MG428 is a novel positive regulator of recombination that triggers mgpB and mgpC gene variation in Mycoplasma genitalium

Unveiling the stealthy tactics: mycoplasma's immune evasion strategies

Mycoplasmas, the smallest known self-replicating organisms, possess a simple structure, lack a cell wall, and have limited metabolic pathways. They are responsible for causing acute or chronic infections in humans and animals, with a significant number of species exhibiting pathogenicity. Although the innate and adaptive immune responses can effectively combat this pathogen, mycoplasmas are capable of persisting in the host, indicating that the immune system fails to eliminate them completely. Recent studies have shed light on the intricate and sophisticated defense mechanisms developed by mycoplasmas during their long-term co-evolution with the host. These evasion strategies encompass various tactics, including invasion, biofilm formation, and modulation of immune responses, such as inhibition of immune cell activity, suppression of immune cell function, and resistance against immune molecules. Additionally, antigen variation and molecular mimicry are also crucial immune evasion strategies. This review comprehensively summarizes the evasion mechanisms employed by mycoplasmas, providing valuable insights into the pathogenesis of mycoplasma infections.

Pathogenicity and virulence of Mycoplasma genitalium: Unraveling Ariadne's Thread

Mycoplasma genitalium, a pathogen from class Mollicutes, has been linked to sexually transmitted diseases and sparked widespread concern. To adapt to its environment, M. genitalium has evolved specific adhesins and motility mechanisms that allow it to adhere to and invade various eukaryotic cells, thereby causing severe damage to the cells. Even though traditional exotoxins have not been identified, secreted nucleases or membrane lipoproteins have been shown to cause cell death and inflammatory injury in M. genitalium infection. However, as both innate and adaptive immune responses are important for controlling infection, the immune responses that develop upon infection do not necessarily eliminate the organism completely. Antigenic variation, detoxifying enzymes, immunoglobulins, neutrophil extracellular trap-degrading enzymes, cell invasion, and biofilm formation are important factors that help the pathogen overcome the host defence and cause chronic infections in susceptible individuals. Furthermore, M. genitalium can increase the susceptibility to several sexually transmitted pathogens, which significantly complicates the persistence and chronicity of M. genitalium infection. This review aimed to discuss the virulence factors of M. genitalium to shed light on its complex pathogenicity and pathogenesis of the infection.

Extraction, Cloning and Bioinformatics Analysis of Mycoplasma genitalium MG428 Protein

Background: Mycoplasma genitalium is a sexually transmitted human pathogen, causing numerous reproductive tract diseases in both genders. MG428 is a positive regulator of surface exposure protein gene recombination and an alternative sigma factor of M. genitalium. Objectives: We extracted and cloned the MG428 gene and bioinformatics analyzed its protein structure in this study. Methods: We designed specific primers based on the MG428 gene sequence of M. genitalium. The MG428 gene was amplified using PCR techniques and ligated into the pGEM-T easy vector. The positive clones were verified by DNA sequencing. The MG428 protein biological characteristics and structure was analysed by biological characteristics. Results: The MG428 gene of M. genitalium has a length of 513 bp and encodes 171 amino acids. No coiled-coil conformation, possible transmembrane helices, or signal peptide was found in the MG428 protein. The MG428 protein was located in the nucleoid of bacteria, and its 3D structure was similar to that of the sigma-H factor of Pseudomonas aeruginosa. A total of 14 B cell epitopes in MG428 were predicted. Conclusions: We successfully cloned the MG428 protein of M. genitalium and predicted its structure and function. The results of this study could provide a research direction for medicine screening against M. genitalium.

Mycoplasma genitalium: A new superbug

Mycoplasma genitalium (MG) is an emerging sexually transmitted pathogen. It is an important cause of nongonococcal urethritis in men and is associated with cervicitis and pelvic inflammatory disease in women, putting them at risk of infertility. Multiple factors that aid pathogenesis of MG include its ability of adhesion, gliding motility, and intracellular invasion by means of the tip organelle. Through intracellular localization and antigenic variation, MG could result in treatment-resistant chronic infection. There are limited data on the prevalence of MG in Indian patients with urogenital syndromes. Recently, a high prevalence of extra genital infection with MG has been reported. Molecular assays are the major diagnostic techniques of MG infection. Antimicrobial agents such as macrolides, along with fluoroquinolones, are the treatment of choice for MG infections. The issue of drug resistance to azithromycin and fluoroquinolones in MG is rising globally. As molecular tests are becoming available for MG, both for the diagnosis and the detection of antimicrobial resistance, any patient with MG infection should then be tested for antimicrobial resistance. Consideration of MG as a cause of sexually transmitted disease in the Indian population is crucial in diagnostic algorithms and treatment strategies. The purpose of this review is to understand the prevalence of MG in different clinical scenarios, molecular mechanisms of pathogenesis, current status of antimicrobial resistance, and its impact on MG treatment.

The aadE*-sat4-aphA-3 Gene Cluster of Mycoplasma bovirhinis HAZ141_2 Undergoes Genomic Rearrangements Influencing the Primary Promoter Sequence

The 54 kb GC-rich prophage region of Mycoplasma bovirhinis HAZ141_2 contains three structural 'compartments', one of which is a highly transmittable cluster of three genes, aadE-like (aadE*), sat4, and aphA-3. In this study, we characterized recombination events and their consequences occurred within the aadE*-sat4-aphA-3 containing region. Analysis of this region revealed direct repeats (DRs) of 155 and invert repeats (IRs) of 197 base pairs (bps) each, flanking and overlapping with the primary promoter P* located upstream of the aadE*. Two recombination events, including inversions via both 197 and 155-bp IRs (the latter become inverted after the initial 197-bp IRs associated inversion) and the excision of the aadE*-sat4-aphA-3 cluster, were confirmed. Inversion via 155-IRs results in changes within the P* promoter region. Using Escherichia coli JM109 carrying plasmids containing derivatives of the aadE*-sat4-aphA-3 cluster, we validated the expression of those genes from different promoters. Our results showed no difference in the minimal inhibitory concentrations (MICs) to kanamycin and neomycin and only 2-fold decrease in MIC (from 512 to 256 μg/mL) to nourseothricin between the wild type and a P* derivative promoter. However, the MICs to kanamycin and neomycin were at least 4-fold lower in the construct where aphA-3 expressed under its P2 promoter (128 µg/mL) in comparison to the construct where aphA-3 expressed under P1″ promoter located within the sat4 gene (512-1024 µg/mL). PCR confirmed the excision of the aadE*-sat4-aphA-3 cluster via 197- and 155-bp DRs, but no selection of antibiotic-sensitive M. bovirhinis were obtained after 100 passages in kanamycin-free medium.

Molecular epidemiology and antimicrobials resistance mechanism of Mycoplasma genitlaium

Currently, infections caused by Mycoplasma genitalium are ones the most common sexually transmitted infections. Their prevalence is varied from 1.3% to 15.9%. Infections caused by M.genitalium may lead to urethritis in men and a wide spectrum of diseases in women. Antibiotic resistance now is one of the most emerging problems both in the scientific and in the healthcare fields. The usage of antimicrobials inhibiting cell wall synthesis for the treatment of M.genitalium is ineffective, and resistance to macrolides and fluoroquinolones is increasing rapidly. M.genitalium infections diagnostics is complicated due to specific conditions and duration of culture methods. The usage of nucleic acid amplification techniques is the most relevant for laboratory diagnostics, and is used in existing assays. This review compiles current data on the prevalence, molecular mechanisms of pathogenesis and antibiotic resistance, as well as diagnostics methods of M.genitalium.

Protein quality control and regulated proteolysis in the genome-reduced organism Mycoplasma pneumoniae

Protein degradation is a crucial cellular process in all-living systems. Here, using Mycoplasma pneumoniae as a model organism, we defined the minimal protein degradation machinery required to maintain proteome homeostasis. Then, we conditionally depleted the two essential ATP-dependent proteases. Whereas depletion of Lon results in increased protein aggregation and decreased heat tolerance, FtsH depletion induces cell membrane damage, suggesting a role in quality control of membrane proteins. An integrative comparative study combining shotgun proteomics and RNA-seq revealed 62 and 34 candidate substrates, respectively. Cellular localization of substrates and epistasis studies supports separate functions for Lon and FtsH. Protein half-life measurements also suggest a role for Lon-modulated protein decay. Lon plays a key role in protein quality control, degrading misfolded proteins and those not assembled into functional complexes. We propose that regulating complex assembly and degradation of isolated proteins is a mechanism that coordinates important cellular processes like cell division. Finally, by considering the entire set of proteases and chaperones, we provide a fully integrated view of how a minimal cell regulates protein folding and degradation.

Sequence variation and immunogenicity of the Mycoplasma genitalium MgpB and MgpC adherence proteins during persistent infection of men with non-gonococcal urethritis

Mycoplasma genitalium is a sexually transmitted bacterial pathogen that infects men and women. Antigenic variation of MgpB and MgpC, the immunodominant adherence proteins of M. genitalium, is thought to contribute to immune evasion and chronic infection. We investigated the evolution of mgpB and mgpC sequences in men with non-gonococcal urethritis persistently infected with M. genitalium, including two men with anti-M. genitalium antibodies at enrollment and two that developed antibodies during follow-up. Each of the four patients was persistently infected with a different strain type and each patient produced antibodies targeting MgpB and MgpC. Amino acid sequence evolution in the variable regions of MgpB and MgpC occurred in all four patients with changes observed in single and multiple variable regions over time. Using the available crystal structure of MgpC of the G37 type strain we found that predicted conformational B cell epitopes localize predominantly to the variable region of MgpC, amino acids that changed during patient infection lie in these epitopes, and variant amino acids are in close proximity to the conserved sialic acid binding pocket. These findings support the hypothesis that sequence variation functions to avoid specific antibodies thereby contributing to persistence in the genital tract.

The mechanisms underlying antigenic variation and maintenance of genomic integrity in Mycoplasma pneumoniae and Mycoplasma genitalium

Mycoplasma pneumoniae and Mycoplasma genitalium are important causative agents of infections in humans. Like all other mycoplasmas, these species possess genomes that are significantly smaller than that of other prokaryotes. Moreover, both organisms possess an exceptionally compact set of DNA recombination and repair-associated genes. These genes, however, are sufficient to generate antigenic variation by means of homologous recombination between specific repetitive genomic elements. At the same time, these mycoplasmas have likely evolved strategies to maintain the stability and integrity of their 'minimal' genomes. Previous studies have indicated that there are considerable differences between mycoplasmas and other bacteria in the composition of their DNA recombination and repair machinery. However, the complete repertoire of activities executed by the putative recombination and repair enzymes encoded by Mycoplasma species is not yet fully understood. In this paper, we review the current knowledge on the proteins that likely form part of the DNA repair and recombination pathways of two of the most clinically relevant Mycoplasma species, M. pneumoniae and M. genitalium. The characterization of these proteins will help to define the minimal enzymatic requirements for creating bacterial genetic diversity (antigenic variation) on the one hand, while maintaining genomic integrity on the other.

Subversion of the Immune Response by Human Pathogenic Mycoplasmas

Mycoplasmas are a large group of prokaryotes which is believed to be originated from Gram-positive bacteria via degenerative evolution, and mainly capable of causing a wide range of human and animal infections. Although innate immunity and adaptive immunity play crucial roles in preventing mycoplasma infection, immune response that develops after infection fails to completely eliminate this bacterium under certain circumstances. Thus, it is reasonable to speculate that mycoplasmas employ some mechanisms to deal with coercion of host defense system. In this review, we will highlight and provide a comprehensive overview of immune evasion strategies that have emerged in mycoplasma infection, which can be divided into four aspects: (i) Molecular mimicry and antigenic variation on the surface of the bacteria to evade the immune surveillance; (ii) Overcoming the immune effector molecules assaults: Induction of detoxified enzymes to degradation of reactive oxygen species; Expression of nucleases to degrade the neutrophil extracellular traps to avoid killing by Neutrophil; Capture and cleavage of immunoglobulins to evade humoral immune response; (iii) Persistent survival: Invading into the host cell to escape the immune damage; Formation of a biofilm to establish a persistent infection; (iv) Modulation of the immune system to down-regulate the intensity of immune response. All of these features increase the probability of mycoplasma survival in the host and lead to a persistent, chronic infections. A profound understanding on the mycoplasma to subvert the immune system will help us to better understand why mycoplasma is so difficult to eradicate and ultimately provide new insights on the development of therapeutic regimens against this bacterium in future.

Determination of the Gene Regulatory Network of a Genome-Reduced Bacterium Highlights Alternative Regulation Independent of Transcription Factors

Here, we determined the relative importance of different transcriptional mechanisms in the genome-reduced bacterium Mycoplasma pneumoniae, by employing an array of experimental techniques under multiple genetic and environmental perturbations. Of the 143 genes tested (21% of the bacterium’s annotated proteins), only 55% showed an altered phenotype, highlighting the robustness of biological systems. We identified nine transcription factors (TFs) and their targets, representing 43% of the genome, and 16 regulators that indirectly affect transcription. Only 20% of transcriptional regulation is mediated by canonical TFs when responding to perturbations. Using a Random Forest, we quantified the non-redundant contribution of different mechanisms such as supercoiling, metabolic control, RNA degradation, and chromosome topology to transcriptional changes. Model-predicted gene changes correlate well with experimental data in 95% of the tested perturbations, explaining up to 70% of the total variance when also considering noise. This analysis highlights the importance of considering non-TF-mediated regulation when engineering bacteria.

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Full comprehensive reconstruction of a bacterial gene regulatory network achieved

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Genome-reduced bacterium Mycoplasma pneumoniae is robust to genetic perturbations

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Large part of transcription regulation in bacteria is transcription-factor independent

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Transcription-factor-independent regulation has a smaller dynamic range

Activation of σ20-dependent recombination and horizontal gene transfer in Mycoplasma genitalium

In the human pathogen Mycoplasma genitalium, homologous recombination is under the control of σ20, an alternative sigma factor that boosts the generation of genetic and antigenic diversity in the population. Under laboratory growth conditions, σ20 activation is rare and the factors governing its intermittent activity are unknown. Two σ20-regulated genes, rrlA and rrlB, showed to be important for recombination of homologous DNA sequences in this bacterium. Herein, we demonstrate that rrlA and rrlB code for two small proteins that participate in a feed-forward loop essential for σ20 function. In addition, we identify novel genes regulated by σ20 and show that several non-coding regions, which function as a reservoir for the generation of antigenic diversity, are also activated by this alternative sigma factor. Finally, we reveal that M. genitalium cells can transfer DNA horizontally by a novel mechanism that requires RecA and is facilitated by σ20 over-expression. This DNA transfer system is arguably fundamental for persistence of M. genitalium within the host since it could facilitate a rapid dissemination of successful antigenic variants within the population. Overall, these findings impose a novel conception of genome evolution, genetic variation and survival of M. genitalium within the host.

Mycoplasma genitalium Nonadherent Phase Variants Arise by Multiple Mechanisms and Escape Antibody-Dependent Growth Inhibition

Antigenic variation of the immunodominant MgpB and MgpC proteins has been suggested to be a mechanism of immune evasion of the human pathogen Mycoplasma genitalium, a cause of several reproductive tract disease syndromes. Phase variation resulting in the loss of adherence has also been documented, but the molecular mechanisms underlying this process and its role in pathogenesis are still poorly understood. In this study, we isolated and characterized 40 spontaneous, nonadherent phase variants from in vitro-passaged M. genitalium cultures. In all cases, nonadherence was associated with the loss of MgpBC protein expression, attributable to sequence changes in the mgpBC expression site. Phase variants were grouped into seven classes on the basis of the nature of the mutation. Consistent with the established role of RecA in phase variation, 31 (79.5%) variants arose via recombination with MgPa repeat regions that contain mgpBC variable sequences. The remaining mutants arose via nonsense or frameshift mutations. As expected, revertants were obtained for phase variants that were predicted to be reversible but not for those that arose via an irreversible mechanism. Furthermore, phase variants were enriched in M. genitalium cultures exposed to antibodies reacting to the extracellular, conserved C terminus of MgpB but not in cultures exposed to antibodies reacting to an intracellular domain of MgpB or the cytoplasmic HU protein. Genetic characterization of the antibody-selected phase variants confirmed that they arose via reversible and irreversible recombination and point mutations within mgpBC These phase variants resisted antibody-mediated growth inhibition, suggesting that phase variation promotes immune evasion.

The Unique Microbiology and Molecular Pathogenesis of Mycoplasma genitalium

Mycoplasma genitalium is increasingly appreciated as a common cause of sexually transmitted disease syndromes, including urethritis in men and cervicitis, endometritis, pelvic inflammatory disease, and possibly preterm birth, tubal factor infertility, and ectopic pregnancy in women. Despite these disease associations, which parallel those of Chlamydia trachomatis and Neisseria gonorrhoeae, the mechanisms by which this pathogen elicits inflammation, causes cellular damage, and persists in its only natural host (humans) are unique and are not fully understood. The purpose of this review is to briefly provide a historical background on the discovery, microbiology, and recognition of M. genitalium as a pathogen, and then summarize the recent advances in our understanding of the molecular biology and pathogenesis of this unique urogenital organism. Collectively, the basic scientific discussions herein should provide a framework for understanding the clinical and epidemiological outcomes described in the accompanying articles in this supplemental issue.

Clinical laboratory assessments for Mycoplasma genitalium in a high-prevalence sexually-transmitted infection community reveal epidemiologic dichotomies with Trichomonas vaginalis

INTRODUCTION

Mycoplasma genitalium is an emerging agent of sexually-transmitted infection and is responsible for clinically-significant genital tract disease in both females and males. Similar to scenarios recently experienced with the urogenital flagellate Trichomonas vaginalis, an evolving molecular diagnostic reference standard based on transcription-mediated amplification allows for accurate detection of the organism, plus additional insight into disease epidemiology. Areas covered. The basis for this article includes primary peer-reviewed literature plus compilations of data derived from routine clinical laboratory screening of females and males for agents of sexually-transmitted infection. Introductory laboratory and epidemiologic data related to T. vaginalis provides not only a foreshadowing to the dichotomies inherent to M. genitalium prevalence but also advocacy of a common non-invasive specimen source that could be used to screen females for both agents. This review also documents increased prevalence rates of M. genitalium in both females and males by way of transcription-mediated amplification. Expert commentary. Molecular detection of M. genitalium should be a consideration in the development of comprehensive sexually-transmitted infection screening programs for both females and males. Transcription-mediated amplification has additionally identified novel facets of M. genitalium and T. vaginalis epidemiology that warrant further investigation.

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.

A novel sigma factor reveals a unique regulon controlling cell-specific recombination in Mycoplasma genitalium

The Mycoplasma genitalium MG428 protein shows homology to members of the sigma-70 family of sigma factors. Herein, we found that MG428 activates transcription of recA, ruvA and ruvB as well as several genes with unknown function. Deletion of MG_428 or some of the up-regulated unknown genes led to severe recombination defects. Single cell analyses revealed that activation of the MG428-regulon is a rare event under laboratory growth conditions. A conserved sequence with sigma-70 promoter architecture (TTGTCA-N_18/19-ATTWAT) was identified in the upstream region of all of the MG428-regulated genes or operons. Primer extension analyses demonstrated that transcription initiates immediately downstream of this sigma70-type promoter in a MG428-dependent manner. Furthermore, mutagenesis of the conserved −10 and −35 elements corroborated the requirement of these regions for promoter function. Therefore, a new mycoplasma promoter directs transcription of a unique recombination regulon. Additionally, MG428 was found to interact with the RNAP core enzyme, reinforcing the predicted role of this protein as an alternative sigma factor. Finally, our results indicate that MG428 contributes to the generation of genetic diversity in this model organism. Since recombination is an important mechanism to generate antigenic variation, MG428 emerges as a novel factor contributing to M. genitalium virulence.