Transcript 3.3 Classification of Prokaryotes

3.3 Classification of Prokaryotes
 In the 5K system all prokaryotes were placed in the Kingdom
Monera because they have prokaryotic cells
 Until the late 20th century, prokaryotic taxonomy was based
on phenotypic characters such as shape, motility, Gram stain,
and nutritional mode
 Starting in the 1970s, a molecular systematics approach using
SSU-rRNA DNA sequences as a marker for evolutionary
relationships revealed some startling results
 The genetic diversity of prokaryotes is immense
 Horizontal gene transfer is is important in the evolution of prokaryotes
Major Findings from Molecular Systematics
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There are two distinct evolutionary lineages of prokaryotes,
the Archaea and the Bacteria
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Kingdom Monera is therefore obselete, and Archaea and Bacteria are
both domains in the 3D system
Archaea is actually more closely related to Eukarya than to Bacteria and
shares many characteristics with it.
Major Findings from Molecular Systematics
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Most traditional groupings do not hold up
 Eg. Gram-negative bacteria are not one lineage
 Cyanobacteria is a monophyletic group
Figure
27.12 A tentative
phylogeny of
some of the
major taxa of
prokaryotes
Major Groups of Bacteria
Diversity Within the Archaea
The “extremophiles” - including the thermophiles, the
halophiles and the methanogens
The thermophiles thrive in very hot environments
The halophiles live in highly saline environments
The methanogens are strict anaerobes that use CO2 to oxidize H2 as a
source of energy, releasing CH4 as a waste product
All of the halophiles and methanogens, and some of the
thermophiles, are in the Kingdom Euryarchaeota
Most of the thermophiles are in the Kingdom Crenarchaeota
Methanogens
Some methanogens inhabit the anaerobic guts of animals and aid in their digestion…
Others live in swamps and marshes and produce “marsh gas”!
Extreme Halophiles
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These critters tolerate or even require a high salt environment
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15-20% salinity found in evaporating ponds of San Francisco Bay
The colour is due to bacteriorhodopsin - a photosynthetic pigment
Halobacterium halobium
(A photoheterotroph!)
Extreme Thermophiles
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These little guys tolerate temperatures up to about 113oC,
although the optimal temperature is usually 60-80oC
They tend to inhabit hot springs
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Eg. Sulfolobus solfataricus lives in sulfur-rich volcanic springs, and
obtains energy by using CO2 to oxidize sulfur
3.4 Example of A Heterotrophic Bacterium
Escherichia coli
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Domain Bacteria, Kingdom Gamma Proteobacteria
A colony-forming bacillus (rod-shaped) bacterium
Gram-negative
A nutritional generalist - requires only a single
monosaccharide (eg. glucose) as a carbon & energy source
Part of the human intestinal fauna
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Normally beneficial, but certain strains can cause food poisoning
E. coli photo gallery
3.5 Example of An Autotrophic Bacterium
Nostoc sp.
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Domain Bacteria, Kingdom Cyanobacteria
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A filamentous spherical (coccus) species
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Demonstrates “metabolic cooperation”
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Filaments are also called trichomes
Trichomes form gelatinous colonies
Contains the pigment chlorophyll for oxygenic photosynthesis
Most cells perform photosynthesis
Specialized cells called heterocysts perform nitrogen fixation
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The conversion of atmospheric N2 to NH3
O2 deactivates enzymes for nitrogen fixation
A very independent organism
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Needs only light energy from its environment, makes everything
else
Nostoc sp. Photo Gallery