Download Prokaryotes

Biol 3400
Tortora et al, Chap 11
The Prokaryotes: Domains Bacteria and Archaea
A.
Bacterial Phylogeny
 Phylogenetic studies (16S rRNA, 23S rRNA, EF’s and b subunits of ATPase) have identified
at least 23 major evolutionary divergences
 modes of generating cellular energy and nutrition are more superficial than other more basic
housekeeping and basic biochemical functions
 Diversity is described in some detail in Chapter 11 – have a quite read through this chapter
B.
Archaea
 Phylogenetic studies suggest that this group of organisms is distinct from bacteria and
eukaryotes.
 They are believed to have evolved more slowly than members of the other domains.
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Major Archaeal Phenotypes
Methanogens – Note: there are no known bacterial methanogens
Sulfate utilizers
Halophiles
Thermophiles with sulfur dependent metabolism
Many archaea are anaerobes and chemoautotrophs
i. Crenarchaeota
 Thermophiles and hyperthermophiles
 branch closest to the root of the universal tree
ii. Euryarchaeota
 collection of the major archaeal phenotypes
 dominated by methanogens and extreme halophiles
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Physiological adaptations for a more primitive earth
i. Ether linkages in membrane lipids
ii. Diverse non-peptidoglycan cell wall
iii. Archaeal histone-like proteins associated with circular chromosome (stabilizes structure)
iv. Proteins that are relatively resistant to denaturation - stabilized by amino acid sequences and
hydrophobic regions - no apparent consensus regions or domains
3.
Ecology
 Many Archaea inhabit extreme environments - high temperature, salinity, anaerobic conditions.
i. Thermophiles
e.g., Pyrodictium sp. have optimal temperatures over 100C
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Biol 3400
Tortora et al, Chap 11
Features
 Membrane structure - phytanylglycerol diethers and biphytanyldiglycerol tetraethers
 Thermostable proteins - what makes a protein thermostable - amino acid sequences; secondary and
tertiary structures; hydrophobic amino acids
 Genomes - high G + C content
ii. Halophiles
e.g., Halobacterium - require high salt concentration to grow (12 - 15 %)
Features
 High internal concentration of KCl
 Enzymes are salt tolerant
iii. Animal associations
 Methanogens form symbiotic associations with other microbes - apparent in the sediments of water
bodies as well as in the digestive tracts of various animals.
 Methanogens consume H2 that is produced by other anaerobic microbes that are actively involved in
the degradation of cellulosic plant material.
 Found in niches with little competition (e.g., rumen)
C.
Eukarya
 Comparative sequencing of 18S rRNA has been used to develop phylogenetic trees of
species in the domain Eukarya
 Microbial Eukarya biology and diversity are discussed in Chapter 12
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