Bacteria and Viruses

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Bacteria and Viruses

• Biology
• Mrs. Volin

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Prokaryotes

• Single celled organisms that lack a nucleus
• Once called Kingdom Monera
• Now Kingdom Eubacteria and
• Kingdom Archaebacteria

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Eubacteria

• Live almost everywhere
• Cell wall contains peptidoglycan

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Archaebacteria

• Live in harsh environments extremophiles
• Thermophiles
• Halophiles
• Methanogens
• Lack peptidoglycan in cell walls
• Different membrane lipids from eubacteria

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Identifying prokaryotes --- shape
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Identifying prokaryotes --- cell walls

• In eubacteria---
• Some bacteria have cell wall high in
  peptidoglycan Gram-positive
• Stain violet
• Some bacteria have cell wall containing
  peptidoglycan and outer layer of
  lipid/carbohydrates Gram-negative
• Stain pink

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Gram Stain
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Gram negative Ex E.coli, Salmonella
Gram positive Ex Staphylococcus, Streptococcus
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Identifying prokaryotes ---movement

• Movement by flagella
• Movement by slithering, lashing, spiralling
• Movement by gliding on slime layer
• No movement at all

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Identifying prokaryotes --- method of obtaining
energy
Lyngbia sp.

• Autotrophs
• Photoautotrophs carry out photosynthesis
• Chemoautotrophs obtain energy from chemicals
  (ammonia, H2S, nitrite, sulfur, iron)

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Identifying prokaryotes --- method of obtaining
energy

• Heterotrophs use organic compounds as food
• Photoheterotrophs Carry out photosynthesis and
  need organic compounds for food (carbon source)

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Bacteria obtain their energy through cellular
respiration and fermentation

• Bacteria that require oxygen obligate aerobes
• Bacteria that cannot tolerate oxygen obligate
  anaerobes
• (example Botulism caused by Clostridium
  botulinum)
• Bacteria that survive with or without oxygen
  facultative anaerobes

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Reproduction of bacteria

• Binary fission
• Asexual
• Conjugation transfer of genetic information from
  one cell to another

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Some bacteria form endospores

• Dormant state when faced with unfavorable
  environment (heat, dryness, lack of nutrients)
• Endospore is enclosed by thick wall, which
  resists environmental conditions
• Allows bacterium to survive harsh
  conditions---some for centuries

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Roles of bacteria

• Decomposers/recyclers
• Photosynthesizers
• Nitrogen fixation
• Rhizobium uses nutrients in soybean roots/
  converts N2 gas in air to ammonia
  fertilizer-----a symbiotic relationship

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Roles of bacteria

• Food production
• Cheese, yogurt, pickles, sauerkraut
• Industry
• Digestion of petroleum
• Synthesis of drugs

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Bacteria and Disease

• Bacteria are everywhere in nature, but only a few
  cause disease.
• Disease causing agents pathogens
• Two ways of causing disease
• Breakdown of tissues (example tuberculosis)
• Release of toxins (example strep throat)

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2000 years ago---Immunity to disease noted by
Hippocrates

• When people survive certain diseases, they never
  develop those diseases again----they are
  permanently immune

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1796---Edward Jenner---the first vaccine

• Noticed that milkmaids who contracted cowpox from
  cows were immune to smallpox
• Prepared first vaccine from pus of a cowpox
  patient
• Applied the fluid to cut on 8-year old Jamie
  Phipps
• Later, exposed Phipps to smallpox

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Louis Pasteur

• Could a weakened bacterium
• produce immunity?
• - Weakened anthrax given to 25 sheep.
• - One week later, anthrax was injected
• into those sheep. 25 untreated sheep served as
  a control.
• - The next day, the 25 untreated sheep died of
  anthrax.

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Vaccines

• 1885 --- Pasteur developed first vaccine for
  rabies
• 1950s --- Jonas Salk developed first polio
  vaccine

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Preventing bacterial growth in food

• Sterilization - Destroys bacteria with heat or
  chemicals
• Low temperature
• Thorough cooking
• Canning
• Chemical preservation

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Viruses

• Viruses do not have all the characteristics of
  life
• They are not cells
• Cannot reproduce independently
• Viruses have some characteristics of living cells
• Can copy themselves
• Regulate gene expression
• They evolve
• Viruses probably developed after living cells

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Viruses

• Made up of nucleic acid and protein only
• Reproduce only by infecting living cells
• Can only be viewed with electron microscope
• Contain few genes (usually lt100)
• Highly specific to certain cells

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Some virus structures
HIV
HIV
capsid ---protein coat
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Lytic infection

• Example T4 Bacteriophage
• T4 Bacteriophage enters cell, makes many copies
  of itself, causes cell to burst (to lyse)

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T4 Bacteriophage Lytic Infection
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Lysogenic Infection

• Example Bacteriophage lambda
• The host cell makes copies of the virus
  indefinitely
• Virus inserts its DNA into host DNA creating a
  prophage
• Host cell replicates many generations creating
  many cells containing prophages
• Cycle eventually switched to lytic infection

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Lysogenic Infection
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Retroviruses

• Some RNA-containing viruses are retroviruses
• retro because they produce a DNA copy of
  their RNA when they infect cell
• Viral DNA inserts into host DNA
• Example AIDS
• Enzyme reverse transcriptase catalyzes production
  of DNA from RNA

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Prions

• Unknown until 1986
• Made of protein only / No nucleic acids
• Convert host protein into prions
• Uses host protein, but folds them differently

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Diseases caused by prions

• Mad cow disease / Creutzfeldt-Jacob disease
  (CJD)
• Prions infect and destroy brain tissue
• Other diseases
• GSS Gerstmann-Straussler-Scheinker syndrome
• FFI Fatal familial Insomnia
• Kuru
• Alpers Syndrome
• Alzheimers disease?
• Parkinsons disease?