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