BSCI 124 Lecture Notes

Undergraduate Program in Plant Biology, University of Maryland

LECTURE 15 - Viruses and Prokaryotes

Overview of the classification of organisms - biologists divide living organisms into kingdoms as a first step in organizing how they are related to each other. The classification of kingdoms is based on cell structure and details of metabolism. For example, plants are a separate kingdom, but certain plant-like organisms are in other kingdoms due to differences in cellular organization. New kingdoms have been recently added as scientists have recognized forms of life that are significantly different than others. [For a detailed review of the Plant Kingdom, see the site maintained by Cardillo & Samuels]

  1. Non-living organisms Virus
    1. Technically non-living since they can not self-replicate, thus not a kingdom
    2. consists of just a protein coat for protection and a nucleic acid (RNA or DNA) for information how to make more copies of the same virus
    3. Cellular parasite- uses cell machinery of a host cell to replicate and so produce more viruses
    4. Wide variety of : EM pictures: sizes and shapes
    5. Cause numerous diseases of plants, animals (including humans), bacteria, fungi
      1. examples of human viruses:
        1. herpes virus ,
        2. hepatitis virus ,
        3. rabies,
        4. ebola ,  -emerging epidemics (video and pictures of 1995 outbreak in Zaire)
        5. influenza , -recombination between avian(bird) and pig viruses and human viruses can produce new strains which spread world-wide- e.g. the Hong Kong avian flu of Fall 1997 .  Flu fact sheet- CDC. Dealing with the flu
        6. HIV (AIDS) (infection process-cartoon HIV info ).
      2. Examples of plant viruses:
        1. potyvirus causing streaking ,
        2. Tobacco Mosaic Virus causing mosaic (mottling) symptoms ,
        3. rose mosaic symptoms ,
        4. spots on fruit
    6. Virus-like agents
      1. Viroids- Segments of RNA which are not packaged into a protein coat
      2. Prion- infectious proteins. e.g. Mad Cow Disease, (WHO FAQ, less technical description) Kuru, CJ,
  2. Living Organisms-two main groups
    1. PROKARYOTIC - lack membrane-bounded organelles
      1. Kingdom Eubacteria (bacteria) - originally classified as plants because they have cell walls -- Also known as Monera.
      2. Kingdom Archaea (or Archaebacteria) early evolution of life
    2. EUKARYOTIC - membrane-bounded organelles present
  3. Summary of the kingdoms of life
    1. Kingdom Fungi - molds, mildews, an mushrooms (originally called plants because they have cell walls and some are "rooted" in the ground)
    2. Kingdom Protista - includes algae and slime molds, protozoa (animal-like protists) - originally considered plants because they have cell wall (not cellulose) -- Also known as Protoctista
    3. Kingdom Plantae
      1. Complex multicellular eukaryotes
      2. Obtain nutrients by photosynthesis
    4. Kingdom Animalia
      1. Complex multicellular eukaryotes
      2. Obtain nutrients by eating food (ingest)
  4. Details on the Prokaryotes (Bacteria and Archaea)
    1. Prokaryotic - little internal organization, lack membrane- bounded organelles: Includes bacteria and archaea (archibacteria) Features  bacteria in infected lung
    2. Have cell wall, but not made of cellulose
    3. Obtain nutrients in a variety of ways, most through absorption
      1. some are photosynthetic, called cyanobacteria (previously known as blue-green algae) . Often found in extreme environments or as stromatolitesprehistoric or modern ) that were involved in the formation of an oxygen atmosphere on earth. Many are toxic especially in water
    4. Rapid growth through division of one cell into two
      1. produces exact copy of itself - (termed asexual reproduction) -produces very rapid growth
    5. No membranes except plasma membrane
    6. No mitochondria, chloroplasts, ER, nucleus
    7. No mitosis- simple division
    8. Genetic material(1 loop of DNA) but no nuclear membrane surrounding it. No true sexual reproduction but it does have means of Genetic exchange
    9. Can survive millions of years
    10. Eubacteria (bacteria)
      1. B. Size - probably smallest living organisms; some about 1/25,000th inch
      2. shapes: cocci (spherical), bacilli (cigar shaped), spirilli (helical)
    11. Archaea (or Archaebacteria) versus true bacteria (or Eubacteria). Archea were once thought to be bacteria. However, they have certain features that are unique or are shared with eukaryotes; thus they have been placed in a separate kingdom.
      1. Archaea are probably found all around us but are unique in being found in extreme environments
        1. high temperature environments: steam vents, deep ocean vents , hot springs derive energy from oxidation of organic compounds with sulfur (S2) rather than O2
        2. high salt environments: salt lakes or evaporating ponds
        3. methanogens: derive energy from organic compounds by combining with hydrogen gas to form methane (e.g. intestinesDental plaque bacteria of animals and people)
  5. Significance of bacteria to humans
    1. Beneficial bacteria (about 90 percent)
      1. Nitrogen-fixation in the biosphere (convert atmospheric nitrogen, a very stable molecule, to useful nitrogen) - 78% atmos N2

        nitrogen gas ---> plants ---> animals
      2. Decomposition in the biosphere - live on dead organisms, natures recyclers
      3. Intestinal bacteria - supply vitamins ( especially vitamin K)
    2. Pathogenic bacteria-invade host organism, derive nutrition from cells for reproduction (mechanisms of how they cause disease- e.g. toxins)
      1. Human diseases -
        1. pneumonia (1 by bacteria, 1 by virus),
        2. Cholera
        3. Lyme disease- carried by ticks (carry a range of diseases)
        4. gonorrhea, and other sexually transmitted diseases
        5. botulism (food poisoning) - toxins
        6. E. coli -source of many recent food poisonings-e.g. hamburger
        7. Salmonella of food (e.g. eggs)
        8. Campylobacter- bacterial diarrhea
        9. Also some diseases which were not previously thought to be bacterial infections- e.g. ulcers or heart disease
      2. Plant diseases - soft rot (e.g. lettuce in your refrigerator), crown rot (e.g. that African Violet on your windowsill that is looking limp (about 200 different diseases)
        1. diseases you may notice around your yard/garden or kitchen: bacterial wilt , spot of tomatoes , fire blight of apples and pears
      3. how to control bacteria to prevent disease
        1. heating/cooking (e.g. in canning)
        2. cold temperatures- limit bacterial growth (e.g. refrigeration)
        3. disinfectants-kills most living organisms (e.g. bleach, alcohol, iodine)
        4. antibiotics (e.g. penicillin , tetracycline , erythromycin ) - drugs that will selectively kill bacteria without killing the host  (several different ways of doing this) and so allow treatment of the host. Movie of bacterial inhibition by penicillin .
        5. However problems are arising with antibiotic-resistant bacteria(e.g. hospital staph infections)
    3. Commercial uses
      1. Yogurt, sour cream, sauerkraut; fermentation
      2. Genetically-engineered bacteria produce insulin , interferon, bovine somatotropin (BSt) and other important medicines

Others Sites of Interest:
Basic Review
Bacterial nomenclature
Technical information on names of bacteria
Images of Viruses
Baltimore Classification of Viruses: technical
Classification of Virus Taxa: Technical
World Data Center for Microorganisms
Glossary of Microbiology
Microbes in the news pictures of plant viruses

FDA food poisoning information
Biological Weapons-Scientific American Article

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last updated Feb 10, 1999, Straney