Fossil range: Hadean – Recent
| Prokaryotes collage|
| Included groups
| Excluded groups
Monera (// mə-NEER-ə) is a kingdom that contains unicellular organisms with a prokaryotic cell organization (having no nuclear membrane), such as bacteria. The taxon Monera was first proposed as a phylum by Ernst Haeckel in 1866. Subsequently, the phylum was elevated to the rank of kingdom in 1925 by Édouard Chatton. 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 of taxonomy, introduced by Carl Woese in 1977, which reflects the evolutionary history of life, the organisms found in kingdom Monera have been divided into two domains, Archaea and Bacteria (with Eukarya as the third domain). Furthermore, the taxon Monera is paraphyletic (not all members descended from their most recent common ancestor), as Archaea and Eukarya are currently believed to be more closely related than either is to 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.
Traditionally the natural world was classified as animal, vegetable, or mineral as in Systema Naturae. After the development of the microscope, attempts were made to fit microscopic organisms into either the plant or animal kingdoms. In 1676, Antonie van Leeuwenhoek 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 by Charles Darwin, in 1866 Ernst Haeckel, a supporter of evolution, 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 composed of the monerans (called Moneres in ) and defines them as completely structureless 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 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, such as Nostoc, which were placed in the phylum Archephyta of Algae (vide infra: Blue-green algae).
The Neolatin noun Monera and the German noun Moneren/Moneres are derived from the ancient Greek noun moneres (μονήρης) which Haeckel states to mean "simple", however it actually means "single, solitary". Haeckel also describes the protist genus Monas 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 [sic.]): Gymnomonera
- Protogenes — such as Protogenes primordialis, an unidentified amoeba (eukaryote) and not a bacterium
- Protamaeba — an incorrectly described/fabricated species
- Vibrio — a genus of comma-shaped bacteria first described in 1854
- Bacterium — a genus of rod-shaped bacteria first described in 1828. Haeckel does not explicitly assign this genus to the Monera.
- 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
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, Häkel'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 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 by 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 Bacterien) became prominently used to informally describe this group of species without a nucleus: Bacterium 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 2 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 subdiveded the kingdom into two branches containing several phyla:
- Myxomonera branch
- Mastigomonera branch
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)
- Firmacutes [sic] (gram positive, subsequently corrected to Firmicutes)
- several orders such as Bacillales and Actinomycetales (now in the phylum Actinobacteria)
- Mollicutes (gram variable, e.g. Mycoplasma)
- Mendocutes (uneven gram stain, "methanogenic bacteria" now known as the Archaea)
In 1977, a PNAS paper by Carl Woese and George Fox demonstrated that the archaea (initially called archaebacteria) are not significantly closer in relationship to the 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 kingdoms Bacteria and 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.
Although it was generally accepted that one could distinguish prokaryotes from eukaryotes on the basis of the presence of a 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 (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. 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.
| Woese et al.
|2 kingdoms||3 kingdoms||2 empires||4 kingdoms||5 kingdoms||3 domains||6 kingdoms|
- "Moneran", Encyclopædia Britannica Online, 2011, retrieved 2011-08-09
- Ernst Heinrich Philipp August Haeckel (1867). Generelle Morphologie der Organismen. Reimer, Berlin. ISBN 1-144-00186-2.
- van Leeuwenhoek A (1684). "An abstract of a letter from Mr. Anthony Leevvenhoek at Delft, dated Sep. 17, 1683, Containing Some Microscopical Observations, about Animals in the Scurf of the Teeth, the Substance Call'd Worms in the Nose, the Cuticula Consisting of Scales". Philosophical Transactions (1683–1775) 14 (155–166): 568–574. doi:10.1098/rstl.1684.0030. Retrieved 2007-08-19.
- van Leeuwenhoek A (1700). "Part of a Letter from Mr Antony van Leeuwenhoek, concerning the Worms in Sheeps Livers, Gnats, and Animalcula in the Excrements of Frogs". Philosophical Transactions (1684–1775) 22 (260–276): 509–518. doi:10.1098/rstl.1700.0013. Retrieved 2007-08-19.
- van Leeuwenhoek A (1702). "Part of a Letter from Mr Antony van Leeuwenhoek, F. R. S. concerning Green Weeds Growing in Water, and Some Animalcula Found about Them". Philosophical Transactions (1683–1775) 23 (277–288): 1304–11. doi:10.1098/rstl.1702.0042. Retrieved 2007-08-19.
- Don J. Brenner, Noel R. Krieg, James T. Staley (July 26, 2005) [1984(Williams & Wilkins)]. George M. Garrity, ed. Introductory Essays. Bergey's Manual of Systematic Bacteriology 2A (2nd ed.). New York: Springer. p. 304. ISBN 978-0-387-24143-2. British Library no. GBA561951.
- Copeland, H. (1938). "The kingdoms of organisms". Quarterly Review of Biology 13: 383–420. doi:10.1086/394568.
- Woese, C. R. (1987). "Bacterial evolution". Microbiological reviews 51 (2): 221–271. PMC 373105. PMID 2439888.
- μονήρης. Liddell, Henry George; Scott, Robert; A Greek–English Lexicon at the Perseus Project.
- Francis Polkinghorne Pascoe (1880). Zoological classification; a handy book of reference with tables of the subkingdoms, classes, orders, etc., of the animal kingdom, their characters and lists of the families and principal genera.
- PACINI (F.): Osservazione microscopiche e deduzioni patologiche sul cholera asiatico. Gazette Medicale de Italiana Toscano Firenze, 1854, 6, 405-412.
- EHRENBERG (C.G.): Dritter Beitrag zur Erkenntniss grosser Organisation in der Richtung des kleinsten Raumes. Physikalische Abhandlungen der Koeniglichen Akademie der Wissenschaften zu Berlin aus den Jahren 1833-1835, 1835, pp. 143-336.
- EHRENBERG (C.G.): Dritter Beitrag zur Erkenntniss grosser Organisation in der Richtung des kleinsten Raumes. Abhandlungen der Preussischen Akademie der Wissenschaften (Berlin) aus den Jahre 1833-1835, pp. 143-336.
- EHRENBERG (C.G.): Beiträge zur Kenntnis der Organization der Infusorien und ihrer geographischen Verbreitung besonders in Sibirien. Abhandlungen der Koniglichen Akademie der Wissenschaften zu Berlin, 1832, 1830, 1-88.
- Protomonas entry in LPSN [Euzéby, J.P. (1997). "List of Bacterial Names with Standing in Nomenclature: a folder available on the Internet". Int J Syst Bacteriol 47 (2): 590–2. ISSN 0020-7713. PMID 9103655. doi:10.1099/00207713-47-2-590.]
- C. Von Nägeli (1857). R. Caspary, ed. "Bericht über die Verhandlungen der 33. Versammlung deutscher Naturforscher und Aerzte, gehalten in Bonn von 18 bis 24 September 1857" [Report on the negotiations on 33 Meeting of German Natural Scientists and Physicians, held in Bonn, 18 to 24 September 1857]. Botanische Zeitung 15: 749–776.
- Migula W (1894). "Über ein neues System der Bakterien". Arb Bakteriol Inst Karlsruhe 1: 235–328.
- CHESTER F. D. (1897). "Classification of the Schizomycetes". Annual Report Delaware College Agricultural Experiment Station 9: 62.
- Buchanan R E (Nov 1916). "Studies in the Nomenclature and Classification of Bacteria: The Problem of Bacterial Nomenclature". J Bacteriol 1 (6): 591–6. PMC 378679. PMID 16558720.
- Ferdinand Cohn (1872). "Untersuchungen uber Bakterien". Beiträge zur Biologie der Pflanzen 1 (1). pp. 127–224.
- Ferdinand Cohn (1875). "Untersuchungen uber Bakterien". Beiträge zur Biologie der Pflanzen 1 (3). pp. 141–208.
- Ernst Haeckel. The Wonders of Life. Translated by Joseph McCabe. New York and London. I904.
- Chatton, É. (1925). "Pansporella perplexa. Réflexions sur la biologie et la phylogénie des protozoaires". Annales des Sciences Naturelles - Zoologie et Biologie Animale. 10-VII: 1–84.
- R H Whittaker (1969). "New concepts of kingdoms or organisms. Evolutionary relations are better represented by new classifications than by the traditional two kingdoms". Science 163 (3863): 150–160. Bibcode:1969Sci...163..150W. PMID 5762760. doi:10.1126/science.163.3863.150.
- Jan Sapp (June 2005). "The Prokaryote-Eukaryote Dichotomy: Meanings and Mythology". Microbiology and Molecular Biology Reviews 69 (2): 292–305. PMC 1197417. PMID 15944457. doi:10.1128/MMBR.69.2.292-305.2005.
- GIBBONS (N.E.) and MURRAY (R.G.E.): Proposals concerning the higher taxa of bacteria. International Journal of Systematic Bacteriology, 1978, 28, 1-6.
- MURRAY (R.G.E.): The higher taxa, or, a place for everything...? In: N.R. KRIEG and J.G. HOLT (ed.) Bergey's Manual of Systematic Bacteriology, vol. 1, The Williams & Wilkins Co., Baltimore, 1984, p. 31-34
- Lyons, Richard D. (Nov 3, 1977). "Scientists Discover a Form of Life That Predates Higher Organisms". The New York Times. pp. A1, A20.
- Holland L. (22 May 1990). "Woese,Carl in the forefront of bacterial evolution revolution". scientist 4 (10).
- Cavalier-Smith, T. (1998). "A revised six-kingdom system of life". Biological Reviews 73 (03): 203–66. PMID 9809012. doi:10.1111/j.1469-185X.1998.tb00030.x.
- Roger Stanier to Peter Raven, 5 November 1970, National Archives of Canada, MG 31, accession J35, vol. 6, as quoted in Sapp, 2005
- Linnaeus, C. (1735). Systemae Naturae, sive regna tria naturae, systematics proposita per classes, ordines, genera & species.
- Woese, C.; Kandler, O.; Wheelis, M. (1990). "Towards a natural system of organisms: proposal for the domains Archaea, Bacteria, and Eucarya.". Proceedings of the National Academy of Sciences of the United States of America 87 (12): 4576–9. Bibcode:1990PNAS...87.4576W. PMC 54159. PMID 2112744. doi:10.1073/pnas.87.12.4576.