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Monera (/məˈnɪərə/) (Greek - μονήρης (monḗrēs), "single", "solitary") is a biological kingdom that is made up of
prokaryote A prokaryote () is a single-celled organism A unicellular organism, also known as a single-celled organism, is an organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organismos'') is any individual conti ...
s (particularly
bacteria Bacteria (; common noun bacteria, singular bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of prokaryotic microorganisms. Typ ...

bacteria
). As such, it is composed of single-celled organisms that lack a true
nucleus ''Nucleus'' (plural nuclei) is a Latin word for the seed inside a fruit. It most often refers to: *Atomic nucleus, the very dense central region of an atom *Cell nucleus, a central organelle of a eukaryotic cell, containing most of the cell's DNA ...

nucleus
. The taxon Monera was first proposed as a phylum by
Ernst Haeckel Ernst Heinrich Philipp August Haeckel (; 16 February 1834 – 9 August 1919) was a German zoologist Zoology ()The pronunciation of zoology as is usually regarded as nonstandard, though it is not uncommon. is the branch of biology that stud ...

Ernst Haeckel
in 1866. Subsequently, the phylum was elevated to the rank of kingdom in 1925 by
Édouard Chatton Édouard Chatton (; 11 October 1883 – 23 April 1947) was a French biologist who first characterized the distinction between the prokaryotic and eukaryotic cellular types. Chatton coined the terms and published them first in his 1937 paper "Pa ...
. The last commonly accepted mega-classification with the taxon Monera was the five-kingdom classification system established by Robert Whittaker in 1969. Under the
three-domain system The three-domain system is a biological classification In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, ...
of
taxonomy Taxonomy is the practice and science of categorization Categorization is the human ability and activity of recognizing shared features or similarities between the elements of the experience Experience refers to conscious , an English Par ...
, introduced by
Carl Woese Carl Richard Woese (; July 15, 1928 – December 30, 2012) was an American microbiologist A microbiologist (from Greek ) is a scientist A scientist is a person who conducts Scientific method, scientific research to advance knowledge in an B ...

Carl Woese
in 1977, which reflects the evolutionary history of life, the organisms found in kingdom Monera have been divided into two domains,
Archaea Archaea ( ; singular archaeon ) constitute a domain Domain may refer to: Mathematics *Domain of a function, the set of input values for which the (total) function is defined **Domain of definition of a partial function **Natural domain of a pa ...

Archaea
and
Bacteria Bacteria (; common noun bacteria, singular bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of prokaryotic microorganisms. Typ ...

Bacteria
(with
Eukarya Eukaryotes () are organism In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interact ...
as the third domain). Furthermore, the taxon Monera is
paraphyletic In taxonomy Taxonomy (general) is the practice and science of classification of things or concepts, including the principles that underlie such classification. The term may also refer to a specific classification scheme. Originally used only ...

paraphyletic
(does not include all descendants of their most-recent common ancestor), as
Archaea Archaea ( ; singular archaeon ) constitute a domain Domain may refer to: Mathematics *Domain of a function, the set of input values for which the (total) function is defined **Domain of definition of a partial function **Natural domain of a pa ...

Archaea
and
Eukarya Eukaryotes () are organism In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interact ...
are currently believed to be more closely related than either is to
Bacteria Bacteria (; common noun bacteria, singular bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of prokaryotic microorganisms. Typ ...

Bacteria
. The term "moneran" is the informal name of members of this group and is still sometimes used (as is the term "prokaryote") to denote a member of either domain. Eubacteria Commonly referred to as "true bacteria" or simply "bacteria.“ They are more common and widely distributed in most habitats (water, soil, inside and on extracellular organisms, etc.) across the globe and are prokaryotes. Eubacteria can be
Gram-negative Gram-negative bacteria are bacteria Bacteria (; common noun bacteria, singular bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), do ...
or
Gram-positive In bacteriology, gram-positive bacteria are bacteria that give a positive result in the Gram stain test, which is traditionally used to quickly classify bacteria into two broad categories according to their type of cell wall. Gram-positive bacte ...
, and they are important in the economy, agriculture, and medicine. ''
E. coli ''Escherichia coli'' (),Wells, J. C. (2000) Longman Pronunciation Dictionary. Harlow ngland Pearson Education Ltd. also known as ''E. coli'' (), is a Gram-negative Gram-negative bacteria are bacteria Bacteria (; common noun bacteri ...

E. coli
'', ''
Lactobacilli The ''Lactobacillaceae'' are a family of lactic acid bacteria Lactobacillales are an order of gram-positive, GC-content, low-GC, acid-tolerant, generally nonsporulating, Aerotolerant anaerobe, nonrespiring, either rod-shaped (bacillus (shape ...
'', and ''
Azospirillum ''Azospirillum'' is a Gram-negative, microaerophilic, non-fermentative and nitrogen-fixing bacterial genus from the family of Rhodospirillaceae. ''Azospirillum'' bacteria can promote plant growth. Characteristics The genus ''Azospirillum'' bel ...
'' are among them. Archaebacteria Archaebacteria are a group of microorganisms that are thought to be an ancient form of life that evolved independently from bacteria and blue-green algae, and they are sometimes classified as a kingdom. These bacteria that thrive at high temperatures represent life at the known upper temperature limit. Most bacteria were classified under Monera; however, some
Cyanobacteria Cyanobacteria (), also known as Cyanophyta, are a phylum In biology, a phylum (; plural The plural (sometimes list of glossing abbreviations, abbreviated ), in many languages, is one of the values of the grammatical number, grammatical ...

Cyanobacteria
(often called the blue-green algae) were initially classified under
Plantae Plants are predominantly photosynthetic eukaryotes of the Kingdom (biology), kingdom Plantae. Historically, the plant kingdom encompassed all living things that were not animals, and included algae and fungi; however, all current definitions ...
due to their ability to
photosynthesize Photosynthesis is a process used by plants and other organisms to convert Conversion or convert may refer to: Arts, entertainment, and media * Conversion (Doctor Who audio), "Conversion" (''Doctor Who'' audio), an episode of the audio drama ' ...
.


History


Haeckel's classification

Traditionally the natural world was classified as animal, vegetable, or mineral as in
Systema Naturae ' (originally in Latin Latin (, or , ) is a classical language A classical language is a language A language is a structured system of communication Communication (from Latin ''communicare'', meaning "to share" or "to be in ...
. After the development of the
microscope A microscope (from grc, μικρός ''mikrós'' 'small' and ''skopeîn'' 'to look (at); examine, inspect') is a laboratory instrument used to examine objects that are too small to be seen by the naked eye Naked eye, also called bare ...

microscope
, attempts were made to fit microscopic organisms into either the plant or animal kingdoms. In 1675,
Antonie van Leeuwenhoek Antonie Philips van Leeuwenhoek ( ; ; 24 October 1632 – 26 August 1723) was a Dutch Dutch commonly refers to: * Something of, from, or related to the Netherlands * Dutch people () * Dutch language () *Dutch language , spoken in Belgium ...
discovered bacteria and called them "animalcules", assigning them to the class Vermes of the Animalia. Due to the limited tools — the sole references for this group were shape, behaviour, and habitat — the description of genera and their classification was extremely limited, which was accentuated by the perceived lack of importance of the group. Ten years after ''
The Origin of Species ''On the Origin of Species'' (or, more completely, ''On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life''),The book's full original title was ''On the Origin of Species by Me ...
'' by
Charles Darwin Charles Robert Darwin (; ; 12 February 1809 – 19 April 1882) was an English naturalist Natural history is a domain of inquiry involving organism In biology, an organism () is any organic, life, living system that fu ...

Charles Darwin
, in 1866
Ernst Haeckel Ernst Heinrich Philipp August Haeckel (; 16 February 1834 – 9 August 1919) was a German zoologist Zoology ()The pronunciation of zoology as is usually regarded as nonstandard, though it is not uncommon. is the branch of biology that stud ...

Ernst Haeckel
, a supporter of evolutionary theory, proposed a three-kingdom system that added the Protista as a new kingdom that contained most microscopic organisms. One of his eight major divisions of Protista was composed of the monerans (called Moneres by Haeckel), which he defined as completely structure-less and homogeneous organisms, consisting only of a piece of plasma. Haeckel's Monera included not only bacterial groups of early discovery but also several small eukaryotic organisms; in fact the genus
Vibrio ''Vibrio'' is a genus Genus /ˈdʒiː.nəs/ (plural genera /ˈdʒen.ər.ə/) is a taxonomic rank In biological classification In biology, taxonomy () is the scientific study of naming, defining (Circumscription (taxonomy), circumscr ...
is the only bacterial genus explicitly assigned to the phylum, while others are mentioned indirectly, which led Copeland to speculate that Haeckel considered all bacteria to belong to the genus Vibrio, ignoring other bacterial genera. One notable exception were the members of the modern phylum
Cyanobacteria Cyanobacteria (), also known as Cyanophyta, are a phylum In biology, a phylum (; plural The plural (sometimes list of glossing abbreviations, abbreviated ), in many languages, is one of the values of the grammatical number, grammatical ...

Cyanobacteria
, such as ''
Nostoc ''Nostoc'', also known as star jelly Star jelly (also called astromyxin, astral jelly) is a gelatinous substance sometimes found on grass or even on branches of trees. According to folklore, it is deposited on the Earth during meteor showers. St ...

Nostoc
'', which were placed in the phylum Archephyta of
Algae Algae (; singular alga ) is an informal term for a large and diverse group of photosynthetic Photosynthesis is a process used by plants and other organisms to convert Conversion or convert may refer to: Arts, entertainment, and media * Co ...

Algae
(vide infra:
Blue-green algae Cyanobacteria (), also known as Cyanophyta, are a phylum (biology), phylum of Gram-negative bacteria that obtain energy via photosynthesis. The name ''cyanobacteria'' refers to their color (), giving them their other name, "blue-green algae", ...
). The Neolatin noun Monera and the German noun Moneren/Moneres are derived from the ancient Greek noun ''moneres'', which Haeckel stated meant "simple"; however, it actually means "single, solitary". Haeckel also describes the protist genus
Monas The National Monument ( id, Monumen Nasional, abbreviated ''Monas'') is a 132 m (433 ft) obelisk in the centre of Merdeka Square, Jakarta, Merdeka Square, Central Jakarta, symbolizing the fight for Indonesia. It is the national monumen ...
in the two pages about Monera in his 1866 book. The informal name of a member of the Monera was initially moneron, but later moneran was used. Due to its lack of features, the phylum was not fully subdivided, but the genera therein were divided into two groups: * die Gymnomoneren (no envelope ic./nowiki>): Gymnomonera ** ''Protogenes'' — such as ''Protogenes primordialis'', an unidentified amoeba (eukaryote) and not a bacterium ** ''Protamaeba''— an incorrectly described/fabricated species ** ''
Vibrio ''Vibrio'' is a genus Genus /ˈdʒiː.nəs/ (plural genera /ˈdʒen.ər.ə/) is a taxonomic rank In biological classification In biology, taxonomy () is the scientific study of naming, defining (Circumscription (taxonomy), circumscr ...
'' — a genus of comma-shaped bacteria first described in 1854 ** ''
Bacterium Bacteria (; common noun bacteria, singular bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell The cell (from Latin ''cella'', meaning "small room") is the basic structural, functional, and ...
'' — a genus of rod-shaped bacteria first described in 1828. Haeckel does not explicitly assign this genus to the Monera. ** ''
Bacillus ''Bacillus'' (Latin "stick") is a genus Genus /ˈdʒiː.nəs/ (plural genera /ˈdʒen.ər.ə/) is a taxonomic rank In biological classification In biology, taxonomy () is the scientific study of naming, defining (Circumscription (t ...

Bacillus
'' — a genus of spore-forming rod-shaped bacteria first described in 1835 Haeckel does not explicitly assign this genus to the Monera kingdom. ** ''Spirochaeta'' — thin spiral-shaped bacteria first described in 1835 Haeckel does not explicitly assign this genus to the Monera. ** ''Spirillum'' — spiral-shaped bacteria first described in 1832 Haeckel does not explicitly assign this genus to the Monera. ** ''etc.'': Haeckel does provide a comprehensive list. * die Lepomoneren (with envelope): Lepomonera ** ''Protomonas'' — identified to a synonym of ''
Monas The National Monument ( id, Monumen Nasional, abbreviated ''Monas'') is a 132 m (433 ft) obelisk in the centre of Merdeka Square, Jakarta, Merdeka Square, Central Jakarta, symbolizing the fight for Indonesia. It is the national monumen ...
'', a flagellated protozoan, and not a bacterium. The name was reused in 1984 for an unrelated genus of bacteria. ** ''Vampyrella'' — now classed as a eukaryote and not a bacterium.


Subsequent classifications

Like Protista, the Monera classification was not fully followed at first and several different ranks were used and located with animals, plants, protists or fungi. Furthermore, Haeckel's classification lacked specificity and was not exhaustive — it in fact covers only a few pages—, consequently a lot of confusion arose even to the point that the Monera did not contain bacterial genera and others according to Huxley. They were first recognized as a kingdom by Enderlein in 1925 (Bakterien-Cyclogenie. de Gruyter, Berlin). The most popular scheme was created in 1859 by C. Von Nägeli who classified non-phototrophic Bacteria as the class Schizomycetes. The class Schizomycetes was then emended by Walter Migula (along with the coinage of the genus ''Pseudomonas'' in 1894) and others. This term was in dominant use even in 1916 as reported b
Robert Earle Buchanan
as it had priority over other terms such as Monera. However, starting with Ferdinand Cohn in 1872 the term ''bacteria'' (or in German ') became prominently used to informally describe this group of species without a nucleus:
Bacterium Bacteria (; common noun bacteria, singular bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell The cell (from Latin ''cella'', meaning "small room") is the basic structural, functional, and ...
was in fact a genus created in 1828 by Christian Gottfried Ehrenberg Additionally, Cohn divided the bacteria according to shape namely: * Spherobacteria for the cocci * Microbacteria for the short, non-filamentous rods * Desmobacteria for the longer, filamentous rods and Spirobacteria for the spiral forms. Successively, Cohn created the Schizophyta of Plants, which contained the non-photrophic bacteria in the family Schizomycetes and the phototrophic bacteria (blue green algae/Cyanobacteria) in the Schizophyceae This union of blue green algae and Bacteria was much later followed by Haeckel, who classified the two families in a revised phylum Monera in the Protista. Stanier and van Neil (1941, The main outlines of bacterial classification. J Bacteriol 42: 437- 466) recognized the Kingdom Monera with two phyla, Myxophyta and Schizomycetae, the latter comprising classes Eubacteriae (3 orders), Myxobacteriae (1 order), and Spirochetae (1 order); Bisset (1962, Bacteria, 2nd ed., Livingston, London) distinguished 1 class and 4 orders: Eubacteriales, Actinomycetales, Streptomycetales, and Flexibacteriales; Orla-Jensen (1909, Die Hauptlinien des naturalischen Bakteriensystems nebst einer Ubersicht der Garungsphenomene. Zentr. Bakt. Parasitenk., II, 22: 305-346) and Bergey et al (1925, Bergey's Manual of Determinative Bacteriology, Baltimore : Williams & Wilkins Co.) with many subsequent editions) also presented classifications.


Rise to prominence

The term Monera became well established in the 20s and 30s when to rightfully increase the importance of the difference between species with a nucleus and without. In 1925, Édouard Chatton divided all living organisms into two empires Prokaryotes and Eukaryotes: the Kingdom Monera being the sole member of the Prokaryotes empire. The anthropic importance of the crown group of animals, plants and fungi was hard to depose; consequently, several other megaclassification schemes ignored on the empire rank but maintained the kingdom Monera consisting of bacteria, such Copeland in 1938 and Whittaker in 1969. The latter classification system was widely followed, in which Robert Whittaker proposed a 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. Whittaker subdivided the kingdom into two branches containing several phyla: * Myxomonera branch ** Cyanophyta, now called
Cyanobacteria Cyanobacteria (), also known as Cyanophyta, are a phylum In biology, a phylum (; plural The plural (sometimes list of glossing abbreviations, abbreviated ), in many languages, is one of the values of the grammatical number, grammatical ...

Cyanobacteria
** Myxobacteria * Mastigomonera branch ** Eubacterium, Eubacteriae ** Actinomycota ** Spirochaetae Alternative commonly followed subdivision systems were based on Gram stains. This culminated in the Gibbons and Murray classification of 1978: * Gracilicutes (gram negative) ** Photobacteria (photosynthetic): class Oxyphotobacteriae (water as electron acceptor, includes the order Cyanobacteriales = blue green algae, now phylum Cyanobacteria) and class Anoxyphotobacteriae (anaerobic phototrophs, orders: Rhodospirillales and Chlorobiales ** Scotobacteria (non-photosynthetic, now the Proteobacteria and other gram negative nonphotosynthetic phyla) eg. ''Pseudomonas aeruginosa, Salmonella enterica, E.coli.'' * Firmacutes [sic] (gram positive, subsequently corrected to Firmicutes) **several orders such as Bacillales and Actinomycetales (now in the phylum Actinobacteria) eg. ''Bacillus cerus, Streptococcus, Staphylococcus.'' * Mollicutes (gram variable, e.g. Mycoplasma) * Mendocutes (uneven gram stain, "methanogenic bacteria" now known as the Archaea)


Three-domain system

In 1977, a Proceedings of the National Academy of Sciences, PNAS paper by
Carl Woese Carl Richard Woese (; July 15, 1928 – December 30, 2012) was an American microbiologist A microbiologist (from Greek ) is a scientist A scientist is a person who conducts Scientific method, scientific research to advance knowledge in an B ...

Carl Woese
and George E. Fox, George Fox demonstrated that the archaea (initially called archaebacteria) are not significantly closer in relationship to the
bacteria Bacteria (; common noun bacteria, singular bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of prokaryotic microorganisms. Typ ...

bacteria
than they are to eukaryotes. The paper received front-page coverage in ''The New York Times'', and great controversy initially. The conclusions have since become accepted, leading to replacement of the kingdom Monera with the two domains
Bacteria Bacteria (; common noun bacteria, singular bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of prokaryotic microorganisms. Typ ...

Bacteria
and
Archaea Archaea ( ; singular archaeon ) constitute a domain Domain may refer to: Mathematics *Domain of a function, the set of input values for which the (total) function is defined **Domain of definition of a partial function **Natural domain of a pa ...

Archaea
. A minority of scientists, including Thomas Cavalier-Smith, continue to reject the widely accepted division between these two groups. Cavalier-Smith has published classifications in which the archaebacteria are part of a subkingdom of the Kingdom Bacteria.


Blue-green algae

Although it was generally accepted that one could distinguish prokaryotes from eukaryotes on the basis of the presence of a
nucleus ''Nucleus'' (plural nuclei) is a Latin word for the seed inside a fruit. It most often refers to: *Atomic nucleus, the very dense central region of an atom *Cell nucleus, a central organelle of a eukaryotic cell, containing most of the cell's DNA ...

nucleus
, mitosis versus binary fission as a way of reproducing, size, and other traits, the monophyly 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 Chatton Édouard Chatton (; 11 October 1883 – 23 April 1947) was a French biologist who first characterized the distinction between the prokaryotic and eukaryotic cellular types. Chatton coined the terms and published them first in his 1937 paper "Pa ...
(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 that 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".Roger Stanier to Peter Raven, 5 November 1970, National Archives of Canada, MG 31, accession J35, vol. 6, as quoted in Sapp, 2005 Other researchers, such as Ernst Pringsheim Jr., E. G. Pringsheim 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.


Summary

Monerans are a group of organisms having prokaryotic structure. Archaea differ from Bacteria in having a different 16S srna. They also have a different cell wall structure.


See also

* Bacterial cell structure * Endosymbiont * Kingdom (biology) * Prokaryote * Symbiogenesis


References


External links

* Woese reviewed the historical steps leading to the use of the term "Monera" and its later abandonment.
What is Monera? A descriptive details of the entire kingdom
{{Taxonbar, from=Q842610 Obsolete taxa