Monera is a kingdom that contains unicellular organisms with a prokaryotic cell organization,,
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. Furthermore the taxon Monera is paraphyletic, 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 to denote a member of either domain. Most bacteria were classified under Monera
however, Cyanobacteria were initially classified under Plantae due to their ability to photosynthesize.
History
Haeckel's classification
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 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 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. The Neolatin noun Monera and the German noun
Moneren/Moneres are derived from the ancient Greek noun moneres 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: Gymnomonera
Protogenes — such as Protogenes primordialis, an unidentified amoeba 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: Lepomonera Protomonas — identified to a synonym of
Monas, 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, 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.
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 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 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 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 recognized the Kingdom
Monera with 2 phyla, Myxophyta and Schizomycetae, the latter comprising classes Eubacteriae,
Myxobacteriae, and Spirochetae; Bisset distinguished 1 class and 4 orders: Eubacteriales, Actinomycetales,
Streptomycetales, and Flexibacteriales; Orla-Jensen and Bergey et al 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 Cyanophyta, now called Cyanobacteria
Myxobacteria
Mastigomonera branch Eubacteriae
Actinomycota Spirochaetae
Alternative commonly followed subdivision systems were based on Gram stains. This culminated
in the Gibbons and Murray classification of 1978:
Gracilicutes Photobacteria: class Oxyphotobacteriae and
class Anoxyphotobacteriae (anaerobic phototrophs, orders: Rhodospirillales and Chlorobiales
Scotobacteria
Firmacutes [sic] several orders such as Bacillales and Actinomycetales
Mollicutes Mendocutes
Three-domain system
In 1977, a PNAS paper by Carl Woese and George Fox demonstrated that the archaea 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. Blue-green algae
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 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, he did not emphasize
this distinction more than other biologists of his era. Roger Stanier and C. B. van Niel
believed that the bacteria 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.
Summary
See also Bacterial cell structure
Endosymbiont Kingdom
Prokaryote Symbiogenesis
References
External links Woese CR. "Bacterial evolution". Microbiol.
Rev. 51: 221–71. PMC 373105. PMID 2439888. 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