Chapter 4: Archaea

Who started the studies of Archaea?

Woese and Fox began the studies in the 1970s

First portion termed Archaeons were called….

Methanogens—→ a poorly characterized group of microbes that produced methane

Halobacterium salinarum

3.0 to 5.0 M NaCl

Pyrococcus furiosus

100*C

Picrophilus oshimae

0.7 pH

Methanogenium frigidum

15*C

Archaea size

0.5 to 5 micrometers in diameter

Archaea and Bacteria both have…

singular, circular chromosomes and lack a membrane-bound nucleus

Archaeal DNA has…

histones like Eukarya

Archaeal cell structure

Rods, spheres, spirals…along with irregular pleiomorphic shapes and rectangular shapes

Histones

form structures that DNA wraps around

Histone structure/wrapping is different in

Archaea

Inclusion bodies

such as gas vacuoles have been observed in some Archaea

All archaeons possess a

plasma membrane

Most archaeons have a

cell wall

Both structures are different from their equivalents in

Bacteria and Eukarya

The archaeal plasma membrane has a different

bilayer construction

The plasma membrane can even be a

monolayer

In Archaea, the cell envelope may be composed of

pseudomurein (slightly different from peptidoglycan structure)

S-layer

(single layer of many identical armorlike

subunits) to protect against predation/viruses and to mediate adhesion

Cannulae

hollow glycoprotein tubes that link cells

together to form a complex network.

Archaeal Flagella

They rotate like bacteria but are thinner than bacteria

Most well-characterized archaeons can be classified in either the

Euryarchaeota or Crenarchaeota phylum.

Crenarchaeota

Many members are thermophiles or hyperthermophiles

(growing at temperatures greater than 55°C or 80°C,

respectively).

Crenarchaeota —→ Many are also acidophiles

thriving in low pH

Some are also barophiles

thriving in high pressures., at the bottom of the ocean)

Mesophiles

15 to 40°C

Psychrophiles

<15°C

Euryarchaeota

Methanogens—→strict anaerobes; they reduce CO2 with H2 to produce methane (CH4) and water (H2O)

in an unusual reaction. Energy released can be used to fix carbon

Halophiles

Require NaCl concentration

greater than 1.5M. High salt environments are

fairly rare