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

El filo Tenericutes, comúnmente conocido como micoplasmas, incluye una sola clase, Mollicutes. Estas bacterias carecen de paredes celulares y se encuentran entre los organismos más pequeños conocidos.Los micoplasmas a menudo viven en estrecha asociación con huéspedes animales o plantas en diversos entornos.A pesar de la falta de paredes celulares, las membranas de micoplasma son resistentes a la lisis osmótica en parte debido a la presencia de esteroles y lipoglicanos.Los micoplasmas exhiben formas pleomórficas, con cultivos que a menudo muestran pequeñas células cocoides, grandes células hinchadas y formas filamentosas que pueden ser ramificadas.El género Spiroplasma es helicoidal o en forma de espiral. Carece de paredes celulares y flagelos, pero exhibe motilidad a través de movimientos en forma de tornillo u ondulaciones lentas.Las especies de Spiroplasma se encuentran en varios lugares, desde las superficies externas de insectos y plantas hasta sus tejidos internos.Una especie notable, Spiroplasma citri, causa la enfermedad persistente de los cítricos en las plantas de cítricos.Otras especies, como Mycoplasma pneumoniae, Ureaplasma urealyticum y Metamycoplasma hominis, son patógenas para los humanos.

bacterias gram positivas: bacilli y mycoplasma

Bacterial Phylum Tenericutes

El filo Tenericutes, que incluye la &#250;nica clase Mollicutes, comprende bacterias que carecen de pared celular. El t&#233;rmino "Mollicutes" proviene del lat&#237;n mollis, que significa &#8220;blando&#8221;. Estos organismos, conocidos com&#250;nmente como micoplasmas debido a la prominencia del g&#233;nero Mycoplasma, que incluye pat&#243;genos humanos bien conocidos, est&#225;n entre los m&#225;s peque&#241;os que se conocen. A pesar de su incapacidad para te&#241;irse como Gram positivos (resultado de la ausencia de pared celular), los micoplasmas est&#225;n filogen&#233;ticamente relacionados con los Firmicutes.
Los micoplasmas suelen vivir en estrecha asociaci&#243;n con hu&#233;spedes animales o vegetales, donde la ausencia de pared celular Gram positiva puede representar una ventaja. Poseen genomas peque&#241;os, que var&#237;an entre 0,6 y 2,2 megabases (Mbp), una caracter&#237;stica t&#237;pica de los simbiontes obligados.
Propiedades estructurales
La ausencia de pared celular en los micoplasmas ha sido confirmada mediante microscop&#237;a electr&#243;nica y an&#225;lisis qu&#237;micos, los cuales revelan la ausencia de peptidoglicano. Aunque se asemejan a los protoplastos (bacterias desprovistas de pared celular), los micoplasmas son m&#225;s resistentes a la lisis osm&#243;tica. Esta resistencia se debe en parte a la presencia de esteroles, que estabilizan su membrana citoplasm&#225;tica. Algunos micoplasmas requieren esteroles en su medio de cultivo, lo que resulta &#250;til para su clasificaci&#243;n. Adem&#225;s de esteroles, muchos micoplasmas poseen lipoglicanos, heteropolisac&#225;ridos de cadena larga unidos covalentemente a l&#237;pidos de membrana. Estos compuestos, incrustados en la membrana citoplasm&#225;tica, se asemejan a los lipopolisac&#225;ridos de las bacterias Gram negativas, aunque carecen del esqueleto lip&#237;dico A. Los lipoglicanos contribuyen a la estabilidad de la membrana y facilitan la adhesi&#243;n a receptores de la superficie celular animal.
Los micoplasmas presentan formas pleom&#243;rficas, con cultivos que a menudo muestran c&#233;lulas peque&#241;as cocoides (0,2&#8211;0,3 &#956;m), c&#233;lulas aumentadas de tama&#241;o y formas filamentosas ramificadas. En cultivos sobre agar, las colonias exhiben una apariencia caracter&#237;stica en forma de &#8220;huevo frito&#8221;, con un n&#250;cleo central denso incrustado en el medio y una zona circundante m&#225;s clara. A diferencia de las bacterias con pared celular, los micoplasmas no se ven afectados por antibi&#243;ticos que inhiben la s&#237;ntesis de pared celular, pero son susceptibles a antibi&#243;ticos que afectan otros procesos celulares.
Los micoplasmas se cultivan en medios complejos que suelen requerir la adici&#243;n de suero fresco o l&#237;quido asc&#237;tico para proporcionar esteroles y &#225;cidos grasos insaturados. Aunque algunas especies crecen mal incluso en medios ricos, otras prosperan en medios definidos. La mayor&#237;a utiliza carbohidratos como fuente energ&#233;tica y requieren vitaminas, amino&#225;cidos, purinas y pirimidinas. Su metabolismo energ&#233;tico es variable puede observarse crecimiento aer&#243;bico, aer&#243;bico facultativo o anaer&#243;bico, dependiendo de la especie.
Spiroplasma, un g&#233;nero de Mollicutes con forma helicoidal o en espiral, carece tanto de pared celular como de flagelos, pero exhibe motilidad mediante un movimiento rotatorio (tipo tornillo) o mediante ondulaciones lentas. Se cree que esta motilidad implica fibrillas intracelulares. Las especies de Spiroplasma se encuentran en diversos entornos, incluidos garrapatas, la hemolinfa y el intestino de insectos, fluidos vasculares de plantas y superficies vegetales como flores y hojas.
Una especie destacada, Spiroplasma citri, causa la enfermedad del enanismo obstinado de los c&#237;tricos y tambi&#233;n se ha relacionado con la enfermedad del achaparramiento del ma&#237;z. Otros Mollicutes asociados a plantas han sido identificados mediante microscop&#237;a electr&#243;nica, lo que sugiere la existencia de un grupo amplio y diverso. Adem&#225;s, algunas especies de Spiroplasma provocan enfermedades en insectos, como la espiroplasmosis de las abejas y la enfermedad de la letargia en escarabajos del g&#233;nero Melolontha.

Bacterias Gram positivas: Bacilli y Mycoplasma

El filo Tenericutes, que incluye la &#250;nica clase Mollicutes, comprende bacterias que carecen de pared celular. El t&#233;rmino "Mollicutes" proviene ...

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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.

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Mycoplasmas and Wall-Less Bacteria

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