Early evolution of life on Earth
Wachtershauser
Miller and Urey experiment
Early catabolism
Evolution of cell types
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
Summary
First evidence for potential life 3.8 billion yrs ago
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other fossil evidence
molecular fossils
chemolithotrophy vs heterotrophs, who
came first?
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anoxygenic photosynthesis
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oxygenic photosynthesis
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Banded iron formations (BIFs)-red beds
Evolution of cell types
Endosymbiosis
Taxonomy
• Until recently, life on Earth in 5 kingdoms:
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Bacteria
Fungi
Protists
Plants
Animals
• Division between Bacteria, Archaea, and Eukarya
more profound than former kingdoms: level called
domains
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)
Bacterial Taxonomy
• Bacterial species is the base unit for
taxonomy
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Definition of any given species is subjective
>70% sequence similarity of genome
>98% sequence similarity of rRNA
Each species is phenotypically distinct
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)
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
Range of G+C contents
DNA hybridization
16S rRNA as evolutionary
chronometer
Evolution of sequences
Evolutionary distance and correction
for back- or multiple mutations
Generation of evolutionary trees
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)
Community analysis by
molecular methods