Name: mycoplasmas and wall-less bacteria
Uploaded: 2025-06-12T09:23:08.000Z
Duration: 1 min 24 s
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Il phylum Tenericutes, comunemente noto come micoplasma, comprende un'unica classe, i Mollicutes. Questi batteri mancano di pareti cellulari e sono tra i più piccoli organismi conosciuti.I micoplasmi vivono spesso in stretta associazione con ospiti animali o vegetali in ambienti diversi.Nonostante la mancanza di pareti cellulari, le membrane dei micoplasmi sono resistenti alla lisi osmotica in parte a causa della presenza di steroli e lipoglicani.I micoplasmi mostrano forme pleomorfe, con colture che spesso mostrano piccole cellule coccoidi, grandi cellule gonfie e forme filamentose che possono essere ramificate.Il genere Spiroplasma è elicoidale o a forma di spirale. Manca di pareti cellulari e flagelli, ma mostra motilità attraverso movimenti a vite o ondulazioni lente.Le specie di Spiroplasma si trovano in vari luoghi, dalle superfici esterne di insetti e piante ai loro tessuti interni.Una specie notevole, lo Spiroplasma citri, causa la malattia ostinata degli agrumi nelle piante di agrumi.Altre specie, come il Mycoplasma pneumoniae, l'Ureaplasma urealyticum e il Metamycoplasma hominis, sono patogene per l'uomo.

batteri gram-positivi: bacilli e mycoplasma

Bacterial Phylum Tenericutes

Il phylum Tenericutes, che comprende la sola classe Mollicutes, include batteri privi di parete cellulare. Il termine Mollicutes deriva dal latino mollis, che significa &#8220;molle.&#8221; Questi organismi, tra i pi&#249; piccoli conosciuti, sono comunemente noti come micoplasmi, a causa della prominenza del genere Mycoplasma, che include noti patogeni umani. Nonostante non siano colorabili con la colorazione di Gram (a causa della mancanza di parete cellulare), i micoplasmi sono filogeneticamente imparentati con i Firmicutes.
I micoplasmi vivono spesso in stretta associazione con ospiti animali o vegetali, situazione in cui l&#8217;assenza della parete cellulare Gram-positiva pu&#242; rappresentare un vantaggio. Possiedono genomi di dimensioni ridotte, compresi tra 0,6 e 2,2 megabasi (Mbp), caratteristica tipica dei simbionti obbligati.
Propriet&#224; Strutturali
L&#8217;assenza di parete cellulare nei micoplasmi &#232; stata confermata mediante microscopia elettronica e analisi chimiche che evidenziano la mancanza di peptidoglicano. Sebbene somiglino a protoplasti (batteri privati della parete cellulare), i micoplasmi sono pi&#249; resistenti alla lisi osmotica. Tale resistenza &#232; in parte attribuibile alla presenza di steroli, che stabilizzano la membrana citoplasmatica. Alcuni micoplasmi richiedono steroli nei terreni di coltura, una caratteristica utile nella loro classificazione. Oltre agli steroli, molti micoplasmi possiedono lipoglicani&#8212;eteropolisaccaridi a catena lunga legati covalentemente ai lipidi di membrana. Questi composti, incorporati nella membrana citoplasmatica, somigliano ai lipopolisaccaridi dei batteri Gram-negativi, ma mancano della componente lipidica A. I lipoglicani contribuiscono alla stabilit&#224; della membrana e facilitano l&#8217;adesione ai recettori delle cellule animali.
I micoplasmi presentano forme pleomorfe; le colture mostrano spesso piccole cellule coccoidi (0,2&#8211;0,3 &#956;m), cellule rigonfie e forme filamentose o ramificate. Nelle colture su agar, le colonie mostrano un aspetto caratteristico &#8220;a uovo fritto,&#8221; con un nucleo centrale denso, incorporato nel mezzo e un&#8217;area periferica pi&#249; chiara. A differenza dei batteri con parete cellulare, i micoplasmi non sono sensibili agli antibiotici che inibiscono la sintesi della parete cellulare, ma risultano suscettibili ad antibiotici che colpiscono altri processi cellulari.
I micoplasmi si coltivano su terreni complessi, spesso contenenti siero fresco o liquido ascitico per fornire steroli e acidi grassi insaturi. Mentre alcune specie crescono con difficolt&#224; anche su terreni ricchi, altre possono prosperare su determinati terreni. La maggior parte dei micoplasmi utilizza carboidrati per l&#8217;energia e necessita di vitamine, amminoacidi, purine e pirimidine. Il loro metabolismo energetico varia: alcune specie crescono in condizioni aerobiche, altre sono aerobi facoltativi o anaerobi.
Spiroplasma, un genere di Mollicutes a forma elicoidale o spiralata, &#232; privo sia di parete cellulare sia di flagelli, ma mostra motilit&#224; tramite movimento rotatorio (a vite) o lente ondulazioni. Si ritiene che tale motilit&#224; sia mediata da fibrille intracellulari. Le specie di Spiroplasma si trovano in ambienti diversi, tra cui zecche, emolinfa e intestino di insetti, fluidi vascolari delle piante e superfici vegetali come fiori e foglie.
Una specie degna di nota, Spiroplasma citri, causa la malattia stubborn degli agrumi ed &#232; stata collegata anche alla crescita stentata del mais. Altri Mollicutes associati alle piante sono stati identificati tramite microscopia elettronica, suggerendo l&#8217;esistenza di un ampio e diversificato gruppo. Inoltre, alcune specie di Spiroplasma provocano malattie negli insetti, come la spiroplasmosi delle api da miele e la malattia della letargia in coleotteri come Melolontha.

Batteri Gram-positivi: Bacilli e Mycoplasma

Il phylum Tenericutes, che comprende la sola classe Mollicutes, include batteri privi di parete cellulare. Il termine Mollicutes deriva dal latino mollis, ...

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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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