Mycoplasma - WikiHQ

Mycoplasma is a genus of bacteria that, like the other members of the class Mollicutes, lack a cell wall (peptidoglycan) around their cell membrane. The absence of peptidoglycan makes them naturally resistant to antibiotics such as the beta-lactam antibiotics that target cell wall synthesis. They can be parasitic or saprotrophic.

In casual speech, the name "mycoplasma" (plural mycoplasmas or mycoplasms) generally refers to all members of the class Mollicutes. In formal scientific classification, the designation Mycoplasma refers exclusively to the genus, a member of the Mycoplasmataceae, the only family in the order Mycoplasmatales (see "scientific classification"). In 2018, Mycoplasma was split with many clinically significant species moved to other genera in Mollicutes; see the page Mollicutes for an overview.

Etymology

The term "mycoplasma", from the Greek μύκης, ' (fungus) and πλάσμα, ' (formed), was first used by Albert Bernhard Frank in 1889 to describe an altered state of plant cell cytoplasm resulting from infiltration by fungus-like microorganisms. Julian Nowak later proposed the name mycoplasma for certain filamentous microorganisms imagined to have both cellular and acellular stages in their lifecycles, which could explain how they were visible with a microscope, but passed through filters impermeable to other bacteria.

Later, the name for these mycoplasmas was pleuropneumonia-like organisms (PPLO), broadly referring to organisms similar in colonial morphology and filterability to the causative agent (a Mycoplasma species) of contagious bovine pleuropneumonia. At present, all these organisms are classified as Mollicutes, and the term Mycoplasma solely refers to the genus.

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The lack of a cell wall conveys some unique properties of mycoplasmas such as sensitivity to osmotic shock and detergents, resistance to penicillin and other beta-lactam antibiotics, and formation of fried-egg shaped colonies. Sections of mycoplasmas reveal that their cells are essentially built of three organelles: the cell membrane, ribosomes, and a circular double-stranded DNA tightly packed molecule. Their mode of replication is no different from that of other prokaryotes dividing by binary fission. For binary fission to happen, cytoplasmic division must fully synchronize with genome replication and in mycoplasma, cytoplasmic replication lags behind genome replication, which ultimately results in the formation of multinucleated filaments.

From in vitro cultivation of mycoplasmas, it has been discovered that they are "fastidious", i.e. difficult to cultivate. The reason for these difficulties for species such as Mycoplasma genitalium and Mycoplasma pneumoniae is the lack of all the genes involved in amino acid synthesis, making them dependent on exogenous supply of amino acids and other nutrients. This dependence on exogenous supplies of fatty acids and cholesterol serves as an advantage to conduct further studies on these organisms. In order to compensate for these deficiencies mycoplasmas are grown on complex media, usually consisting of beef heart infusion, peptone, yeast extract, and serum with various supplements.

Mycoplasmas' lack of a cell wall makes them good models for membrane studies. Due to this reason the availability of these membranes in pure state have enabled their chemical, enzymatic and antigenic characterization. The membrane is made of 60% to 70% protein with the remaining 20% to 30% being lipids.-->

Characteristics

Over 100 species were formerly included in the genus Mycoplasma, a member of the class Mollicutes. They are parasites or commensals of humans, animals, and plants. The genus Mycoplasma uses vertebrate and arthropod hosts. Dietary nitrogen availability has been shown to alter codon bias and genome evolution in Mycoplasma and the plant parasites Phytoplasma.

Mycoplasma species are among the smallest free-living organisms (about 0.2–0.3 μm in diameter). They have been found in the pleural cavities of cattle suffering from pleuropneumonia. These organisms are often called MLO (mycoplasma-like organisms) or, formerly, PPLO (pleuropneumonia-like organisms).

thumb|Colony morphology of Mycoplasma on Hayflick agar

Colonies show the typical "fried egg" appearance (about 0.5 mm in diameter).

Taxonomy

History of taxonomy

Before 1980, Mycoplasma species (often commonly called "mycoplasmas", now classified as Mollicutes) were sometimes considered stable L-form bacteria or even viruses, but phylogenetic analysis has identified them as bacteria that have lost their cell walls in the course of evolution.

<!-- possible WP:COPYVIOThe bacteria of the genus Mycoplasma (trivial name: mycoplasmas) and their close relatives are characterized by lack of a cell wall, which makes them resistant to antibiotics such as penicillin, cephalosporin, and vancomycin, the major antigen determinants are their cell membrane glycolipids and proteins. Furthermore, the lack of cell walls (no peptidoglycan layer) is the reason that they are gram-negative. Despite this, the cells often present a certain shape, with a characteristic small size (it is the smallest free-living bacteria), with typically about 10% of the volume of an Escherichia coli cell. These cell shapes presumably contribute to the ability of mycoplasmas to thrive in their respective environments. Most are pseudococcoidal, but there are notable exceptions. Species of the M. fastidiosum cluster are rod-shaped. Species of the M. pneumoniae cluster, including M. pneumoniae, possess a polar extension protruding from the pseudococcoidal cell body. This tip structure, designated an attachment organelle or terminal organelle, is essential for adherence to host cells and for movement along solid surfaces (gliding motility) and is implicated in normal cell division. M. pneumoniae cells are pleomorphic, with an attachment organelle of regular dimensions at one pole and a trailing filament of variable length and uncertain function at the other end, whereas other species in the cluster typically lack the trailing filament. Other species like M. mobile and M. pulmonis have similar structures with similar functions.

Mycoplasmas are unusual among bacteria in that most require sterols for the stability of their cytoplasmic membrane. Sterols are acquired from the environment, usually as cholesterol from the animal host. Mycoplasmas generally possess a relatively small genome of 0. 58-1. 38 megabases, which results in drastically reduced biosynthetic capabilities and explains their dependence on a host. Additionally they use an alternate genetic code in which the codon UGA encodes the amino acid tryptophan instead of the usual stop codon. They have a low GC-content (23–40 mol).-->

<!--== First isolation ==

possible WP:COPYVIO In 1898 Nocard and Roux reported the cultivation of the causative agent of CBPP, which was at that time a grave and widespread disease in cattle herds. The disease is caused by M. mycoides subsp. mycoides SC (small-colony type), and the work of Nocard and Roux represented the first isolation of a mycoplasma species. Cultivation was, and still is difficult because of the complex growth requirements.

These researchers succeeded by inoculating a semipermeable pouch of sterile medium with pulmonary fluid from an infected animal and depositing this pouch intraperitoneally into a live rabbit. After fifteen to twenty days, the fluid inside of the recovered pouch was opaque, indicating the growth of a microorganism. Opacity of the fluid was not seen in the control. This turbid broth could then be used to inoculate a second and third round and subsequently introduced into a healthy animal, causing disease. However, this did not work if the material was heated, indicating a biological agent at work. Uninoculated media in the pouch, after removal from the rabbit, could be used to grow the organism in vitro, demonstrating the possibility of cell-free cultivation and ruling out viral causes, although this was not fully appreciated at the time. The M. pneumoniae genome sequence was published soon afterwards and was the first genome sequence determined by primer walking of a cosmid library instead of the whole-genome shotgun method. Mycoplasma genomics and proteomics continue in efforts to understand the

so-called minimal cell, to catalog the entire protein content of a cell, and generally continue to take advantage of the small genome of these organisms to understand broad biological concepts.-->

The medical and agricultural importance of members of the genus Mycoplasma and related genera have led to the extensive cataloging of many of these organisms by culture, serology, and small sub-unit rRNA gene and whole-genome sequencing. A recent focus in the sub-discipline of molecular phylogenetics has both clarified and confused certain aspects of the organization of the class Mollicutes.

Taxonomists once classified Mycoplasma and relatives in the phylum Firmicutes, consisting of low G+C Gram-positive bacteria such as Clostridium, Lactobacillus, and Streptococcus; but modern polyphasic analyses situate them in the phylum Tenericutes.

By the 1990s, it had become readily apparent that this approach was problematic: the type species, M. mycoides, along with other significant mycoplasma species like M. capricolum, is evolutionarily more closely related to the genus Spiroplasma in the order Entomoplasmatales than to the other members of the genus Mycoplasma. As a result, if the group was to be rearranged to match phylogeny, a number of medically important species (e.g. M. pneumoniae, M. genitalium) would have to be put in a different genus, causing widespread confusion in medical and agricultural communities. The genus was discussed multiple times by the International Committee on Systematic Bacteriology's (ICSB) subcommittee on Mollicutes between 1992 and 2011, to no effect. The taxonomy was accepted by the ICSB with validation list 184 in 2018 and became the correct name. Both List of Prokaryotic names with Standing in Nomenclature (LPSN) and National Center for Biotechnology Information (NCBI) now use the new nomenclature.

Gupta's proposed taxonomy, as expected, moved the medically important "pneumoniae" group out of Mycoplasma into its own genus. As a result, a number of mycoplasmologists petitioned to the ICSB to reject the name in 2019. They argue that although Gupta's phylogenetic methods were likely solid, the proposed name changes are too sweeping to be practically adopted, citing some principles of the Code such as "name stability". Gupta and Oren wrote a rebuttal in 2020, further detailing the pre-existing taxonomic problems. In 2022, the ICSP's Judicial Opinion 122 ruled in favor of the name changes proposed by Gupta, meaning they remain valid under the Prokaryotic Code

Gupta et al. 2019 performed some uncontroversial sorting of the order Mycoplasmatales.

{| class="wikitable"

|+ Phylogenies of Mycoplasma sensu stricto/sensu Gupta

! colspan=1 | 16S rRNA based LTP_10_2024

! colspan=1 | 120 marker proteins based GTDB 09-RS220

| style="vertical-align:top|

Unassigned species

The GTDB and LTP phylogeny above does not include a number of names published under this genus that are either correct or pro-correct according to the LPSN. These species likely belong to a different genus under the standards of the 2018 reorganization, but has not been moved because a new combination has not been proposed, or because the new combination has not been made valid publication, or because the taxonomic opinion of the LPSN/LoRN refuses to use the new name as the correct name. The classification of LTP and GTDB is used here to assign a probable target genus.

Many new species have been proposed in Mycoplasma while disregarding the 2018 reorganization; see LPSN for a list. These will be included here and sorted by lineage eventually.

Hemotrophic mycoplasmas: This category includes species that should be moved to Eperythrozoon under the Gupta reorganization.

"Ca. M. aoti" Barker et al. 2011
"Ca. M. erythrocervae" Watanabe et al. 2010
"Ca. M. haematobrackenitadaridae" Becker et al. 2025
"Ca. M. haematocervi" corrig. Watanabe et al. 2010
"Ca. M. haematodidelphidis" corrig. Messick et al. 2002
"Ca. M. haematohominis" corrig. Millán et al. 2015
"Ca. M. haematohydrochoeri" corrig. Vieira et al. 2021
"Ca. M. haematomacacae" corrig. Maggi et al. 2013
"Ca. M. haematominiopteri" corrig. Millán et al. 2015
"Ca. M. haematomolossi" Becker et al. 2025
"M. haematomyotis" Volokhov et al. 2023
"Ca. M. haematonasuae" corrig. Collere et al. 2021
"Ca. M. haematoparvum" Sykes et al. 2005
"M. haematophyllostomi" Volokhov et al. 2023
"Ca. M. haematoselmanitadaridae" Becker et al. 2025
"Ca. M. haematosphigguri" corrig. Valente et al. 2021
"Ca. M. haematotapirus" Mongruel et al. 2022
"Ca. M. haematoterrestris" Mongruel et al. 2022
"Ca. M. haematotraderitadaridae" Becker et al. 2025
"Ca. M. haematovis" corrig. Hornok et al. 2009
"Ca. M. haemobovis" Meli et al. 2010
"Ca. M. haemomeles" Harasawa, Orusa & Giangaspero 2014
"Ca. M. haemomuris" (Mayer 1921) Neimark et al. 2002
"Ca. M. haemoparvum" Kenny et al. 2004
"Ca. M. hemominiopterus" Millán et al. 2015

Nested in Mycoplasmoides:

"M. bradburyae" Ramírez et al. 2023 – in GTDB

Nested in Mycoplasmopsis:

M. hafezii Ziegler et al. 2019 – in LTP, close to Mycoplsmopsis alligatoris
M. phocimorsus Skafte-Holm et al. 2023 – in LTP, close to "Mycoplasmopsis elephantis"

Synonimized before 2018 reorganization:

"M. incognitus" Lo et al. 1989 → M. fermentans

Not in LTP/GTDB, some of which have a 16S in GenBank that can be used to assign the genus:

"Ca. M. corallicola" Neulinger et al. 2009 – Mycoplsmopsis (among species mentioned in Gupta et al. (2018), "Mycoplsmopsis iguanae" was the highest 16S BLAST hit)
"Ca. M. coregoni" corrig. Rasmussen et al. 2021
"Ca. M. didelphidis" corrig. Pontarolo et al. 2021
"M. insons" May et al. 2007
"Ca. M. kahanei" Neimark et al. 2002
"M. monodon" Ghadersohi & Owens 1998
"M. pneumophila" Lyerova et al. 2008
"Ca. M. ravipulmonis" Neimark, Mitchelmore & Leach 1998
"Ca. M. salmoniarum" corrig. Rasmussen et al. 2021
"M. sphenisci" Frasca et al. 2005
"M. timone" Greub & Raoult 2001
"Ca. M. tructae" Sanchez et al. 2020
"Ca. M. turicense" corrig. Willi et al. 2006
"M. volis" Dillehay et al. 1995
"M. vulturii" Oaks et al. 2004

Synthetic mycoplasma genome

A chemically synthesized genome of a mycoplasmal cell based entirely on synthetic DNA which can self-replicate has been referred to as Mycoplasma laboratorium. M. laboratorium serves as a model for a minimal genome, that is, a genome that is reduced to mostly essential genes.

References

External links

Ureaplasma Infection: eMedicine Infectious Diseases