Gliding Motility of Mycoplasma mobile on Uniform Oligosaccharides

Motility Assays of Mycoplasma mobile Under Light Microscopy

Mycoplasma mobile forms a membrane protrusion at a pole as an organelle. M. mobile cells bind to solid surfaces and glide in the direction of the protrusion. In gliding motility, M. mobile cells catch, pull and release sialylated oligosaccharides on host cells. The observation of Mycoplasma species under light microscopy is useful for the analysis of adhesion ability and the motility mechanism.

Purification and Structural Analysis of the Gliding Motility Machinery in Mycoplasma mobile

Isolating functional units from large insoluble protein complexes are a complex but valuable approach for quantitative and structural analysis. Mycoplasma mobile, a gliding bacterium, contains a large insoluble protein complex called gliding machinery. The machinery contains several chain structures formed by motors that are evolutionarily related to the F₁-ATPase. Recently, we developed a method to purify functional motors and their chain structures using Triton X-100 and a high salt concentration buffer and resolved their structures using electron microscopy. In this chapter, we describe the processes of purification and structural analysis of functional motors for the gliding of M. mobile using negative-staining electron microscopy.

Chained Structure of Dimeric F1-like ATPase in Mycoplasma mobile Gliding Machinery

Mycoplasma mobile, a fish pathogen, exhibits gliding motility using ATP hydrolysis on solid surfaces, including animal cells. The gliding machinery can be divided into surface and internal structures. The internal structure of the motor is composed of 28 so-called “chains” that are each composed of 17 repeating protein units called “particles.” These proteins include homologs of the catalytic α and β subunits of F₁-ATPase. In this study, we isolated the particles and determined their structures using negative-staining electron microscopy and high-speed atomic force microscopy. The isolated particles were composed of five proteins, MMOB1660 (α-subunit homolog), -1670 (β-subunit homolog), -1630, -1620, and -4530, and showed ATP hydrolyzing activity. The two-dimensional (2D) structure, with dimensions of 35 and 26 nm, showed a dimer of hexameric ring approximately 12 nm in diameter, resembling F₁-ATPase catalytic (αβ)₃. We isolated the F₁-like ATPase unit, which is composed of MMOB1660, -1670, and -1630. Furthermore, we isolated the chain and analyzed the three-dimensional (3D) structure, showing that dimers of mushroom-like structures resembling F₁-ATPase were connected and aligned along the dimer axis at 31-nm intervals. An atomic model of F₁-ATPase catalytic (αβ)₃ from Bacillus PS3 was successfully fitted to each hexameric ring of the mushroom-like structure. These results suggest that the motor for M. mobile gliding shares an evolutionary origin with F₁-ATPase. Based on the obtained structure, we propose possible force transmission processes in the gliding mechanism.

Movements of Mycoplasma mobile Gliding Machinery Detected by High-Speed Atomic Force Microscopy

Mycoplasma mobile, a parasitic bacterium, glides on solid surfaces, such as animal cells and glass, by a special mechanism. This process is driven by the force generated through ATP hydrolysis on an internal structure. However, the spatial and temporal behaviors of the internal structures in living cells are unclear. In this study, we detected the movements of the internal structure by scanning cells immobilized on a glass substrate using high-speed atomic force microscopy (HS-AFM). By scanning the surface of a cell, we succeeded in visualizing particles, 2 nm in height and aligned mostly along the cell axis with a pitch of 31.5 nm, consistent with previously reported features based on electron microscopy. Movements of individual particles were then analyzed by HS-AFM. In the presence of sodium azide, the average speed of particle movements was reduced, suggesting that movement is linked to ATP hydrolysis. Partial inhibition of the reaction by sodium azide enabled us to analyze particle behavior in detail, showing that the particles move 9 nm right, relative to the gliding direction, and 2 nm into the cell interior in 330 ms and then return to their original position, based on ATP hydrolysis.

Exploring Spiroplasma Biology: Opportunities and Challenges

Spiroplasmas are cell-wall-deficient helical bacteria belonging to the class Mollicutes. Their ability to maintain a helical shape in the absence of cell wall and their motility in the absence of external appendages have attracted attention from the scientific community for a long time. In this review we compare and contrast motility, shape determination and cytokinesis mechanisms of Spiroplasma with those of other Mollicutes and cell-walled bacteria. The current models for rod-shape determination and cytokinesis in cell-walled bacteria propose a prominent role for the cell wall synthesis machinery. These models also involve the cooperation of the actin-like protein MreB and FtsZ, the bacterial homolog of tubulin. However the exact role of the cytoskeletal proteins is still under much debate. Spiroplasma possess MreBs, exhibit a rod-shape dependent helical morphology, and divide by an FtsZ-dependent mechanism. Hence, spiroplasmas represent model organisms for deciphering the roles of MreBs and FtsZ in fundamental mechanisms of non-spherical shape determination and cytokinesis in bacteria, in the absence of a cell wall. Identification of components implicated in these processes and deciphering their functions would require genetic experiments. Challenges in genetic manipulations in spiroplasmas are a major bottleneck in understanding their biology. We discuss advancements in genome sequencing, gene editing technologies, super-resolution microscopy and electron cryomicroscopy and tomography, which can be employed for addressing long-standing questions related to Spiroplasma biology.

Peptidoglycan layer and disruption processes in Bacillus subtilis cells visualized using quick-freeze, deep-etch electron microscopy

Peptidoglycan, which is the main component of the bacterial cell wall, is a heterogeneous polymer of glycan strands cross-linked with short peptides and is synthesized in cooperation with the cell division cycle. Although it plays a critical role in bacterial survival, its architecture is not well understood. Herein, we visualized the architecture of the peptidoglycan surface in Bacillus subtilis at the nanometer resolution, using quick-freeze, deep-etch electron microscopy (EM). Filamentous structures were observed on the entire surface of the cell, where filaments about 11 nm wide formed concentric circles on cell poles, filaments about 13 nm wide formed a circumferential mesh-like structure on the cylindrical part and a 'piecrust' structure was observed at the boundary. When growing cells were treated with lysozyme, the entire cell mass migrated to one side and came out from the cell envelope. Fluorescence labeling showed that lysozyme preferentially bound to a cell pole and cell division site, where the peptidoglycan synthesis was not complete. Ruffling of surface structures was observed during EM. When cells were treated with penicillin, the cell mass came out from a cleft around the cell division site. Outward curvature of the protoplast at the cleft seen using EM suggested that turgor pressure was applied as the peptidoglycan was not damaged at other positions. When muropeptides were depleted, surface filaments were lost while the rod shape of the cell was maintained. These changes can be explained on the basis of the working points of the chemical structure of peptidoglycan.

Identification and sequence analyses of the gliding machinery proteins from Mycoplasma mobile

Mycoplasma mobile, a fish pathogen, exhibits its own specialized gliding motility on host cells based on ATP hydrolysis. The special protein machinery enabling this motility is composed of surface and internal protein complexes. Four proteins, MMOBs 1630, 1660, 1670, and 4860 constitute the internal complex, including paralogs of F-type ATPase/synthase α and β subunits. In the present study, the cellular localisation for the candidate gliding machinery proteins, MMOBs 1620, 1640, 1650, and 5430 was investigated by using a total internal reflection fluorescence microscopy system after tagging these proteins with the enhanced yellow fluorescent protein (EYFP). The M. mobile strain expressing a fusion protein MMOB1620-EYFP exhibited reduced cell-binding activity and a strain expressing MMOB1640 fused with EYFP exhibited increased gliding speed, showing the involvement of these proteins in the gliding mechanism. Based on the genomic sequences, we analysed the sequence conservativity in the proteins of the internal and the surface complexes from four gliding mycoplasma species. The proteins in the internal complex were more conserved compared to the surface complex, suggesting that the surface complex undergoes modifications depending on the host. The analyses suggested that the internal gliding complex was highly conserved probably due to its role in the motility mechanism.

Three-Dimensional Observations of an Aperiodic Oscillatory Gliding Behavior in Myxococcus xanthus Using Confocal Interference Reflection Microscopy

3D imaging of live bacteria with optical microscopy techniques is a challenge due to the small size of bacterial cells, meaning that previous studies have been limited to observing motility behavior in 2D. We introduce the application of confocal multiwavelength interference reflection microscopy to bacteria, which enables visualization of 3D motility behaviors in a single 2D image. Using the model organism Myxococcus xanthus, we identified novel motility behaviors that are not explained by current motility models, where gliding bacteria exhibit aperiodic changes in their adhesion to an underlying solid surface. We concluded that the 3D behavior was not linked to canonical motility mechanisms and that IRM could be applied to study a range of microbiological specimens with minimal adaptation to a commercial microscope.

The deltaproteobacterium Myxococcus xanthus is a model for bacterial motility and has provided unprecedented insights into bacterial swarming behaviors. Fluorescence microscopy techniques have been invaluable in defining the mechanisms that are involved in gliding motility, but these have almost entirely been limited to two-dimensional (2D) studies, and there is currently no understanding of gliding motility in a three-dimensional (3D) context. We present here the first use of confocal interference reflection microscopy (IRM) to study gliding bacteria, revealing aperiodic oscillatory behavior with changes in the position of the basal membrane relative to the substrate on the order of 90 nm in vitro. First, we use a model planoconvex lens specimen to show how topological information can be obtained from the wavelength-dependent interference pattern in IRM. We then use IRM to observe gliding M. xanthus bacteria and show that cells undergo previously unobserved changes in their adhesion profile as they glide. We compare the wild type with mutants that have reduced motility, which also exhibit the same changes in the adhesion profile during gliding. We find that the general gliding behavior is independent of the proton motive force-generating complex AglRQS and suggest that the novel behavior that we present here may be a result of recoil and force transmission along the length of the cell body following firing of the type IV pili.

IMPORTANCE 3D imaging of live bacteria with optical microscopy techniques is a challenge due to the small size of bacterial cells, meaning that previous studies have been limited to observing motility behavior in 2D. We introduce the application of confocal multiwavelength interference reflection microscopy to bacteria, which enables visualization of 3D motility behaviors in a single 2D image. Using the model organism Myxococcus xanthus, we identified novel motility behaviors that are not explained by current motility models, where gliding bacteria exhibit aperiodic changes in their adhesion to an underlying solid surface. We concluded that the 3D behavior was not linked to canonical motility mechanisms and that IRM could be applied to study a range of microbiological specimens with minimal adaptation to a commercial microscope.

Refined Mechanism of Mycoplasma mobile Gliding Based on Structure, ATPase Activity, and Sialic Acid Binding of Machinery

Mycoplasma mobile, a fish pathogen, glides on solid surfaces by repeated catch, pull, and release of sialylated oligosaccharides by a unique mechanism based on ATP energy. The gliding machinery is composed of huge surface proteins and an internal "jellyfish"-like structure. Here, we elucidated the detailed three-dimensional structures of the machinery by electron cryotomography. The internal "tentacle"-like structure hydrolyzed ATP, which was consistent with the fact that the paralogs of the α- and β-subunits of F₁-ATPase are at the tentacle structure. The electron microscopy suggested conformational changes of the tentacle structure depending on the presence of ATP analogs. The gliding machinery was isolated and showed that the binding activity to sialylated oligosaccharide was higher in the presence of ADP than in the presence of ATP. Based on these results, we proposed a model to explain the mechanism of M. mobile gliding.IMPORTANCE The genus Mycoplasma is made up of the smallest parasitic and sometimes commensal bacteria; Mycoplasma pneumoniae, which causes human "walking pneumonia," is representative. More than ten Mycoplasma species glide on host tissues by novel mechanisms, always in the direction of the distal side of the machinery. Mycoplasma mobile, the fastest species in the genus, catches, pulls, and releases sialylated oligosaccharides (SOs), the carbohydrate molecules also targeted by influenza viruses, by means of a specific receptor and using ATP hydrolysis for energy. Here, the architecture of the gliding machinery was visualized three dimensionally by electron cryotomography (ECT), and changes in the structure and binding activity coupled to ATP hydrolysis were discovered. Based on the results, a refined mechanism was proposed for this unique motility.

Identification of novel protein domain for sialyloligosaccharide binding essential to Mycoplasma mobile gliding

Sialic acids, terminal structures of sialylated glycoconjugates, are widely distributed in animal tissues and are often involved in intercellular recognitions, including some bacteria and viruses. Mycoplasma mobile, a fish pathogenic bacterium, binds to sialyloligosaccharide (SO) through adhesin Gli349 and glides on host cell surfaces. The amino acid sequence of Gli349 shows no similarity to known SO-binding proteins. In the present study, we predicted the binding part of Gli349, produced it in Escherichia coli and proved its binding activity to SOs of fetuin using atomic force microscopy. Binding was detected with a frequency of 10.3% under retraction speed of 400 nm/s and was shown to be specific for SO, as binding events were competitively inhibited by the addition of free 3'-sialyllactose. The histogram of the unbinding forces showed 24 pN and additional peaks. These results suggested that the distal end of Gli349 constitutes a novel sialoadhesin domain and is directly involved in the gliding mechanism of M. mobile.

Production and characterization of recombinant P1 adhesin essential for adhesion, gliding, and antigenic variation in the human pathogenic bacterium, Mycoplasma pneumoniae

Mycoplasma pneumoniae forms an attachment organelle at one cell pole, binds to the host cell surface, and glides via a unique mechanism. A 170-kDa protein, P1 adhesin, present on the organelle surface plays a critical role in the binding and gliding process. In this study, we obtained a recombinant P1 adhesin comprising 1476 amino acid residues, excluding the C-terminal domain of 109 amino acids that carried the transmembrane segment, that were fused to additional 17 amino acid residues carrying a hexa-histidine (6 × His) tag using an Escherichia coli expression system. The recombinant protein showed solubility, and chirality in circular dichroism (CD). The results of analytical gel filtration, ultracentrifugation, negative-staining electron microscopy, and small-angle X-ray scattering (SAXS) showed that the recombinant protein exists in a monomeric form with a uniformly folded structure. SAXS analysis suggested the presence of a compact and ellipsoidal structure rather than random or molten globule-like conformation. Structure model based on SAXS results fitted well with the corresponding structure obtained with cryo-electron tomography from a closely related species, M. genitalium. This recombinant protein may be useful for structural and functional studies as well as for the preparation of antibodies for medical applications.

Linear motor driven-rotary motion of a membrane-permeabilized ghost in Mycoplasma mobile

Mycoplasma mobile exhibits a smooth gliding movement as does its membrane-permeabilized ghost model. Ghost experiments revealed that the energy source for M. mobile motility is adenosine triphosphate (ATP) and that the gliding comprises repetitions of 70 nm steps. Here we show a new motility mode, in which the ghost model prepared with 0.013% Triton X-100 exhibits directed rotational motions with an average speed of approximately 2.1 Hz when ATP concentration is greater than 3.0 × 10⁻¹ mM. We found that rotary ghosts treated with sialyllactose, the binding target for leg proteins, were stopped. Although the origin of the rotation has not been conclusively determined, this result suggested that biomolecules embedded on the cell membrane nonspecifically attach to the glass and work as a fluid pivot point and that the linear motion of the leg is a driving force for the rotary motion. This simple geometry exemplifies the new motility mode, by which the movement of a linear motor is efficiently converted to a constant rotation of the object on a micrometer scale.

Detailed Analyses of Stall Force Generation in Mycoplasma mobile Gliding

Mycoplasma mobile is a bacterium that uses a unique mechanism to glide on solid surfaces at a velocity of up to 4.5 μm/s. Its gliding machinery comprises hundreds of units that generate the force for gliding based on the energy derived from ATP; the units catch and pull sialylated oligosaccharides fixed to solid surfaces. In this study, we measured the stall force of wild-type and mutant strains of M. mobile carrying a bead manipulated using optical tweezers. The strains that had been enhanced for binding exhibited weaker stall forces than the wild-type strain, indicating that stall force is related to force generation rather than to binding. The stall force of the wild-type strain decreased linearly from 113 to 19 picoNewtons after the addition of 0-0.5 mM free sialyllactose (a sialylated oligosaccharide), with a decrease in the number of working units. After the addition of 0.5 mM sialyllactose, the cells carrying a bead loaded using optical tweezers exhibited stepwise movements with force increments. The force increments ranged from 1 to 2 picoNewtons. Considering the 70-nm step size, this small-unit force may be explained by the large gear ratio involved in the M. mobile gliding machinery.

Chemotaxis without Conventional Two-Component System, Based on Cell Polarity and Aerobic Conditions in Helicity-Switching Swimming of Spiroplasma eriocheiris

Spiroplasma eriocheiris is a pathogen that causes mass mortality in Chinese mitten crab, Eriocheir sinensis. S. eriocheiris causes tremor disease and infects almost all of the artificial breeding crustaceans, resulting in disastrous effects on the aquaculture economy in China. S. eriocheiris is a wall-less helical bacterium, measuring 2.0 to 10.0 μm long, and can swim up to 5 μm per second in a viscous medium without flagella by switching the cell helicity at a kink traveling from the front to the tail. In this study, we showed that S. eriocheiris performs chemotaxis without the conventional two-component system, a system commonly found in bacterial chemotaxis. The chemotaxis of S. eriocheiris was observed more clearly when the cells were cultivated under anaerobic conditions. The cells were polarized as evidenced by a tip structure, swimming in the direction of the tip, and were shown to reverse their swimming direction in response to attractants. Triton X-100 treatment revealed the internal structure, a dumbbell-shaped core in the tip that is connected by a flat ribbon, which traces the shortest line in the helical cell shape from the tip to the other pole. Sixteen proteins were identified as the components of the internal structure by mass spectrometry, including Fibril protein and four types of MreB proteins.

Directed Binding of Gliding Bacterium, Mycoplasma mobile, Shown by Detachment Force and Bond Lifetime

Mycoplasma mobile, a fish-pathogenic bacterium, features a protrusion that enables it to glide smoothly on solid surfaces at a velocity of up to 4.5 µm s⁻¹ in the direction of the protrusion. M. mobile glides by a repeated catch-pull-release of sialylated oligosaccharides fixed on a solid surface by hundreds of 50-nm flexible “legs” sticking out from the protrusion. This gliding mechanism may be explained by a possible directed binding of each leg with sialylated oligosaccharides, by which the leg can be detached more easily forward than backward. In the present study, we used a polystyrene bead held by optical tweezers to detach a starved cell at rest from a glass surface coated with sialylated oligosaccharides and concluded that the detachment force forward is 1.6- to 1.8-fold less than that backward, which may be linked to a catch bond-like behavior of the cell. These results suggest that this directed binding has a critical role in the gliding mechanism.

Mycoplasma species are the smallest bacteria and are parasitic and occasionally commensal, as represented by Mycoplasma pneumoniae, which causes so-called “walking pneumonia” in humans. Dozens of species glide on host tissues, always in the direction of the characteristic cellular protrusion, by novel mechanisms. The fastest species, Mycoplasma mobile, catches, pulls, and releases sialylated oligosaccharides (SOs), which are common targets among influenza viruses, by means of a specific receptor based on the energy of ATP hydrolysis. Here, force measurements made with optical tweezers revealed that the force required to detach a cell from SOs is smaller forward than backward along the gliding direction. The directed binding should be a clue to elucidate this novel motility mechanism.

Integrated Information and Prospects for Gliding Mechanism of the Pathogenic Bacterium Mycoplasma pneumoniae

Mycoplasma pneumoniae forms a membrane protrusion at a cell pole and is known to adhere to solid surfaces, including animal cells, and can glide on these surfaces with a speed up to 1 μm per second. Notably, gliding appears to be involved in the infectious process in addition to providing the bacteria with a means of escaping the host's immune systems. However, the genome of M. pneumoniae does not encode any of the known genes found in other bacterial motility systems or any conventional motor proteins that are responsible for eukaryotic motility. Thus, further analysis of the mechanism underlying M. pneumoniae gliding is warranted. The gliding machinery formed as the membrane protrusion can be divided into the surface and internal structures. On the surface, P1 adhesin, a 170 kDa transmembrane protein forms an adhesin complex with other two proteins. The internal structure features a terminal button, paired plates, and a bowl (wheel) complex. In total, the organelle is composed of more than 15 proteins. By integrating the currently available information by genetics, microscopy, and structural analyses, we have suggested a working model for the architecture of the organelle. Furthermore, in this article, we suggest and discuss a possible mechanism of gliding based on the structural model, in which the force generated around the bowl complex transmits through the paired plates, reaching the adhesin complex, resulting in the repeated catch of sialylated oligosaccharides on the host surface by the adhesin complex.

Periodicity in Attachment Organelle Revealed by Electron Cryotomography Suggests Conformational Changes in Gliding Mechanism of Mycoplasma pneumoniae

Mycoplasma pneumoniae, a pathogenic bacterium, glides on host surfaces using a unique mechanism. It forms an attachment organelle at a cell pole as a protrusion comprised of knoblike surface structures and an internal core. Here, we analyzed the three-dimensional structure of the organelle in detail by electron cryotomography. On the surface, knoblike particles formed a two-dimensional array, albeit with limited regularity. Analyses using a nonbinding mutant and an antibody showed that the knoblike particles correspond to a naplike structure that has been observed by negative-staining electron microscopy and is likely to be formed as a complex of P1 adhesin, the key protein for binding and gliding. The paired thin and thick plates feature a rigid hexagonal lattice and striations with highly variable repeat distances, respectively. The combination of variable and invariant structures in the internal core and the P1 adhesin array on the surface suggest a model in which axial extension and compression of the thick plate along a rigid thin plate is coupled with attachment to and detachment from the substrate during gliding.

Human mycoplasma pneumonia, epidemic all over the world in recent years, is caused by a pathogenic bacterium, Mycoplasma pneumoniae. This tiny bacterium, about 2 µm in cell body length, glides on the surface of the human trachea to infect the host by binding to sialylated oligosaccharides, which are also the binding targets of influenza viruses. The mechanism of mycoplasmal gliding motility is not related to any other well-studied motility systems, such as bacterial flagella and cytoplasmic motor proteins. Here, we visualized the attachment organelle, a cellular architecture for gliding, three dimensionally by using electron cryotomography and other conventional methods. A possible gliding mechanism has been suggested based on the architectural images.

Reprint of “Prospects for the gliding mechanism of Mycoplasma mobile”

Mycoplasma mobile forms gliding machinery at a cell pole and glides continuously in the direction of the cell pole at up to 4.5 μm per second on solid surfaces such as animal cells. This motility system is not related to those of any other bacteria or eukaryotes. M. mobile uses ATP energy to repeatedly catch, pull, and release sialylated oligosaccharides on host cells with its approximately 50-nm long legs. The gliding machinery is a large structure composed of huge surface proteins and internal jellyfish-like structure. This system may have developed from an accidental combination between an adhesin and a rotary ATPase, both of which are essential for the adhesive parasitic life of Mycoplasmas.

Gliding Direction of Mycoplasma mobile

Mycoplasma mobile glides in the direction of its cell pole by a unique mechanism in which hundreds of legs, each protruding from its own gliding unit, catch, pull, and release sialylated oligosaccharides fixed on a solid surface. In this study, we found that 77% of cells glided to the left with a change in direction of 8.4° ± 17.6° μm(-1) displacement. The cell body did not roll around the cell axis, and elongated, thinner cells also glided while tracing a curved trajectory to the left. Under viscous conditions, the range of deviation of the gliding direction decreased. In the presence of 250 μM free sialyllactose, in which the binding of the legs (i.e., the catching of sialylated oligosaccharides) was reduced, 70% and 30% of cells glided to the left and the right, respectively, with changes in direction of ∼30° μm(-1). The gliding ghosts, in which a cell was permeabilized by Triton X-100 and reactivated by ATP, glided more straightly. These results can be explained by the following assumptions based on the suggested gliding machinery and mechanism: (i) the units of gliding machinery may be aligned helically around the cell, (ii) the legs extend via the process of thermal fluctuation and catch the sialylated oligosaccharides, and (iii) the legs generate a propulsion force that is tilted from the cell axis to the left in 70% and to the right in 30% of cells.

IMPORTANCE

Mycoplasmas are bacteria that are generally parasitic to animals and plants. Some Mycoplasma species form a protrusion at a pole, bind to solid surfaces, and glide. Although these species appear to consistently glide in the direction of the protrusion, their exact gliding direction has not been examined. This study analyzed the gliding direction in detail under various conditions and, based on the results, suggested features of the machinery and the mechanism of gliding.

Prospects for the gliding mechanism of Mycoplasma mobile

Mycoplasma mobile forms gliding machinery at a cell pole and glides continuously in the direction of the cell pole at up to 4.5μm per second on solid surfaces such as animal cells. This motility system is not related to those of any other bacteria or eukaryotes. M. mobile uses ATP energy to repeatedly catch, pull, and release sialylated oligosaccharides on host cells with its approximately 50-nm long legs. The gliding machinery is a large structure composed of huge surface proteins and internal jellyfish-like structure. This system may have developed from an accidental combination between an adhesin and a rotary ATPase, both of which are essential for the adhesive parasitic life of Mycoplasmas.