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Prokaryote diversity

Prokaryote diversity. Level 1 Biological Diversity Jim Provan. Campbell: Chapter 27. Prokaryotes are (almost) everywhere. Prokaryotes dominate the biosphere: Collective mass of prokaryotes outweighs eukaryotes tenfold

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Prokaryote diversity

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  1. Prokaryote diversity Level 1 Biological Diversity Jim Provan Campbell: Chapter 27

  2. 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

  3. The three domains of life Domain Bacteria Domain Archaea Domain Eukarya

  4. Diversity of prokaryotic cell shapes

  5. Prokaryote cell walls

  6. 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

  7. 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

  8. Prokaryote organisation

  9. 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

  10. Mode Energy source Carbon source Example Chemoheterotroph Organic compounds Organic compounds Prokaryotes, protists, fungi, animals, parasitic plants Prokaryote metabolic diversity Photoautotroph Light CO2 Cyanobacteria, plants, protists Chemoautotroph Inorganic compounds CO2 Some prokaryotes (Sulfolobus) Photoheterotroph Light Organic compoundsSome prokaryotes

  11. DOMAIN BACTERIA DOMAIN ARCHAEA Proteobacteria Chlamydias Spirochetes Gram positive bacteria Cyanobacteria Euryarchaeota Crenarchaeota a b g d e A survey of prokaryote diversity DOMAIN EUKARYA

  12. DOMAIN CHARACTERISTIC Nuclear envelope Organelles Peptidoglycan cell wall Membrane lipids RNA polymerase Initiator amino acid Introns Antibiotic response Histones Bacteria x x  Unbranched One f-Met x Inhibited x Archaea x x x Some branched Several Met  Not inhibited  Eukarya   x Unbranched Several Met  Not inhibited  The three domains of life

  13. 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

  14. Domain Bacteria: Proteobacteria

  15. Domain Bacteria: others

  16. 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

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

  18. 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

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