Haeckel's classification '' by
Charles Darwin, in 1866
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 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. Haeckel also describes the protist genus
Monas in the two pages about Monera in his 1866 book. but later moneran was used. •
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 •
Protomonas — identified to a synonym of
Monas, a flagellated protozoan, and not a bacterium. •
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. 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 '''') 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 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 importance 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 sections, Prokaryotes and Eukaryotes: the Kingdom Monera being the sole member of the Prokaryotes section. 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. •
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
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 domains
Bacteria and
Archaea. 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==