Archaea
Archaea can exist in very hot and very cold environments, making them resilient
microorganisms that can survive attacks that destroy other bacteria. For example,
archaea can survive and grow in an oxygen-free environment (anaerobic) and in
a high-salt (hypersaline) environment.
There are three ways microbiologists identify archaea. Archaea:- Have a unique sequence of rRNA.
- Have cell walls that lack peptidoglycan. The cell wall of most bacteria con-
tains peptidoglycan. - Have a membrane lipid that has a branched chain of hydrocarbons con-
nected to glycerol ester links. The membrane lipid of most bacteria has
glycerol connected to fatty acids by ester bonds.
Unfortunately, two of the more common techniques used to identify bacteria
are not very useful in identifying archaea. You’ll recall from Chapter 4 that
microbiologists identify bacteria by using the Gram stain. A bacterium is
either gram-positive or gram-negative. However, archaea could be gram-positive
or gram-negative, which makes the Gram stain test useless when trying to iden-
tify archaea.
The shape of a bacterium is another common way microbiologists identify bac-
teria. Many bacteria have a distinctive appearance. However, archaea are pleo-
morphic, which means they can have various shapes. Sometimes archaea are spiracle,
spiral, lobed, plate-shaped, or irregularly shaped.
Archaea also have various types of metabolism. Some archaea are organ-
otrophs while others are autotrophs. Archaea also break down (catabolize) glu-
cose for energy in various ways. It is these variations that enable archaea to
survive in environments that are fatal to other bacteria.THE ARCHAEA CLAN
Archaea are not bacteria and can be organized into subgroups. Microbiologists
use one of two subgroup classifications for archaea. One classification method
divides archaea into five subgroups. These are:- Methanogenic archaea.Asingle-celled archaea that produces methane
and carbon dioxide (CO 2 ) through the fermentation of simple organic car-
bon compounds or the oxidation of H 2 without oxygen to produce CO 2.
(^152) CHAPTER 10 The Prokaryotes