BACTERIA AND ARCHAEA

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BACTERIA AND ARCHAEA

• Chapter 20

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• A. Prokaryote Cell Structure

• All prokaryotes have
• cell membrane
• cytoplasm
• ribosomes
• nucleoid region containing DNA
• Most have a cell wall

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• Some prokaryotes have
• plasmids
• pili
• flagella
• glycocalyx

Some prokaryotes form endospores that enable them
to survive harsh conditions.
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• B. Prokaryote Classification
• 1. Traditional Methods of Classification
• Based on observable characteristics groupings do
  not necessarily reflect evolutionary
  relationships.
• Based on Cell Morphology
• Cocci - have spherical shaped cells

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• Bacilli - have rod shaped cells

• Spirilla - have spiral shaped cells

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• Based on Staining Characteristics
• Gram positive () bacteria
• Cell walls have thick peptidoglycan layer stain
  purple.

• Gram negative (-) bacteria
• Cell walls have thin peptidoglycan layer an
  outer membrane stain pink.

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• Based on Method of Acquiring Carbon Energy
• Autotrophs - acquire carbon from inorganic
  sources (CO2).
• Heterotrophs - acquire carbon from organic
  sources (other organisms).
• Phototrophs - obtain energy from the sun.
• Chemotrophs - obtain energy by oxidizing
  inorganic or organic chemicals.

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• Based on Oxygen Requirements
• Obligate aerobe - requires oxygen to generate ATP
  (cellular respiration).
• Ex. Bacillus
• Obligate anaerobe - generates ATP without oxygen
  oxygen is toxic.
• Ex. Clostridium tetani
• Facultative anaerobe - generates ATP with or
  without oxygen.
• Ex. Escherichia coli Salmonella

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• Based on Habitat
• Acidophile - prefers a low pH (1.0-5.4)
  environment. hot springs
• Halophile - prefers an extremely salty (3.5-30)
  environment. ocean
• Methanogen - prefers an anaerobic environment
  produces methane as a byproduct. human
  gastrointestinal tract
• Thermophile - prefers extreme heat (50oC-100oC).
  compost heaps

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• 2. Modern Methods of Classification
• Based on molecular data groupings reflect
  evolutionary relationships.
• Ribosomal RNA (rRNA) sequences of prokaryotes are
  compared to identify signature sequences.
• Signature sequences are short stretches of
  nucleotides that are unique to certain types of
  organisms.

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• C. Prokaryote Gene Transfer
• Genes can be transferred vertically or
  horizontally.
• 1. Vertical Gene Transfer
• Transmission of DNA from a parent cell to
  daughter cells.
• Occurs by binary fission.

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• 2. Horizontal Gene Transfer
• Transmission of DNA from one cell to another cell
  that is not a daughter cell.
• Occurs by transformation, transduction, and
  conjugation.
• Transformation
• Cell takes up DNA fragments or plasmids from the
  environment.

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• Transduction
• A virus picks up DNA from one cell and transfers
  it to another.

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• Conjugation
• A sex pilus (cytoplasmic bridge) transfers DNA
  from one cell to another.

Sex pilus
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• D. Prokaryotes and Man
• 1. Harmful effects
• A few species of bacteria are harmful to man
  because they are pathogenic.
• Bacterial infections may be spread by
• Air - Legionella pneumophila (causes
  legionellosis, a form of pneumonia).
• Arthropods - Yersinia pestis (causes bubonic
  plague) is transmitted to humans by rat fleas.

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• Direct Contact - Neisseria gonorrhoeae (causes
  gonorrhea) is transmitted by sexual contact.
• Food Water - Vibrio cholerae (causes cholera)
  Salmonella enteritidis (causes food poisoning).
• The use of pathogenic organisms as bioweapons
  continues to be a major area of concern despite
  the fact that germ warfare was banned by
  international law in 1925.

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• 2. Beneficial effects
• Most prokaryotes are beneficial in that they
• break down organic wastes dead organisms.
• cycle chemical elements (oxygen, nitrogen)
  between organisms the environment.
• are used in the production of food. (vinegar,
  pickles, sauerkraut, olives, yogurt, cheese)

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• are used to mass-produce certain non- food items.
  (vitamins, enzymes, ethanol, acetone, human
  insulin blood clotting factors)
• are used in water and waste treatment.
• are used in bioremediation. (certain microbes
  degrade oil, while others remove heavy metals
  from water)