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 There are two distinct evolutionary lineages of prokaryotes,

the Archaea and the Bacteria 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

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 environmentsThe halophiles live in highly saline environmentsThe 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

MethanogensSome methanogens inhabit the anaerobic guts of animals and aid in their digestion…

Others live in swamps and marshes and produce “marsh gas”!

Extreme Halophiles These critters tolerate or even require a high salt environment

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 These little guys tolerate temperatures up to about 113oC,

although the optimal temperature is usually 60-80oC They tend to inhabit hot springs

Eg. Sulfolobus solfataricus lives in sulfur-rich volcanic springs, and obtains energy by using CO2 to oxidize sulfur

3.4 Example of A Heterotrophic BacteriumEscherichia coli

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

• Normally beneficial, but certain strains can cause food poisoning

E. coli photo gallery

3.5 Example of An Autotrophic BacteriumNostoc sp.

Domain Bacteria, Kingdom Cyanobacteria A filamentous spherical (coccus) species

• Filaments are also called trichomes• Trichomes form gelatinous colonies• Contains the pigment chlorophyll for oxygenic photosynthesis

Demonstrates “metabolic cooperation”• Most cells perform photosynthesis• Specialized cells called heterocysts perform nitrogen fixation

• The conversion of atmospheric N2 to NH3

• O2 deactivates enzymes for nitrogen fixation A very independent organism

• Needs only light energy from its environment, makes everything else

Nostoc sp. Photo Gallery