Acholeplasmatales is an order

Order (biology)

In scientific classification used in biology, the order is# a taxonomic rank used in the classification of organisms. Other well-known ranks are life, domain, kingdom, phylum, class, family, genus, and species, with order fitting in between class and family...

 in the Class Mollicutes

Mollicutes

The Mollicutes are a class of bacteria distinguished by the absence of a cell wall. The word "Mollicutes" is derived from the Latin mollis , and cutis . They are parasites of various animals and plants, living on or in the host's cells. Individuals are very small, typically only 0.2–0.3 μm in size...

, containing merely one family, Acholeplasmataceae, comprising the genera Acholeplasma

Acholeplasma

Acholeplasma are wall-less bacteria in the Mollicutes class. They include saprotrophic or pathogenic species. There are 15 recognised species. The G+C content is low, ranging from 26 - 36% . The genomes of Acholeplasma species range in size from 1.5 to 1.65 Mbp. Cholesterol is not required for...

and Phytoplasma

Phytoplasma

Phytoplasma are specialised bacteria that are obligate parasites of plant phloem tissue and transmitting insects . They were first discovered by scientists in 1967 and were named mycoplasma-like organisms or MLOs. They cannot be cultured in vitro in cell-free media...

. Yet, Phytoplasma has the Candidatus

Candidatus

Candidatus is in scientific classification a component of the taxonomic name for a bacterium that cannot be maintained in a Bacteriology Culture Collection. It is an interim taxonomic status for noncultivable organisms. An example would be "Candidatus Phytoplasma allocasuarinae"...

 state, because members still could not be cultured.

Etymology

Etymology

Etymology is the study of the history of words, their origins, and how their form and meaning have changed over time.For languages with a long written history, etymologists make use of texts in these languages and texts about the languages to gather knowledge about how words were used during...

: The name Acholeplasmatales is derived from the Greek a = not, cholè = bile and plasma = anything moulded or formed.


Species in the order Acholeplasmatales can grow in a medium without cholesterol, unlike species in the order Mycoplasmatales. Cholesterol

Cholesterol

Cholesterol is a complex isoprenoid. Specifically, it is a waxy steroid of fat that is produced in the liver or intestines. It is used to produce hormones and cell membranes and is transported in the blood plasma of all mammals. It is an essential structural component of mammalian cell membranes...

 is a sterol

Sterol

Sterols, also known as steroid alcohols, are a subgroup of the steroids and an important class of organic molecules. They occur naturally in plants, animals, and fungi, with the most familiar type of animal sterol being cholesterol...

 that is an important component of the cell membrane

Cell membrane

The cell membrane or plasma membrane is a biological membrane that separates the interior of all cells from the outside environment. The cell membrane is selectively permeable to ions and organic molecules and controls the movement of substances in and out of cells. It basically protects the cell...

 of mycoplasmas, whereas in acholeplasmas and in bacteria in general it is absent.

Characteristics

Members of Acholeplasmatales are facultative anaerobic. They are parasites or commensals of vertebrates, insects or plants; some are saprophyte.
Phytoplasma

Phytoplasma

Phytoplasma are specialised bacteria that are obligate parasites of plant phloem tissue and transmitting insects . They were first discovered by scientists in 1967 and were named mycoplasma-like organisms or MLOs. They cannot be cultured in vitro in cell-free media...

s colonize the phloem sieve elements of vascular plant

Vascular plant

Vascular plants are those plants that have lignified tissues for conducting water, minerals, and photosynthetic products through the plant. Vascular plants include the clubmosses, Equisetum, ferns, gymnosperms and angiosperms...

s, causing diseases. They are transmitted by sap-sucking insects (primarily leafhoppers, planthoppers, and psyllids

), living in the gut, haemolymph, salivary gland and other organs. Like other mollicutes, they show a high host specificity.

Classification

In the first taxonomy of Mollicutes the classification was based on requiring or not requiring cholesterol for growth. The old order Mycoplasmatales consisted of two families: the family Mycoplasmataceae

Mycoplasmataceae

The Mycoplasmataceae is a family of bacteria in the order Mycoplasmatales. This family comprises the species Mycoplasma and Ureaplasma.In 1967 the Order Mycoplasmatales was incorporated into the class Mollicutes....

, which requires cholesterol and the sterol-nonrequiring family Acholeplasmataceae.

In view of the many properties in which the acholeplasmas distinguish from species in Mycoplasmataceae and Spiroplasmataceae, Freundt et al. proposed in 1984 to elevate the family Acholeplasmataceae to the ordinal rank Acholeplasmatales, thus separating it from Mycoplasmatales.
In 1987, the division in sterol requiring and nonrequiring changed with the addition of a third order, Anaeroplasmatales

Anaeroplasmatales

The Anaeroplasmatales are an order of mollicute bacteria. An example is the pathogenic species Erysipelothrix rhusiopathiae....

, taking into account that dependence on anaerobic growth conditions is an important characteristic.