Prokaryote%20diversity

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Prokaryote diversity

• Level 1 Biological Diversity
• Jim Provan

Campbell Chapter 27
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Prokaryotes are (almost) everywhere

• Prokaryotes dominate the biosphere
• Collective mass of prokaryotes outweighs
  eukaryotes tenfold
• More prokaryotes in the average human mouth than
  all the humans that ever lived
• Prokaryote diversity
• About 5,000 species known
• Actual numbers believed to be 400,000 to 4 million

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The three domains of life
Domain Bacteria
Domain Archaea
Domain Eukarya
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Diversity of prokaryotic cell shapes
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Prokaryote cell walls
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Prokaryote cell walls

• Present in nearly all prokaryotes
• Provides physical protection
• Prevents cells from bursting in hypotonic
  environment
• Reason prokaryotes were sometimes grouped with
  plants in early classification systems
• Cell wall contains peptidoglycan, rather than
  cellulose
• Gram-negative bacteria generally more pathogenic
  than gram-positive bacteria
• Lipopolysaccharides can be toxic
• Outer membrane less permeable to antibiotics
• Antibiotics inhibit cross-linking of peptidoglycan

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Prokaryote organisation

• Prokaryotes have smaller, simpler genomes than
  eukaryotes
• On average, about one-thousandth as much DNA
• Concentrated in twisted nucleoid region
• Single, circular chromosome
• Also have accessory DNA plasmids
• General mechanism of DNA replication and protein
  translation is largely the same as in eukaryotes
• No organelles, but some have specialised
  membranes which carry out similar functions

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Prokaryote organisation
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Prokaryote reproduction

• Prokaryotes reproduce only asexually by binary
  fission
• DNA synthesis is almost continuous
• No mitosis or meiosis
• Gene transfer is possible
• Transformation take up of genes from
  surroundings
• Conjugation direct transfer of genes between
  cells
• Transduction gene transfer by viruses
• Mutation is the major source of genetic variation
• Growth is actually increase in numbers, which
  effectively proceeds geometrically

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Prokaryote metabolic diversity
Photoautotroph Light CO2 Cyanobacteria, plants,
protists
Chemoautotroph Inorganic compounds CO2 Some
prokaryotes (Sulfolobus)
Photoheterotroph Light Organic compounds Some
prokaryotes
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A survey of prokaryote diversity
DOMAIN EUKARYA
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The three domains of life
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Domain Archaea

• Inhabit most extreme environments
• Methanogens - strict anaerobes which use H2 to
  reduce CO2 to methane (CH4)
• Extreme halophiles - live in saline environments
  five to ten times saltier than sea water
• Extreme thermophiles - live in very hot
  environments such as sulphur springs of deep-sea
  hydrothermal vents

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Domain Bacteria Proteobacteria
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Domain Bacteria others
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Ecological impact of prokaryotes

• Prokaryotes are crucial components of ecosystems
• Decomposition of waste products
• Recycling of elements from inorganic sources
  (soil, air etc.)
• Many prokaryotes are symbiotic
• Rhizobium N2 fixation
• Bioluminescence

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Some prokaryotes are pathogenic

• Pathogenic prokaryotes cause half of all human
  disease
• Some pathogens are opportunistic they cause
  illness when the hosts defences are weakened
• Mostly produce toxins
• Exotoxins secreted by prokaryotes e.g. in food or
  water
• Endotoxins are components of bacterial membranes

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Humans use prokaryotes

• Used as model systems to study genetics e.g.
  Escherichia coli
• Used in bioremediation
• Sewage treatment
• Decomposition of oil spills by soil bacteria
• Metabolic factories
• Organic solvents
• Antibiotic production
• Food industry