHAPTER 2 Microorganisms in the Environment (1) Their simple, acellular（非细胞） organization ； (2) The absence of both DNA and RNA in the same virion； (3) Their inability to reproduce independently of cells and carry out cell division as prokaryotes and eukaryotes do. Viruses differ from living cells in at least three ways: 2.1.2 General Properties of Viruses Wang Guohui CHAPTER 2 Microorganisms in the Environment The extracellular phase: Virion can not reproduce independently. The intracellular phase: Viruses exist primarily as replicating nucleic acids that induce host metabolism to synthesize virion components; eventually complete virus particles or virions are released. Extracellular and Intracellular Existence of Viruses (in two phases) Wang Guohui CHAPTER 2 Microorganisms in the Environment Hosts The particular host range of a virus is determined by the viruss requirements for its specific attachment to the host cell and cellular factors required for viral multiplication. Three main classes - animal viruses, bacterial viruses (bacteriophages), and plant viruses. Wang Guohui CHAPTER 2 Microorganisms in the Environment Viruses vary considerably in size. Although most are quite a bit smaller than bacteria, some of the larger viruses (such as the smallpox virus) are about the same size as some very small bacteria (such as the mycoplasmas(支原体), rickettsias（斑疹伤寒病原体 ）, and chlamydias（衣原体）. Size Viruses range from 20 to 300 nm in diameter Wang Guohui CHAPTER 2 Microorganisms in the Environment Viruses are smaller than cells, ranging in size from 0.02 to 0.3 um. Smallpox virus, one of the largest viruses, is about 200 nm in diameter; poliovirus, one of the smallest, is only 28 nm in diameter. Wang Guohui CHAPTER 2 Microorganisms in the Environment FIGURE 2.2 Comparative sizes of selected bacteria, viruses, and nucleic acids. Wang Guohui CHAPTER 2 Microorganisms in the Environment Wang Guohui CHAPTER 2 Microorganisms in the Environment (1) Virus particles Virus particles consist of only an inner nucleic acid genome, an outer protein capsid, and sometimes an additional membrane envelope. They are relatively simple in organization. Virus particles may or may not be infectious. (2) virion（毒粒） virion is the name given to an infectious virus particle. (3)Viroids（类病毒） Viroids are free RNA sequences（序列） able to reproduce in several genetically different hosts. 类病毒是无蛋白质外壳保护的游离的共价闭合环状单链RNA分子,侵入宿主细胞后自我复制, 并使宿主致病或死亡。 Several Important Concepts of Virus : Virus particles, virion（毒粒）, Viroids （类病毒）, Prions(朊病毒) Wang Guohui CHAPTER 2 Microorganisms in the Environment (4) Prions prions (proteinaceous （蛋白质的）infectious particles) （“朊病毒”就是“蛋白质病毒”的意思）. Prions are not subject to nucleic acid degradative enzymes(酶), Bovine（牛的）spongiform（海绵状的）encephalopathy（脑病 ） (BSE), known as “mad cow”is caused prions （“朊病毒”就是“蛋白质病毒”的意思。 ） Wang Guohui CHAPTER 2 Microorganisms in the Environment TABLE 2.2 Comparison ofViral particles,Virions, Viroids, Prions Wang Guohui CHAPTER 2 Microorganisms in the Environment 2.1.3 Structure Basic virus structures include a protein coat and internal nucleic acid, either RNA or DNA. All viruses have a nucleic acid genome and an outer protein capsid,but some may also have protein and lipid envelopes,glycoprotein（糖蛋白） spikes(刺 突), or more complex tail and sheath（衣壳） structures. Wang Guohui CHAPTER 2 Microorganisms in the Environment Structure of viruses Most viruses are too small to be seen under light microscope. All viruses consists of an RNA or DNA core genome surrounded by a protein coat capsid. The combined viral genome and capsid is called the nucleocapsid.capsomere Wang Guohui CHAPTER 2 Microorganisms in the Environment FIGURE 2.4 Simple forms of viruses and their components. The naked icosahedral viruses (A) resemble small crystals: the enveloped icosahedral viruses (B) are made up of icosahedral nucleocapsids surrounded by the envelope: naked helical viruses (C) resemble rods with a fine regular helical pattern in their surface: enveloped helical viruses (D) are helical nucleocapsids surrounded by the envelope: and complex viruses (E) are mixtures of helical and icosahedral and other structural shapes. Wang Guohui CHAPTER 2 Microorganisms in the Environment The genomes of viruses can be composed of either DNA or RNA, and some use both as their genomic material at different stages in their life cycle. However , only one type of nucleic acid is found in the virion of any particular type of virus. Wang Guohui CHAPTER 2 Microorganisms in the Environment Genome in virion Wang Guohui CHAPTER 2 Microorganisms in the Environment Viruses may be classified into several morphological types on the basis of their capsid architecture as revealed by electron microscopy and a technique called x-ray crystallography(晶 体学). 2.1.4 General Morphology Wang Guohui CHAPTER 2 Microorganisms in the Environment (A)Tobacco mosaic virus, have a helical symmetry with the capsid surrounding an RNA genome. (B).Many viruses that infect bacteria, such as the T-even bacteriophage, have a complex capsid with DNA contained within the head structure. (C) Adenovirus（腺病毒）, have isometric( 等大的) symmetry and a DNA genome. (D) Coronavirus（冠状病毒）, have complex capsids and an envelope with protruding（伸出、突 出） proteins surrounding an RNA genome. Wang Guohui CHAPTER 2 Microorganisms in the Environment Helical viruses resemble long rods that may be rigid or flexible. Surrounding the nucleic acid, their capsid is a hollow cylinder with a helical structure. An example of a helical virus that is a rigid rod is the tobacco mosaic virus. Helical viruses Wang Guohui CHAPTER 2 Microorganisms in the Environment The capsid of most polyhedral viruses is in the shape of a regular polyhedron with 20 triangular faces and 12 corners. The capsomeres of each face form an equilateral triangle. An example of a polyhedral virus is the adenovirus. Another is the poliovirus. Polyhedral（多面体的） viruses Wang Guohui CHAPTER 2 Microorganisms in the Environment The capsid of viruses is covered by an envelope. Enveloped viruses are roughly spherical but variable in shape. When helical or polyhedral viruses are enclosed by envelopes, they are called enveloped helical and enveloped polyhedral viruses. Enveloped viruses Wang Guohui CHAPTER 2 Microorganisms in the Environment Bacteriophages Complex viruses Wang Guohui CHAPTER 2 Microorganisms in the Environment 2.1.5 General Features of Virus Reproduction The virus must induce a living host cell to synthesize all the components needed to make virus particles. These components must then be assembled into the proper structure, and the new virions must escape from the cell and infect other cells. The phases of this replication process in a bacteriophage can be categorized in seven steps. Wang Guohui CHAPTER 2 Microorganisms in the Environment 1. Attachment 2. Penetration 3. Early steps in replication 4. Replication 5. Synthesisof proteins 6. Assembly 7. Release Wang Guohui CHAPTER 2 Microorganisms in the Environment Wang Guohui CHAPTER 2 Microorganisms in the Environment 1. Attachment (adsorption) of the virion to a susceptible host cell. 2. Penetration (injection) of the virion or its nucleic acid into the cell. 3. Early steps in replication during which the host cell biosynthetic machinery is altered as a prelude to virus nucleic acid synthesis. Virus-specific enzymes are typically made. Multiplication of bacteriophages Wang Guohui CHAPTER 2 Microorganisms in the Environment 4. Replication of the virus nucleic acid. 5. Synthesis of proteins used as structural subunits of the virus coat. 6. Assembly of structural subunits (and membrane components in enveloped viruses) and packaging of nucleic acid into new virus particles. 7. Release of mature virions from the cell. Wang Guohui CHAPTER 2 Microorganisms in the Environment Attachment of phage to host cell After a chance collision between phage particles and bacteria, an attachment site on the virus attaches to a complementary receptor site on the bacterial cell. Wang Guohui CHAPTER 2 Microorganisms in the EnvironmentPenetration（入侵）: During the process of penetration, the bacteriophages tail releases an enzyme, phage lysozyme, which breaks down a portion of the bacterial cell wall. then the bacteriophage injects its DNA (nucleic acid) into the bacterium. Wang Guohui CHAPTER 2 Microorganisms in the Environment Biosynthesis of viral components: Any RNA transcribed in the cell is mRNA transcribed from phage DNA for biosynthesis of phage enzymes and capsid protein. The host cells ribosomes, enzymes, and amino acids are used for translation. Wang Guohui CHAPTER 2 Microorganisms in the Environment Maturation and release: The phage heads and tails are separately assembled from protein subunits, the head is packaged with phage DNA, and the tail is attached. Wang Guohui CHAPTER 2 Microorganisms in the EnvironmentRelease: Lysozyme, whose code is provided by a phage gene, is synthesized within the cell. This enzyme causes a breakdown of the bacterial cell wall, and the newly produced bactedophages are released from the host cell. The number of newly synthesized phage particles released from a single cell usually ranges from about 50 to 200. Wang Guohui CHAPTER 2 Microorganisms in the Environment FIGURE 2.6 The basic steps of virus multiplication. Representation of an icosahedral DNA virus showing the main steps including adsorption, penetration, replication, maturation, and release. Wang Guohui CHAPTER 2 Microorganisms in the Environment 1. A dilution of a suspension containing the virus material is mixed in a small amount of melted agar with the sensitive host bacteria. 3. The host bacteria begin to grow, and after overnight incubation form a lawn of confluent growth. 2.1.6 Quantification of bacterial virus by plaque assay 2. The mixture poured on the surface of a nutrient agar plate. Wang Guohui CHAPTER 2 Microorganisms in the Environment Photograph of a plate showing plaques formed by bacteriophage on a lawn of sensitive bacteria. The plaques shown are about 1-2 mm in diameter. The size of the plaque formed depends on the virus, the host, and conditions of culture. Phage plaques Wang Guohui CHAPTER 2 Microorganisms in the Environment A virus that is parasitic in bacteria; it uses the bacteriums machinery and energy to produce more phage until the bacterium is destroyed and phage is released to invade surrounding bacteria Bacteriophage: Wang Guohui CHAPTER 2 Microorganisms in the Environment The alternatives on infection are integration of the virus DNA into the host DNA (lysogenization) or replication and release of mature virus (lysis). The lysogenic cell can also be induced to produce mature virus and lyse. Wang Guohui CHAPTER 2 Microorganisms in the Environment 2.1.7 Indigenous Virus Populations in the Environment 环境中土著的病毒种群 FIGURE 2.1 The role of bacteriophage in the microbial food web. Wang Guohui CHAPTER 2 Microorganisms in the Environment Wang Guohui CHAPTER 2 Microorganisms in the Environment Summary Viruses Bacteria Fungi Algae Protozoa Wang Guohui CHAPTER 2 Microorganisms in the Environment Thank you! 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