Name: mycoplasmas and wall-less bacteria
Uploaded: 2025-06-12T09:23:08.000Z
Duration: 1 min 24 s
Channel: JoVE

Der Stamm Tenericutes — allgemein bekannt als Mykoplasmen — umfasst eine einzige Klasse, Mollicutes. Diese Bakterien haben keine Zellwände und gehören zu den kleinsten bekannten Organismen. Mykoplasmen leben oft in enger Verbindung mit tierischen oder pflanzlichen Wirten in unterschiedlichen Umgebungen. Trotz des Fehlens von Zellwänden sind Mykoplasmenmembranen resistent gegen osmotische Lyse, teilweise aufgrund des Vorhandenseins von Sterolen und Lipoglykanen. Mykoplasmen weisen pleomorphe Formen auf, wobei Kulturen oft kleine kokzoide Zellen, große geschwollene Zellen und filamentöse Formen aufweisen, die verzweigt sein können. Gattung Spiroplasma ist spiralförmig. Es fehlen Zellwände und Flagellen, es zeigt aber Beweglichkeit durch schraubenartige Bewegungen oder langsame Wellen. Spiroplasma-Spezies kommen an verschiedenen Stellen vor, von der Außenseite von Insekten und Pflanzen bis hin zu ihrem inneren Gewebe. Eine bemerkenswerte Art, Spiroplasma citri, verursacht bei Zitruspflanzen die hartnäckige Zitruskrankheit. Andere Spezies, wie z. B. Mycoplasma pneumoniae, Ureaplasma urealyticum, und Metamycoplasma hominis, sind für den Menschen pathogen.

gram-positive bakterien: bazillen und mykoplasmen

Bacterial Phylum Tenericutes

Der Stamm Tenericutes, der die einzige Klasse Mollicutes umfasst, besteht aus Bakterien, die keine Zellwand besitzen. Der Begriff &#8222;Mollicutes&#8220; stammt vom lateinischen Wort mollis, was &#8222;weich&#8220; bedeutet. Diese Organismen geh&#246;ren zu den kleinsten bekannten Bakterien und werden aufgrund der Dominanz der Gattung Mycoplasma, zu der bekannte humanpathogene Arten z&#228;hlen, h&#228;ufig als Mykoplasmen bezeichnet. Trotz ihrer Unf&#228;higkeit, grampositiv zu f&#228;rben (bedingt durch das Fehlen einer Zellwand), sind Mykoplasmen phylogenetisch mit den Firmicutes verwandt.
Mykoplasmen leben h&#228;ufig in enger Assoziation mit tierischen oder pflanzlichen Wirten, wobei das Fehlen einer grampositiven Zellwand m&#246;glicherweise vorteilhaft ist. Sie verf&#252;gen &#252;ber kleine Genome im Bereich von 0,6 bis 2,2 Megabasenpaaren (Mbp), ein typisches Merkmal obligater Symbionten.
Strukturelle Eigenschaften
Das Fehlen von Zellw&#228;nden bei Mykoplasmen wurde durch Elektronenmikroskopie und chemische Analysen best&#228;tigt, die einen Mangel an Peptidoglycan nachweisen. Obwohl sie Protoplasten &#228;hneln (Bakterien ohne Zellwand), sind Mykoplasmen widerstandsf&#228;higer gegen osmotische Lyse. Diese Widerstandsf&#228;higkeit ist teilweise auf das Vorhandensein von Sterolen zur&#252;ckzuf&#252;hren, die ihre zytoplasmatische Membran stabilisieren. Einige Mykoplasmen ben&#246;tigen Sterole im N&#228;hrmedium, ein Merkmal, das zur Klassifikation herangezogen wird. Neben Sterolen besitzen viele Mykoplasmen Lipoglykane&#8212;langkettige Heteropolysaccharide, die kovalent an Membranlipide gebunden sind. Diese Verbindungen, die in der zytoplasmatischen Membran verankert sind, &#228;hneln den Lipopolysacchariden gramnegativer Bakterien, weisen jedoch kein Lipid-A-R&#252;ckgrat auf. Lipoglykane tragen zur Membranstabilit&#228;t bei und erleichtern die Anheftung an tierische Zelloberfl&#228;chenrezeptoren.
Mykoplasmen zeigen pleomorphe Formen, wobei Kulturen h&#228;ufig kleine kokkoide Zellen (0,2&#8211;0,3 &#956;m), geschwollene Zellen sowie filament&#246;se und verzweigte Formen aufweisen. In Agar-Kulturen zeigen Kolonien ein charakteristisches &#8222;Spiegelei&#8220;-Erscheinungsbild mit einem dichten zentralen Kern, der im Medium eingebettet ist, und einem helleren &#228;u&#223;eren Bereich. Im Gegensatz zu Bakterien mit Zellw&#228;nden sind Mykoplasmen unempfindlich gegen&#252;ber Antibiotika, die die Zellwandsynthese hemmen, aber anf&#228;llig f&#252;r Antibiotika, die andere zellul&#228;re Prozesse beeinflussen.
Mykoplasmen werden auf komplexen N&#228;hrmedien kultiviert, wobei h&#228;ufig frisches Serum oder Aszitesfl&#252;ssigkeit notwendig ist, um Sterole und unges&#228;ttigte Fetts&#228;uren bereitzustellen. W&#228;hrend einige Arten selbst auf n&#228;hrstoffreichen Medien schlecht wachsen, gedeihen andere auf definierten Medien. Die meisten Mykoplasmen nutzen Kohlenhydrate zur Energiegewinnung und ben&#246;tigen Vitamine, Aminos&#228;uren, Purine und Pyrimidine. Ihr Energiestoffwechsel variiert, wobei aerober, fakultativ aerober oder anaerober Wuchs m&#246;glich ist.
Spiroplasma, eine Gattung spiral- oder helixf&#246;rmiger Mollicutes, besitzt weder Zellw&#228;nde noch Flagellen, zeigt jedoch eine aktive Motilit&#228;t durch rotatorische (schraubenartige) Bewegung oder langsame Undulationen. Diese Beweglichkeit wird vermutlich durch intrazellul&#228;re Fibrillen erm&#246;glicht. Spiroplasma-Arten kommen in vielf&#228;ltigen Umgebungen vor, darunter Zecken, H&#228;molymphe und Darm von Insekten, pflanzliche Leitb&#252;ndel und auf Pflanzenoberfl&#228;chen wie Bl&#252;ten und Bl&#228;ttern.
Eine bemerkenswerte Art, Spiroplasma citri, verursacht die Citrus Stubborn Krankheit und wird auch mit der Maisz&#252;nsler-Krankheit in Verbindung gebracht. Weitere pflanzenassoziierte Mollicutes wurden mittels Elektronenmikroskopie identifiziert, was auf das Vorhandensein einer gro&#223;en, vielf&#228;ltigen Gruppe hindeutet. Dar&#252;ber hinaus verursachen einige Spiroplasma-Arten Krankheiten in Insekten wie die Spiroplasmose der Honigbiene und Lethargiekrankheit bei K&#228;fern wie Melolontha.

Gram-positive Bakterien: Bazillen und Mykoplasmen

Der Stamm Tenericutes, der die einzige Klasse Mollicutes umfasst, besteht aus Bakterien, die keine Zellwand besitzen. Der Begriff &#8222;Mollicutes&#8220; ...

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mycoplasmas and wall-less bacteria

Mycoplasmas are wall-less bacteria in the phylum Tenericutes. This group includes the single class Mollicutes, a name that comes from the Latin mollis, meaning soft. These bacteria are among the smallest known. They are often called mycoplasmas because the genus Mycoplasma includes many well-known human pathogens.

Mycoplasmas cannot stain gram-positive because they lack cell walls. Even so, they are related to the Firmicutes. They often live closely with animal or plant hosts. Their small genomes, about 0.6 to 2.2 megabase pairs, fit the pattern seen in many obligate symbionts.

Electron microscopy and chemical tests show that mycoplasmas do not have peptidoglycan, the main material in bacterial cell walls. They can look like protoplasts, which are bacteria stripped of their walls. However, mycoplasmas are more resistant to osmotic lysis. Sterols in the cytoplasmic membrane help stabilize them, and some species need sterols in their growth media.

Many mycoplasmas also contain lipoglycans, which are long-chain heteropolysaccharides linked to membrane lipids. These molecules sit in the cytoplasmic membrane and resemble the lipopolysaccharides of gram-negative bacteria, but they do not have a lipid A backbone. Lipoglycans help stabilize the membrane and aid attachment to animal cell surface receptors. Mycoplasmas also show pleomorphic forms, so cultures may contain small coccoid cells, swollen cells, and filamentous or branched forms.

On agar, mycoplasma colonies often have a “fried egg” look. A dense center grows down into the medium, while a lighter area surrounds it. Antibiotics that block cell wall synthesis do not affect these bacteria. They are instead sensitive to antibiotics that target other cell processes. To grow them in the lab, scientists often use complex media with fresh serum or ascitic fluid. These ingredients supply sterols and unsaturated fatty acids.

Some mycoplasma species grow poorly even on rich media, while others can grow on defined media. Most use carbohydrates for energy and need vitamins, amino acids, purines, and pyrimidines. Their energy use varies, and species may be aerobic, facultative aerobic, or anaerobic.

Spiroplasma is a helical, or spiral-shaped, genus within the Mollicutes. It also lacks a cell wall and flagella, yet it moves by rotary, screw-like motion or slow undulations. This movement is thought to involve intracellular fibrils. Spiroplasma species are found in ticks, the hemolymph and gut of insects, plant vascular fluids, and on plant surfaces such as flowers and leaves.

One species, Spiroplasma citri, causes citrus stubborn disease and has also been linked to corn stunt disease. Electron microscopy has also revealed other plant-associated Mollicutes, suggesting a large and diverse group. Some Spiroplasma species also cause insect diseases, including honeybee spiroplasmosis and lethargy disease in beetles such as Melolontha.

Mycoplasmas and Wall-Less Bacteria

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key terms and concepts

Learn how mycoplasmas lack cell walls, survive with sterols, form “fried egg” colonies, and include Spiroplasma species that infect plants and insects.

Mycoplasmas and Wall-Less Bacteria | JoVE K12

JoVE Core Microbiology provides an engaging introduction to the microbial world and its influence on health, industry, and the environment. This comprehensive collection covers key concepts such as microbial structure, metabolism, genetics, and ecology. It introduces essential laboratory techniques and microscopy methods through visually engaging animations. Corresponding scientist-in-action videos bridge classroom concepts with real-world research and applications.

microbiology

Mycoplasmas and Wall-Less Bacteria

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