Classification of Microorganisms |
||||
Taxonomy is the science of the classification of organisms, with the goal of showing relationships among organisms.
Taxonomy also provides a means of identifying organisms.
Phylogeny is the evolutionary history of a group of organisms.
The taxonomic hierarchy shows evolutionary, or phylogenetic, relationships among organisms.
Bacteria were separated into the Kingdom Prokaryotae in 1968.
Living organisms were divided into five kingdoms in 1969.
Living organisms are currently classified into three domains. A domain can be divided into kingdoms.
In this system, plants, animals, fungi, and protists belong to the Domain Eukarya.
Bacteria (with peptidoglycan) form a second domain.
Archaea (with unusual cell walls) are placed in the Domain Archaea.
It appears that the universal ancestor split into three lineages, giving rise to Archaea, Bacteria, and eventually the eukaryotes.
|
Infoldings in the plasma membrane of a prokaryotic cell may have produced both a nuclear membrane and endoplasmic reticulum.
Endosymbiosis could then have provided membrane-bound organelles. |
 |
Cyanophora paradoxa - eukaryotic host and bacterium require each other for survival.
Organisms are grouped into taxa according to phylogenetic relationships (from a common ancestor).
Some of the information for eukaryotic relationships is obtained from the fossil record.
Prokaryotic relationships are determined by rRNA sequencing, although some fossils of prokaryotes exist.
Fossilized prokaryotes
(a) Coccoid cyanobacteria from the Late Precambrian (850 million years ago) of central Australia. |
|
(b) Filamentous prokaryotes from the Early Precambrian (3.5 billion years ago) of western Australia. |