Visualization of the attachment organelle and cytadherence proteins of Mycoplasma pneumoniae by immunofluorescence microscopy

Proteomic and Phenotypic Studies of Mycoplasma pneumoniae Revealed Macrolide-Resistant Mutation (A2063G) Associated Changes in Protein Composition and Pathogenicity of Type I Strains

Mycoplasma pneumoniae (MP) is an important respiratory pathogen, the prevalence of macrolide-resistant MP (mainly containing A2063G mutation in 23S rRNA) increased in recent years. Epidemiological studies suggest a higher prevalence of type I resistant (IR) strains than corresponding sensitive (IS/IIS) strains, but not type II resistant (IIR) strains. Here, we aimed to analyze the factors underlying the altered prevalence of IR strains. First, proteomic analyses exhibit the protein compositions were type specific, while more differential proteins were detected between IS and IR (227) than IIS and IIR strains (81). mRNA level detection suggested posttranscriptional regulation of these differential proteins. Differential protein-related phenotypic changes were also detected: (i) P1 abundance was different between genotypes (I < II, IR < IS), the adhesion of MPs showed accordance to P1 abundance within IS and IIS strains; (ii) type I, especially IR, strains had a higher proliferation rate, which is potentially associated with differential proteins participating in glycolysis and one carbon pool metabolisms; (iii) A549 cells infected with IR strains had lower activity of caspase-3 and higher levels IL-8, but the differences were not significant between groups (P > 0.05). Correlations of P1 abundance to caspase-3 activity and proliferation rate to the level of IL-8 were obtained. These results suggest changes in protein composition influenced the pathogenicity of MP, especially in IR strains, which may impact the prevalence of MP strains of different genotypes. IMPORTANCE The prevalence of macrolide-resistant MPs increased the difficulty in treatment of MP infections and posed potential threats to children's health. Epidemiological studies showed a high prevalence of IR-resistant strains (mainly A2063G in 23S rRNA) in these years. However, the trigger mechanisms for this phenomenon are not clear. In this paper, proteomic and phenotypic studies suggest that IR strains have reduced levels of multiple adhesion proteins and increased proliferation rate, which may lead to higher transmission rate of IR strains in the population. This suggests that we should pay attention to the prevalence of IR strains.

Galacto-Oligosaccharides as an Anti-Infective and Anti-Microbial Agent for Macrolide-Resistant and -Sensitive Mycoplasma pneumoniae

The worldwide increase in the incidence of antibiotic resistance of the atypical bacterium Mycoplasma pneumoniae (MP) challenges the treatment of MP infections, especially in children. Therefore, alternative strategies for the treatment of MP infections are warranted. Galacto- and fructo-oligosaccharides (GOS and FOS) are a specific group of complex carbohydrates that were recently shown to possess direct anti-pathogenic properties. In this study, we assessed whether GOS and FOS exert anti-microbial and anti-infective effects against MP and, especially, macrolide-resistant MP (MRMP) in vitro. The MIC values of GOS for MP and MRMP were 4%. In contrast, the MIC values of FOS for both MP and MRMP were 16%. A time-kill kinetic assay showed that FOS possess bacteriostatic properties, while for GOS, a bactericidal effect against MP and MRMP was observed after 24 h at a concentration of 4x MIC. In co-cultures with human alveolar A549 epithelial cells, GOS killed adherent MP and MRMP and also concentration-dependently inhibited their adherence to A549 cells. Further, GOS suppressed (MR)MP-induced IL-6 and IL-8 in A549 cells. None of the aforementioned parameters were affected when FOS were added to these co-cultures. In conclusion, the anti-infective and anti-microbial properties of GOS could provide an alternative treatment against MRMP and MP infections.

Cell shape controls rheotaxis in small parasitic bacteria

Mycoplasmas, a group of small parasitic bacteria, adhere to and move across host cell surfaces. The role of motility across host cell surfaces in pathogenesis remains unclear. Here, we used optical microscopy to visualize rheotactic behavior in three phylogenetically distant species of Mycoplasma using a microfluidic chamber that enabled the application of precisely controlled fluid flow. We show that directional movements against fluid flow occur synchronously with the polarized cell orienting itself to be parallel against the direction of flow. Analysis of depolarized cells revealed that morphology itself functions as a sensor to recognize rheological properties that mimic those found on host-cell surfaces. These results demonstrate the vital role of cell morphology and motility in responding to mechanical forces encountered in the native environment.

The small, parasitic bacterium Mycoplasma pneumoniae attaches to, and moves over, host cell surfaces. Adherence to host surfaces and motility are critical for the pathogenicity of M. pneumoniae. The role of motility by M. pneumoniae in vivo, however, is poorly understood. Host airways generate constant fluid flow toward the mouth as part of their defense against pathogens and irritants. Consequently, pulmonary invaders must counter the rheological forces found in host airways in order to successfully colonize the host. Here, we demonstrate that M. pneumoniae exhibits directional movement against fluid flow. These findings suggest there is a vital role for rheotactic motility that has evolved in order to overcome host defense mechanisms such as mucociliary clearance.

Imaging Minimal Bacteria at the Nanoscale: a Reliable and Versatile Process to Perform Single-Molecule Localization Microscopy in Mycoplasmas

Mycoplasmas are the smallest free-living organisms. These bacteria are important models for both fundamental and synthetic biology, owing to their highly reduced genomes. They are also relevant in the medical and veterinary fields, as they are pathogenic to both humans and most livestock species. Mycoplasma cells have minute sizes, often in the 300- to 800-nm range. As these dimensions are close to the diffraction limit of visible light, fluorescence imaging in mycoplasmas is often poorly informative. Recently developed superresolution imaging techniques can break this diffraction limit, improving the imaging resolution by an order of magnitude and offering a new nanoscale vision of the organization of these bacteria. These techniques have, however, not been applied to mycoplasmas before. Here, we describe an efficient and reliable protocol to perform single-molecule localization microscopy (SMLM) imaging in mycoplasmas. We provide a polyvalent transposon-based system to express the photoconvertible fluorescent protein mEos3.2, enabling photo-activated localization microscopy (PALM) in most Mycoplasma species. We also describe the application of direct stochastic optical reconstruction microscopy (dSTORM). We showcase the potential of these techniques by studying the subcellular localization of two proteins of interest. Our work highlights the benefits of state-of-the-art microscopy techniques for mycoplasmology and provides an incentive to further the development of SMLM strategies to study these organisms in the future.

IMPORTANCE Mycoplasmas are important models in biology, as well as highly problematic pathogens in the medical and veterinary fields. The very small sizes of these bacteria, well below a micron, limits the usefulness of traditional fluorescence imaging methods, as their resolution limit is similar to the dimensions of the cells. Here, to bypass this issue, we established a set of state-of-the-art superresolution microscopy techniques in a wide range of Mycoplasma species. We describe two strategies: PALM, based on the expression of a specific photoconvertible fluorescent protein, and dSTORM, based on fluorophore-coupled antibody labeling. With these methods, we successfully performed single-molecule imaging of proteins of interest at the surface of the cells and in the cytoplasm, at lateral resolutions well below 50 nm. Our work paves the way toward a better understanding of mycoplasma biology through imaging of subcellular structures at the nanometer scale.

Comparative Proteomic Analysis of the Mycoplasma gallisepticum Nucleoid Fraction before and after Infection

Mycoplasma gallisepticum belongs to the class Mollicutes and induces severe chronic respiratory disease in chickens. It lacks the cell wall and contains a very small genome and, accordingly, a reduced set of regulatory proteins. It is assumed that one of the regulatory mechanisms in mycoplasmas may be the dynamics of the spatial organization of the chromosome. M. gallisepticum has only two known nucleoid-associated (NAP) histone-like proteins (Hup_1 and Hup_2). To search for new potential NAP that may play a role in the infection process, we isolated nucleoid fractions from M. gallisepticum cells before and after infection of HD3 chicken erythroblast cell line and performed a comparative proteomic analysis of these fractions. We identified several potential NAP that included the components of the terminal organelle and adhesion, VlhA antigen, NADH oxidase, and PykF pyruvate kinase.

Force and Stepwise Movements of Gliding Motility in Human Pathogenic Bacterium Mycoplasma pneumoniae

Mycoplasma pneumoniae, a human pathogenic bacterium, binds to sialylated oligosaccharides and glides on host cell surfaces via a unique mechanism. Gliding motility is essential for initiating the infectious process. In the present study, we measured the stall force of an M. pneumoniae cell carrying a bead that was manipulated using optical tweezers on two strains. The stall forces of M129 and FH strains were averaged to be 23.7 and 19.7 pN, respectively, much weaker than those of other bacterial surface motilities. The binding activity and gliding speed of the M129 strain on sialylated oligosaccharides were eight and two times higher than those of the FH strain, respectively, showing that binding activity is not linked to gliding force. Gliding speed decreased when cell binding was reduced by addition of free sialylated oligosaccharides, indicating the existence of a drag force during gliding. We detected stepwise movements, likely caused by a single leg under 0.2-0.3 mM free sialylated oligosaccharides. A step size of 14-19 nm showed that 25-35 propulsion steps per second are required to achieve the usual gliding speed. The step size was reduced to less than half with the load applied using optical tweezers, showing that a 2.5 pN force from a cell is exerted on a leg. The work performed in this step was 16-30% of the free energy of the hydrolysis of ATP molecules, suggesting that this step is linked to the elementary process of M. pneumoniae gliding. We discuss a model to explain the gliding mechanism, based on the information currently available.

Molecular ruler of the attachment organelle in Mycoplasma pneumoniae

Length control is a fundamental requirement for molecular architecture. Even small wall-less bacteria have specially developed macro-molecular structures to support their survival. Mycoplasma pneumoniae, a human pathogen, forms a polar extension called an attachment organelle, which mediates cell division, cytadherence, and cell movement at host cell surface. This characteristic ultrastructure has a constant size of 250–300 nm, but its design principle remains unclear. In this study, we constructed several mutants by genetic manipulation to increase or decrease coiled-coil regions of HMW2, a major component protein of 200 kDa aligned in parallel along the cell axis. HMW2-engineered mutants produced both long and short attachment organelles, which we quantified by transmission electron microscopy and fluorescent microscopy with nano-meter precision. This simple design of HMW2 acting as a molecular ruler for the attachment organelle should provide an insight into bacterial cellular organization and its function for their parasitic lifestyles.

Mycoplasma pneumoniae, a pathogen of “walking pneumonia”, have a membrane protrusion with a precise length of 250–300 nm specially developed to support their parasitic lifestyles. To date, however, there has been no report focusing on the potential length-control mechanisms of this characteristic architecture called an attachment organelle. Here, we found that the coiled-coil domains of the 200-kDa protein HMW2 are aligned in parallel along the cell axis, and acts as a molecular ruler by the assembly into a physical scaffold. The molecular ruler could be engineered by genetic modification to produce both longer and shorter attachment organelle. The analyses of the length-controlled mutant highlight a simple design principle of cellular organization in a small bacterium.

Computational identification of putative common genomic drug and vaccine targets in Mycoplasma genitalium

Mycoplasma genitalium is an obligate intracellular bacterium that is responsible for several sexually transmitted infections, including non-gonococcal urethritis in men and several inflammatory reproductive tract syndromes in women. Here, we applied subtractive genomics and reverse vaccinology approaches for in silico prediction of potential vaccine and drug targets against five strains of M. genitalium. We identified 403 genes shared by all five strains, from which 104 non-host homologous proteins were selected, comprising of 44 exposed/secreted/membrane proteins and 60 cytoplasmic proteins. Based on the essentiality, functionality, and structure-based binding affinity, we finally predicted 19 (14 novel) putative vaccine and 7 (2 novel) candidate drug targets. The docking analysis showed six molecules from the ZINC database as promising drug candidates against the identified targets. Altogether, both vaccine candidates and drug targets identified here may contribute to the future development of therapeutic strategies to control the spread of M. genitalium worldwide.

A Review of Ureaplasma diversum: A Representative of the Mollicute Class Associated With Reproductive and Respiratory Disorders in Cattle

The Mollicutes class encompasses wall-less microbes with a reduced genome. They may infect plants, insects, humans, and animals including those on farms and in livestock. Ureaplasma diversum is a mollicute associated with decreased reproduction mainly in the conception rate in cattle, as well as weight loss and decreased quality in milk production. Therefore, U. diversum infection contributes to important economic losses, mainly in large cattle-producing countries such as the United States, China, Brazil, and India. The characteristics of Mollicutes, virulence, and pathogenic variations make it difficult to control their infections. Genomic analysis, prevalence studies, and immunomodulation assays help better understand the pathogenesis of bovine ureaplasma. Here we present the main features of transmission, virulence, immune response, and pathogenesis of U. diversum in bovines.

Pathogenic Analysis of the Bronchoalveolar Lavage Fluid Samples With Pediatric Refractory Mycoplasma pneumoniae Pneumonia

Background: We conducted a pathogenic analysis in the bronchoalveolar lavage fluid (BALF) samples from refractory Mycoplasma pneumoniae pneumonia (RMPP) children.

Methods: A total of 150 BALF samples from 60 RMPP patients were analyzed to investigate pathogenic changes. The characteristics of M. pneumoniae were analyzed through culture, real-time PCR, genotyping, antimicrobial susceptibility testing and proteomics. The other pathogens were determined using culture, sequencing and nucleic acid detection.

Results: In 60 RMPP cases, the bacterial co-infection rate was 5%, while that of virus was 33.3%. The poor prognosis rate was 61.7%. The DNA positive rate among the 150 samples was 98.7%, while the culture positive rate was 56.7% for M. pneumoniae. Significant differences were noticed in the positivity of M. pneumoniae culture obtained from samples with a disease course of at least 3 weeks compared with those within 3 weeks. The genotype 1 M. pneumoniae strains showed a macrolide resistant (MLr) rate of 100%, and that for genotype 2 was 90.1%. Proteomics showed that there were 57 proteins up-regulated in the MLs M. pneumoniae, half of which were membrane-associated protein with adhesion or toxicity.

Conclusions: Pediatric RMPP usually presented with viral co-infection, but it caused limited effects on the progression and prognosis of RMPP. Persistent presence of viable M. pneumoniae is not necessary in the later stage of RMPP. The expression of virulence factor in the MLr M. pneumoniae was higher than that of the MLs M. pneumoniae, which was more common in the RMPP children.

RNA localization in prokaryotes: Where, when, how, and why

Only recently has it been recognized that the transcriptome of bacteria and archaea can be spatiotemporally regulated. All types of prokaryotic transcripts-rRNAs, tRNAs, mRNAs, and regulatory RNAs-may acquire specific localization and these patterns can be temporally regulated. In some cases bacterial RNAs reside in the vicinity of the transcription site, but in many others, transcripts show distinct localizations to the cytoplasm, the inner membrane, or the pole of rod-shaped species. This localization, which often overlaps with that of the encoded proteins, can be achieved either in a translation-dependent or translation-independent fashion. The latter implies that RNAs carry sequence-level features that determine their final localization with the aid of RNA-targeting factors. Localization of transcripts regulates their posttranscriptional fate by affecting their degradation and processing, translation efficiency, sRNA-mediated regulation, and/or propensity to undergo RNA modifications. By facilitating complex assembly and liquid-liquid phase separation, RNA localization is not only a consequence but also a driver of subcellular spatiotemporal complexity. We foresee that in the coming years the study of RNA localization in prokaryotes will produce important novel insights regarding the fundamental understanding of membrane-less subcellular organization and lead to practical outputs with biotechnological and therapeutic implications. This article is categorized under: RNA Export and Localization > RNA Localization Regulatory RNAs/RNAi/Riboswitches > Regulatory RNAs RNA Interactions with Proteins and Other Molecules > Protein-RNA Interactions: Functional Implications.

Cell surface processing of the P1 adhesin of Mycoplasma pneumoniae identifies novel domains that bind host molecules

Mycoplasma pneumoniae is a genome reduced pathogen and causative agent of community acquired pneumonia. The major cellular adhesin, P1, localises to the tip of the attachment organelle forming a complex with P40 and P90, two cleavage fragments derived by processing Mpn142, and other molecules with adhesive and mobility functions. LC-MS/MS analysis of M. pneumoniae M129 proteins derived from whole cell lysates and eluents from affinity matrices coupled with chemically diverse host molecules identified 22 proteoforms of P1. Terminomics was used to characterise 17 cleavage events many of which were independently verified by the identification of semi-tryptic peptides in our proteome studies and by immunoblotting. One cleavage event released ¹⁵⁹⁷TSAAKPGAPRPPVPPKPGAPKPPVQPPKKPA¹⁶²⁷ from the C-terminus of P1 and this peptide was shown to bind to a range of host molecules. A smaller synthetic peptide comprising the C-terminal 15 amino acids, ¹⁶¹³PGAPKPPVQPPKKPA¹⁶²⁷, selectively bound cytoskeletal intermediate filament proteins cytokeratin 7, cytokeratin 8, cytokeratin 18, and vimentin from a native A549 cell lysate. Collectively, our data suggests that ectodomain shedding occurs on the surface of M. pneumoniae where it may alter the functional diversity of P1, Mpn142 and other surface proteins such as elongation factor Tu via a mechanism similar to that described in Mycoplasma hyopneumoniae.

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.

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.

Electron cryotomography of Mycoplasma pneumoniae mutants correlates terminal organelle architectural features and function

The Mycoplasma pneumoniae terminal organelle functions in adherence and gliding motility and is comprised of at least eleven substructures. We used electron cryotomography to correlate impaired gliding and adherence function with changes in architecture in diverse terminal organelle mutants. All eleven substructures were accounted for in the prkC, prpC and P200 mutants, and variably so for the HMW3 mutant. Conversely, no terminal organelle substructures were evident in HMW1 and HMW2 mutants. The P41 mutant exhibits a terminal organelle detachment phenotype and lacked the bowl element normally present at the terminal organelle base. Complementation restored this substructure, establishing P41 as either a component of the bowl element or required for its assembly or stability, and that this bowl element is essential to anchor the terminal organelle but not for leverage in gliding. Mutants II-3, III-4 and topJ exhibited a visibly lower density of protein knobs on the terminal organelle surface. Mutants II-3 and III-4 lack accessory proteins required for a functional adhesin complex, while the topJ mutant lacks a DnaJ-like co-chaperone essential for its assembly. Taken together, these observations expand our understanding of the roles of certain terminal organelle proteins in the architecture and function of this complex structure.

Development of Mycoplasma pneumoniae biofilms in vitro and the limited role of motility

Mycoplasma pneumoniae is a bacterial pathogen of humans that is a major causative agent of chronic respiratory disease. M. pneumoniae infections often recur even after successful treatment of symptoms with antibiotics, and resistance to antibiotics is increasing worldwide, with nearly complete resistance in some places. Although biofilms often contribute to chronicity and resistance, M. pneumoniae biofilms remain poorly characterized. Scanning electron microscopy revealed that cells of wild-type (WT) M. pneumoniae strain M129 biofilms, as well as mutants II-3 and II-3R, in vitro became increasingly rounded as the biofilm towers matured over 5 days. The role of gliding motility in biofilm formation was addressed by analyzing differences in biofilm architecture in non-motile mutant II-3R and hypermotile mutant prpC-and by using time-lapse microcinematography to measure flux of cells around biofilm towers. There were no major differences in biofilm architecture between WT and motility mutants, with perhaps a slight tendency for the prpC- cells to spread outside towers during early stages of biofilm formation. Consistent with an insignificant role of motility in biofilm development, flux of cells near towers, which was low, was dominated by exit of cells. Immunofluorescence microscopy revealed that motility-associated attachment organelle (AO) proteins exhibited no discernable changes in localization to foci over time, but immunoblotting identified a decrease in steady-state levels of protein P200, which is required for normal gliding speed, as the WT culture aged. Non-adherent strain II-3 and non-motile strain II-3R also exhibited a steady decrease in P200 steady-state levels, suggesting that the decrease in P200 levels was not a response to changes in gliding behavior during maturation. We conclude that M. pneumoniae cells undergo morphological changes as biofilms mature, motility plays no major role in biofilm development, and P200 loss might be related to maturation of cells. This study helps to characterize potential therapeutic targets for M. pneumoniae infections.

Mycoplasma pneumoniae from the Respiratory Tract and Beyond

Mycoplasma pneumoniae is an important cause of respiratory tract infections in children as well as adults that can range in severity from mild to life-threatening. Over the past several years there has been much new information published concerning infections caused by this organism. New molecular-based tests for M. pneumoniae detection are now commercially available in the United States, and advances in molecular typing systems have enhanced understanding of the epidemiology of infections. More strains have had their entire genome sequences published, providing additional insights into pathogenic mechanisms. Clinically significant acquired macrolide resistance has emerged worldwide and is now complicating treatment. In vitro susceptibility testing methods have been standardized, and several new drugs that may be effective against this organism are undergoing development. This review focuses on the many new developments that have occurred over the past several years that enhance our understanding of this microbe, which is among the smallest bacterial pathogens but one of great clinical importance.

Transformation of crustacean pathogenic bacterium Spiroplasma eriocheiris and expression of yellow fluorescent protein

Spiroplasma eriocheiris, the cause of crab trembling disease, is a wall-less bacterium, related to Mycoplasmas, measuring 2.0-10.0 μm long. It features a helical cell shape and a unique swimming mechanism that does not use flagella; instead, it moves by switching the cell helicity at a kink traveling from the front to the tail. S. eriocheiris seems to use a novel chemotactic system that is based on the frequency of reversal swimming behaviors rather than the conventional two-component system, which is generally essential for bacterial chemotaxis. To identify the genes involved in these novel mechanisms, we developed a transformation system by using oriC plasmid harboring the tetracycline resistant gene, tetM, which is under the control of a strong promoter for an abundant protein, elongation factor-Tu. The transformation efficiency achieved was 1.6 × 10^-5 colony forming unit (CFU) for 1 μg DNA, enabling the expression of the enhanced yellow fluorescent protein (EYFP).

Defined chromosome structure in the genome-reduced bacterium Mycoplasma pneumoniae

DNA-binding proteins are central regulators of chromosome organization; however, in genome-reduced bacteria their diversity is largely diminished. Whether the chromosomes of such bacteria adopt defined three-dimensional structures remains unexplored. Here we combine Hi-C and super-resolution microscopy to determine the structure of the Mycoplasma pneumoniae chromosome at a 10 kb resolution. We find a defined structure, with a global symmetry between two arms that connect opposite poles, one bearing the chromosomal Ori and the other the midpoint. Analysis of local structures at a 3 kb resolution indicates that the chromosome is organized into domains ranging from 15 to 33 kb. We provide evidence that genes within the same domain tend to be co-regulated, suggesting that chromosome organization influences transcriptional regulation, and that supercoiling regulates local organization. This study extends the current understanding of bacterial genome organization and demonstrates that a defined chromosomal structure is a universal feature of living systems.

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.

Structure-Guided Mutations in the Terminal Organelle Protein MG491 Cause Major Motility and Morphologic Alterations on Mycoplasma genitalium

The emergent human pathogen Mycoplasma genitalium, with one of the smallest genomes among cells capable of growing in axenic cultures, presents a flask-shaped morphology due to a protrusion of the cell membrane, known as the terminal organelle, that is involved in cell adhesion and motility and is an important virulence factor of this microorganism. The terminal organelle is supported by a cytoskeleton complex of about 300 nm in length that includes three substructures: the terminal button, the rod and the wheel complex. The crystal structure of the MG491 protein, a proposed component of the wheel complex, has been determined at ~3 Å resolution. MG491 subunits are composed of a 60-residue N-terminus, a central three-helix-bundle spanning about 150 residues and a C-terminal region that appears to be quite flexible and contains the region that interacts with MG200, another key protein of the terminal organelle. The MG491 molecule is a tetramer presenting a unique organization as a dimer of asymmetric pairs of subunits. The asymmetric arrangement results in two very different intersubunit interfaces between the central three-helix-bundle domains, which correlates with the formation of only ~50% of the intersubunit disulfide bridges of the single cysteine residue found in MG491 (Cys87). Moreover, M. genitalium cells with a point mutation in the MG491 gene causing the change of Cys87 to Ser present a drastic reduction in motility (as determined by microcinematography) and important alterations in morphology (as determined by electron microscopy), while preserving normal levels of the terminal organelle proteins. Other variants of MG491, designed also according to the structural information, altered significantly the motility and/or the cell morphology. Together, these results indicate that MG491 plays a key role in the functioning, organization and stabilization of the terminal organelle.

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.

Potential Molecular Targets for Narrow-Spectrum Agents to Combat Mycoplasma pneumoniae Infection and Disease

As Mycoplasma pneumoniae macrolide resistance grows and spreads worldwide, it is becoming more important to develop new drugs to prevent infection or limit disease. Because other mycoplasma species have acquired resistance to other classes of antibiotics, it is reasonable to presume that M. pneumoniae can do the same, so switching to commonly used antibiotics like fluoroquinolones will not result in forms of therapy with long-term utility. Moreover, broad-spectrum antibiotics can have serious consequences for the patient, as these drugs may have severe impacts on the natural microbiota of the individual, compromising the health of the patient either short-term or long-term. Therefore, developing narrow-spectrum antibiotics that effectively target only M. pneumoniae and no more than a small portion of the microbiota is likely to yield impactful, positive results that can be used perhaps indefinitely to combat M. pneumoniae. Development of these agents requires a deep understanding of the basic biology of M. pneumoniae, in many areas deeper than what is currently known. In this review, we discuss potential targets for new, narrow-spectrum agents and both the positive and negative aspects of selecting these targets, which include toxic molecules, metabolic pathways, and attachment and motility. By gathering this information together, we anticipate that it will be easier for researchers to evaluate topics of priority for study of M. pneumoniae.

P19 contributes to Mycoplasma mycoides subsp. mycoides adhesion to EBL cells

Mycoplasma mycoides subsp. mycoides (Mmm) is the causative agent of contagious bovine pleuropneumonia (CBPP). The virulent Mmm Ben-1 strain was isolated from the lung of a CBPP-infected cow in China in the 1950s. To attenuate the virulence of the Ben-1 strain and preserve its protective ability, the isolate was re-isolated after inoculation into the testicles of rabbits and into the rabbit thorax. As a result, after the subsequent isolates were continuously passaged 468 times in rabbits, its pathogenicity to cattle decreased. However, the molecular mechanisms leading to attenuation of the Mmm Ben-1 remain unknown. We compared the entire genomes of the Ben-1 strain and the 468 th generation strain passaged in rabbits (Ben-468) and discovered that a putative protein gene named p19 was absent from the Ben-468 strain. The p19 gene was cloned and expressed in Escherichia coli to obtain recombinant P19 (rP19). Western blot analysis demonstrated that the P19 protein is detected in the cell-membrane fraction, the cell-soluble cytosolic fraction and whole-cell lysate of the Mmm Ben-1 strain. The rP19 can interact with international standard serum against CBPP. Immunostaining visualised via confocal laser scanning microscopy indicated that P19 is able to adhere to embryonic bovine lung (EBL) cells, and this finding was also confirmed by a sandwich ELISA. We also found that anti-rP19 serum could inhibit the adhesion of the Mmm Ben-1 total proteins to EBL cells.

P40 and P90 from Mpn142 are Targets of Multiple Processing Events on the Surface of Mycoplasma pneumoniae

Mycoplasma pneumoniae is a significant cause of community acquired pneumonia globally. Despite having a genome less than 1 Mb in size, M. pneumoniae presents a structurally sophisticated attachment organelle that (i) provides cell polarity, (ii) directs adherence to receptors presented on respiratory epithelium, and (iii) plays a major role in cell motility. The major adhesins, P1 (Mpn141) and P30 (Mpn453), are localised to the tip of the attachment organelle by the surface accessible cleavage fragments P90 and P40 derived from Mpn142. Two events play a defining role in the formation of P90 and P40; removal of a leader peptide at position 26 (²³SLA↓NTY²⁸) during secretion to the cell surface and cleavage at amino acid 455 (⁴⁵²GPL↓RAG⁴⁵⁷) generating P40 and P90. Liquid Chromatography Tandem Mass Spectrometry (LC-MS/MS) analysis of tryptic peptides generated by digesting size-fractionated cell lysates of M. pneumoniae identified 15 cleavage fragments of Mpn142 ranging in mass from 9–84 kDa. Further evidence for the existence of cleavage fragments of Mpn142 was generated by mapping tryptic peptides to proteins recovered from size fractionated eluents from affinity columns loaded with heparin, fibronectin, fetuin, actin, plasminogen and A549 surface proteins as bait. To define the sites of cleavage in Mpn142, neo-N-termini in cell lysates of M. pneumoniae were dimethyl-labelled and characterised by LC-MS/MS. Our data suggests that Mpn142 is cleaved to generate adhesins that are auxiliary to P1 and P30.

Systematic Structural Analyses of Attachment Organelle in Mycoplasma pneumoniae

Mycoplasma pneumoniae, a human pathogenic bacterium, glides on host cell surfaces by a unique and unknown mechanism. It forms an attachment organelle at a cell pole as a membrane protrusion composed of surface and internal structures, with a highly organized architecture. In the present study, we succeeded in isolating the internal structure of the organelle by sucrose-gradient centrifugation. The negative-staining electron microscopy clarified the details and dimensions of the internal structure, which is composed of terminal button, paired plates, and bowl complex from the end of cell front. Peptide mass fingerprinting of the structure suggested 25 novel components for the organelle, and 3 of them were suggested for their involvement in the structure through their subcellular localization determined by enhanced yellow fluorescent protein (EYFP) tagging. Thirteen component proteins including the previously reported ones were mapped on the organelle systematically for the first time, in nanometer order by EYFP tagging and immunoelectron microscopy. Two, three, and six specific proteins localized specifically to the terminal button, the paired plates, and the bowl, respectively and interestingly, HMW2 molecules were aligned parallel to form the plate. The integration of these results gave the whole image of the organelle and allowed us to discuss possible gliding mechanisms.

Human mycoplasma pneumonia, an epidemic of which occurred around the world a few years ago, is caused by a pathogenic bacterium, Mycoplasma pneumoniae. This tiny bacterium, about 2 μm long, infects humans by gliding on the surface of the trachea through binding to sialylated oligosaccharides, which are also the binding targets of influenza viruses. The mechanism underlying Mycoplasma "gliding motility" is not related to any other well-studied motility systems, such as bacterial flagella and eukaryotic motor proteins. Here, we isolated the internal structure of “attachment organelle", a cellular architecture, and suggested novel component proteins. The organelle was analyzed systematically by focusing on the protein components under fluorescence and electron microscopy, and a possible gliding mechanism was suggested.

High quality draft genomes of the Mycoplasma mycoides subsp. mycoides challenge strains Afadé and B237

Members of the Mycoplasma mycoides cluster' represent important livestock pathogens worldwide. Mycoplasma mycoides subsp. mycoides is the etiologic agent of contagious bovine pleuropneumonia (CBPP), which is still endemic in many parts of Africa. We report the genome sequences and annotation of two frequently used challenge strains of Mycoplasma mycoides subsp. mycoides, Afadé and B237. The information provided will enable downstream 'omics' applications such as proteomics, transcriptomics and reverse vaccinology approaches. Despite the absence of Mycoplasma pneumoniae like cyto-adhesion encoding genes, the two strains showed the presence of protrusions. This phenotype is likely encoded by another set of genes.

Mycoplasma pneumoniae, an underutilized model for bacterial cell biology

In recent decades, bacterial cell biology has seen great advances, and numerous model systems have been developed to study a wide variety of cellular processes, including cell division, motility, assembly of macromolecular structures, and biogenesis of cell polarity. Considerable attention has been given to these model organisms, which include Escherichia coli, Bacillus subtilis, Caulobacter crescentus, and Myxococcus xanthus. Studies of these processes in the pathogenic bacterium Mycoplasma pneumoniae and its close relatives have also been carried out on a smaller scale, but this work is often overlooked, in part due to this organism's reputation as minimalistic and simple. In this minireview, I discuss recent work on the role of the M. pneumoniae attachment organelle (AO), a structure required for adherence to host cells, in these processes. The AO is constructed from proteins that generally lack homology to those found in other organisms, and this construction occurs in coordination with cell cycle events. The proteins of the M. pneumoniae AO share compositional features with proteins with related roles in model organisms. Once constructed, the AO becomes activated for its role in a form of gliding motility whose underlying mechanism appears to be distinct from that of other gliding bacteria, including Mycoplasma mobile. Together with the FtsZ cytoskeletal protein, motility participates in the cell division process. My intention is to bring this deceptively complex organism into alignment with the better-known model systems.

The Iho670 fibers of Ignicoccus hospitalis are anchored in the cell by a spherical structure located beneath the inner membrane

The Iho670 fibers of the hyperthermophilic crenarchaeon of Ignicoccus hospitalis were shown to contain several features that indicate them as type IV pilus-like structures. The application of different visualization methods, including electron tomography and the reconstruction of a three-dimensional model, enabled a detailed description of a hitherto undescribed anchoring structure of the cell appendages. It could be identified as a spherical structure beneath the inner membrane. Furthermore, pools of the fiber protein Iho670 could be localized in the inner as well as the outer cellular membrane of I. hospitalis cells and in the tubes/vesicles in the intermembrane compartment by immunological methods.

Localization of P42 and F(1)-ATPase α-subunit homolog of the gliding machinery in Mycoplasma mobile revealed by newly developed gene manipulation and fluorescent protein tagging

Mycoplasma mobile has a unique mechanism that enables it to glide on solid surfaces faster than any other gliding mycoplasma. To elucidate the gliding mechanism, we developed a transformation system for M. mobile based on a transposon derived from Tn4001. Modification of the electroporation conditions, outgrowth time, and colony formation from the standard method for Mycoplasma species enabled successful transformation. A fluorescent-protein tagging technique was developed using the enhanced yellow fluorescent protein (EYFP) and applied to two proteins that have been suggested to be involved in the gliding mechanism: P42 (MMOB1050), which is transcribed as continuous mRNA with other proteins essential for gliding, and a homolog of the F1-ATPase α-subunit (MMOB1660). Analysis of the amino acid sequence of P42 by PSI-BLAST suggested that P42 evolved from a common ancestor with FtsZ, the bacterial tubulin homologue. The roles of P42 and the F(1)-ATPase subunit homolog are discussed as part of our proposed gliding mechanism.

Molecular cloning and characterization of a surface-localized adhesion protein in Mycoplasma bovis Hubei-1 strain

Mycoplasma bovis (M. bovis) is an important pathogen that causes various bovine diseases, such as mastitis in cows and pneumonia in calves. The surface proteins are generally thought to play a central role in the pathogenesis of this organism. We screened the entire genome of M. bovis Hubei-1 and discovered a gene named vpmaX that encodes the 25 kDa variable surface lipoprotein A (VpmaX). Sequence analysis revealed that VpmaX contains several repetitive units and a typical bacterial lipoprotein signal sequence. The vpmaX gene was cloned and expressed in E. coli to obtain recombinant VpmaX (rVpmaX). Western blot analysis using a rabbit antibody against rVpmaX demonstrated that VpmaX is a membrane protein. Immunostaining visualized via confocal laser scanning microscopy showed that rVpmaX was able to adhere to embryonic bovine lung cells (EBL), and this was also confirmed by a sandwich ELISA. In summary, a surface-localized adhesion protein was identified in M. bovis Hubei-1.

MalF is essential for persistence of Mycoplasma gallisepticum in vivo

There is limited understanding of the molecular basis of virulence in the important avian pathogen Mycoplasma gallisepticum. To define genes that may be involved in colonization of chickens, a collection of mutants of the virulent Ap3AS strain of M. gallisepticum were generated by signature-tagged transposon mutagenesis. The collection included mutants with single insertions in the genes encoding the adhesin GapA and the cytadherence-related protein CrmA, and Western blotting confirmed that these mutants did not express these proteins. In two separate in vivo screenings, two GapA-deficient mutants (ST mutants 02-1 and 06-1) were occasionally recovered from birds, suggesting that GapA expression may not always be essential for persistence of strain Ap3AS. CrmA-deficient ST mutant 33-1 colonized birds poorly and had reduced virulence, indicating that CrmA was a significant virulence factor, but was not absolutely essential for colonization. ST mutant 04-1 contained a single transposon insertion in malF, a predicted ABC sugar transport permease, and could not be reisolated even when inoculated by itself into a group of birds, suggesting that expression of MalF was essential for persistence of M. galliseptium strain Ap3AS in infected birds.

Cellular organization of the transfer of genetic information

Each step involved in the transfer of genetic information is spatially regulated in eukaryotic cells, as transcription, translation and mRNA degradation mostly occur in distinct functional compartments (e.g., nucleus, cytoplasm and P-bodies). At first glance in bacteria, these processes seem to take place in the same compartment - the cytoplasm - because of the conspicuous absence of membrane-enclosed organelles. However, it is becoming increasingly evident that mRNA-related processes are also spatially organized inside bacterial cells, and that this organization affects cellular function. The aims of this review are to summarize the current knowledge about this organization and to consider the mechanisms and forces shaping the cell interior. The field stands at an exciting point where new technologies are making long-standing questions amenable to experimentation.

P65 truncation impacts P30 dynamics during Mycoplasma pneumoniae gliding

The cell wall-less prokaryote Mycoplasma pneumoniae is a major cause of community-acquired bronchitis and pneumonia in humans. Colonization is mediated largely by a differentiated terminal organelle, which is also the leading end in gliding motility. Cytadherence-associated proteins P30 and P65 appear to traffic concurrently to the distal end of developing terminal organelles. Here, truncation of P65 due to transposon insertion in the corresponding gene resulted in lower gliding velocity, reduced cytadherence, and decreased steady-state levels of several terminal organelle proteins, including P30. Utilizing fluorescent protein fusions, we followed terminal organelle development over time. New P30 foci appeared at nascent terminal organelles in P65 mutants, as in the wild type. However, with forward cell motility, P30 in the P65 mutants appeared to drag toward the trailing cell pole, where it was released, yielding a fluorescent trail to which truncated P65 colocalized. In contrast, P30 was only rarely observed at the trailing end of gliding wild-type cells. Complementation with the recombinant wild-type P65 allele by transposon delivery restored P65 levels and stabilized P30 localization to the terminal organelle.

"Mycoplasmal antigen modulation," a novel surface variation suggested for a lipoprotein specifically localized on Mycoplasma mobile

Mycoplasma mobile, a pathogen of freshwater fish, glides easily across surfaces, colonizes on the fish gill, and causes necrosis. The cell surface is differentiated into three parts: the head, neck, and body. Mobile variable surface proteins (Mvsps) localizing at each of these parts may be involved in surface variation including phase variation and antigenic variation, although no proof exists. In this study, we examined this possibility by focusing on MvspI, the largest Mvsp. Immunofluorescence microscopy showed that MvspI is expressed on the surfaces of all cells. When anti-MvspI antibody was added at concentrations over 0.8 nM, MvspI was observed to decrease over time. After 72 h of cultivation with the antibody, the fluorescence intensity and amount of MvspI decreased up to 13 and 39%, respectively, compared to those of cells grown without antibody. These changes were reversed by the removal of the antibody. Such effects were not observed when another antibody targeting other Mvsps was used, suggesting that the decrease is specific to the relationship between MvspI and the antibody. Cell growth was also inhibited by the antibody, but the decrease in MvspI could not be explained by the selective growth of MvspI-negative variants or by the inhibition of growth with other conditions. The decrease in MvspI caused by the antibody binding may suggest a novel type of surface variation, designated here as "mycoplasmal antigen modulation."

Loss of co-chaperone TopJ impacts adhesin P1 presentation and terminal organelle maturation in Mycoplasma pneumoniae

Mycoplasma pneumoniae is a wall-less human respiratory tract pathogen that colonizes mucosal epithelium via a polar terminal organelle having a central electron-dense core and adhesin-related proteins clustered at a terminal button. A mutant lacking J-domain co-chaperone TopJ is non-cytadherent and non-motile, despite having a core and normal levels of the major cytadherence-associated proteins. J-domain co-chaperones work with DnaK to catalyse polypeptide binding and subsequent protein folding. Here we compared features of the topJ mutant with other cytadherence mutants to elucidate the contribution of TopJ to cytadherence function. The topJ mutant was similar ultrastructurally to a non-cytadherent mutant lacking terminal organelle proteins B/C, including aberrant core positioning and cell morphology in thin sections, but exhibited a hybrid satellite growth pattern with features of mutants both having and lacking a core. Time-lapse images of mycoplasmas expressing a YFP fusion with terminal organelle protein P41 suggested that terminal organelle formation/positioning was delayed or poorly co-ordinated with cell growth in the absence of TopJ. TopJ required a core for localization, perhaps involving HMW1. P1 trypsin accessibility on other non-cytadherent mutants was significantly enhanced over wild type but unexpectedly was reduced with topJ mutant cells, suggesting impaired processing, translocation and/or folding of this adhesin.

Unique centipede mechanism of Mycoplasma gliding

Mycoplasma, a genus of pathogenic bacteria, forms a membrane protrusion at a cell pole. It binds to solid surfaces with this protrusion and then glides. The mechanism is not related to known bacterial motility systems, such as flagella or pili, or to conventional motor proteins, including myosin. We have studied the fastest species, Mycoplasma mobile, and have proposed a working model as follows. The gliding machinery is composed of four huge proteins at the base of the membrane protrusion and supported by a cytoskeletal architecture from the cell inside. Many flexible legs approximately 50 nm long are sticking out from the machinery. The movements generated by the ATP hydrolysis cell inside are transmitted to the "leg" protein through a "gear" protein, resulting in repeated binding, pull, and release of the sialylgalactose fixed on the surface by the legs. The gliding of Mycoplasma pneumoniae, a species distantly related to M. mobile, is also discussed.

Isolation and characterization of P1 adhesin, a leg protein of the gliding bacterium Mycoplasma pneumoniae

Mycoplasma pneumoniae, a pathogen causing human pneumonia, binds to solid surfaces at its membrane protrusion and glides by a unique mechanism. In this study, P1 adhesin, which functions as a "leg" in gliding, was isolated from mycoplasma culture and characterized. Using gel filtration, blue-native polyacrylamide gel electrophoresis (BN-PAGE), and chemical cross-linking, the isolated P1 adhesin was shown to form a complex with an accessory protein named P90. The complex included two molecules each of P1 adhesin and P90 (protein B), had a molecular mass of about 480 kDa, and was observed by electron microscopy to form 20-nm-diameter spheres. Partial digestion of isolated P1 adhesin by trypsin showed that the P1 adhesin molecule can be divided into three domains, consistent with the results from trypsin treatment of the cell surface. Sequence analysis of P1 adhesin and its orthologs showed that domain I is well conserved and that a transmembrane segment exists near the link between domains II and III.

Functional domain analysis of the Mycoplasma pneumoniae co-chaperone TopJ

Colonization of conducting airways of humans by the prokaryote Mycoplasma pneumoniae is mediated by a differentiated terminal organelle important in cytadherence, gliding motility and cell division. TopJ is a predicted J-domain co-chaperone also having domains unique to mycoplasma terminal organelle proteins and is essential for terminal organelle function, as well as stabilization of protein P24, which is required for normal initiation of terminal organelle formation. J-domains activate the ATPase of DnaK chaperones, facilitating peptide binding and proper protein folding. We performed mutational analysis of the predicted J-domain, central acidic and proline-rich (APR) domain, and C-terminal domain of TopJ and assessed the phenotypic consequences when introduced into an M. pneumoniae topJ mutant. A TopJ derivative with amino acid substitutions in the canonical J-domain histidine-proline-aspartic acid motif restored P24 levels but not normal motility, morphology or cytadherence, consistent with a J-domain co-chaperone function. In contrast, TopJ derivatives having APR or C-terminal domain deletions were less stable and failed to restore P24, but resulted in normal morphology, intermediate gliding motility and cytadherence levels exceeding that of wild-type cells. Results from immunofluorescence microscopy suggest that both the APR and C-terminal domains, but not the histidine-proline-aspartic acid motif, are critical for TopJ localization to the terminal organelle.

Motor-substrate interactions in mycoplasma motility explains non-Arrhenius temperature dependence

Mycoplasmas exhibit a novel, substrate-dependent gliding motility that is driven by approximately 400 "leg" proteins. The legs interact with the substrate and transmit the forces generated by an assembly of ATPase motors. The velocity of the cell increases linearly by nearly 10-fold over a narrow temperature range of 10-40 degrees C. This corresponds to an Arrhenius factor that decreases from approximately 45 k(B)T at 10 degrees C to approximately 10 k(B)T at 40 degrees C. On the other hand, load-velocity curves at different temperatures extrapolate to nearly the same stall force, suggesting a temperature-insensitive force-generation mechanism near stall. In this article, we propose a leg-substrate interaction mechanism that explains the intriguing temperature sensitivity of this motility. The large Arrhenius factor at low temperature comes about from the addition of many smaller energy barriers arising from many substrate-binding sites at the distal end of the leg protein. The Arrhenius dependence attenuates at high temperature due to two factors: 1), the reduced effective multiplicity of energy barriers intrinsic to the multiple-site binding mechanism; and 2), the temperature-sensitive weakly facilitated leg release that curtails the power stroke. The model suggests an explanation for the similar steep, sub-Arrhenius temperature-velocity curves observed in many molecular motors, such as kinesin and myosin, wherein the temperature behavior is dominated not by the catalytic biochemistry, but by the motor-substrate interaction.

Proteome organization in a genome-reduced bacterium

The genome of Mycoplasma pneumoniae is among the smallest found in self-replicating organisms. To study the basic principles of bacterial proteome organization, we used tandem affinity purification-mass spectrometry (TAP-MS) in a proteome-wide screen. The analysis revealed 62 homomultimeric and 116 heteromultimeric soluble protein complexes, of which the majority are novel. About a third of the heteromultimeric complexes show higher levels of proteome organization, including assembly into larger, multiprotein complex entities, suggesting sequential steps in biological processes, and extensive sharing of components, implying protein multifunctionality. Incorporation of structural models for 484 proteins, single-particle electron microscopy, and cellular electron tomograms provided supporting structural details for this proteome organization. The data set provides a blueprint of the minimal cellular machinery required for life.

Triskelion structure of the Gli521 protein, involved in the gliding mechanism of Mycoplasma mobile

Mycoplasma mobile binds to solid surfaces and glides smoothly and continuously by a unique mechanism. A huge protein, Gli521 (521 kDa), is involved in the gliding machinery, and it is localized in the cell neck, the base of the membrane protrusion. This protein is thought to have the role of force transmission. In this study, the Gli521 protein was purified from M. mobile cells, and its molecular shape was studied. Gel filtration analysis showed that the isolated Gli521 protein forms mainly a monomer in Tween 80-containing buffer and oligomers in Triton X-100-containing buffer. Rotary shadowing electron microscopy showed that the Gli521 monomer consisted of three parts: an oval, a rod, and a hook. The oval was 15 nm long by 11 nm wide, and the filamentous part composed of the rod and the hook was 106 nm long and 3 nm in diameter. The Gli521 molecules form a trimer, producing a "triskelion" reminiscent of eukaryotic clathrin, through association at the hook end. Image averaging of the central part of the triskelion suggested that there are stable and rigid structures. The binding site of a previously isolated monoclonal antibody on Gli521 images showed that the hook end and oval correspond to the C- and N-terminal regions, respectively. Partial digestion of Gli521 showed that the molecule could be divided into three domains, which we assigned to the oval, rod, and hook of the molecular image. The Gli521 molecule's role in the gliding mechanism is discussed.

P110 and P140 cytadherence-related proteins are negative effectors of terminal organelle duplication in Mycoplasma genitalium

BACKGROUND

The terminal organelle is a complex structure involved in many aspects of the biology of mycoplasmas such as cell adherence, motility or cell division. Mycoplasma genitalium cells display a single terminal organelle and duplicate this structure prior to cytokinesis in a coordinated manner with the cell division process. Despite the significance of the terminal organelle in mycoplasma virulence, little is known about the mechanisms governing its duplication.

METHODOLOGY/PRINCIPAL FINDINGS

In this study we describe the isolation of a mutant, named T192, with a transposon insertion close to the 3' end of the mg192 gene encoding for P110 adhesin. This mutant shows a truncated P110, low levels of P140 and P110 adhesins, a large number of non-motile cells and a high frequency of new terminal organelle formation. Further analyses revealed that the high rates of new terminal organelle formation in T192 cells are a direct consequence of the reduced levels of P110 and P140 rather than to the expression of a truncated P110. Consistently, the phenotype of the T192 mutant was successfully complemented by the reintroduction of the mg192 WT allele which restored the levels of P110 and P140 to those of the WT strain. Quantification of DAPI-stained DNA also showed that the increase in the number of terminal organelles in T192 cells is not accompanied by a higher DNA content, indicating that terminal organelle duplication does not trigger DNA replication in mycoplasmas.

CONCLUSIONS/SIGNIFICANCE

Our results demonstrate the existence of a mechanism regulating terminal organelle duplication in M. genitalium and strongly suggest the implication of P110 and P140 adhesins in this mechanism.

Mycoplasma pneumoniae cytoskeletal protein HMW2 and the architecture of the terminal organelle

The terminal organelle of Mycoplasma pneumoniae mediates cytadherence and gliding motility and functions in cell division. The defining feature of this complex membrane-bound cell extension is an electron-dense core of two segmented rods oriented longitudinally and enlarging to form a bulb at the distal end. While the components of the core have not been comprehensively identified, previous evidence suggested that the cytoskeletal protein HMW2 forms parallel bundles oriented lengthwise to yield the major rod of the core. In the present study, we tested predictions emerging from that model by ultrastructural and immunoelectron microscopy analyses of cores from wild-type M. pneumoniae and mutants producing HMW2 derivatives. Antibodies specific for the N or C terminus of HMW2 labeled primarily peripheral to the core along its entire length. Furthermore, truncation of HMW2 did not correlate specifically with core length. However, mutant analysis correlated specific HMW2 domains with core assembly, and examination of core-enriched preparations confirmed that HMW2 was a major component of these fractions. Taken together, these findings yielded a revised model for HMW2 in terminal organelle architecture.

Cytoskeletal asymmetrical dumbbell structure of a gliding mycoplasma, Mycoplasma gallisepticum, revealed by negative-staining electron microscopy

Several mycoplasma species feature a membrane protrusion at a cell pole, and unknown mechanisms provide gliding motility in the direction of the pole defined by the protrusion. Mycoplasma gallisepticum, an avian pathogen, is known to form a membrane protrusion composed of bleb and infrableb and to glide. Here, we analyzed the gliding motility of M. gallisepticum cells in detail. They glided in the direction of the bleb at an average speed of 0.4 microm/s and remained attached around the bleb to a glass surface, suggesting that the gliding mechanism is similar to that of a related species, Mycoplasma pneumoniae. Next, to elucidate the cytoskeletal structure of M. gallisepticum, we stripped the envelopes by treatment with Triton X-100 under various conditions and observed the remaining structure by negative-staining transmission electron microscopy. A unique cytoskeletal structure, about 300 nm long and 100 nm wide, was found in the bleb and infrableb. The structure, resembling an asymmetrical dumbbell, is composed of five major parts from the distal end: a cap, a small oval, a rod, a large oval, and a bowl. Sonication likely divided the asymmetrical dumbbell into a core and other structures. The cytoskeletal structures of M. gallisepticum were compared with those of M. pneumoniae in detail, and the possible protein components of these structures were considered.

Mycoplasma pneumoniae J-domain protein required for terminal organelle function

The cell wall-less prokaryote Mycoplasma pneumoniae causes tracheobronchitis and primary atypical pneumonia in humans. Colonization of the respiratory epithelium requires proper assembly of a complex, multifunctional, polar terminal organelle. Loss of a predicted J-domain protein also having domains unique to mycoplasma terminal organelle proteins (TopJ) resulted in a non-motile, adherence-deficient phenotype. J-domain proteins typically stimulate ATPase activity of Hsp70 chaperones to bind nascent peptides for proper folding, translocation or macromolecular assembly, or to resolve stress-induced protein aggregates. By Western immunoblotting all defined terminal organelle proteins examined except protein P24 remained at wild-type levels in the topJ mutant; previous studies established that P24 is required for normal initiation of terminal organelle formation. Nevertheless, terminal organelle proteins P1, P30, HMW1 and P41 failed to localize to a cell pole, and when evaluated quantitatively, P30 and HMW1 foci were undetectable in >40% of cells. Complementation of the topJ mutant with the recombinant wild-type topJ allele largely restored terminal organelle development, gliding motility and cytadherence. We propose that this J-domain protein, which localizes to the base of the terminal organelle in wild-type M. pneumoniae, functions in the late stages of assembly, positioning, or both, of nascent terminal organelles.

Deletion of the Mycoplasma genitalium MG_217 gene modifies cell gliding behaviour by altering terminal organelle curvature

Motility is often a virulence factor of pathogenic bacteria. Although recent works have identified genes involved in gliding motility of mycoplasmas, little is known about the mechanisms governing the cell gliding behaviour. Here, we report that Mycoplasma genitalium MG217 is a novel protein involved in the gliding apparatus of this organism and it is, at least, one of the genes that are directing cells to move in narrow circles when they glide. In the absence of MG_217 gene, cells are still able to glide but they mainly move drawing erratic or wide circular paths. This change in the gliding behaviour correlates with a rearrangement in the terminal organelle disposition, suggesting that the terminal organelle operates as a guide to steer the mycoplasma cell in a specific direction. Immunogold labelling reveals that MG217 protein is located intracellular at the distal end of the terminal organelle, between the cell membrane and the terminal button. Such location is consistent with the idea that MG217 could act as a modulator of the terminal organelle curvature, allowing cells to move in specific directions.