Micro exam 4

• Consortium


  Physical association of two organisms (beneficial)
• Ectosymbiont


  • One organism on the surface of the other
• Endosymbiont


  • One organism within the other
• Types of microbial interactions

  • Positive
  • Negative
• Positive interactions

  • Mutualism
  • Syntrophism
  • Commensalism
• Negative interactions

  • Predation
  • Parasitism
  • Amensalism
  • Competition
• Mutualism


  Some benefit occurs to both partners (mutualist and host), mutualist and host are metabolically interdependent
• Mutualism example

  • Ruminants (herbivorous animals like cow, deer, camel) and cellulose digesters that break up 1-4 bonds of cellulose
• Commensalism


  Commensal benefits while other (host) is unaffected
• Commensalism example

  • Nitromonas produces nitrite, Nitrobacter uses nitrite for energy
• Syntrophism


  Growth of one depends on or is improved by another growing nearby through production of nutrients, growth factors or substrates
• Predation


  Predator attacks the prey
• Parasitism

  One (parasite) benefits at the expense of the host
• Parasitism example

  • Tapeworms
• Amensalism


  Negative effect of one on the other (unidirectional) by release of specific compounds
• Amensalism example


  • Antibiotic production
• Competition


  Different members of a population try to acquire the same resource
• Biogeochemical cycles

  • Carbon Cycle
  • Nitrogen Cycle
  • Mercury Cycle
• Edward Jenner inoculated a boy with cow pox virus and protected him against small pox infection


  1798
• Charles Chamberland invented porcelain filters to separate bacteria


  1884
• Dimitri Ivanowski - leaf extracts even after filtration were able to cause the disease tobacco mosaic disease (said was a toxin)


  1892
• Martinus Beijerink proposed disease (TMV) caused by a virus


  1898
• Fredrick Twort isolated viruses that infect bacteria (phages)


  1915
• Felix d'Herelle proved bacteria are infected by viruses by performing the plaque assay, demonstrated viruses needed live cells to reproduce, termed them bacteriophage


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• Virus properties

  • Acellular - not living organisms
  • Obligate intracellular parasites
  • Presence of DNA or RNA

  
• Virion


  A complete virus particle - genetic material surrounded by protein coat (other layers), extracellular existence

  
• Virus


  Intracellular existence, outside cell, inside cell

  
• Virus reproduction


  Acellular, not living organisms

  
• Cultivation of Viruses


  Depend on living cells for reproduction

  
• Cultivation of Viruses

  • Egg host (mumps virus)
  • Cell tissue cultures - monolayer of animal cells in dish, infect with virus, cells lyse (plaque), viruses are released

  
• Virus Purification


  1. Differential Centrifugation - separate virus from cellular parts

  2. Gradient Centrifugation - separates on basis of size and density (sedimentation coefficient)

  3. Enzymatic digestion - cellular proteins and nucleic acids can be removed

  4. Organic solvent treatment - viruses more resistant to denaturation
• Viral Assays


  • Electron microscope - beads of specific size and concentration are counted with the viruses, virus concentration is determined as a proportion compared to bead concentration
  • Hemagglutination assay - some viruses can bind to erythrocytes, if concentration is large enough they will link erythrocytes together and the mesh will precipitate out of solution, get a measure of the relative quantity of virus
  • Plaque assay - single plaque is due to a single virus, can enumerate the number of plaque forming units (PFU) = viruses
• Nucleocapsid


  Nucleic acid held within a protein coat (capsid)
• Virion Structure


  • Nucleocapsid - nucleic acid held within a protein coat (capsid)
  • Capsid morphology - icosahedral, capsomeres, protomers
  • Influenza virus (enveloped) - nucleocapsid, viral nucleic acids
• 1. Even Phage (complex phage)


  Maximise bacteria, reinfect
• Bacteriophage


  Viruses that specifically infect bacteria
• Classification of Bacteriophage

  • Morphology - what they look like
  • Nucleic acid content - type of nucleic acid they contain
• Major Bacteriophage Families and Genera

  • Positive strand - always mRNA
• Reproduction of DNA phage: The lytic cycle


  1. Adsorption / Attachment

  2. Entry Into Host

  3. Synthesis of phage nucleic acids and proteins

  4. Assembly of phage particles

  5. Release of phage
• Adsorption and penetration (T-4 phage)

  • Adsorption - attachment to receptor sites on the cell via tail fibers, receptor sites determine host preference: Flagella, Pili, Teichoic acids, Cell Wall proteins, LPS
  • Electrostatic forces, Baseplate attachment, dsDNA gives specificity