Post on 15-Jan-2016
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
• other fossil evidence • molecular fossils • chemolithotrophy vs heterotrophs, who
came first? • anoxygenic photosynthesis • oxygenic photosynthesis • Banded iron formations (BIFs)-red beds
Evolution of cell types
Endosymbiosis
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
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– 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