Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings PowerPoint ® Lecture Slide Presentation prepared by Christine L. Case Microbiology B.E Pruitt & Jane J. Stein AN INTRODUCTION EIGHTH EDITION TORTORA FUNKE CASE Chapter 13, part A Viruses, Viroids, and Prions

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Viruses Viruses contain DNA or RNA And a protein coat Some are enclosed by an envelope Some viruses have spikes Most viruses infect only specific types of cells in one host Host range is determined by specific host attachment sites and cellular factors

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Viruses versus cellular organisms Viruses simple organization DNA or RNA but not both (one exception) unable to reproduce outside of living cells obligate intracellular parasites Cellular Organisms complex organization both DNA and RNA carry out cell division some are obligate intracellular parasites

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Viruses Figure 13.1

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Helical Viruses Figure 13.4a, b

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Polyhedral Viruses Figure 13.2a, b

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Complex Viruses Figure 13.5a

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Viral Taxonomy Family names end in -viridae Genus names end in -virus Viral species: A group of viruses sharing the same genetic information and ecological niche (host). Common names are used for species Subspecies are designated by a number

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Viral Taxonomy Herpesviridae Herpesvirus Human herpes virus 1, HHV 2, HHV 3 Retroviridae Lentivirus Human Immunodeficiency Virus 1, HIV 2

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Growing Viruses Viruses must be grown in living cells. Bacteriophages form plaques on a lawn of bacteria. Figure 13.6

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings The Cultivation of Viruses requires inoculation of appropriate living host

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Hosts for animal viruses suitable animals embryonated eggs tissue (cell) cultures monolayers of animal cells plaques localized area of cellular destruction and lysis cytopathic effects microscopic or macroscopic degenerative changes or abnormalities in host cells and tissues

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Growing Viruses Animal viruses may be grown in living animals or in embryonated eggs. Figure 13.7

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Growing Viruses Animal and plants viruses may be grown in cell culture. Continuous cell lines may be maintained indefinitely. Figure 13.8

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Cytopathic effects Serological tests Detect antibodies against viruses in a patient Use antibodies to identify viruses in neutralization tests, viral hemagglutination, and Western blot Nucleic acids RFLPs PCR Virus Identification

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Hosts for bacteriophages usually cultivated in broth or agar cultures of suitable, young, actively growing bacteria broth cultures lose turbidity as viruses reproduce plaques observed on agar cultures

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings AttachmentPhage attaches by tail fibers to host cell PenetrationPhage lysozyme opens cell wall, tail sheath contracts to force tail core and DNA into cell BiosynthesisProduction of phage DNA and proteins MaturationAssembly of phage particles ReleasePhage lysozyme breaks cell wall Multiplication of Bacteriophages (Lytic Cycle)

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Figure Attachment: Phage attaches to host cell. Penetration: Phage penetrates host cell and injects its DNA. Biosynthesis: DNA and Protein Bacterial cell wall Bacterial chromosome Capsid DNA Capsid Sheath Tail fiber Base plate Pin Cell wall Tail Plasma membrane Sheath contracted Tail core

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Figure Maturation: Viral components are assembled into virions. Tail 5 Release: Host cell lyses and new virions are released. DNA Capsid Tail fibers

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings One-step Growth Curve Figure 13.11

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Lytic cyclePhage causes lysis and death of host cell Lysogenic cycleProphage DNA incorporated in host DNA

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings The Lysogenic Cycle Figure 13.12

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Specialized Transduction Figure Prophage exists in galactose-using host (containing the gal gene). Phage genome excises, carrying with it the adjacent gal gene from the host. Phage matures and cell lyses, releasing phage carrying gal gene Prophage gal gene Bacterial DNA Galactose-positive donor cell gal gene Phage infects a cell that cannot utilize galactose (lacking gal gene). 4 Galactose-negative recipient cell Along with the prophage, the bacterial gal gene becomes integrated into the new host’s DNA. 5 Lysogenic cell can now metabolize galactose. 6 Galactose-positive recombinant cell

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings AttachmentViruses attaches to cell membrane PenetrationBy endocytosis or fusion UncoatingBy viral or host enzymes BiosynthesisProduction of nucleic acid and proteins MaturationNucleic acid and capsid proteins assemble ReleaseBy budding (enveloped viruses) or rupture Multiplication of Animal viruses

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Virus Purification and Assays development of virology closely linked to development of these methods

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Virus Purification four commonly used methods differential centrifugation and density gradient centrifugation precipitation of viruses denaturation of contaminants enzymatic digestion of cell constituents

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Differential centrifugation separates based on size

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Density gradient centrifugation

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Measuring concentration of infectious units plaque assays dilutions of virus preparation made and plated on lawn of host cells number of plaques counted results expressed as plaque-forming units (PFU)

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings

Measuring concentration of infectious units… infectious dose and lethal dose assays determine smallest amount of virus needed to cause infection or death of 50% of exposed host cells or organisms results expressed as ID 50 or LD 50

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