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While the Monera were briefly understood to be one of five biological kingdoms, they were soon understood to comprise two kingdoms: the eubacteria and the archaebacteria (later renamed Bacteria and Archaea). The Monera kingdom included most organisms with a
prokaryoticThe prokaryotes are a group of organisms that lack a cell nucleus , or any other membrane-bound organelles. They differ from the eukaryotes, which have a cell nucleus. Most are unicellular, but a few prokaryotes such as myxobacteria have multicellular stages in their life cycles...
cellThe cell is the basic structural and functional unit of all known living organisms. It is the smallest unit of an organism that is classified as living, and is often called the building block of life. The Alberts text discusses how the "cellular building blocks" move to shape developing embryos...
organization (that is, no nucleus). For this reason, the kingdom was sometimes called
ProkaryotaThe prokaryotes are a group of organisms that lack a cell nucleus , or any other membrane-bound organelles. They differ from the eukaryotes, which have a cell nucleus. Most are unicellular, but a few prokaryotes such as myxobacteria have multicellular stages in their life cycles...
or
Prokaryotae.
Prokaryotes (formerly Monera) have since been divided into two domains,
ArchaeaThe Archaea are a group of single-celled microorganisms. A single individual or species from this domain is called an archaeon . They have no cell nucleus or any other organelles within their cells...
and
BacteriaThe bacteria are a large group of unicellular microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...
, forming the more recent
three-domain systemThe three-domain system is a biological classification introduced by Carl Woese in 1990 that divides cellular life forms into archaea, bacteria, and eukaryote domains. In particular, it emphasizes the separation of prokaryotes into two groups, originally called Eubacteria and Archaebacteria...
.
r>
While the Monera were briefly understood to be one of five biological kingdoms, they were soon understood to comprise two kingdoms: the eubacteria and the archaebacteria (later renamed Bacteria and Archaea). The Monera kingdom included most organisms with a
prokaryoticThe prokaryotes are a group of organisms that lack a cell nucleus , or any other membrane-bound organelles. They differ from the eukaryotes, which have a cell nucleus. Most are unicellular, but a few prokaryotes such as myxobacteria have multicellular stages in their life cycles...
cellThe cell is the basic structural and functional unit of all known living organisms. It is the smallest unit of an organism that is classified as living, and is often called the building block of life. The Alberts text discusses how the "cellular building blocks" move to shape developing embryos...
organization (that is, no nucleus). For this reason, the kingdom was sometimes called
ProkaryotaThe prokaryotes are a group of organisms that lack a cell nucleus , or any other membrane-bound organelles. They differ from the eukaryotes, which have a cell nucleus. Most are unicellular, but a few prokaryotes such as myxobacteria have multicellular stages in their life cycles...
or
Prokaryotae.
Prokaryotes (formerly Monera) have since been divided into two domains,
ArchaeaThe Archaea are a group of single-celled microorganisms. A single individual or species from this domain is called an archaeon . They have no cell nucleus or any other organelles within their cells...
and
BacteriaThe bacteria are a large group of unicellular microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...
, forming the more recent
three-domain systemThe three-domain system is a biological classification introduced by Carl Woese in 1990 that divides cellular life forms into archaea, bacteria, and eukaryote domains. In particular, it emphasizes the separation of prokaryotes into two groups, originally called Eubacteria and Archaebacteria...
. All new schemes abandon the Monera and now treat the
BacteriaThe bacteria are a large group of unicellular microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...
,
ArchaeaThe Archaea are a group of single-celled microorganisms. A single individual or species from this domain is called an archaeon . They have no cell nucleus or any other organelles within their cells...
, and
EukaryaA eukaryote is an organism whose cells contain complex structures enclosed within membranes. The defining membrane-bound structure that sets eukaryotic cells apart from prokaryotic cells is the nucleus, or nuclear envelope, within which the genetic material is carried...
as separate domains.
Prior to the five-kingdom model with its Monera kingdom, these organisms were classified as two separate divisions of plants: the Schizomycetes (bacteria) were considered fungi, and the Cyanophyta were considered blue-green
algaeAlgae are a large and diverse group of simple, typically autotrophic organisms, ranging from unicellular to multicellular forms. The largest and most complex marine forms are called seaweeds. They are photosynthetic, like plants, and "simple" because they lack the many distinct organs found in...
. The latter are now considered a group of
bacteriaThe bacteria are a large group of unicellular microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...
, typically called the
cyanobacteriaCyanobacteria, also known as blue-green algae, blue-green bacteria or Cyanophyta, is a phylum of bacteria that obtain their energy through photosynthesis. The name "cyanobacteria" comes from the color of the bacteria = blue)...
and are now known not to be closely related to
plantPlants are living organisms belonging to the kingdom Plantae. They include familiar organisms such as trees, herbs, bushes, grasses, vines, ferns, mosses, and green algae. The scientific study of plants, known as botany, has identified about 350,000 extant species of plants, defined as seed plants,...
s, fungi, or
animalAnimals are a major group of mostly multicellular, eukaryotic organisms of the kingdom Animalia or Metazoa. Their body plan eventually becomes fixed as they develop, although some undergo a process of metamorphosis later on in their life. Most animals are motile, meaning they can move spontaneously...
s.
History
Traditionally the natural world was classified as animal, vegetable, or mineral as in
Systema NaturaeThe book Systema Naturae was one of the major works of the Swedish botanist, zoologist and physician Carolus Linnaeus. Its full title is Systema naturae per regna tria naturae, secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis or translated: "System of...
. After the discovery of
microscopyA microscope is an instrument to see objects too tiny for the naked eye. The science of investigating small objects using such an instrument is called microscopy. Microscopic means invisible to the eye unless aided by a microscope.-History:An early microscope was made in 1590 in Middelburg, The...
, attempts were made to fit microscopic organisms into either the plant or animal kingdoms. In 1866
Ernst HaeckelErnst Heinrich Philipp August Haeckel ,also written von Haeckel, was an eminent German biologist, naturalist, philosopher, physician, professor and artist who discovered, described and named thousands of new species, mapped a genealogical tree relating all life forms, and coined many terms in...
proposed a three kingdom system which added the Protista as a new kingdom that contained most microscopic organisms. One of his eight major divisions of Protista was called Moneres. Haeckel's Moneres included known bacterial groups such as
VibrioVibrio is a genus of Gram-negative bacteria possessing a curved rod shape. Typically found in saltwater, Vibrio are facultative anaerobes that test positive for oxidase and do not form spores. All members of the genus are motile and have polar flagella with sheaths...
. Haeckel's Protista kingdom also included eukaryotic organisms now classified as
ProtistProtists , are a diverse group of eukaryotic microorganisms. Historically, protists were treated as the kingdom Protista but this group is no longer recognized in modern taxonomy...
. It was later decided that Haeckel's Protista kingdom had proven to be too diverse to be seriously considered one single kingdom.
Although it was generally accepted that one could distinguish prokaryotes from eukaryotes on the basis of the presence of a
nucleusIn cell biology, the nucleus , also sometimes referred to as the "control center", is a membrane-enclosed organelle found in eukaryotic cells. It contains most of the cell's genetic material, organized as multiple long linear DNA molecules in complex with a large variety of proteins, such as...
,
mitosisMitosis is the process by which a eukaryotic cell separates the chromosomes in its cell nucleus into two identical sets in two daughter nuclei. It is generally followed immediately by cytokinesis, which divides the nuclei, cytoplasm, organelles and cell membrane into two daughter cells containing...
versus
binary fissionBinary fission, or prokaryotic fission, is the form of asexual reproduction and cell division used by all prokaryotic and some eukaryotic organisms...
as a way of reproducing, size, and other traits, the
monophylyIn common cladistic usage, a monophyletic group is a taxon which forms a clade, meaning that it consists of an ancestor and all its descendants. The term is synonymous with the uncommon term holophyly...
of the kingdom Monera (or for that matter, whether classification should be according to phylogeny) was controversial for many decades. Although distinguishing between prokaryotes from eukaryotes as a fundamental distinction is often credited to a 1937 paper by
Édouard ChattonÉdouard Chatton Édouard Chatton (1883 — 1947) Édouard Chatton (1883 — 1947) (} was a French biologist who first distinguished between the eukaryotic and prokaryotic systems of cellular organisation, and coined the terms themselves in his 1925 paper, Pansporella perplex: Reflections on the Biology...
(little noted until 1962), he did not emphasize this distinction more than other biologists of his era. Roger Stanier and C. B. van Niel believed that the bacteria (a term which at the time did not include blue-green algae) and the blue-green algae had a single origin, a conviction which culminated in Stanier writing in a letter in 1970, "I think it is now quite evident that the blue-green algae are not distinguishable from bacteria by any fundamental feature of their cellular organization". Other researchers, such as
E. G. PringsheimErnst Pringsheim, Jr., Ernst Georg Pringsheim jun., or Ernst Georg Pringsheim was a German Natural scientist and plant physiologist .He taught as a professor for biochemistry and botany, in the University of Berlin, University of Prague, and Cambridge...
writing in 1949, suspected separate origins for bacteria and blue-green algae. In 1974, the influential
Bergey's Manual published a new edition coining the term cyanobacteria to refer to what had been called blue-green algae, marking the acceptance of this group within the Monera.
In 1969,
Robert WhittakerRobert Harding Whittaker was an American vegetation ecologist, active in the 1950s to the 1970s.Born in Wichita, Kansas, he obtained a B.A. at Washburn Municipal College in Topeka, Kansas, and, following military service, his Ph.D...
published a proposed five kingdom system for classification of living organisms. Whittaker's system placed most single celled organisms into either the prokaryotic Monera or the eukaryotic Protista. The other three kingdoms in his system were the eukaryotic Fungi, Animalia, and Plantae. Whittaker, however, did not believe that all his kingdoms were monophyletic.
In 1977, a
PNASThe Proceedings of the National Academy of Sciences of the United States of America, usually referred to as PNAS, is the official journal of the United States National Academy of Sciences...
paper by
Carl WoeseCarl Richard Woese is an American microbiologist and physicist. Woese is famous for defining the Archaea in 1977 by phylogenetic taxonomy of 16S ribosomal RNA, a technique pioneered by Woese and which is now standard practice...
and
George FoxGeorge Edward Fox is a researcher at the University of Houston. Co-discoverer of Archaea, the third domain of life and the concept of a progenote as a primordial entity, with Carl Woese in the early 1970s. While with Woese, he pioneered use of comparative analysis in prediction of RNA secondary...
demonstrated that the
archaeaThe Archaea are a group of single-celled microorganisms. A single individual or species from this domain is called an archaeon . They have no cell nucleus or any other organelles within their cells...
(initially called archaebacteria) are not significantly closer in relationship to the
bacteriaThe bacteria are a large group of unicellular microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...
than they are to
eukaryoteA eukaryote is an organism whose cells contain complex structures enclosed within membranes. The defining membrane-bound structure that sets eukaryotic cells apart from prokaryotic cells is the nucleus, or nuclear envelope, within which the genetic material is carried...
s. The paper received front-page coverage in
The New York TimesThe New York Times is an American daily newspaper founded in 1851 and published in New York City. The largest metropolitan newspaper in the United States, "The Gray Lady"—named for its staid appearance and style—is regarded as a national newspaper of record...
and great controversy initially, but the conclusions have since become accepted, leading to replacement of the kingdom Monera with the two kingdoms
BacteriaThe bacteria are a large group of unicellular microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...
and
ArchaeaThe Archaea are a group of single-celled microorganisms. A single individual or species from this domain is called an archaeon . They have no cell nucleus or any other organelles within their cells...
.
See also
- Prokaryote
The prokaryotes are a group of organisms that lack a cell nucleus , or any other membrane-bound organelles. They differ from the eukaryotes, which have a cell nucleus. Most are unicellular, but a few prokaryotes such as myxobacteria have multicellular stages in their life cycles...
- Bacterial cell structure
Bacteria, despite their simplicity, contain a well developed cell structure which is responsible for many of their unique biological properties. Many structural features are unique to bacteria and are not found among archaea or eukaryotes...
- Kingdom (biology)
In biological taxonomy, kingdom and/or regnum is a taxonomic rank in either the highest rank, or the rank below domain. Each kingdom is divided into smaller groups called phyla...
- Endosymbiont
An endosymbiont is any organism that lives within the body or cells of another organism, i.e. forming an endosymbiosis...
- Symbiogenesis
Symbiogenesis is the merging of two separate organisms to form a single new organism. The idea originated with Konstantin Mereschkowsky in his 1926 book Symbiogenesis and the Origin of Species, which proposed that chloroplasts originate from cyanobacteria captured by a protozoan...
External links
- Bacterial evolution by Carl Woese
Carl Richard Woese is an American microbiologist and physicist. Woese is famous for defining the Archaea in 1977 by phylogenetic taxonomy of 16S ribosomal RNA, a technique pioneered by Woese and which is now standard practice...
(1987). Woese reviewed the historical steps leading to the use of the term "Monera" and its later abandonment (full text online).
Category:Prokaryotes
Category:Obsolete taxonomic groups
Category:Microbiology
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