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Early evolution of life on Earth

Early evolution of life on Earth

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Early evolution of life on Earth

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  1. Early evolution of life on Earth Wachtershauser

  2. Miller and Urey experiment

  3. Early catabolism

  4. Evolution of cell types

  5. Primitive Metabolism • Early catabolism must make use of chemical disequilibria • Later, photosynthetic energetics may have evolved • First photosynthetics were undoubtedly anaerobic photosynthetic bacteria • Later, oxygenic photosynthesis changed the chemistry of the Earth • In addition to O2 being an electron acceptor for respiration, it caused development of an O3 layer

  6. Summary First evidence for potential life 3.8 billion yrs ago • other fossil evidence • molecular fossils • chemolithotrophy vs heterotrophs, who came first? • anoxygenic photosynthesis • oxygenic photosynthesis • Banded iron formations (BIFs)-red beds

  7. Evolution of cell types

  8. Endosymbiosis

  9. Taxonomy • Until recently, life on Earth in 5 kingdoms: • Bacteria • Fungi • Protists • Plants • Animals • Division between Bacteria, Archaea, and Eukarya more profound than former kingdoms: level called domains

  10. Taxonomic Ranks • Empire or Domain • Kingdoms (Bacteria and Eukarya not yet divided into kingdoms) • Phylum • Class • Order • Family • Genus • Species (name is binomial: genus + epithet)

  11. Bacterial Taxonomy • Bacterial species is the base unit for taxonomy • Definition of any given species is subjective • >70% sequence similarity of genome • >98% sequence similarity of rRNA • Each species is phenotypically distinct

  12. Evolutionary Chronometers • Phenotypic characteristics • Mole percent Guanine + Cytosine • DNA sequence similarity (gross sequence similarity) • Good at the species level • Small-subunit RNA (16S rRNA of prokaryotes; 18S of eukaryotes)

  13. Phenotypic Taxonomies • Phenotype determination is classic taxonomic method • Today more reliance on molecular methods for taxonomies above the genus level • Still, phenotypic differentiation is considered requirement for separation of species • Some methods collect large amounts of phenotypic data quickly • FAME analysis • Pyrolysis/GC • Automated testing of enzymatic activities

  14. Range of G+C contents

  15. DNA hybridization

  16. 16S rRNA as evolutionary chronometer

  17. Evolution of sequences

  18. Evolutionary distance and correction for back- or multiple mutations

  19. Generation of evolutionary trees

  20. Molecular microbial ecology • Signature sequences identify phylogenetic groups • 16S & 18S sequences identify Bacteria, Archaea, and Eucarya • Probes can be developed for FISH (fluorescent in situ hybridization)

  21. Community analysis by molecular methods