Glycerol metabolism is important for cytotoxicity of Mycoplasma pneumoniae

Glycerol Metabolism Contributes to Competition by Oral Streptococci through Production of Hydrogen Peroxide

As a biological byproduct from both humans and microbes, glycerol's contribution to microbial homeostasis in the oral cavity remains understudied. Here we examined glycerol metabolism by Streptococcus sanguinis, a commensal associated with oral health. Genetic mutants of glucose-PTS enzyme II ( manL ), glycerol metabolism ( glp and dha pathways), and transcriptional regulators were characterized with regard to glycerol catabolism, growth, production of hydrogen peroxide (H 2 O 2 ), transcription, and competition with Streptococcus mutans . Biochemical assays identified the glp pathway as a novel source of H 2 O 2 production by S. sanguinis that is independent of pyruvate oxidase (SpxB). Genetic analysis indicated that the glp pathway requires glycerol and a transcriptional regulator, GlpR, for expression and is negatively regulated by PTS, but not the catabolite control protein, CcpA. Conversely, deletion of either manL or ccpA increased expression of spxB and a second, H 2 O 2 -non-producing glycerol metabolic pathway ( dha ), indicative of a mode of regulation consistent with conventional carbon catabolite repression (CCR). In a plate-based antagonism assay and competition assays performed with planktonic and biofilm-grown cells, glycerol greatly benefited the competitive fitness of S. sanguinis against S. mutans. The glp pathway appears to be conserved in several commensal streptococci and actively expressed in caries-free plaque samples. Our study suggests that glycerol metabolism plays a more significant role in the ecology of the oral cavity than previously understood. Commensal streptococci, though not able to use glycerol as a sole carbohydrate for growth, benefit from catabolism of glycerol through production of both ATP and H 2 O 2 .

Importance

Glycerol is an abundant carbohydrate found in oral cavity, both due to biological activities of humans and microbes, and as a common ingredient of foods and health care products. However, very little is understood regarding the metabolism of glycerol by some of the most abundant oral bacteria, commensal streptococci. This was in part because most streptococci cannot grow on glycerol as the sole carbon source. Here we show that Streptococcus sanguinis , an oral commensal associated with dental health, can degrade glycerol for persistence and competition through two independent pathways, one of which generates hydrogen peroxide at levels capable of inhibiting a dental pathobiont, Streptococcus mutans . Preliminary studies suggest that several other commensal streptococci are also able to catabolize glycerol, and glycerol-related genes are being actively expressed in human dental plaque samples. Our findings reveal the potential of glycerol to significantly impact microbial homeostasis which warrants further exploration.

Unveiling genome plasticity and a novel phage in Mycoplasma felis: Genomic investigations of four feline isolates

Mycoplasma felis has been isolated from diseased cats and horses, but to date only a single fully assembled genome of this species, of an isolate from a horse, has been characterized. This study aimed to characterize and compare the completely assembled genomes of four clinical isolates of M. felis from three domestic cats, assembled with the aid of short- and long-read sequencing methods. The completed genomes encoded a median of 759 ORFs (range 743-777) and had a median average nucleotide identity of 98.2 % with the genome of the available equid origin reference strain. Comparative genomic analysis revealed the occurrence of multiple horizontal gene transfer events and significant genome reassortment. This had resulted in the acquisition or loss of numerous genes within the Australian felid isolate genomes, encoding putative proteins involved in DNA transfer, metabolism, DNA replication, host cell interaction and restriction modification systems. Additionally, a novel mycoplasma phage was detected in one Australian felid M. felis isolate by genomic analysis and visualized using cryo-transmission electron microscopy. This study has highlighted the complex genomic dynamics in different host environments. Furthermore, the sequences obtained in this work will enable the development of new diagnostic tools, and identification of future infection control and treatment options for the respiratory disease complex in cats.

Pathogenic mycoplasmas of humans regulate the long noncoding RNAs in epithelial cells

Non-coding RNAs (ncRNAs), specifically long ncRNAs (lncRNAs), regulate cellular processes by affecting gene expression at the transcriptional, post-transcriptional, and epigenetic levels. Emerging evidence indicates that pathogenic microbes dysregulate the expression of host lncRNAs to suppress cellular defense mechanisms and promote survival. To understand whether the pathogenic human mycoplasmas dysregulate host lncRNAs, we infected HeLa cells with Mycoplasma genitalium (Mg) and Mycoplasma penumoniae (Mp) and assessed the expression of lncRNAs by directional RNA-seq analysis. HeLa cells infected with these species showed up-and-down regulation of lncRNAs expression, indicating that both species can modulate host lncRNAs. However, the number of upregulated (200 for Mg and 112 for Mp) and downregulated lncRNAs (30 for Mg and 62 for Mp) differ widely between these two species. GREAT analysis of the noncoding regions associated with differentially expressed lncRNAs showed that Mg and Mp regulate a discrete set of lncRNA plausibly related to transcription, metabolism, and inflammation. Further, signaling network analysis of the differentially regulated lncRNAs exhibited diverse pathways such as neurodegeneration, NOD-like receptor signaling, MAPK signaling, p53 signaling, and PI3K signaling, suggesting that both species primarily target signaling mechanisms. Overall, the study's results suggest that Mg and Mp modulate lncRNAs to promote their survival within the host but in distinct manners.

Development of a Serum-Free Medium To Aid Large-Scale Production of Mycoplasma-Based Therapies

To assist in the advancement of the large-scale production of safe Mycoplasma vaccines and other Mycoplasma-based therapies, we developed a culture medium free of animal serum and other animal components for Mycoplasma pneumoniae growth. By establishing a workflow method to systematically test different compounds and concentrations, we provide optimized formulations capable of supporting serial passaging and robust growth reaching 60 to 70% of the biomass obtained in rich medium. Global transcriptomic and proteomic analysis showed minor physiological changes upon cell culture in the animal component-free medium, supporting its suitability for the production of M. pneumoniae-based therapies. The major contributors to growth performance were found to be glucose as a carbon source, glycerol, cholesterol, and phospholipids as a source of fatty acids. Bovine serum albumin or cyclodextrin (in the animal component-free medium) were required as lipid carriers to prevent lipid toxicity. Connaught Medical Research Laboratories medium (CMRL) used to simplify medium preparation as a source of amino acids, nucleotide precursors, vitamins, and other cofactors could be substituted by cysteine. In fact, the presence of protein hydrolysates such as yeastolate or peptones was found to be essential and preferred over free amino acids, except for the cysteine. Supplementation of nucleotide precursors and vitamins is not strictly necessary in the presence of yeastolate, suggesting that this animal origin-free hydrolysate serves as an efficient source for these compounds. Finally, we adapted the serum-free medium formulation to support growth of Mycoplasma hyopneumoniae, a swine pathogen for which inactivated whole-cell vaccines are available. IMPORTANCE Mycoplasma infections have a significant negative impact on both livestock production and human health. Vaccination is often the first option to control disease and alleviate the economic impact that some Mycoplasma infections cause on milk production, weight gain, and animal health. The fastidious nutrient requirements of these bacteria, however, challenges the industrial production of attenuated or inactivated whole-cell vaccines, which depends on the use of animal serum and other animal raw materials. Apart from their clinical relevance, some Mycoplasma species have become cellular models for systems and synthetic biology, owing to the small size of their genomes and the absence of a cell wall, which offers unique opportunities for the secretion and delivery of biotherapeutics. This study proposes medium formulations free of serum and animal components with the potential of supporting large-scale production upon industrial optimization, thus contributing to the development of safe vaccines and other Mycoplasma-based therapies.

Novel mechanisms of macrolide resistance revealed by in vitro selection and genome analysis in Mycoplasma pneumoniae

Mycoplasma pneumoniae is an important pathogen causing upper and lower respiratory tract infections in children and other age groups. Macrolides are the recommended treatments of choice for M. pneumoniae infections. However, macrolide resistance in M. pneumoniae is increasing worldwide, which complicates the treatment strategies. The mechanisms of macrolide resistance have been extensively studied focusing on the mutations in 23S rRNA and ribosomal proteins. Since the secondary treatment choice for pediatric patients is very limited, we decided to look for potential new treatment strategies in macrolide drugs and investigate possible new mechanisms of resistance. We performed an in vitro selection of mutants resistant to five macrolides (erythromycin, roxithromycin, azithromycin, josamycin, and midecamycin) by inducing the parent M. pneumoniae strain M129 with increasing concentrations of the drugs. The evolving cultures in every passage were tested for their antimicrobial susceptibilities to eight drugs and mutations known to be associated with macrolide resistance by PCR and sequencing. The final selected mutants were also analyzed by whole-genome sequencing. Results showed that roxithromycin is the drug that most easily induces resistance (at 0.25 mg/L, with two passages, 23 days), while with midecamycin it is most difficult (at 5.12 mg/L, with seven passages, 87 days). Point mutations C2617A/T, A2063G, or A2064C in domain V of 23S rRNA were detected in mutants resistant to the 14- and 15-membered macrolides, while A2067G/C was selected for the 16-membered macrolides. Single amino acid changes (G72R, G72V) in ribosomal protein L4 emerged during the induction by midecamycin. Genome sequencing identified sequence variations in dnaK, rpoC, glpK, MPN449, and in one of the hsdS (MPN365) genes in the mutants. Mutants induced by the 14- or 15-membered macrolides were resistant to all macrolides, while those induced by the 16-membered macrolides (midecamycin and josamycin) remained susceptible to the 14- and 15-membered macrolides. In summary, these data demonstrated that midecamycin is less potent in inducing resistance than other macrolides, and the induced resistance is restrained to the 16-membered macrolides, suggesting a potential benefit of using midecamycin as a first treatment choice if the strain is susceptible.

Characterization of Virulence-Associated Traits in Mycoplasma penetrans Strains Acting as Likely Etiological Agents of Idiopathic Nongonococcal Urethritis

Mycoplasma penetrans is an emerging pathogen with a reduced genome. This bacterium has only previously been cultured from individuals with chronic immunodeficiencies. Here we report the characteristics of 4 M. penetrans isolates from the urine of immunocompetent males with nongonococcal urethritis, in comparison with strain HF-2 from an immunocompromised patient. Several features exhibited distinct differences between these isolates and HF-2. Unlike HF-2, all 4 were resistant to azithromycin. They exhibited greater sialic acid-dependent binding to erythrocytes, gliding motility speed, and H2O2 production than HF-2. All new isolates produced thinner capsules than HF-2. Invasiveness varied, with some isolates being more invasive than HF-2 and some less invasive. Cytotoxicity to HeLa cells was similar to HF-2, and all strains could clear extracellular traps produced by innate immune cells. We conclude that subtle differences among M. penetrans strains may be critical for this organism to establish an infection in an otherwise healthy individual.

Bacterial expression of a designed single-chain IL-10 prevents severe lung inflammation

Interleukin-10 (IL-10) is an anti-inflammatory cytokine that is active as a swapped domain dimer and is used in bacterial therapy of gut inflammation. IL-10 can be used as treatment of a wide range of pulmonary diseases. Here we have developed a non-pathogenic chassis (CV8) of the human lung bacterium Mycoplasma pneumoniae (MPN) to treat lung diseases. We find that IL-10 expression by MPN has a limited impact on the lung inflammatory response in mice. To solve these issues, we rationally designed a single-chain IL-10 (SC-IL10) with or without surface mutations, using our protein design software (ModelX and FoldX). As compared to the IL-10 WT, the designed SC-IL10 molecules increase the effective expression in MPN four-fold, and the activity in mouse and human cell lines between 10 and 60 times, depending on the cell line. The SC-IL10 molecules expressed in the mouse lung by CV8 in vivo have a powerful anti-inflammatory effect on Pseudomonas aeruginosa lung infection. This rational design strategy could be used to other molecules with immunomodulatory properties used in bacterial therapy.

Genome Engineering of the Fast-Growing Mycoplasma feriruminatoris toward a Live Vaccine Chassis

Development of a new generation of vaccines is a key challenge for the control of infectious diseases affecting both humans and animals. Synthetic biology methods offer new ways to engineer bacterial chassis that can be used as vectors to present heterologous antigens and train the immune system against pathogens. Here, we describe the construction of a bacterial chassis based on the fast-growing Mycoplasma feriruminatoris, and the first steps toward its application as a live vaccine against contagious caprine pleuropneumonia (CCPP). To do so, the M. feriruminatoris genome was cloned in yeast, modified by iterative cycles of Cas9-mediated deletion of loci encoding virulence factors, and transplanted back in Mycoplasma capricolum subsp. capricolum recipient cells to produce the designed M. feriruminatoris chassis. Deleted genes encoded the glycerol transport and metabolism systems GtsABCD and GlpOKF and the Mycoplasma Ig binding protein-Mycoplasma Ig protease (MIB-MIP) immunoglobulin cleavage system. Phenotypic assays of the M. feriruminatoris chassis confirmed the corresponding loss of H₂O₂ production and IgG cleavage activities, while growth remained unaltered. The resulting mycoplasma chassis was further evaluated as a platform for the expression of heterologous surface proteins. A genome locus encoding an inactivated MIB-MIP system from the CCPP-causative agent Mycoplasma capricolum subsp. capripneumoniae was grafted in replacement of its homolog at the original locus in the chassis genome. Both heterologous proteins were detected in the resulting strain using proteomics, confirming their expression. This study demonstrates that advanced genome engineering methods are henceforth available for the fast-growing M. feriruminatoris, facilitating the development of novel vaccines, in particular against major mycoplasma diseases.

Refractory Mycoplasma pneumoniae Pneumonia in Children: Early Recognition and Management

Refractory Mycoplasma pneumoniae pneumonia (RMPP) is a severe state of M. pneumoniae infection that has attracted increasing universal attention in recent years. The pathogenesis of RMPP remains unknown, but the excessive host immune responses as well as macrolide resistance of M. pneumoniae might play important roles in the development of RMPP. To improve the prognosis of RMPP, it is mandatory to recognize RMPP in the early stages, and the detection of macrolide-resistant MP, clinical unresponsiveness to macrolides and elevated proinflammatory cytokines might be clues. Timely and effective anti-mycoplasmal therapy and immunomodulating therapy are the main strategies for RMPP.

The Mycoplasma spp. ‘Releasome’: A New Concept for a Long-Known Phenomenon

The bacterial secretome comprises polypeptides expressed at the cell surface or released into the extracellular environment as well as the corresponding secretion machineries. Despite their reduced coding capacities, Mycoplasma spp. are able to produce and release several components into their environment, including polypeptides, exopolysaccharides and extracellular vesicles. Technical difficulties in purifying these elements from the complex broth media used to grow mycoplasmas have recently been overcome by optimizing growth conditions and switching to chemically defined culture media. However, the secretion pathways responsible for the release of these structurally varied elements are still poorly described in mycoplasmas. We propose the use of the term ‘releasome,’ instead of secretome, to refer to molecules released by mycoplasmas into their environment. The aim of this review is to more precisely delineate the elements that should be considered part of the mycoplasmal releasome and their role in the interplay of mycoplasmas with host cells and tissues.

Mycoplasma genitalium and M. pneumoniae Regulate a Distinct Set of Protein-Coding Genes in Epithelial Cells

Mycoplasma genitalium and M. pneumoniae are two significant mycoplasmas that infect the urogenital and respiratory tracts of humans. Despite distinct tissue tropisms, they both have similar pathogenic mechanisms and infect/invade epithelial cells in the respective regions and persist within these cells. However, the pathogenic mechanisms of these species in terms of bacterium-host interactions are poorly understood. To gain insights on this, we infected HeLa cells independently with M. genitalium and M. pneumoniae and assessed gene expression by whole transcriptome sequencing (RNA-seq) approach. The results revealed that HeLa cells respond to M. genitalium and M. pneumoniae differently by regulating various protein-coding genes. Though there is a significant overlap between the genes regulated by these species, many of the differentially expressed genes were specific to each species. KEGG pathway and signaling network analyses revealed that the genes specific to M. genitalium are more related to cellular processes. In contrast, the genes specific to M. pneumoniae infection are correlated with immune response and inflammation, possibly suggesting that M. pneumoniae has some inherent ability to modulate host immune pathways.

Engineering a genome-reduced bacterium to eliminate Staphylococcus aureus biofilms in vivo

Bacteria present a promising delivery system for treating human diseases. Here, we engineered the genome‐reduced human lung pathogen Mycoplasma pneumoniae as a live biotherapeutic to treat biofilm‐associated bacterial infections. This strain has a unique genetic code, which hinders gene transfer to most other bacterial genera, and it lacks a cell wall, which allows it to express proteins that target peptidoglycans of pathogenic bacteria. We first determined that removal of the pathogenic factors fully attenuated the chassis strain in vivo. We then designed synthetic promoters and identified an endogenous peptide signal sequence that, when fused to heterologous proteins, promotes efficient secretion. Based on this, we equipped the chassis strain with a genetic platform designed to secrete antibiofilm and bactericidal enzymes, resulting in a strain capable of dissolving Staphylococcus aureus biofilms preformed on catheters in vitro, ex vivo, and in vivo. To our knowledge, this is the first engineered genome‐reduced bacterium that can fight against clinically relevant biofilm‐associated bacterial infections.

Pathogenicity & virulence of Mycoplasma hyopneumoniae

Mycoplasma hyopneumoniae: is the etiological agent of porcine enzootic pneumonia (EP), a disease that impacts the swine industry worldwide. Pathogen-induced damage, as well as the elicited host-response, contribute to disease. Here, we provide an overview of EP epidemiology, control and prevention, and a more in-depth review of M. hyopneumoniae pathogenicity determinants, highlighting some molecular mechanisms of pathogen-host interactions relevant for pathogenesis. Based on recent functional, immunological, and comparative “omics” results, we discuss the roles of many known or putative M. hyopneumoniae virulence factors, along with host molecules involved in EP. Moreover, the known molecular bases of pathogenicity mechanisms, including M. hyopneumoniae adhesion to host respiratory epithelium, protein secretion, cell damage, host microbicidal response and its modulation, and maintenance of M. hyopneumoniae homeostasis during infection are described. Recent findings regarding M. hyopneumoniae pathogenicity determinants also contribute to the development of novel diagnostic tests, vaccines, and treatments for EP.

Attenuation of Mycoplasma hyopneumoniae Strain ES-2 and Comparative Genomic Analysis of ES-2 and Its Attenuated Form ES-2L

Mycoplasma hyopneumoniae causes swine respiratory disease worldwide. Due to the difficulty of isolating and cultivating M. hyopneumoniae, very few attenuated strains have been successfully isolated, which hampers the development of attenuated vaccines. In order to produce an attenuated M. hyopneumoniae strain, we used the highly virulent M. hyopneumoniae strain ES-2, which was serially passaged in vitro 200 times to produce the attenuated strain ES-2L, and its virulence was evidenced to be low in an animal experiment. In order to elucidate the mechanisms underlying virulence attenuation, we performed whole-genome sequencing of both strains and conducted comparative genomic analyses of strain ES-2 and its attenuated form ES-2L. Strain ES-2L showed three large fragment deletion regions including a total of 18 deleted genes, compared with strain ES-2. Analysis of single-nucleotide polymorphisms (SNPs) and indels indicated that 22 dels were located in 19 predicted coding sequences. In addition to these indels, 348 single-nucleotide variations (SNVs) were identified between strains ES-2L and ES-2. These SNVs mapped to 99 genes where they appeared to induce amino acid substitutions and translation stops. The deleted genes and SNVs may be associated with decreased virulence of strain ES-2L. Our work provides a foundation for further examining virulence factors of M. hyopneumoniae and for the development of attenuated vaccines.

Mycoplasma pneumoniae biofilms grown in vitro: traits associated with persistence and cytotoxicity

The atypical bacterial pathogen Mycoplasma pneumoniae is a leading etiological agent of community-acquired pneumonia in humans; infections are often recalcitrant, recurrent and resistant to antibiotic treatment. These characteristics suggest a mechanism that facilitates long-term colonization in hosts. In an in vitro setting, M. pneumoniae forms biofilms that are unusual in that motility plays no more than a very limited role in their formation and development. Given the unusual nature of M. pneumoniae biofilms, open questions remain concerning phenotypes associated with persistence, such as what properties might favour the bacteria while minimizing host damage. M. pneumoniae also produces several cytotoxic molecules including community-acquired respiratory distress syndrome (CARDS) toxin, H₂S and H₂O₂, but how it deploys these agents during growth is unknown. Whereas several biochemical techniques for biofilm disruption were ineffective, sonication was required for disruption of M. pneumoniae biofilms to generate individual cells for comparative studies, suggesting unusual physical properties likely related to the atypical cell envelope. Nonetheless, like for other bacteria, biofilms were less susceptible to antibiotic inhibition and complement killing than dispersed cells, with resistance increasing as the biofilms matured. CARDS toxin levels and enzymatic activities associated with H₂S and H₂O₂ production were highest during early biofilm formation and decreased over time, suggesting attenuation of virulence in connection with chronic infection. Collectively, these findings result in a model of how M. pneumoniae biofilms contribute to both the establishment and propagation of M. pneumoniae infections, and how both biofilm towers and individual cells participate in persistence and chronic disease.

A Mycoplasma gallisepticum Glycerol ABC Transporter Involved in Pathogenicity

MalF has been shown to be required for virulence in the important avian pathogen Mycoplasma gallisepticum To characterize the function of MalF, predicted to be part of a putative ABC transporter, we compared metabolite profiles of a mutant with a transposon inserted in malF (MalF-deficient ST mutant 04-1; ΔmalF) with those of wild-type bacteria using gas chromatography-mass spectrometry and liquid chromatography-mass spectrometry. Of the substrates likely to be transported by an ABC transport system, glycerol was detected at significantly lower abundance in the ΔmalF mutant, compared to the wild type. Stable isotope labeling using [U-¹³C]glycerol and reverse transcription-quantitative PCR analysis indicated that MalF was responsible for the import of glycerol into M. gallisepticum and that, in the absence of MalF, the transcription of gtsA, which encodes a second transporter, GtsA, was upregulated, potentially to increase the import of glycerol-3-phosphate into the cell to compensate for the loss of MalF. The loss of MalF appeared to have a global effect on glycerol metabolism, suggesting that it may also play a regulatory role, and cellular morphology was also affected, indicating that the change to glycerol metabolism may have a broader effect on cellular organization. Overall, this study suggests that the reduced virulence of the ΔmalF mutant is due to perturbed glycerol uptake and metabolism and that the operon including malF should be reannotated as golABC to reflect its function in glycerol transport.IMPORTANCE Many mycoplasmas are pathogenic and cause disease in humans and animals. M. gallisepticum causes chronic respiratory disease in chickens and infectious sinusitis in turkeys, resulting in economic losses in poultry industries throughout the world. Expanding our knowledge about the pathogenesis of mycoplasma infections requires better understanding of the specific gene functions of these bacteria. In this study, we have characterized the metabolic function of a protein involved in the pathogenicity of M. gallisepticum, as well as its effect on expression of selected genes, cell phenotype, and H₂O₂ production. This study is a key step forward in elucidating why this protein plays a key role in virulence in chickens. This study also emphasizes the importance of functional characterization of mycoplasma proteins, using tools such as metabolomics, since prediction of function based on homology to other bacterial proteins is not always accurate.

Infection strategies of mycoplasmas: Unraveling the panoply of virulence factors

Mycoplasmas, the smallest bacteria lacking a cell wall, can cause various diseases in both humans and animals. Mycoplasmas harbor a variety of virulence factors that enable them to overcome numerous barriers of entry into the host; using accessory proteins, mycoplasma adhesins can bind to the receptors or extracellular matrix of the host cell. Although the host immune system can eradicate the invading mycoplasma in most cases, a few sagacious mycoplasmas employ a series of invasion and immune escape strategies to ensure their continued survival within their hosts. For instance, capsular polysaccharides are crucial for anti-phagocytosis and immunomodulation. Invasive enzymes degrade reactive oxygen species, neutrophil extracellular traps, and immunoglobulins. Biofilm formation is important for establishing a persistent infection. During proliferation, successfully surviving mycoplasmas generate numerous metabolites, including hydrogen peroxide, ammonia and hydrogen sulfide; or secrete various exotoxins, such as community-acquired respiratory distress syndrome toxin, and hemolysins; and express various pathogenic enzymes, all of which have potent toxic effects on host cells. Furthermore, some inherent components of mycoplasmas, such as lipids, membrane lipoproteins, and even mycoplasma-generated superantigens, can exert a significant pathogenic impact on the host cells or the immune system. In this review, we describe the proposed virulence factors in the toolkit of notorious mycoplasmas to better understand the pathogenic features of these bacteria, along with their pathogenic mechanisms.

Proteomic and Phenotypic Analyses of a Putative Glycerol-3-Phosphate Dehydrogenase Required for Virulence in Acidovorax citrulli

Acidovorax citrulli (Ac) is the causal agent of bacterial fruit blotch (BFB) in watermelon, a disease that poses a serious threat to watermelon production. Because of the lack of resistant cultivars against BFB, virulence factors or mechanisms need to be elucidated to control the disease. Glycerol-3-phosphate dehydrogenase is the enzyme involved in glycerol production from glucose during glycolysis. In this study, we report the functions of a putative glycerol-3-phosphate dehydrogenase in Ac (GlpdAc) using comparative proteomic analysis and phenotypic observation. A glpdAc knockout mutant, AcΔglpdAc(EV), lost virulence against watermelon in two pathogenicity tests. The putative 3D structure and amino acid sequence of GlpdAc showed high similarity with glycerol-3-phosphate dehydrogenases from other bacteria. Comparative proteomic analysis revealed that many proteins related to various metabolic pathways, including carbohydrate metabolism, were affected by GlpdAc. Although AcΔglpdAc(EV) could not use glucose as a sole carbon source, it showed growth in the presence of glycerol, indicating that GlpdAc is involved in glycolysis. AcΔglpdAc(EV) also displayed higher cell-to-cell aggregation than the wild-type bacteria, and tolerance to osmotic stress and ciprofloxacin was reduced and enhanced in the mutant, respectively. These results indicate that GlpdAc is involved in glycerol metabolism and other mechanisms, including virulence, demonstrating that the protein has pleiotropic effects. Our study expands the understanding of the functions of proteins associated with virulence in Ac.

Pseudomonas aeruginosa Planktonic- and Biofilm-Conditioned Media Elicit Discrete Metabolic Responses in Human Macrophages

Macrophages (MΦs) are prevalent innate immune cells, present throughout human bodily tissues where they orchestrate innate and adaptive immune responses to maintain cellular homeostasis. MΦs have the capacity to display a wide array of functional phenotypes due to different microenvironmental cues, particularly soluble bacterial secretory products. Recent evidence has emerged demonstrating that metabolism supports MΦ function and plasticity, in addition to energy and biomolecular precursor production. In this study, 1D ¹H-NMR-based metabolomics was used to identify the metabolic pathways that are differentially altered following primary human monocyte-derived MΦ exposure to P. aeruginosa planktonic- and biofilm-conditioned media (PCM and BCM). Metabolic profiling of PCM- and BCM-exposed MΦs indicated a significant increase in glycolytic metabolism, purine biosynthesis, and inositol phosphate metabolism. In addition, these metabolic patterns suggested that BCM-exposed MΦs exhibit a hyperinflammatory metabolic profile with reduced glycerol metabolism and elevated catabolism of lactate and amino acids, relative to PCM-exposed MΦs. Altogether, our study reveals novel findings concerning the metabolic modulation of human MΦs after exposure to secretory microbial products and contributes additional knowledge to the field of immunometabolism in MΦs.

Preliminary comparative analysis of the genomes of selected field reisolates of the Mycoplasma synoviae vaccine strain MS-H reveals both stable and unstable mutations after passage in vivo

Background

Genomic comparison of Mycoplasma synoviae vaccine strain MS-H and the MS-H parental strain 86,079/7NS established a preliminary profile of genes related to attenuation of MS-H. In this study we aimed to identify the stability of mutations found in MS-H after passage in experimental or field chickens, and to evaluate if any reverse mutation may be associated with changes in characteristics of MS-H in vitro or in vivo.

Results

Whole genome sequence analysis of 5 selected MS-H field reisolates revealed that out of 32 mutations reported previously in MS-H, 28 remained stable, while four found to be reversible to the wild-type. Each isolate possessed mutations in one to three of the genes obg, oppF₁ and gap and/or a non-coding region. Examination of the 4 reversible mutations by protein modeling predicted that only two of them (in obg and oppF₁ genes) could potentially restore the function of the respective protein to that of the wild-type.

Conclusions

These results suggest that the majority of the MS-H mutations are stable after passage in vaccinated chickens. Characterisation of stable mutations found in MS-H could be utilised to develop rapid diagnostic techniques for differentiation of vaccine from field strains or ts- MS-H reisolates.

Mycoplasma hyopneumoniae J elicits an antioxidant response and decreases the expression of ciliary genes in infected swine epithelial cells

Mycoplasma hyopneumoniae is the most costly pathogen for swine production. Although several studies have focused on the host-bacterium association, little is known about the changes in gene expression of swine cells upon infection. To improve our understanding of this interaction, we infected swine epithelial NPTr cells with M. hyopneumoniae strain J to identify differentially expressed mRNAs and miRNAs. The levels of 1,268 genes and 170 miRNAs were significantly modified post-infection. Up-regulated mRNAs were enriched in genes related to redox homeostasis and antioxidant defense, known to be regulated by the transcription factor NRF2 in related species. Down-regulated mRNAs were enriched in genes associated with cytoskeleton and ciliary functions. Bioinformatic analyses suggested a correlation between changes in miRNA and mRNA levels, since we detected down-regulation of miRNAs predicted to target antioxidant genes and up-regulation of miRNAs targeting ciliary and cytoskeleton genes. Interestingly, most down-regulated miRNAs were detected in exosome-like vesicles suggesting that M. hyopneumoniae infection induced a modification of the composition of NPTr-released vesicles. Taken together, our data indicate that M. hyopneumoniae elicits an antioxidant response induced by NRF2 in infected cells. In addition, we propose that ciliostasis caused by this pathogen is partially explained by the down-regulation of ciliary genes.

Methionine sulfoxide reductase A (MsrA) modulates cells and protects against Mycoplasma genitalium induced cytotoxicity

Methionine sulfoxide reductase A (MsrA) is a ubiquitous antioxidant repair enzyme which specifically reduces the oxidized methionine (Met-O) in proteins to methionine (Met). Previous studies have shown that lack of or overexpression of MsrA in cells affects the function of proteins and can lead to altered cellular processes. Interestingly, some pathogenic bacteria secrete and/or carry MsrA on their surface, suggesting some key roles for this enzyme in the modulation of host cellular processes. Therefore, we investigated how exogenously added MsrA affects the ability of the host cells in combating infection by using an in vitroMycoplasma genitalium cytotoxicity model. HeLa cells pretreated with MsrA and infected with M. genitalium showed significantly lower necrosis (cytotoxicity) than untreated cells infected with M. genitalium. Intriguingly, necrotic cell death pathway specific real time RT-PCR revealed that M. genitalium infection upregulates the expression of the TNF gene in HeLa cells and that MsrA pretreatment of the cells downregulates its expression significantly. Consistent with this, enzyme linked immunosorbent assay (ELISA) results showed that HeLa cells pretreated with MsrA secreted reduced levels of TNF-α following M. genitalium infection. Also, our study demonstrates that MsrA treatment of cells affects the phosphorylation status of transcriptional regulators such as NF-кB, JNK and p53 that regulate different cytokines. Further, fluorescent microscopy showed the cellular uptake of exogenously added MsrA fused with red fluorescent protein (MsrA-RFP). Altogether, our results suggest that secreted MsrA may help pathogens to modulate host cellular processes.

Characterization of an Immunoglobulin Binding Protein (IbpM) From Mycoplasma pneumoniae

Bacteria evolved many ways to invade, colonize and survive in the host tissue. Such complex infection strategies of other bacteria are not present in the cell-wall less Mycoplasmas. Due to their strongly reduced genomes, these bacteria have only a minimal metabolism. Mycoplasma pneumoniae is a pathogenic bacterium using its virulence repertoire very efficiently, infecting the human lung. M. pneumoniae can cause a variety of conditions including fever, inflammation, atypical pneumoniae, and even death. Due to its strongly reduced metabolism, M. pneumoniae is dependent on nutrients from the host and aims to persist as long as possible, resulting in chronic diseases. Mycoplasmas evolved strategies to subvert the host immune system which involve proteins fending off immunoglobulins (Igs). In this study, we investigated the role of MPN400 as the putative factor responsible for Ig-binding and host immune evasion. MPN400 is a cell-surface localized protein which binds strongly to human IgG, IgA, and IgM. We therefore named the protein MPN400 immunoglobulin binding protein of Mycoplasma (IbpM). A strain devoid of IbpM is slightly compromised in cytotoxicity. Taken together, our study indicates that M. pneumoniae uses a refined mechanism for immune evasion.

Transcriptional response to metal starvation in the emerging pathogen Mycoplasma genitalium is mediated by Fur-dependent and -independent regulatory pathways

Transition metals participate in numerous enzymatic reactions and they are essential for survival in all living organisms. For this reason, bacterial pathogens have evolved dedicated machineries to effectively compete with their hosts and scavenge metals at the site of infection. In this study, we investigated the mechanisms controlling metal acquisition in the emerging human pathogen Mycoplasma genitalium. We observed a robust transcriptional response to metal starvation, and many genes coding for predicted lipoproteins and ABC-transporters were significantly up-regulated. Transcriptional analysis of a mutant strain lacking a metalloregulator of the Fur family revealed the activation of a full operon encoding a putative metal transporter system and a gene coding for a Histidine-rich lipoprotein (Hrl). We recognized a conserved sequence with dyad symmetry within the promoter region of the Fur-regulated genes. Mutagenesis of the predicted Fur operator within the hrl promoter abrogated Fur- and metal-dependent expression of a reporter gene. Metal starvation still impelled a strong transcriptional response in the fur mutant, demonstrating the existence of Fur-independent regulatory pathways controlling metal homeostasis. Finally, analysis of metal accumulation in the wild-type strain and the fur mutant by ICP-MS revealed an important role of Fur in nickel acquisition.

Toll-Like Receptor 2 (TLR2) and TLR4 Mediate the IgA Immune Response Induced by Mycoplasma hyopneumoniae

IgA plays an important role in mucosal immunity against infectious pathogens; however, the molecular mechanism of IgA secretion in response to infection remains largely unknown, particularly in Mycoplasma spp. In this study, we found that the levels of IgA in the peripheral blood serum, bronchoalveolar lavage fluid, nasal mucosa, trachea, hilar lymph nodes, and lung tissues of pigs increased significantly after infection with Mycoplasma hyopneumoniae.

IgA plays an important role in mucosal immunity against infectious pathogens; however, the molecular mechanism of IgA secretion in response to infection remains largely unknown, particularly in Mycoplasma spp. In this study, we found that the levels of IgA in the peripheral blood serum, bronchoalveolar lavage fluid, nasal mucosa, trachea, hilar lymph nodes, and lung tissues of pigs increased significantly after infection with Mycoplasma hyopneumoniae. Furthermore, IgA and CD11c were detected in the lungs and hilar lymph nodes by immunohistochemical analysis, and colocalization of these two markers indicates that CD11c⁺ cells play an important role in IgA mucosal immunity induced by M. hyopneumoniae. To investigate the regulatory mechanism of IgA, we separated mouse dendritic cells (DCs) from different tissues and mouse macrophages from the lungs and then cultured mouse B cells together with either DCs or macrophages in vitro. In the mouse lung-DC/B (LDC/B) cell coculture, IgA secretion was increased significantly after the addition of whole-cell lysates of M. hyopneumoniae. The expression of both Toll-like receptor 2 (TLR2) and TLR4 was also upregulated, as determined by mRNA and protein expression analyses, whereas no obvious change in the expression of TLR3 and TLR7 was detected. Moreover, the IgA level decreased to the same as the control group when TLR2 or TLR4 was inhibited instead of TLR8 or TLR7/9. In conclusion, M. hyopneumoniae can stimulate the response of IgA through TLR2 and TLR4 in a mouse LDC/B cell coculture model, and the coculture model is an ideal tool for studying the IgA response mechanism, particularly that with Mycoplasma spp.

Integrated dual RNA-seq and dual iTRAQ of infected tissue reveals the functions of a diguanylate cyclase gene of Pseudomonas plecoglossicida in host-pathogen interactions with Epinephelus coioides

The interactions between host and pathogen is exceedingly complex, which involves alterations at multiple molecular layers. However, research to simultaneously monitor the alterations of transcriptome and proteome between a bacterial pathogen and aquatic animal host through integrated dual RNA-seq and dual iTRAQ of tissue during infection is currently lacking. The important role of a diguanylate cyclase gene (L321_RS15240) in pathogenicity of Pseudomonas plecoglossicida against Epinephelus coioides was suggested by previous dual RNA-seq of our lab. Then L321_RS15240-RNAi strains of P. plecoglossicida were constructed with pCM130/tac, and the mutant with the best silencing effect was selected for follow-up study. The RNAi of L321_RS15240 resulted in a significant decrease in bacterial virulence of P. plecoglossicida. The E. coioides spleens infected by wild type strain or L321_RS15240-RNAi strain of P. plecoglossicida were subjected to dual RNA-seq and dual iTRAQ, respectively. The results showed that: RNAi of L321_RS15240 led to 1)alterations of host transcriptome associated with complement and coagulation cascades, ribosome, arginine and proline metabolism, and oxidative phosphorylation; 2)high expression of host proteins which related to phagosome and metabolism responses (metabolism of glutathione, amino sugar and nucleotide sugar); 3)the highly differentially expression of host lncRNAs and miRNAs. The differentially expressed proteins and mRNAs of pathogen were different after infection, but the functions of these proteins and mRNAs were mainly related to metabolism and virulence. This study provides a new insight to comprehensively understand the gene functions of pathogens and hosts at multiple molecular layers during in vivo infection.

Adaptive Laboratory Evolution of Cupriavidus necator H16 for Carbon Co-Utilization with Glycerol

Cupriavidus necator H16 is a non-pathogenic Gram-negative betaproteobacterium that can utilize a broad range of renewable heterotrophic resources to produce chemicals ranging from polyhydroxybutyrate (biopolymer) to alcohols, alkanes, and alkenes. However, C. necator H16 utilizes carbon sources to different efficiency, for example its growth in glycerol is 11.4 times slower than a favorable substrate like gluconate. This work used adaptive laboratory evolution to enhance the glycerol assimilation in C. necator H16 and identified a variant (v6C6) that can co-utilize gluconate and glycerol. The v6C6 variant has a specific growth rate in glycerol 9.5 times faster than the wild-type strain and grows faster in mixed gluconate-glycerol carbon sources compared to gluconate alone. It also accumulated more PHB when cultivated in glycerol medium compared to gluconate medium while the inverse is true for the wild-type strain. Through genome sequencing and expression studies, glycerol kinase was identified as the key enzyme for its improved glycerol utilization. The superior performance of v6C6 in assimilating pure glycerol was extended to crude glycerol (sweetwater) from an industrial fat splitting process. These results highlight the robustness of adaptive laboratory evolution for strain engineering and the versatility and potential of C. necator H16 for industrial waste glycerol valorization.

Phenotypic diversity in an emerging mycoplasmal disease

The avian pathogen Mycoplasma gallisepticum (MG) is a known pathogen of poultry, and newly emerged pathogen of house finches wherein it is associated with lethal conjunctivitis. Factors present in MG that are known to mediate virulence include cytadherence, sialidase activity, peroxide production, and biofilm formation. We have quantitatively assessed these factors for MG isolates from house finches from a temporal and geographic distribution across the continental United States that show differing capacity for virulence in vivo. Statistically significant (P < 0.05) differences were observed across strains for sialidase activity, cytadherence, and hydrogen peroxide production. Sialidase activity increased over time in geographically static populations, but did not correlate with time overall. All strains were able to bind α-2,6-linked sialic acid. No strains were found to bind α-2,3-linked sialic acid. All strains produced biofilms in vitro; however, no significant differences were observed in the density of biofilms across strains. Quantitative variance in virulence-associated traits is consistent with within-host evolutionary adaptation in response to a change in ecological niche by a parasitic pathogen.

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

Novel Candidates for Vaccine Development Against Mycoplasma Capricolum Subspecies Capripneumoniae (Mccp)-Current Knowledge and Future Prospects

Exploration of novel candidates for vaccine development against Mycoplasma capricolum subspecies capripneumoniae (Mccp), the causative agent of contagious caprine pleuropneumonia (CCPP), has recently gained immense importance due to both the increased number of outbreaks and the alarming risk of transboundary spread of disease. Treatment by antibiotics as the only therapeutic strategy is not a viable option due to pathogen persistence, economic issues, and concerns of antibiotic resistance. Therefore, prophylactics or vaccines are becoming important under the current scenario. For quite some time inactivated, killed, or attenuated vaccines proved to be beneficial and provided good immunity up to a year. However, their adverse effects and requirement for larger doses led to the need for production of large quantities of Mccp. This is challenging because the required culture medium is costly and Mycoplasma growth is fastidious and slow. Furthermore, quality control is always an issue with such vaccines. Currently, novel candidate antigens including capsular polysaccharides (CPS), proteins, enzymes, and genes are being evaluated for potential use as vaccines. These have shown potential immunogenicity with promising results in eliciting protective immune responses. Being easy to produce, specific, effective and free from side effects, these novel vaccine candidates can revolutionize vaccination against CCPP. Use of novel proteomic approaches, including sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE), two-dimensional gel electrophoresis, immunoblotting, matrix-assisted laser desorption/ionization-time-of-flight (MALDI-TOF) mass spectrometry, tandem mass spectroscopy, fast protein liquid chromatography (FPLC), bioinformatics, computerized simulation and genomic approaches, including multilocus sequence analysis, next-generation sequencing, basic local alignment search tool (BLAST), gene expression, and recombinant expression, will further enable recognition of ideal antigenic proteins and virulence genes with vaccination potential.

Evidence for the Cytoplasmic Localization of the L-α-Glycerophosphate Oxidase in Members of the "Mycoplasma mycoides Cluster"

Members of the "Mycoplasma mycoides cluster" are important animal pathogens causing diseases including contagious bovine pleuropneumonia and contagious caprine pleuropneumonia, which are of utmost importance in Africa or Asia. Even if all existing vaccines have shortcomings, vaccination of herds is still considered the best way to fight mycoplasma diseases, especially with the recent and dramatic increase of antimicrobial resistance observed in many mycoplasma species. A new generation of vaccines will benefit from a better understanding of the pathogenesis of mycoplasmas, which is very patchy up to now. In particular, surface-exposed virulence traits are likely to induce a protective immune response when formulated in a vaccine. The candidate virulence factor L-α-glycerophosphate oxidase (GlpO), shared by many mycoplasmas including Mycoplasma pneumoniae, was suggested to be a surface-exposed enzyme in Mycoplasma mycoides subsp. mycoides responsible for the production of hydrogen peroxide directly into the host cells. We produced a glpO isogenic mutant GM12::YCpMmyc1.1-ΔglpO using in-yeast synthetic genomics tools including the tandem-repeat endonuclease cleavage (TREC) technique followed by the back-transplantation of the engineered genome into a mycoplasma recipient cell. GlpO localization in the mutant and its parental strain was assessed using scanning electron microscopy (SEM). We obtained conflicting results and this led us to re-evaluate the localization of GlpO using a combination of in silico and in vitro techniques, such as Triton X-114 fractionation or tryptic shaving followed by immunoblotting. Our in vitro results unambiguously support the finding that GlpO is a cytoplasmic protein throughout the "Mycoplasma mycoides cluster." Thus, the use of GlpO as a candidate vaccine antigen is unlikely to induce a protective immune response.

Development of Molecular Methods for Rapid Differentiation of Mycoplasma gallisepticum Vaccine Strains from Field Isolates

Mycoplasma gallisepticum is among the most economically significant mycoplasmas causing production losses in poultry. Seven melt-curve and agarose gel-based mismatch amplification mutation assays (MAMAs) and one PCR are provided in the present study to distinguish the M. gallisepticum vaccine strains and field isolates based on mutations in the crmA, gapA, lpd, plpA, potC, glpK, and hlp2 genes. A total of 239 samples (M. gallisepticum vaccine and type strains, pure cultures, and clinical samples) originating from 16 countries and from at least eight avian species were submitted to the presented assays for validation or in blind tests. A comparison of the data from 126 samples (including sequences available at GenBank) examined by the developed assays and a recently developed multilocus sequence typing assay showed congruent typing results. The sensitivity of the melt-MAMA assays varied between 10¹ and 10⁴ M. gallisepticum template copies/reaction, while that of the agarose-MAMAs ranged from 10³ to 10⁵ template copies/reaction, and no cross-reactions occurred with other Mycoplasma species colonizing birds. The presented assays are also suitable for discriminating multiple strains in a single sample. The developed assays enable the differentiation of live vaccine strains by targeting two or three markers/vaccine strain; however, considering the high variability of the species, the combined use of all assays is recommended. The suggested combination provides a reliable tool for routine diagnostics due to the sensitivity and specificity of the assays, and they can be performed directly on clinical samples and in laboratories with basic PCR equipment.

Comparative proteomics of two Mycoplasma hyopneumoniae strains and Mycoplasma flocculare identified potential porcine enzootic pneumonia determinants

Mycoplasma hyopneumoniae and Mycoplasma flocculare are genetically similar bacteria, which coinhabit the porcine respiratory tract. These mycoplasmas share most of the known virulence factors, but, while M. hyopneumoniae causes porcine enzootic pneumonia (PEP), M. flocculare is a commensal species. To identify potential PEP determinants and provide novel insights on mycoplasma-host interactions, the whole cell proteomes of two M. hyopneumoniae strains, one pathogenic (7448) and other non-pathogenic (J), and M. flocculare were compared. A cell fractioning approach combined with mass spectrometry (LC-MS/MS) proteomics was used to analyze cytoplasmic and surface-enriched protein fractions. Average detection of ~ 50% of the predicted proteomes of M. hyopneumoniae 7448 and J, and M. flocculare was achieved. Many of the identified proteins were differentially represented in M. hyopneumoniae 7448 in comparison to M. hyopneumoniae J and M. flocculare, including potential PEP determinants, such as adhesins, proteases, and redox-balancing proteins, among others. The LC-MS/MS data also provided experimental validation for several genes previously regarded as hypothetical for all analyzed mycoplasmas, including some coding for proteins bearing virulence-related functional domains. The comprehensive proteome profiling of two M. hyopneumoniae strains and M. flocculare provided tens of novel candidates to PEP determinants or virulence factors, beyond those classically described.

Mycoplasma pneumoniae protects infected epithelial cells from hydrogen peroxide-induced cell detachment

Epithelial cell shedding is a defence mechanism against infectious microbes that use these cells as an infection foothold and that eliminate microbes from infection foci by removing infected cells. Mycoplasma pneumoniae, a causative agent of respiratory infections, is known to adhere to and colonise the surface of ciliated airway epithelial cells; it produces a large amount of hydrogen peroxide, indicating its capability of regulating hydrogen peroxide-induced infected cell detachment. In this study, we found that M. pneumoniae reduces exogenous hydrogen peroxide-induced detachment of the infected cells from culture plates. This cell detachment occurred dependently of DNA damage-initiated, poly (ADP-ribose) polymerase 1 (PARP1)-mediated cell death, or parthanatos. In cells infected with M. pneumoniae, exogenous hydrogen peroxide failed to induce DNA damage-initiated poly (ADP-ribose) (PAR) synthesis and concomitant increased cytoplasmic membrane rupture, both of which are biochemical hallmarks of parthanatos. The impairment of PAR synthesis was attributed to a reduction in the amount of cytosolic nicotinamide adenine dinucleotide (NAD), a substrate of PARP1, caused by M. pneumoniae. On the other hand, nonadherent mutant strains of M. pneumoniae showed a lower ability to reduce cell detachment than wild-type strains, but the extent to which NAD was decreased in infected cells was comparable to that seen in the wild-type strain. We found that NAD depletion could induce PARP1-independent cell detachment pathways following stimulation with hydrogen peroxide and that M. pneumoniae could also regulate PARP1-independent cell detachment in a cytoadhesion-dependent manner. These results suggest that M. pneumoniae might regulate infected cell detachment induced by hydrogen peroxide that it produces itself, and such a mechanism may contribute to sustaining the bacterial infection.

Reproduction of contagious caprine pleuropneumonia reveals the ability of convalescent sera to reduce hydrogen peroxide production in vitro

Contagious caprine pleuropneumonia (CCPP), caused by Mycoplasma capricolum subsp. capripneumoniae is a severe disease widespread in Africa and Asia. Limited knowledge is available on the pathogenesis of this organism, mainly due to the lack of a robust in vivo challenge model and the means to do site-directed mutagenesis. This work describes the establishment of a novel caprine challenge model for CCPP that resulted in 100% morbidity using a combination of repeated intranasal spray infection followed by a single transtracheal infection employing the recent Kenyan outbreak strain ILRI181. Diseased animals displayed CCPP-related pathology and the bacteria could subsequently be isolated from pleural exudates and lung tissues in concentrations of up to 10⁹ bacteria per mL as well as in the trachea using immunohistochemistry. Reannotation of the genome sequence of ILRI181 and F38^T revealed the existence of genes encoding the complete glycerol uptake and metabolic pathways involved in hydrogen peroxide (H₂O₂) production in the phylogenetically related pathogen M. mycoides subsp. mycoides. Furthermore, the expression of L-α-glycerophosphate oxidase (GlpO) in vivo was confirmed. In addition, the function of the glycerol metabolism was verified by measurement of production of H₂O₂ in medium containing physiological serum concentrations of glycerol. Peroxide production could be inhibited with serum from convalescent animals. These results will pave the way for a better understanding of host-pathogen interactions during CCPP and subsequent vaccine development.

Genome-Wide Analysis of Mycoplasma dispar Provides Insights into Putative Virulence Factors and Phylogenetic Relationships

Mycoplasma dispar is an important pathogen involved in bovine respiratory disease, which causes huge economic losses worldwide. Our knowledge regarding the genomics, pathogenic mechanisms, and genetics of M. dispar is rather limited. In this study, the complete genome of M. dispar GS01 strain was sequenced using PacBio SMRT technology and first genome-wide analyzed. M. dispar GS01 has a single circular chromosome of 1,065,810 bp encoding 825 predicted proteins. Twenty-three potential virulence genes and two pathogenicity islands were identified in M. dispar This pathogen was cytopathogenic, could form prolific biofilms, and could produce a large amount of H₂O₂ Methylation analysis revealed adenine and cytosine methylation across the genome and 13 distinct nucleotide motifs. Comparative analysis showed a high collinearity relationship between M. dispar GS01 and type strain ATCC 27140. Phylogenetic analysis demonstrated that M. dispar is genetically close to M. flocculare and M. hyopneumoniae The data presented in this study will aid further study on the pathogenic mechanisms and evolution of M. dispar.

Development of a replicating plasmid based on the native oriC in Mycoplasma pneumoniae

Bacteria of the genus Mycoplasma have recently attracted considerable interest as model organisms in synthetic and systems biology. In particular, Mycoplasma pneumoniae is one of the most intensively studied organisms in the field of systems biology. However, the genetic manipulation of these bacteria is often difficult due to the lack of efficient genetic systems and some intrinsic peculiarities such as an aberrant genetic code. One major disadvantage in working with M. pneumoniae is the lack of replicating plasmids that can be used for the complementation of mutants and the expression of proteins. In this study, we have analysed the genomic region around the gene encoding the replication initiation protein, DnaA, and detected putative binding sites for DnaA (DnaA boxes) that are, however, less conserved than in other bacteria. The construction of several plasmids encompassing this region allowed the selection of plasmid pGP2756 that is stably inherited and that can be used for genetic experiments, as shown by the complementation assays with the glpQ gene encoding the glycerophosphoryl diester phosphodiesterase. Plasmid-borne complementation of the glpQ mutant restored the formation of hydrogen peroxide when bacteria were cultivated in the presence of glycerol phosphocholine. Interestingly, the replicating plasmid can also be used in the close relative, Mycoplasma genitalium but not in more distantly related members of the genus Mycoplasma. Thus, plasmid pGP2756 is a valuable tool for the genetic analysis of M. pneumoniae and M. genitalium.

Convergent Evolution among Ruminant-Pathogenic Mycoplasma Involved Extensive Gene Content Changes

Convergent evolution, a process by which organisms evolved independently to have similar traits, provides opportunities to understand adaptation. The bacterial genus Mycoplasma contains multiple species that evolved independently to become ruminant pathogens, which represents an interesting study system for investigating the process. In this work, we determined the genome sequences of 11 Entomoplasma/Mesoplasma species. This new data set, together with the other available Mollicutes genomes, provided comprehensive taxon sampling for inferring the gene content evolution that led to the emergence of Mycoplasma Mycoides cluster. Our results indicated that the most recent common ancestor (MRCA) of the Mycoides-Entomoplasmataceae clade lost ∼15% of the core genes when it diverged from the Spiroplasma Apis clade. After this initial wave of genome reduction, relatively few gene gains or losses were inferred until the emergence of the Mycoides cluster. Compared with those Entomoplasmataceae lineages that maintained the association with insects, the MRCA of the Mycoides cluster experienced a second wave of gene losses, as well as acquiring >100 novel genes through horizontal gene transfer. These gene acquisitions involved many with the Mycoplasma Hominis/Pneumoniae lineages as the putative donors, suggesting that gene exchanges among these vertebrate symbionts with distinct phylogenetic affiliations may be important in the emergence of the Mycoides cluster. These findings demonstrated that the gene content of bacterial genomes could be exceedingly dynamic, even for those symbionts with highly reduced genomes. Moreover, the emergence of novel pathogens may involve extensive remodeling of gene content, rather than acquisition of few virulence genes.

Horizontal Acquisition and Transcriptional Integration of Novel Genes in Mosquito-Associated Spiroplasma

Genetic differentiation among symbiotic bacteria is important in shaping biodiversity. The genus Spiroplasma contains species occupying diverse niches and is a model system for symbiont evolution. Previous studies have established that two mosquito-associated species have diverged extensively in their carbohydrate metabolism genes despite having a close phylogenetic relationship. Notably, although the commensal Spiroplasma diminutum lacks identifiable pathogenicity factors, the pathogenic Spiroplasma taiwanense was found to have acquired a virulence factor glpO and its associated genes through horizontal transfer. However, it is unclear if these acquired genes have been integrated into the regulatory network. In this study, we inferred the gene content evolution in these bacteria, as well as examined their transcriptomes in response to glucose availability. The results indicated that both species have many more gene acquisitions from the Mycoides-Entomoplasmataceae clade, which contains several important pathogens of ruminants, than previously thought. Moreover, several acquired genes have higher expression levels than the vertically inherited homologs, indicating possible functional replacement. Finally, the virulence factor and its functionally linked genes in S. taiwanense were up-regulated in response to glucose starvation, suggesting that these acquired genes are under expression regulation and the pathogenicity may be a stress response. In summary, although differential gene losses are a major process for symbiont divergence, gene gains are critical in counteracting genome degradation and driving diversification among facultative symbionts.

Genome-Wide Analysis of Mycoplasma bovirhinis GS01 Reveals Potential Virulence Factors and Phylogenetic Relationships

Mycoplasma bovirhinis is a significant etiology in bovine pneumonia and mastitis, but our knowledge about the genetic and pathogenic mechanisms of M. bovirhinis is very limited. In this study, we sequenced the complete genome of M. bovirhinis strain GS01 isolated from the nasal swab of pneumonic calves in Gansu, China, and we found that its genome forms a 847,985 bp single circular chromosome with a GC content of 27.57% and with 707 protein-coding genes. The putative virulence determinants of M. bovirhinis were then analyzed. Results showed that three genomic islands and 16 putative virulence genes, including one adhesion gene enolase, seven surface lipoproteins, proteins involved in glycerol metabolism, and cation transporters, might be potential virulence factors. Glycerol and pyruvate metabolic pathways were defective. Comparative analysis revealed remarkable genome variations between GS01 and a recently reported HAZ141_2 strain, and extremely low homology with others mycoplasma species. Phylogenetic analysis demonstrated that M. bovirhinis was most genetically close to M. canis, distant from other bovine Mycoplasma species. Genomic dissection may provide useful information on the pathogenic mechanisms and genetics of M. bovirhinis.

Hydrogen peroxide production and myo-inositol metabolism as important traits for virulence of Mycoplasma hyopneumoniae

Mycoplasma hyopneumoniae is the causative agent of enzootic pneumonia. In our previous work, we reconstructed the metabolic models of this species along with two other mycoplasmas from the respiratory tract of swine: Mycoplasma hyorhinis, considered less pathogenic but which nonetheless causes disease and Mycoplasma flocculare, a commensal bacterium. We identified metabolic differences that partially explained their different levels of pathogenicity. One important trait was the production of hydrogen peroxide from the glycerol metabolism only in the pathogenic species. Another important feature was a pathway for the metabolism of myo-inositol in M. hyopneumoniae. Here, we tested these traits to understand their relation to the different levels of pathogenicity, comparing not only the species but also pathogenic and attenuated strains of M. hyopneumoniae. Regarding the myo-inositol metabolism, we show that only M. hyopneumoniae assimilated this carbohydrate and remained viable when myo-inositol was the primary energy source. Strikingly, only the two pathogenic strains of M. hyopneumoniae produced hydrogen peroxide in complex medium. We also show that this production was dependent on the presence of glycerol. Although further functional tests are needed, we present in this work two interesting metabolic traits of M. hyopneumoniae that might be directly related to its enhanced virulence.

Glycerol metabolism and its implication in virulence in Mycoplasma

Glycerol and glycerol-containing compounds such as lipids belong to the most abundant organic compounds that may serve as nutrient for many bacteria. For the cell wall-less bacteria of the genus Mycoplasma, glycerol derived from phospholipids of their human or animal hosts is the major source of carbon and energy. The lipids are first degraded by lipases, and the resulting glycerophosphodiesters are transported into the cell and cleaved to release glycerol-3-phosphate. Alternatively, free glycerol can be transported, and then become phosphorylated. The oxidation of glycerol-3-phosphate in Mycoplasma spp. as well as in related firmicutes involves a hydrogen peroxide-generating glycerol-3-phosphate oxidase. This enzyme is a key player in the virulence of Mycoplasma spp. as the produced hydrogen peroxide is one of the major virulence factors of these bacteria. In this review, the different components involved in the utilization of lipids and glycerol in Mycoplasma pneumoniae and related bacteria are discussed.

Response induced in Mycoplasma gallisepticum under heat shock might be relevant to infection process

Despite the fact the term "proteome" was proposed to characterize a set of proteins in one of mycoplasma species, proteome response to various exposures in this bacteria are still obscure. Commonly, authors studying proteomic response on perturbation models in mycoplasmas use single approach and do not confirm their findings by alternative methods. Consequently, the results of proteomic analysis should be validated by complementary techniques. In this study we utilized three complementary approaches (SWATH, MRM, 2D-DIGE) to assess response of Mycoplasma gallisepticum under heat stress on proteomic level and combined these findings with metabolic response and the results of transcriptional profiling. We divide response into two modes - one is directly related to heat stress and other is triggered during heat stress, but not directly relevant to it. The latter includes accumulation of ATP and shedding of antigens. Both of these phenomena may be relevant to evasion of host's immune system and dissemination during mycoplasmosis in vivo.

Genome-Wide Analysis of the First Sequenced Mycoplasma capricolum subsp. capripneumoniae Strain M1601

Mycoplasma capricolum subsp. capripneumoniae (Mccp) is a common pathogen of goats that causes contagious caprine pleuropneumonia. We closed the gap and corrected rRNA operons in the draft genome of Mccp M1601: a strain isolated from an infected goat in a farm in Gansu, China. The genome size of M1601 is 1,016,707 bp with a GC content of 23.67%. We identified 915 genes (occupying 90.27% of the genome), of which 713 are protein-coding genes (excluding 163 pseudogenes). No genomic islands and complete insertion sequences were found in the genome. Putative determinants associated with the organism’s virulence were analyzed, and 26 genes (including one adhesion protein gene, two capsule synthesis gene clusters, two lipoproteins, hemolysin A, ClpB, and proteins involved in pyruvate metabolism and cation transport) were potential virulence factors. In addition, two transporter systems (ATP-binding cassette [ABC] transporters and phosphotransferase) and two secretion systems (Sec and signal recognition particle [SRP] pathways) were observed in the Mccp genome. Genome synteny analysis reveals a good collinear relationship between M1601 and Mccp type strain F38. Phylogenetic analysis based on 11 single-copy core genes of 31 Mycoplasma strains revealed good collinearity between M1601 and Mycoplasma capricolum subsp. capricolum (Mcc) and close relationship among Mycoplasma mycoides cluster strains. Our genome-wide analysis of Mccp M1601 provides helpful information on the pathogenic mechanisms and genetics of Mccp.

Update on Mycoplasma hyopneumoniae infections in pigs: Knowledge gaps for improved disease control

Mycoplasma hyopneumoniae (M. hyopneumoniae) is the primary pathogen of enzootic pneumonia, a chronic respiratory disease in pigs. Infections occur worldwide and cause major economic losses to the pig industry. The present paper reviews the current knowledge on M. hyopneumoniae infections, with emphasis on identification and analysis of knowledge gaps for optimizing control of the disease. Close contact between infected and susceptible pigs is the main route of M. hyopneumoniae transmission. Management and housing conditions predisposing for infection or disease are known, but further research is needed to better understand M. hyopneumoniae transmission patterns in modern pig production systems, and to assess the importance of the breeding population for downstream disease control. The organism is primarily found on the mucosal surface of the trachea, bronchi and bronchioles. Different adhesins and lipoproteins are involved in the adherence process. However, a clear picture of the virulence and pathogenicity of M. hyopneumoniae is still missing. The role of glycerol metabolism, myoinositol metabolism and the Mycoplasma Ig binding protein-Mycoplasma Ig protease system should be further investigated for their contribution to virulence. The destruction of the mucociliary apparatus, together with modulating the immune response, enhances the susceptibility of infected pigs to secondary pathogens. Clinical signs and severity of lesions depend on different factors, such as management, environmental conditions and likely also M. hyopneumoniae strain. The potential impact of strain variability on disease severity is not well defined. Diagnostics could be improved by developing tests that may detect virulent strains, by improving sampling in live animals and by designing ELISAs allowing discrimination between infected and vaccinated pigs. The currently available vaccines are often cost-efficient, but the ongoing research on developing new vaccines that confer protective immunity and reduce transmission should be continued, as well as optimization of protocols to eliminate M. hyopneumoniae from pig herds.

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.