Bio 119
Bacterial Evolution and Taxonomy
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Bacterial Evolution and Taxonomy
READING:
Sec. 14.2
sec. 14.3
Sec. 14.4
Sec. 14.6
Sec. 14.8
Sec. 14.1
Formation and Early History of Earth
Origin of Cellular :ife
p. 369
Microbial Diversification: Consequences for Earth's Biosphere
p. 373
Endosymbiotic Origin of Eukaryotes
p. 375
Evolutionary Analysis: Theoretical Aspects
p. 377
Microbial Phylogeny
p. 381
Review Questions relevant to these sections.
p. 396.
Application Questions #1, 2, 3
p. 397
Also see front and rear endpapers for phylogenetic trees.
Additional Study Questions
1.
What are the three major lines of evolutionary descent (Domains) among cellular organisms
suggested by comparisons of their 16S and 18S rRNA sequences?
2.
Where, specifically, would you find Escherichia coli on the phylogenetic trees presented on
the front and rear endpapers of the text?
3.
Which groups of prokaryotic organisms have 16S rRNA sequences most similar to those of
eucaryotic mitochondria and chloroplasts?
4.
Which major groups of bacteria have photosynthesis based on chlorophyll?
5.
Speculate about the structure, physiology, and life style of the nearest common ancestor
of all contemporary organisms.
6.
What is a stromatolite? Why are stromatolites significant?
7.
What 2 implications did oxygenation of the atmosphere have for evolution (according to
the text)?
8.
What experimental evidence supports the endosymbiotic theory for evolution of
chloroplasts and mitochondria?.
9.
Describe the basic assumptions inherent in the concept of a "molecular clock".
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Evolution of Earth and Earliest Life Forms
Origin of Earth:
Approximate age of earth 4.6 by.
Probably no liquid water until 4.0 bya.
Evidence for Microbial Life on Early Earth
Geological Formation
Current
Location
Greenland
3.86 by
Warrawoona Series
Towers Formation
Pilbara Supergroups
Australia
3.5 bya
Swaziland Supergroup
(See Fig. 11.1
Africa
3.5 bya
Itsaq Gneiss
Age
Significance
presence of liquid water
13
C/12C enriched “carbonaceous
materials”
Fossil stromatolites
Fossil prokayotes visible in SEM?
Fossil prokayotes visible in SEM?
Origin of Cellular Life
ORIGIN OF LIFE SCENARIOS
Miller-Urey
CH4 NH3 H2O H2
“Primordial Soup”
Mesophile
Organotroph
Heterotroph
Emerging Paradigm
CO2 N2
Hydrothermal Vent
Hyperthermophile
Lithotroph
Autotroph
The COSMIC CONNECTIONS
Some investigators believe that organic molecules were not created in situ, but were seeded
onto the early earth by comets and meteorites.
Some investigators have suggested that organisms did not originate on earth, but arrived from
elsewhere. The current status of bacteria in the martian meteorite is very dubious.
Primitive Life: The RNA World and Molecular Coding
RNA before DNA
RNA before Protein
The Modern Cell: DNA —> RNA —> Protein
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Primitive Life: Energy and Carbon Metabolism
Fig. 14.8 The NET reaction for the energy-producing components of the scheme is:
FeS + S0 + 2 H2O ---> FeS2 + 2 H+ + 2 OHThe key point is that the protons and hydroxyl ions shown on the right side of the
equation are generated on opposite sides of an impermeable membrane. This
constitutes "charge separation" and represents "capture and storage" of the
chemical energy of the reaction.
Molecular Oxygen: Banded Iron Formations
Oxygenated Atmosphere: 2.0-2.5 bya.
Eukaryotes and Organelles: Endosymbiosis
Origin of the Nucleus
Endosymbiosis
Symbiotic organeles acquired within past 2 By.
Chloroplast: Cyanobacteria
Mitochondrion:
 Proteobacteria
One of the most interesting aspects of endosymbiosis is the phenomenon of genomic
reshuffling. The genomes of modern chloroplasts and mitochondria are much smaller than the
genomes of the bacterial ancestors from which they were derived. Some of the ancestral genes
have simply been lost, while many others are now encoded in the nuclear genome. A few genes
have apparently been transferred between chloroplast and mitochondrial genomoes in plants.
Evidence for Endosymbiosis
Biological Evolution and Geological Time Scales
14.6
Evolutionary Analysis: Theoretical Aspects
Another potential drawback to building phylogenies on the basis of sequencing a single molecue
(like SSU rRNA) is "horizontal gene transfer.
Microbial Phylogeny Derived from Ribosomal RNA Sequences
The Universal Tree of Life
Nature of Universal Common Ancestor:
hyperthermophile
dsDNA
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lipid bilayer
transcription & translation
Major Conclusions regarding evolution of Bacteria:
•Many traditional taxonomic characters are highly unreliable (ie aerobic vs anaerobic)
•Evolution of chlorophyll based photosynthesis happened only once at > 3 bya.
•Streamlining by loss of function (ie photosynthesis, outer membrane, wall) has been a major
trend. Groups with simple strategies like the lactic acid bacteria are often highly evolved rather
than primitive.
•Endosymbiotic origin of chloroplasts and mitochondria.
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