World of Prokaryotes

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Chapter 27

• World of Prokaryotes

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Everywhere

• Contain the most biomass of any living thing
• Live in extreme conditions
• Mostly only hear about disease causing bacteria,
  but most are very helpful
• Cycle nutrients
• Provide us with vitamins
• Live in symbiotic relationships with some
  organisms

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Bacteria and Archaea

• Two main branches of prokaryote evolution
• Archaea inhabit extreme conditions
• Bacteria are the most commonly studied
  prokaryotes
• Five Kingdom system has been reworked into a
  three domain system

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Structure and Function

• Unicellular
• Some form colonies with division of labor
• Cell shapes among prokaryote
• Spheres cocci
• Rods bacilli
• Helices spirilla
• Diameters range from 1-5 um
• Eukaryotes range from 10-100 um

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Structure of Prokaryotes

• Cell walls exist external to plasma membrane
• Contain peptidoglycan (plants use cellulose)
• Walls of Archaea do not contain peptidoglycan
• Gram positive and gram negative stains
• Useful for identifying bacteria

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Gram stain
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Mobility

• Half of all prokaryotes are capable of
  directional movements
• Most use flagella
• Flagella can be scattered over the cell surface
  or concentrated at one or both ends

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Mobility

• Spirochetes helix shaped bacteria, with basal
  motor powered filaments propel the organism like
  a cork screw
• Some secrete slime then as the slime grows the
  bacteria can move
• Flagellated bacteria are capable of taxis

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Cellular and Genomic Organization

• Prokaryotes differ from eukaryotes in this topic
• Remember that prokaryotes have no nucleus
  enclosed membrane
• They do however have specialized membranes that
  do specific jobs
• Prokaryotes have smaller genomes
• 1/1000th as much DNA as eukaryotes
• One chromosome in ring form

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Plasmids

• Accessory pieces of DNA
• Normally not needed
• Some give resistance to antibiotics,
• And can be transferred from one bacteria to
  another

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Growth and Adaptation

• Reproduce by binary fission
• Not meiosis or mitosis
• They do reproduce asexually, but they can
  transfer genes from one individual to another
• Transformation cell takes up genes from the
  environment
• Conjugation direct transfer of genes from one
  individual to another
• Transduction viruses transfer genes from one to
  another

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Adaptation

• Generations are measured in minutes
• Favorable mutations can be rapidly propagated
  into the population
• Endospores dormant state for a bacteria to
  survive harsh conditions
• Some can last for 250 million years

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Nutrition and Metabolic Diversity

• Nutrition refers to how an organism obtains
  energy and a carbon source
• Phototrophs use light energy
• Chemotrophs use chemical energy
• Autotrophs need only CO2 as a carbon source
• Heterotrophs require at least one organic
  molecule as a carbon source

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Nutritional and Metabolic Diversity
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Prokaryotic Diversity
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Domain Archaea

• Archaea are sometimes called extremophiles
  because they thrive in difficult areas
• Methanogens use CO2 to oxidize H2 producing
  methane as a byproduct.
• Poisoned by oxygen
• Extreme halophiles live in very salty seas and
  lakes
• Extreme thermophiles - live in deep water vents,
  and
• Two main groups
• Euryarchaeota methanogens and halophiles
• Crenarchaeota - thermophiles

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Domain Bacteria

• Most known prokaryotes are bacteria
• Five main groups (several have been omitted)

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Proteobacteria

• Large and diverse group containing both gram
  negative and positive individuals
• Alpha this group has close relationships with
  eukaryotes
• Beta contains nitrogen fixing bacteria
• Gamma E. coli
• Delta myxobacteria, form elaborate colonies
• Epsilon Helicobacter pylori

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Chlamydias

• Parasites on animal cells
• Most common cause of blindness in the world
• Most common STD in the US.

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Spirochetes

• Helical shaped heterotrophs
• Most are free living
• But some parasitic like the species that causes
  syphilis

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Gram-positive bacteria

• Very diverse group
• Some very close relatives of gram-negative
  bacteria in this group

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Cyanobacteria

• Plantlike photosynthesizers
• Abundant in wherever there is water

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Ecological Impact of Prokaryotes

• Decomposers
• Symbiotic relationships
• Mutualism
• Commensalism
• Parasitism

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Human Diseases

• Most of us have harmful bacteria living on or in
  us now
• When resistance is low we can become sick
• Opportunistic diseases
• Bacteria also produce exotoxins and endotoxins
• Exotoxins botulism (1 g of toxin is enough to
  kill 1 million people)
• Endotoxins toxins present on the walls of
  bacteria
• Salmonella