The Chroococcales () are an order of

cyanobacteria Cyanobacteria ( ) are a group of autotrophic gram-negative bacteria that can obtain biological energy via oxygenic photosynthesis. The name "cyanobacteria" () refers to their bluish green (cyan) color, which forms the basis of cyanobacteri ...

in some classifications which includes the harmful algal bloom '' Microcystis aeruginosa''. Molecular data indicate that Chroococcales may be

polyphyletic A polyphyletic group is an assemblage that includes organisms with mixed evolutionary origin but does not include their most recent common ancestor. The term is often applied to groups that share similar features known as Homoplasy, homoplasies ...

, meaning its members may not all belong to the same

clade In biology, a clade (), also known as a Monophyly, monophyletic group or natural group, is a group of organisms that is composed of a common ancestor and all of its descendants. Clades are the fundamental unit of cladistics, a modern approach t ...

or have the same common ancestor.

Characteristics

The order is characterized by single, floating cells or colonies which are embedded to a matrix. Also, a lack of differentiation between apical and basal structures exists.

Prochlorales

A heterotypic synonym of Chroococcales is (order) Prochlorales , with type genus "''

Prochloron ''Prochloron'' (from the Greek ''pro'' (before) and the Greek ''chloros'' (green) ) is a genus of unicellular oxygenic photosynthetic prokaryotes commonly found as an extracellular symbiont on coral reefs, particularly in didemnid ascidians (sea ...

''". Additional names of the same nature included: * Division Prochlorophyta Lewin, 1976 * Class Prochlorophyceae Lewin, 1977 * Family Prochloraceae Lewin, 1977 * Chloroxybacteria Margulis & Schwartz, 1982 * Subdivision Prochlorobacteria Jeffrey 1982 * Division Prochlorophycota Shameel 2008 The assignment as a division/subdivision was based on a belief that because this class lack red and blue phycobilin pigments and have stacked thylakoids, they are so distinct from typical

as to warrant a high rank. The four taxa with "Lewin 1977" became validly published names under the ICNP in 1986, as the revised version , by virtue of being published in '' Int. J. Syst. Bacteriol.'' with a description.

Ecology

They are an important component of

photosynthetic picoplankton Photosynthetic picoplankton or picophytoplankton is the fraction of the photosynthetic phytoplankton of cell sizes between 0.2 and 2 μm (i.e. picoplankton). It is especially important in the central oligotrophic regions of the world ocea ...

. These oligotrophic organisms are abundant in nutrient poor tropical waters and use a unique photosynthetic pigment, divinyl-chlorophyll, to absorb light and acquire energy.

Discovery and naming

This unique group of phytoplankton, with no phycobilin pigments, were initially found in 1975 near the

Great Barrier Reef The Great Barrier Reef is the world's largest coral reef system, composed of over 2,900 individual reefs and 900 islands stretching for over over an area of approximately . The reef is located in the Coral Sea, off the coast of Queensland, ...

and off the coast of Mexico (''

''). Prochlorophyta was soon assigned as a new algal sub-class in 1976 by Ralph A. Lewin of the Scripps Institution of Oceanography. Other phytoplankton that lacked phycobilin pigments were later found in freshwater lakes in the Netherlands by Tineke Burger-Wiersma and colleagues and were termed ''Prochlorothrix'' (additional reading on ''Prochlorothrix'' can be found in a journal article by A.V. Pinevich ). In 1986 ''

Prochlorococcus ''Prochlorococcus'' is a genus of very small (0.6 μm) marine cyanobacteria with an unusual pigmentation ( chlorophyll ''a2'' and ''b2''). These bacteria belong to the photosynthetic picoplankton and are probably the most abundant photosyn ...

'' was found by Sallie W. (Penny) Chisholm and colleagues. ''

'' may be responsible for a significant portion of the global primary production.

Morphology

Prochlorophytes are very small microbes generally between 0.2 and 2 μm (

). They morphologically resemble

Cyanobacteria Cyanobacteria ( ) are a group of autotrophic gram-negative bacteria that can obtain biological energy via oxygenic photosynthesis. The name "cyanobacteria" () refers to their bluish green (cyan) color, which forms the basis of cyanobacteri ...

(formerly known as Blue Green Algae). Members of Prochlorophyta have been found as coccoid (spherical) ( Coccus) shaped, as in ''

'', and as filaments, as in ''Prochlorothrix''.

References

External links

Prochlorophytes
Bacteria orders {{cyanobacteria-stub