Classification of life review

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Classification of life (review)

• Taxonomy is the naming of organisms
• Begun with Linnaeus
• Systematics is the classification of organisms
  based on our best guess about their phylogeny
• Evolutionary history
• Members of the same genus diverged from a common
  ancestor more recently than two species from
  different genera

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Domain - highest level of classification

• Domain Bacteria
• Domain Archaea
• Domain Eukarya
• Where are viruses classified?

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Domain Bacteria

• Small cells (generally 1 - 5 mm)
• DNA in circular chromosome (nucleoid region)
• Also smaller circles of DNA plasmids
• Can take up DNA transformation
• Recall Griffith experiment
• Cell wall composed of peptidoglycan
• Motile cells have flagella (thinner than
  eukaryotes)
• Capable of taxis (move toward or away from X)

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Bacteria

• Come in common shapes
• Bacillus (rod-shaped)
• Coccus (spherical)
• Diplococcus (pairs)
• Streptococcus (chains)
• Staphycoccus (bunches)
• Spirillum (spiral)

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Terminology on nutritional modes

• Nutritional mode energy source carbon source
• Autotrophs
• Photoautotrophs use light energy inorganic C
• Chemoautotrophs inorganic molecules CO2
• Heterotrophs
• Photoheterotrophs light organic C
• Chemoheterotrophs Organic molecules for both

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Bacteria

• Asexual reproduction via binary fission
• Many produce durable endospores
• Survive perhaps millions of years
• Can exchange DNA via conjugation

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Bacterial enzymatic pathways

• Metabolic diversity
• Obligate aerobes (need O2)
• Facultative aerobes
• Obligate anaerobes (O2 is poison)
• Photosynthesis
• Some have just one of two photosystems (not
  releasing oxygen)
• Nitrogen fixation

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Bacterial kingdoms

• Kingdom Proteobacteria
• Very diverse kingdom
• Include many symbionts parasites
• Rhizobium that fixes nitrogen in legume nodules
• E. coli lives in human gut

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Bacterial kingdoms

• Kingdom Chlamydia
• Parasitic bacteria
• Cell walls lack peptidoglycan
• Cause a sexually transmitted disease (infect
  urethra)

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Bacterial kingdoms

• Kingdom Spirochetes
• Have internal flagellum
• produces corkscrew movement
• Examples
• Treponema causes syphilis
• Borrelia causes Lyme disease

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Bacterial kingdoms

• Kingdom Gram-positive bacteria
• Have thick cell wall of peptidoglycan
• Very diverse abundant kingdom
• Many important soil microbes
• E.g Streptomyces source of some antibiotics
• Diseases such as tuberculosis leprosy

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Bacterial kingdoms

• Kingdom Cyanobacteria
• Photoautotrophs
• Oxygen producing photosynthesis
• Ancestor of eukaryotic chloroplast
• Some are nitrogen fixers

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Bacterial phylogeny

• Originally classified by medical importance and
  testable attributes (e.g. Gram stain, nutrient
  req.)
• Modern phylogenetics based on ribosomal genes
• Small subunit rRNA sequence

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Bacteria in ecosystem community

• Decomposers
• Good at using organic molecules for energy
• Used in sewage treatment
• Bioremediation (e.g. break down oil in spills)
• Important for fixing nitrogen

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Bacteria in ecosystem community

• Many form symbiotic associations
• Mutualism (both host symbiont benefit)
• Commensalism (no harm to host)
• Parasitism (harm to host)
• Opportunistic (Streptococcus pneumoniae)
• Exotoxin (released toxins e.g. butulism)
• Endotoxin (on membrane e.g. Salmonella)

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Domain Archaea

• Share features with bacteria with Eukaryotes
• Like bacteria
• No nuclear envelope
• DNA in circular chromosome
• Like Eukaryotes
• No peptidoglycan in cell wall
• Some genes have introns
• DNA coiled with histone protein

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Domain Archaea

• Found in extreme environments (extremophiles)
• Methanogens (obligate anaerobes produce methane,
  CH4, as waste product)
• Halophiles (live in very salty water)
• E.g. the Dead Sea
• Thermophiles (in very hot places)
• E.g. Hot springs