α-Enolase, an adhesion-related factor of Mycoplasma bovis

Integrated Information for Pathogenicity and Treatment of Spiroplasma

Spiroplasma, belonging to the class Mollicutes, is a small, helical, motile bacterium lacking a cell wall. Its host range includes insects, plants, and aquatic crustaceans. Recently, a few human cases of Spiroplasma infection have been reported. The diseases caused by Spiroplasma have brought about serious economic losses and hindered the healthy development of agriculture. The pathogenesis of Spiroplasma involves the ability to adhere, such as through the terminal structure of Spiroplasma, colonization, and invasive enzymes. However, the exact pathogenic mechanism of Spiroplasma remains a mystery. Therefore, we systematically summarize all the information about Spiroplasma in this review article. This provides a reference for future studies on virulence factors and treatment strategies of Spiroplasma.

LppA is a novel plasminogen receptor of Mycoplasma bovis that contributes to adhesion by binding the host extracellular matrix and Annexin A2

Mycoplasma bovis is responsible for various inflammatory diseases in cattle. The prevention and control of M. bovis are complicated by the absence of effective vaccines and the emergence of multidrug-resistant strains, resulting in substantial economic losses worldwide in the cattle industry. Lipoproteins, vital components of the Mycoplasmas cell membrane, are deemed potent antigens for eliciting immune responses in the host upon infection. However, the functions of lipoproteins in M. bovis remain underexplored due to their low sequence similarity with those of other bacteria and the scarcity of genetic manipulation tools for M. bovis. In this study, the lipoprotein LppA was identified in all examined M. bovis strains. Utilizing immunoelectron microscopy and Western blotting, it was observed that LppA localizes to the surface membrane. Recombinant LppA demonstrated dose-dependent adherence to the membrane of embryonic bovine lung (EBL) cells, and this adhesion was inhibited by anti-LppA serum. In vitro binding assays confirmed LppA's ability to associate with fibronectin, collagen IV, laminin, vitronectin, plasminogen, and tPA, thereby facilitating the conversion of plasminogen to plasmin. Moreover, LppA was found to bind and enhance the accumulation of Annexin A2 (ANXA2) on the cell membrane. Disrupting LppA in M. bovis significantly diminished the bacterium's capacity to adhere to EBL cells, underscoring LppA's function as a bacterial adhesin. In conclusion, LppA emerges as a novel adhesion protein that interacts with multiple host extracellular matrix proteins and ANXA2, playing a crucial role in M. bovis's adherence to host cells and dissemination. These insights substantially deepen our comprehension of the molecular pathogenesis of M. bovis.

A genome-wide transposon mutagenesis screening identifies LppB as a key factor associated with Mycoplasma bovis colonization and invasion into host cells

Mycoplasma spp., the smallest self-replicating and genome-reduced organisms, have raised a great concern in both the medical and veterinary fields due to their pathogenicity. The molecular determinants of these wall-less bacterium efficiently use their limited genes to ensure successful infection of the host remain unclear. In the present study, we used the ruminant pathogen Mycoplasma bovis as a model to identify the key factors for colonization and invasion into host cells. We constructed a nonredundant fluorescent transposon mutant library of M. bovis using a modified transposon plasmid, and identified 34 novel adhesion-related genes based on a high-throughput screening approach. Among them, the ΔLppB mutant exhibited the most apparent decrease in adhesion to embryonic bovine lung (EBL) cells. The surface-localized lipoprotein LppB, which is highly conserved in Mycoplasma species, was then confirmed as a key factor for M. bovis adhesion with great immunogenicity. LppB interacted with various components (fibronectin, vitronectin, collagen IV, and laminin) of host extracellular matrix (ECM) and promoted plasminogen activation through tPA to degrade ECM. The 439-502 amino acid region of LppB is a critical domain, and F465 and Y493 are important residues for the plasminogen activation activity. We further revealed LppB as a key factor facilitating internalization through clathrin- and lipid raft-mediated endocytosis, which helps the Mycoplasma invade the host cells. Our study indicates that LppB plays a key role in Mycoplasma infection and is a potential new therapeutic and vaccine target for Mycoplasma species.

NADH oxidase of Mycoplasma synoviae is a potential diagnostic antigen, plasminogen/fibronectin binding protein and a putative adhesin

BACKGROUND

Mycoplasma synoviae (MS) is an important pathogen causing respiratory diseases and arthritis in chickens and turkeys, thus, resulting in serious economic losses to the poultry industry. Membrane-associated proteins are thought to play important roles in cytoadherence and pathogenesis. NADH oxidase (NOX) is an oxidoreductase involved in glycolysis, which is thought to be a multifunctional protein and potential virulence factor in some pathogens. However, little is known regarding the NOX of MS (MSNOX). We previously demonstrated that MSNOX was a metabolic enzyme distributed in not only the cytoplasm but also the MS membrane. This study was aimed at exploring NOX's potential as a diagnostic antigen and its role in MS cytoadherence.

RESULTS

Western blots and ELISAs indicated that recombinant MSNOX (rMSNOX) protein reacted with sera positive for various MS isolates, but not MG isolates or other avian pathogens, thus, suggesting that rMSNOX is a potential diagnostic antigen. In addition, rabbit anti-rMSNOX serum showed substantial complement-dependent mycoplasmacidal activity toward various MS isolates and MG R_low. MSNOX protein was found not only in the cytoplasm but also on the membrane of MS through suspension immunofluorescence and immunogold electron microscopy assays. Indirect immunofluorescence assays indicated that rMSNOX adhered to DF-1 cells, and this adherence was inhibited by rabbit anti-rMSNOX, but not anti-MG serum. Furthermore, indirect immunofluorescence and colony counting assays confirmed that the rabbit anti-rMSNOX serum inhibited the adherence of various MS isolates but not MG R_low to DF-1 cells. Moreover, plasminogen (Plg)- and fibronectin (Fn)-binding assays demonstrated that rMSNOX bound Plg and Fn in a dose-dependent manner, thereby further confirming that MSNOX may be a putative adhesin.

CONCLUSION

MSNOX was identified to be a surface immunogenic protein that has good immunoreactivity and specificity in Western blot and ELISA, and therefore, may be used as a potential diagnostic antigen in the future. In addition, rMSNOX adhered to DF-1 cells, an effect inhibited by rabbit anti-rMSNOX, but not anti-MG serum, and anti-rMSNOX serum inhibited the adherence of various MS isolates, but not MG R_low, to DF-1 cells, thus indicating that the inhibition of adherence by anti-MSNOX serum was MS specific. Moreover, rMSNOX adhered to extracellular matrix proteins including Plg and Fn, thus suggesting that NOX may play important roles in MS cytoadherence and pathogenesis. Besides, rabbit anti-rMSNOX serum presented complement-dependent mycoplasmacidal activity toward both MS and MG, indicating the MSNOX may be further studied as a potential protective vaccine candidate.

Mycoplasma pneumoniae downregulates RECK to promote matrix metalloproteinase-9 secretion by bronchial epithelial cells

Airway epithelial cells function as both a physical barrier against harmful substances and pathogenic microorganisms and as an important participant in the innate immune system. Matrix metalloproteinase-9 (MMP-9) plays a crucial role in modulating inflammatory responses during respiratory infections. However, the signalling cascade that induces MMP-9 secretion from epithelial cells infected with Mycoplasma pneumoniae remains poorly understood. In this study, we investigated the mechanism of MMP-9 secretion in airway epithelial cells infected with M. pneumoniae. Our data clearly showed that M. pneumoniae induced the secretion of MMP-9 from bronchial epithelial cells and upregulated its enzymatic activity in a time- and dose-dependent manner. Using specific inhibitors and chromatin co-precipitation experiments, we confirmed that the expression of MMP-9 is reliant on the activation of the Toll-like receptor 2 (TLR2) and TLR6-dependent mitogen-activated protein kinase/nuclear factor- κB/activator protein-1 (MAPK/NF-κB/AP-1) pathways. Additionally, epigenetic modifications such as histone acetylation and the nuclear transcription factor Sp1 also regulate MMP-9 expression. M. pneumoniae infection also decreased the expression of the tumour suppressor reversion-inducing cysteine-rich protein with Kazal motifs (RECK) by inducing Sp1 phosphorylation. Overexpression of RECK significantly impaired the M. pneumoniae-triggered increase in MMP-9 enzymatic activity, although the level of MMP-9 protein remained constant. The study demonstrated that M. pneumoniae-triggered MMP-9 expression is modulated by TLR2 and 6, the MAPK/NF-κB/AP-1 signalling cascade, and histone acetylation, and M. pneumoniae downregulated the expression of RECK, thereby increasing MMP-9 activity to modulate the inflammatory response, which could play a role in airway remodelling.

Mycoplasma Bovis adhesins and their target proteins

Bovine mycoplasmosis is an important infectious disease of cattle caused by Mycoplasma bovis (M. bovis) which poses a serious threat to the breeding industry. Adhesin is involved in the initial process of M. bovis colonization, which is closely related to the infection, cell invasion, immune escape and virulence of this pathogenic microorganism. For the reason that M. bovis lacks a cell wall, its adhesin is predominantly located on the surface of the cell membrane. The adhesins of M. bovis are usually identified by adhesion and adhesion inhibition analysis, and more than 10 adhesins have been identified so far. These adhesins primarily bind to plasminogen, fibronectin, heparin and amyloid precursor-like protein-2 of host cells. This review aims to concisely summarize the current knowledge regarding the adhesins of M. bovis and their target proteins of the host cell. Additionally, the biological characteristics of the adhesin will be briefly analyzed.

Annexin A2 regulates Mycoplasma bovis adhesion and invasion to embryo bovine lung cells affecting molecular expression essential to inflammatory response

Mycoplasma bovis (M. bovis) is an important pathogen of the bovine respiratory disease complex, invading lower respiratory tracts and causing severe pneumonia. However, its molecular mechanism largely remains unknown. Host annexin A2 (ANXA2) is a calcium-dependent phospholipid-binding protein. The current study sought to determine whether ANXA2 could mediate M. bovis adhesion and invasion thereby affecting its induction of inflammatory response. ANXA2 expression was upregulated in M. bovis-infected bovine lung epithelial cells (EBL), and blocking ANXA2 with an anti-ANXA2 antibody reduced M. bovis adhesion to EBL. Compared with uninfected cells, more ANXA2 was translocated from the cytoplasm to the cell surface after M. bovis infection. Furthermore, RNA interference knockdown of ANXA2 expression in EBL cells resulted in a significant decrease in M. bovis invasion and F-actin polymerization. Next, the transcriptomic study of M. bovis-infected EBL cells with and without ANXA2 knockdown were performed. The data exhibited that ANXA2 knockdown EBL cells had 2487 differentially expressed genes (DEGs), with 1175 upregulated and 1312 downregulated compared to control. According to GO and KEGG analyses, 50 genes potentially linked to inflammatory responses, 23 involved in extracellular matrix (ECM) receptor interaction, and 48 associated with PI3K-AKT signal pathways were upregulated, while 38 mRNA binding genes, 16 mRNA 3′-UTR binding genes, and 34 RNA transport genes were downregulated. Furthermore, 19 genes with various change-folds were selected for qPCR verification, and the results agreed with the RNA-seq findings. Above all, the transcription of two chemokines (IL-8 and CXCL5) and a key bovine β-defensin TAP in IL-17 signaling pathway were significantly increased in ANXA2 knockdown cells. Moreover, ANXA2 knockdown or knockout could increase NF-κB and MAPK phosphorylation activity in response to M. bovis infection. Additionally, ANXA2 knockdown also significantly decreased the CD44 transcripts via exon V3 and V7 skipping after M. bovis infection. We concluded that M. bovis borrowed host ANXA2 to mediate its adhesion and invasion thereby negatively regulating molecular expression essential to IL-17 signal pathway. Furthermore, CD44 V3 and V7 isoforms might contribute to this ANXA2 meditated processes in M. bovis infected EBL cells. These findings revealed a new understanding of pathogenesis for M. bovis infection.

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.

A multifunctional enolase mediates cytoadhesion and interaction with host plasminogen and fibronectin in Mycoplasma hyorhinis

Mycoplasma hyorhinis may cause systemic inflammation of pigs, typically polyserositis and arthritis, and is also associated with several types of human cancer. However, the pathogenesis of M. hyorhinis colonizing and breaching the respiratory barrier to establish systemic infection is poorly understood. Glycolytic enzymes are important moonlighting proteins and virulence-related factors in various bacteria. In this study, we investigated the functions of a glycolytic critical enzyme, enolase in the infection and systemic spread of M. hyorhinis. Bacterial surface localization of enolase was confirmed by flow cytometry and colony hybridization assay. Recombinant M. hyorhinis enolase (rEno) was found to adhere to pig kidney (PK-15) cells, and anti-rEno serum significantly decreased adherence. The enzyme was also found to bind host plasminogen and fibronectin, and interactions were specific and strong, with dissociation constant (K_D) values of 1.4 nM and 14.3 nM, respectively, from surface plasmon resonance analysis. Activation of rEno-bound plasminogen was confirmed by its ability to hydrolyze plasmin-specific substrates and to degrade a reconstituted extracellular matrix. To explore key sites during these interactions, C-terminal lysine residues of enolase were replaced with leucine, and the resulting single-site and double-site mutants show significantly reduced interaction with plasminogen in far-Western blotting and surface plasmon resonance tests. The binding affinities of all mutants to fibronectin were reduced as well. Collectively, these results imply that enolase moonlights as an important adhesin of M. hyorhinis, and interacts with plasminogen and fibronectin. The two lysine residues in the C-terminus are important binding sites for its multiple binding activities.

Evidence for the Rapid and Divergent Evolution of Mycoplasmas: Structural and Phylogenetic Analysis of Enolases

Mycoplasmas are a group of prokaryotes without cell walls that have evolved through several rounds of degenerative evolution. With a low cell DNA G + C content and definitively long genetic lineages, mycoplasmas are thought to be in a state of rapid evolution. However, little associated evidence has been provided. Enolase is a key enzyme in glycolysis that is widely found in all species from the three domains, and it is evolutionarily conserved. In our previous studies, enolase acted as a virulence factor and participated in cell-surface adhesion in Mycoplasma hyopneumoniae. Furthermore, unique loop regions were first found in the crystal structure of Mhp Eno. Here, enolase structures from Mycoplasma pneumoniae and Mycoplasma bovis were determined. An extra helix 7 is specific and conservatively found in almost all mycoplasma enolases, as confirmed by crystal structures and sequence alignment. Particular motifs for helix 7, which is composed of F-K/G-K-L/F-K-X-A-I, have been proposed and could be regarded as molecular markers. To our surprise, the genetic distances between any two mycoplasma enolases were obviously longer than those between the two corresponding species themselves, indicating divergent evolution of mycoplasma enolases, whereas no horizontal gene transfer was detected in mycoplasma enolase genens. Furthermore, different evolutionary patterns were adopted by different loop regions of mycoplasma enolase. Enolases from different Mycoplasma species also showed different affinities for PLG and fibronectin. Our results indicate the rapid and divergent evolution of mycoplasma enolase and mycoplasmas. This study will also aid understanding the independent evolution of Mycoplasma species after separation from their common ancestor.

The presence of adhesion factors NOX, α-enolase, TrmFO, P27, and VpmaX in Mycoplasma bovis wild isolates in Japan

Background

Mycoplasma bovis causes various diseases such as bronchopneumonia, otitis media, arthritis, and mastitis in cattle. Mycoplasma bovis is often isolated from the deep pharynges of healthy cattle and is generally considered not to cause clinical symptoms while in the upper respiratory tract. In mycoplasma infections, adhesion to the host cells is a crucial step. In recent years, five new adhesins, NOX, α-enolase, TrmFO, P27, and VpmaX, have been reported in M. bovis strains from pneumonia cases. However, the presence of these adhesins in wild isolates has not been established.

Aim

This study aimed to investigate the presence of these adhesin genes in wild isolates isolated from cattle nasal cavities and lesion sites (pneumonia, otitis media, arthritis, and mastitis) in various regions in Japan and clarify the relationship between adhesion and the symptoms caused by M. bovis infection.

Methods

A total of 141 M. bovis wild isolates isolated from nasal cavities (healthy or sick cattle), lungs with pneumonia, ears with otitis media, joint fluids of arthritic animals, and milk of mastitic animals. Mycoplasma bovis type strain PG45 was also used. Specific polymerase chain reaction reactions were performed to detect nox, α-enolase, trmFO, P27, and vpmaX, which are adhesins of M. bovis.

Results

This study reports 139 M. bovis wild isolates were positive for nox, α-enolase, trmFO, P27, and vpmaX, while two isolates each lacked α-enolase or P27 genes. Mycoplasma bovis PG45 also had all five adherens genes.

Conclusion

Almost all M. bovis wild isolates possessed all nox, α-enolase, trmFO, P27, and vpmaX genes regardless of the lesion site or region of origin. This means no relationship was found between the presence of the five adhesins and lesion sites in M. bovis and M. bovis isolated from the nasal cavities of asymptomatic cattle have the same numbers and types of adhesins as isolates from symptomatic lesion sites (pneumonia, otitis media, arthritis, and mastitis). This suggests that not only M. bovis isolates from pulmonary lesions, but also M. bovis existing in the nasal cavity has the potential to causes symptoms in the host.

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.

Immune Evasion of Mycoplasma bovis

Mycoplasma bovis (M. bovis) causes various chronic inflammatory diseases, including mastitis and bronchopneumonia, in dairy and feed cattle. It has been found to suppress the host immune response during infection, leading to the development of chronic conditions. Both in vitro and in vivo studies have confirmed that M. bovis can induce proinflammatory cytokines and chemokines in the host. This consists of an inflammatory response in the host that causes pathological immune damage, which is essential for the pathogenic mechanism of M. bovis. Additionally, M. bovis can escape host immune system elimination and, thus, cause chronic infection. This is accomplished by preventing phagocytosis and inhibiting key responses, including the neutrophil respiratory burst and the development of nitric oxide (NO) and inducible nitric oxide synthase (iNOS) that lead to the creation of an extracellular bactericidal network, in addition to inhibiting monocyte and alveolar macrophage apoptosis and inducing monocytes to produce anti-inflammatory factors, thus inducing the apoptosis of peripheral blood mononuclear cells (PBMCs), inhibiting their proliferative response and resulting in their invasion. Together, these conditions lead to long-term M. bovis infection. In terms of the pathogenic mechanism, M. bovis may invade specific T-cell subsets and induce host generation of exhausted T-cells, which helps it to escape immune clearance. Moreover, the M. bovis antigen exhibits high-frequency variation in size and expression period, which allows it to avoid activation of the host humoral immune response. This review includes some recent advances in studying the immune response to M. bovis. These may help to further understand the host immune response against M. bovis and to develop potential therapeutic approaches to control M. bovis infection.

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

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

Mycoplasma bovis mbfN Encodes a Novel LRR Lipoprotein That Undergoes Proteolytic Processing and Binds Host Extracellular Matrix Components

Mycoplasma bovis causes serious infections in ruminants, leading to huge economic losses. Lipoproteins are key components of the mycoplasma membrane and are believed to function in nutrient acquisition, adherence, enzymatic interactions with the host, and induction of the host's immune response to infection. Many genes of M. bovis have not been assigned functions, in part because of their low sequence similarity with other bacteria, making it difficult to extrapolate gene functions. This study examined functions of a surface-localized leucine-rich repeat (LRR) lipoprotein encoded by mbfN of M. bovis PG45. Homologs of MbfN were detected as 48-kDa peptides by Western blotting in all the strains of M. bovis included in this study, with the predicted 70-kDa full-length polypeptide detected in some strains. Sequence analysis of the gene revealed the absence in some strains of a region encoding the carboxyl-terminal 147 amino acids found in strain PG45, which could account for the variation detected by immunoblotting. In silico analysis of MbfN suggested that it may have an adhesion-related function. In vitro binding assays confirmed MbfN to be a fibronectin and heparin-binding protein. Disruption of mbfN in M. bovis PG45 significantly reduced (P = 0.033) the adherence of M. bovis PG45 to MDBK cells in vitro, demonstrating the role of MbfN as an adhesin.IMPORTANCE Experimental validation of the putative functions of genes in M. bovis will advance our understanding of the basic biology of this economically important pathogen and is crucial in developing prevention strategies. This study demonstrated the extracellular matrix binding ability of a novel immunogenic lipoprotein of M. bovis, and the role of this protein in adhesion by M. bovis suggests that it could play a role in virulence.

Mycoplasma hyorhinis as a possible cause of fibrinopurulent meningitis in pigs? - a case series

Background

Mycoplasma hyorhinis is an invader of the upper respiratory tract in swine that is considered to have ubiquitous distribution. It is mainly known for causing polyserositis and polyarthritis in weaned piglets, even though the mechanisms of systemic spread are not fully understood. Mycoplasma hyorhinis has also been associated with other diseases in pigs such as pneumonia or otitis media, but so far has not been known to cause central nervous disorders. This case series reports the isolation of Mycoplasma hyorhinis from cerebrospinal fluid and/ or meningeal swabs from piglets originating from four different piglet producing farms in Austria.

Case presentation

On farm 1, coughing, stiff movement and central nervous signs occurred in nursery piglets. Mycoplasma hyorhinis was the only pathogen isolated from meningeal swabs from two piglets showing central nervous signs. Fibrinopurulent leptomeningitis was only observed in one piglet. Only one of two nursery piglets from farm 2 showed mild central nervous signs but no histologic lesions; Mycoplasma hyorhinis was isolated from cerebrospinal fluid of the piglet with neurologic signs. Mycoplasma hyorhinis was isolated from cerebrospinal fluid of all three investigated piglets from farm 3, all of which showed central nervous signs and purulent leptomeningitis. Further, Streptococcus suis was isolated from the cerebrospinal fluid of one piglet. Fibrinopurulent leptomeningitis was detected in two piglets from farm 4 that had died overnight without showing any clinical signs and Mycoplasma hyorhinis was isolated from meningeal swabs from both piglets.

Conclusion

While causality has yet to be proven by experimental infection and in situ detection of the pathogen in histologic sections, the findings of this study and the absence of other pathogens suggest Mycoplasma hyorhinis as a potential causative agent of meningitis in swine.

Population Genomic Analysis of Mycoplasma bovis Elucidates Geographical Variations and Genes associated with Host-Types

Among more than twenty species belonging to the class Mollecutes, Mycoplasma bovis is the most common cause of bovine mycoplasmosis in North America and Europe. Bovine mycoplasmosis causes significant economic loss in the cattle industry. The number of M. bovis positive herds recently has increased in North America and Europe. Since antibiotic treatment is ineffective and no efficient vaccine is available, M. bovis induced mycoplasmosis is primarily controlled by herd management measures such as the restriction of moving infected animals out of the herds and culling of infected or shedders of M. bovis. To better understand the population structure and genomic factors that may contribute to its transmission, we sequenced 147 M. bovis strains isolated from four different countries viz. USA (n = 121), Canada (n = 22), Israel (n = 3) and Lithuania (n = 1). All except two of the isolates (KRB1 and KRB8) were isolated from two host types i.e., bovine (n = 75) and bison (n = 70). We performed a large-scale comparative analysis of M. bovis genomes by integrating 103 publicly available genomes and our dataset (250 total genomes). Whole genome single nucleotide polymorphism (SNP) based phylogeny using M.agalactiae as an outgroup revealed that M. bovis population structure is composed of five different clades. USA isolates showed a high degree of genomic divergence in comparison to the Australian isolates. Based on host of origin, all the isolates in clade IV was of bovine origin, whereas majority of the isolates in clades III and V was of bison origin. Our comparative genome analysis also revealed that M. bovis has an open pangenome with a large breadth of unexplored diversity of genes. The function based analysis of autogenous vaccine candidates (n = 10) included in this study revealed that their functional diversity does not span the genomic diversity observed in all five clades identified in this study. Our study also found that M. bovis genome harbors a large number of IS elements and their number increases significantly (p = 7.8 × 10⁻⁶) as the genome size increases. Collectively, the genome data and the whole genome-based population analysis in this study may help to develop better understanding of M. bovis induced mycoplasmosis in cattle.

Persistence in Livestock Mycoplasmas—a Key Role in Infection and Pathogenesis

Purpose of Review

Mycoplasma, economically important pathogens in livestock, often establishes immunologically complex persistent infections that drive their pathogenesis and complicate prophylaxis and therapy of the caused diseases. In this review, we summarize some of the recent findings concerning cellular and molecular persistence mechanisms related to the pathogenesis of mycoplasma infections in livestock.

Recent Findings

Data from recent studies prove several mechanisms including intracellular lifestyle, immune dysregulation, and autoimmunity as well as microcolony and biofilm formation and apoptosis of different host cell types as important persistence mechanisms in several clinically significant Mycoplasma species, i.e., M. bovis, M. gallisepticum, M. hyopneumoniae, and M. suis.

Summary

Evasion of the immune system and the establishment of persistent infections are key features in the pathogenesis of livestock mycoplasmas. In-depth knowledge of the underlying mechanisms will provide the basis for the development of therapy and prophylaxis strategies against mycoplasma infections.

Pathogenesis and Virulence of Mycoplasma bovis

Mycoplasma bovis is an important component of the bovine respiratory disease complex and recent reports identified that other species are also affected by M bovis. Control of the disease caused by M bovis has been unsuccessful owing to many factors, including the capacity of M bovis to evade and modulate the immune system of the host; the lack of known virulence factors; the absence of a cell wall, which renders antibiotics targeting cell-wall synthesis unusable; and the failure of vaccines to control disease on the field. The current knowledge on virulence and pathogenesis is presented in this review.

Mbov_0503 Encodes a Novel Cytoadhesin that Facilitates Mycoplasma bovis Interaction with Tight Junctions

Molecules contributing to microbial cytoadhesion are important virulence factors. In Mycoplasma bovis, a minimal bacterium but an important cattle pathogen, binding to host cells is emerging as a complex process involving a broad range of surface-exposed structures. Here, a new cytoadhesin of M. bovis was identified by producing a collection of individual knock-out mutants and evaluating their binding to embryonic bovine lung cells. The cytoadhesive-properties of this surface-exposed protein, which is encoded by Mbov_0503 in strain HB0801, were demonstrated at both the mycoplasma cell and protein levels using confocal microscopy and ELISA. Although Mbov_0503 disruption was only associated in M. bovis with a partial reduction of its binding capacity, this moderate effect was sufficient to affect M. bovis interaction with the host-cell tight junctions, and to reduce the translocation of this mycoplasma across epithelial cell monolayers. Besides demonstrating the capacity of M. bovis to disrupt tight junctions, these results identified novel properties associated with cytoadhesin that might contribute to virulence and host colonization. These findings provide new insights into the complex interplay taking place between wall-less mycoplasmas and the host-cell surface.

Mycoplasma bovis: Interactions with the Immune System and Failure to Generate an Effective Immune Response

Host responses are often ineffective at clearing Mycoplasma bovis infection and may contribute to the pathogenesis of disease. M bovis possesses a surprisingly large repertoire of strategies to evade and modulate host responses. Unopsonized M bovis impairs phagocytosis and killing by neutrophils and macrophages. Apoptosis of neutrophils and lymphocytes is enhanced, whereas it is delayed in macrophages. Both proinflammatory and antiinflammatory cytokines are stimulated during M bovis infection depending on the cell type and location, and overall systemic responses tend to have a T-helper 2 bias. M bovis reduces proliferation of T cells and, in chronic infection, causes T-cell exhaustion.

Large-Scale Analysis of the Mycoplasma bovis Genome Identified Non-essential, Adhesion- and Virulence-Related Genes

Mycoplasma bovis is an important pathogen of cattle causing bovine mycoplasmosis. Clinical manifestations are numerous, but pneumonia, mastitis, and arthritis cases are mainly reported. Currently, no efficient vaccine is available and antibiotic treatments are not always satisfactory. The design of new, efficient prophylactic and therapeutic approaches requires a better understanding of the molecular mechanisms responsible for M. bovis pathogenicity. Random transposon mutagenesis has been widely used in Mycoplasma species to identify potential gene functions. Such an approach can also be used to screen genomes and search for essential and non-essential genes for growth. Here, we generated a random transposon mutant library of M. bovis strain JF4278 containing approximately 4000 independent insertion sites. We then coupled high-throughput screening of this mutant library to transposon sequencing and bioinformatic analysis to identify M. bovis non-essential, adhesion- and virulence-related genes. Three hundred and fifty-two genes of M. bovis were assigned as essential for growth in rich medium. Among the remaining non-essential genes, putative virulence-related factors were subsequently identified. The complete mutant library was screened for adhesion using primary bovine mammary gland epithelial cells. Data from this assay resulted in a list of conditional-essential genes with putative adhesion-related functions by identifying non-essential genes for growth that are essential for host cell-adhesion. By individually assessing the adhesion capacity of six selected mutants, two previously unknown factors and the adhesin TrmFO were associated with a reduced adhesion phenotype. Overall, our study (i) uncovers new, putative virulence-related genes; (ii) offers a list of putative adhesion-related factors; and (iii) provides valuable information for vaccine design and for exploring M. bovis biology, pathogenesis, and host-interaction.

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.

Fructose-1,6-bisphosphate aldolase is involved in Mycoplasma bovis colonization as a fibronectin-binding adhesin

Mycoplasma bovis is a common pathogenic microorganism of cattle and represents an important hazard on the cattle industry. Adherence to host cells is a significant component of mycoplasma-pathogenesis research. Fibronectin (Fn), an extracellular matrix protein, is a common host cell factor that can interact with the adhesions of pathogens. The aims of this study were to investigate the Fn-binding properties of M. bovis fructose-1,6-bisphosphate aldolase (FBA) and evaluate its role as a cell adhesion factor during mycoplasma colonization. The fba (MBOV_RS00435) gene of M. bovis was cloned and expressed, with the resulting recombinant protein used to prepare rabbit polyclonal antibodies. The purified recombinant FBA (rFBA) was shown to have fructose bisphosphate aldolase activity. Western blot indicated that FBA was an antigenically conserved protein in several M. bovis strains. Western blot combined with immunofluorescent assay (IFA) revealed that FBA was dual-localized to both cytoplasm and membrane in M. bovis. IFA showed that rFBA was able to adhere to embryonic bovine lung (EBL) cells. Meanwhile, an adhesion inhibition assay demonstrated that anti-rFBA antibodies could significantly block the adhesion of M. bovis to EBL cells. Moreover, a dose-dependent binding of rFBA to Fn was found by dot blotting and enzyme-linked immunosorbent assays. Together these results provided evidence that FBA is a surface-localized and antigenic protein of M. bovis, suggesting that it may function as a virulence determinant through interacting with host Fn.

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.

Bovine Epithelial in vitro Infection Models for Mycoplasma bovis

Mycoplasma bovis causes bovine mycoplasmosis. The major clinical manifestations are pneumonia and mastitis. Recently an increase in the severity of mastitis cases was reported in Switzerland. At the molecular level, there is limited understanding of the mechanisms of pathogenicity of M. bovis. Host–pathogen interactions were primarily studied using primary bovine blood cells. Therefore, little is known about the impact of M. bovis on other cell types present in infected tissues. Clear in vitro phenotypes linked to the virulence of M. bovis strains or tissue predilection of specific M. bovis strains have not yet been described. We adapted bovine in vitro systems to investigate infection of epithelial cells with M. bovis using a cell line (MDBK: Madin-Darby bovine kidney cells) and two primary cells (PECT: bovine embryonic turbinate cells and bMec: bovine mammary gland epithelial cells). Two strains isolated before and after the emergence of severe mastitis cases were selected. Strain JF4278 isolated from a cow with mastitis and pneumonia in 2008 and strain L22/93 isolated in 1993 were used to assess the virulence of M. bovis genotypes toward epithelial cells with particular emphasis on mammary gland cells. Our findings indicate that M. bovis is able to adhere to and invade different epithelial cell types. Higher titers of JF4278 than L22/93 were observed in co-cultures with cells. The differences in titers reached between the two strains was more prominent for bMec cells than for MDBK and PECT cells. Moreover, M. bovis strain L22/93 induced apoptosis in MDBK cells and cytotoxicity in PECT cells but not in bMec cells. Dose-dependent variations in proliferation of primary epithelial cells were observed after M. bovis infection. Nevertheless, an indisputable phenotype that could be related to the increased virulence toward mammary gland cells is not obvious.

Identification of targets of monoclonal antibodies that inhibit adhesion and growth in Mycoplasma mycoides subspecies mycoides

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A panel of anti-Mmm mAbs was produced and screened for host-pathogen inhibition.

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13 mAbs inhibited adhesion of Mmm to host target cells.

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Anti-capsular polysaccharide inhibited growth and caused agglutination of Mmm.

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Anti-PDHC inhibited adherence of Mmm cells showing the possible role of glycolytic enzymes in host-pathogen interaction.

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One novel antigen that is a promising vaccine candidate against CBPP identified.

Mycoplasma mycoides subspecies mycoides (Mmm) adhesion is tissue and host specific. Inhibition of adhesion will prevent Mmm from binding to lung cells and hence prevent colonization and disease. The aim of this study was to develop a panel of Mmm monoclonal antibodies against Mmm and use these antibodies to investigate their inhibitory effect on the adherence of Mmm to bovine lung epithelial cells (BoLEC), and to further identify an antigen to any of the inhibitory antibodies. Thirteen anti-Mycoplasma mycoides subsp. mycoides (AMMY) monoclonal antibodies (mAbs) inhibited adhesion by at least 30% and ten of the mAbs bound to multiple bands on Western blots suggesting that the antibodies bound to proteins of variable sizes. AMMY 10, a previously characterized Mmm- capsular polysaccharide (CPS) specific antibody, inhibited growth of Mmm in vitro and also caused agglutination of Mmm total cell lysate. AMMY 5, a 2-oxo acid dehydrogenase acyltransferase (Catalytic domain) (MSC_0267) specific antibody, was identified and polyclonal rabbit serum against recombinant MSC_0267 blocked adhesion of Mmm to BoLEC by 41%. Antigens recognized by these antibodies could be vaccine candidate(s) and should be subsequently tested for their ability to induce a protective immune response in vivo.

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.

Gap analysis of Mycoplasma bovis disease, diagnosis and control: An aid to identify future development requirements

There is a worldwide problem of disease caused by Mycoplasma (M.) bovis in cattle; it has a significant detrimental economic and animal welfare impact on cattle rearing. Infection can manifest as a plethora of clinical signs including mastitis, pneumonia, arthritis, keratoconjunctivitis, otitis media and genital disorders that may result in infertility and abortion. Current diagnosis and control information are reviewed and analysed to identify gaps in knowledge of the causative organism in respect of the disease pathology, diagnosis and control methods. The main considerations are as follows: no vaccines are commercially available; antimicrobial resistance is increasing; diagnostic and antimicrobial sensitivity testing needs to be improved; and a pen-side test would facilitate more rapid diagnosis and implementation of treatment with antimicrobials. More data on host susceptibility, stress factors, immune response and infectious dose levels are required. The impact of asymptomatic carriers, M. bovis survival in the environment and the role of wildlife in transmitting the disease also needs investigation. To facilitate development of vaccines, further analysis of more M. bovis genomes, its pathogenic mechanisms, including variable surface proteins, is required, along with reproducible disease models.

Molecular and biochemical characterization of Taenia solium α-enolase

Enolase (EC 4.2.1.11) acts as a multifunctional enzyme in many organisms, being involved in metabolism, transcription regulation and pathogenesis. In the current study, the recombinant α-enolase from Taenia solium (His-Tseno) was prepared and antiserum against His-Tseno was generated in rabbits. Consequently, we analyzed the enzymatic characteristics, plasminogen binding activity, tissue localization and expression patterns of Tseno. The study demonstrated that the enzymatic activity of His-Tseno was enhanced at pH around 7.0-7.5 and affected by addition of metal ions. Kinetic measurements using 2-phospho-d-glycerate (2-PGA) substrates gave a specific activity of 60.72 ± 0.84 U/mg and 1.1 mM of Km_2-PGA value. Plasminogen binding assay showed that His-Tseno could bind to human plasminogen and generate plasmin activated by a tissue-type plasminogen activator (t-PA). In addition, the lysine analogue 6-aminocaproic acid (ε-ACA) could inhibit the binding of plasminogen to His-Tseno. Quantitative real-time PCR confirmed that Tseno was expressed 2.38 folds higher in the adult worms (p < 0.05) than in the cysticerci. Further, an immunolocalization assay indicated that native Tseno was mainly distributed in the tegument and eggs of gravid proglottis from adult T. solium. In conclusion, Tseno executes the innate glycolytic function to supply energy for the growth, egg production, and even invasion of T. solium.

Mycoplasma bovis-Induced Inhibition of Bovine Peripheral Blood Mononuclear Cell Proliferation Is Ameliorated after Blocking the Immune-Inhibitory Programmed Death 1 Receptor

Mycoplasma bovis-induced immune suppression is a major obstacle faced by the host for controlling infections. M. bovis impairment of antigen-specific T-cell responses is achieved through inhibiting the proliferation of peripheral blood mononuclear cells (PBMCs). This impairment may contribute to the persistence of M. bovis infection in various sites, including lungs, and its systemic spread to various organs such as joints, with the underlying mechanisms remaining elusive. Here, we elucidated the role of the immune-inhibitory receptor programmed death 1 (PD-1) and its ligand (PD-L1) in M. bovis infection. Flow cytometry (FCM) analyses revealed an upregulation of PD-L1 expression on tracheal and lung epithelial cell lines after M. bovis infection. In addition, we found increased PD-L1 expression on purified lung lavage macrophages following M. bovis infection by FCM and determined its localization by immunofluorescence analysis comparing infected and control lung tissue sections. Moreover, M. bovis infection increased the expression of the PD-1 receptor on total PBMCs and in gated CD4⁺ and CD8⁺ T-cell subpopulations. We demonstrated that M. bovis infection induced a significant decrease in CD4⁺ PD-1^INT and CD8⁺ PD-1^INT subsets with intermediate PD-1 expression, which functioned as progenitor pools giving rise to CD4⁺ PD-1^HIGH and CD8⁺ PD-1^HIGH subsets with high PD-1 expression levels. We blocked PD-1 receptors on PBMCs using anti-PD-1 antibody at the beginning of infection, leading to a significant restoration of the proliferation of PBMCs. Taken together, our data indicate a significant involvement of the PD-1/PD-L1 inhibitory pathway during M. bovis infection and its associated immune exhaustion, culminating in impaired host immune responses.

Infection Function of Adhesin-Like Protein ALP609 from Spiroplasma melliferum CH-1

Spiroplasma melliferum is the causative agent of spiroplasmosis in honeybees. During infection, adhesion of spiroplasmas to the host cells through adhesion factors is a crucial step. In this study, we identified an adhesin-like protein (ALP609) in S. melliferum CH-1 and investigated its role in the infection. To determine whether ALP609 is an adhesion factor, we performed indirect immunofluorescence microscopy to visualize its adhesion properties. Subsequently, an infection model of S. melliferum CH-1 was established using primary midgut cells of Apis mellifera to examine the adhesion and invasion of spiroplasma using anti-ALP609 antibodies inhibition assays and competition assays with recombinant ALP609 in vitro. We found that anti-ALP609 antibodies could inhibit the adhesion and invasion of spiroplasma to the midgut cells of A. mellifera and reduce midgut cell invasion on increased exposure to recombinant ALP609. To the best of our knowledge, this is the first report identifying adhesion-related factors in S. melliferum. Our results suggested that ALP609 is an adhesin-like protein critical for invasion of S. melliferum CH-1 into midgut cells of A. mellifera.

Mycoplasma bovis co-infection with bovine viral diarrhea virus in bovine macrophages

Several studies suggest that synergisms between Mycoplasma bovis and other microorganisms might exacerbate disease outcome of bovine mycoplasmosis. Screening several bovine cell types to assess their potential use as in vitro infection models for M. bovis, it was observed that a widely used cell line of bovine macrophages (Bomac cells) is in fact persistently infected with bovine viral diarrhea virus (BVDV). The cell line was first cured of this virus allowing comparative studies between both cell lines. Subsequently, uptake and co-culture of two M. bovis strains of different clonal complexes with Bomac cells contaminated with BVDV and in BVDV-free Bomac cells were assessed. Additionally, cell viability, cytotoxicity and induction of apoptosis after infection with M. bovis were evaluated. No differences in the levels of uptake and growth in co-culture were observed between the two Bomac cell types and both M. bovis strains. Cytotoxicity was increased after infection of BVDV-free cells with one of the two strains, while apoptotic cell death was slightly induced by this strain in both cell lines. Overall, the presence or absence of BVDV in Bomac cells did not grossly change the parameters tested upon infection with M. bovis. Nevertheless, this cell model is very useful when studying viral co-infections with bacteria and could also be used for multiple co-infections. Considering the broad contamination of cell cultures with BVDV, careful screening for this virus should routinely be performed as its presence might be relevant depending on the molecular mechanisms being investigated.

Novel role of Vpmas as major adhesins of Mycoplasma agalactiae mediating differential cell adhesion and invasion of Vpma expression variants

Mycoplasma agalactiae exhibits antigenic variation by switching the expression of multiple surface lipoproteins called Vpmas. Although implicated to have a significant influence on the pathogenicity, their exact role in pathogen-host interactions has not been investigated so far. Initial attachment to host cells is regarded as one of the most important steps for colonization but this pathogen lacks the typical mycoplasma attachment organelle. The aim of this study was to determine the role of Vpmas in adhesion of M. agalactiae to host cells. 'Phase-Locked' Mutants (PLMs) steadily expressing single well-characterized Vpma lipoproteins served as ideal tools to evaluate the role of each of the six Vpmas in cytadhesion, which was otherwise not possible due to the high-frequency switching of Vpmas in the wildtype strain PG2. Using in vitro adhesion assays with HeLa and sheep mammary epithelial (MECs) and stromal (MSCs) cells, we could demonstrate differences in the adhesion capabilities of each of the six PLMs compared to the wildtype strain. The PLMV mutant expressing VpmaV exhibited the highest adhesion rate, whereas PLMU, which expresses VpmaU showed the lowest adhesion values explaining the reduced in vivo fitness of PLMU in sheep during experimental intramammary and conjunctival infections. Furthermore, adhesion inhibition assays using Vpma-specific polyclonal antisera were performed to confirm the role of Vpmas in M. agalactiae cytadhesion. This led to a significant decrease (p<0.05) in the adhesion percentage of each PLM. Immunofluorescence staining of TX-114 phase proteins extracted from each PLM showed binding of the respective Vpma to HeLa cells and MECs proving the direct role of Vpmas in cytadhesion. Furthermore, as adhesion is a prerequisite for cell invasion, the ability of the six PLMs to invade HeLa cells was also evaluated using the gentamicin protection assay. The results showed a strong correlation between the adhesion rates and invasion frequencies of the individual PLMs. This is the first report that describes a novel function of Vpma proteins in cell adhesion and invasion. Besides the variability of these proteins causing surface antigenic variation, the newly identified phenotypes are likely to play critical roles in the pathogenicity potential of this ruminant pathogen.

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.

Proteomics analysis and its role in elucidation of functionally significant proteins in Mycoplasma bovis

Mycoplasma bovis (M. bovis) is an emerging devastating cause of pneumonia in dairy and feedlot calves around the world, largely due to its increasing resistance to new generation effective antibiotics and lack of efficient vaccine. Failure of protective measures against M. bovis is mainly due to nonspecific targets. Most of the virulent factors of M. bovis and their underlying mechanisms are obscure to devise an effective control strategy. Full genome sequences of M. bovis strains basically provided a useful platform for the accurate identification of novel proteins and understanding their biological value using proteomics tools. Most of the previously documented proteins of M. bovis are involved in adhesion to host cells and are antigenic in nature. However, host immune response to some antigens proved to be non-protective. For the diagnosis of M. bovis infection, a serological assay based on whole cell proteins of M. bovis is commercially available but the specificity is likely to be improved by identifying and targeting the specific proteins. Many of the predicted proteins of M. bovis remain hypothetical, as their functions are yet to be confirmed experimentally. This review mainly focuses on the proteomics analysis of M. bovis and its role in identification of the virulence related factors and antigenic proteins of M. bovis. Future research directions have also been highlighted in this script for the application of important antigenic factors of M. bovis.

TrmFO, a Fibronectin-Binding Adhesin of Mycoplasma bovis

Mycoplasma bovis is an important pathogenic mycoplasma, causing the cattle industry serious economic losses. Adhesion is a crucial step in the mycoplasmas' infection and colonization process; fibronectin (Fn), an extracellular matrix glycoprotein, is a molecular bridge between the bacterial adhesins and host cell receptors. The present study was designed to characterize the Fn-binding ability of methylenetetrahydrofolate-tRNA-(uracil-5-)-methyltransferase (TrmFO) and its role in M. bovis cytoadherence. The trmFO (MBOV_RS00785) gene was cloned and expressed in E. coli BL21, and polyclonal antibodies against the recombinant TrmFO (rTrmFO) were raised in rabbits. Immunoblotting demonstrated that TrmFO was an immunogenic component, and the TrmFO expression was conserved in different M. bovis isolates. The mycoplasmacidal assay further showed that in the presence of complement, rabbit anti-recombinant TrmFO serum exhibited remarkable mycoplasmacidal efficacy. TrmFO was detected in both the M. bovis membrane and cytoplasm. By ligand dot blot and enzyme-linked immunosorbent assay (ELISA) binding assay, we found that rTrmFO bound Fn in a dose-dependent manner. Immunostaining visualized by confocal laser scanning microscopy showed that rTrmFO had capacity to adhere to the embryonic bovine lung (EBL) cells. In addition, the adhesion of M. bovis and rTrmFO to EBL cells could be inhibited by anti-rTrmFO antibodies. To the best of our knowledge, this is the first report to characterize the Fn-binding ability of TrmFO and its role in the bacterial adhesion to host cells.

Mmm-derived lipid-associated membrane proteins activate IL-1β production through the NF-κB pathway via TLR2, MyD88, and IRAK4

Mycoplasma mycoides subsp.mycoides (Mmm) is a pathogen that causes pneumonia, otitis media, and arthritis in young calves. Its pathogenesis is attributed in part to excessive immune responses. Mmm-derived lipid-associated membrane proteins (LAMPs) are potent inducers of the host innate immune system; however, interactions between Mmm-derived LAMPs as pathogenic agents, toll-like receptors (TLRs), and the signaling pathways responsible for activating inflammation and nuclear factor (NF)-κB have not been fully elucidated. Here, we analyzed the expression kinetics of interleukin (IL)-1β in Mmm-derived LAMP-stimulated embryonic bovine lung (EBL) cells and found that Mmm-derived LAMPs induced IL-1β expression. Subcellular localization analysis revealed the nuclear translocation of the NF-κB p65 subunit after EBL cells were stimulated with Mmm-derived LAMPs. Furthermore, a specific inhibitor assay demonstrated that NF-κB is required for Mmm-derived LAMP-induced IL-1β expression. Additionally, overexpression of TLR2, myeloid differentiation primary response gene 88 (MyD88), and IL-1 receptor-associated kinase 4 (IRAK4) increased IL-1β expression during LAMP stimulation, and TLR2-neutralizing antibodies reduced IL-1β expression in EBL cells during LAMP stimulation. Furthermore, LAMPs inhibited IL-1β expression following transfection with dominant-negative MyD88 and IRAK4 variants. These results suggested that Mmm-derived LAMPs activate IL-1β production through the NF-κB pathway via TLR2, MyD88, and IRAK4.

Immunolocation and enzyme activity analysis of Cryptosporidium parvum enolase

Background

Enolase is an essential multifunctional glycolytic enzyme that is involved in many biological processes of apicomplexan protozoa, such as adhesion and invasion. However, the characteristics of enolase in Cryptosporidium parvum, including the location on the oocyst and the enzyme activity, remain unclear.

Methods

The C. parvum enolase gene (cpeno) was amplified by RT-PCR and sequenced. The deduced amino acid sequence was analysed by bioinformatics software. The gene was expressed in Escherichia coli BL21 (DE3) and purified recombinant protein was used for enzyme activity analysis, binding experiments and antibody preparation. The localisation of enolase on oocysts was examined via immunofluorescence techniques.

Results

A 1,350 bp DNA sequence was amplified from cDNA taken from C. parvum oocysts. The deduced amino acids sequence of C. parvum enolase (CpEno) had 82.1% homology with Cryptosporidium muris enolase, and 54.7–68.0% homology with others selected species. Western blot analysis indicated that recombinant C. parvum enolase (rCpEno) could be recognised by C. parvum-infected cattle sera. Immunolocalization testing showed that CpEno was found to locate mainly on the surface of oocysts. The enzyme activity was 33.5 U/mg, and the Michaelis constant (K_m) was 0.571 mM/l. Kinetic measurements revealed that the most suitable pH value was 7.0–7.5, and there were only minor effects on the activity of rCpEno with a change in the reaction temperature. The enzyme activity decreased when the Ca²⁺, K⁺, Mg²⁺ and Na⁺ concentrations of the reaction solution increased. The binding assays demonstrated that rCpEno could bind to human plasminogen.

Conclusion

This study is the first report of immunolocation, binding activity and enzyme characteristics of CpEno. The results of this study suggest that the surface-associated CpEno not only functions as a glycolytic enzyme but may also participate in attachment and invasion process of the parasite.

Electronic supplementary material

The online version of this article (doi:10.1186/s13071-017-2200-y) contains supplementary material, which is available to authorized users.

Comparative Genomics of Mycoplasma bovis Strains Reveals That Decreased Virulence with Increasing Passages Might Correlate with Potential Virulence-Related Factors

Mycoplasma bovis is an important cause of bovine respiratory disease worldwide. To understand its virulence mechanisms, we sequenced three attenuated M. bovis strains, P115, P150, and P180, which were passaged in vitro 115, 150, and 180 times, respectively, and exhibited progressively decreasing virulence. Comparative genomics was performed among the wild-type M. bovis HB0801 (P1) strain and the P115, P150, and P180 strains, and one 14.2-kb deleted region covering 14 genes was detected in the passaged strains. Additionally, 46 non-sense single-nucleotide polymorphisms and indels were detected, which confirmed that more passages result in more mutations. A subsequent collective bioinformatics analysis of paralogs, metabolic pathways, protein-protein interactions, secretory proteins, functionally conserved domains, and virulence-related factors identified 11 genes that likely contributed to the increased attenuation in the passaged strains. These genes encode ascorbate-specific phosphotransferase system enzyme IIB and IIA components, enolase, L-lactate dehydrogenase, pyruvate kinase, glycerol, and multiple sugar ATP-binding cassette transporters, ATP binding proteins, NADH dehydrogenase, phosphate acetyltransferase, transketolase, and a variable surface protein. Fifteen genes were shown to be enriched in 15 metabolic pathways, and they included the aforementioned genes encoding pyruvate kinase, transketolase, enolase, and L-lactate dehydrogenase. Hydrogen peroxide (H₂O₂) production in M. bovis strains representing seven passages from P1 to P180 decreased progressively with increasing numbers of passages and increased attenuation. However, eight mutants specific to eight individual genes within the 14.2-kb deleted region did not exhibit altered H₂O₂ production. These results enrich the M. bovis genomics database, and they increase our understanding of the mechanisms underlying M. bovis virulence.

Status of the development of a vaccine against Mycoplasma bovis

Mycoplasma bovis is an important pathogen of cattle and, despite numerous efforts an effective vaccine for control of the disease it causes remains elusive. Although we now know more about the biology of this pathogen, information is lacking about appropriate protective antigens, the type of immune response that confers protection and adjuvants selection. The use of conserved recombinant proteins, selected using in silico approaches, as components of a vaccine may be a better choice over bacterin-based vaccines due to the limited protection afforded by them and adverse reactions caused by them. More studies are needed on the characterization of host-pathogen interactions and to elucidate M. bovis products modulating these interactions. These products could be the basis for development of vaccines to control M. bovis infections in dairy farms and feedlots.

Mycoplasma bovis NADH oxidase functions as both a NADH oxidizing and O2 reducing enzyme and an adhesin

Mycoplasma bovis causes considerable economic losses in the cattle industry worldwide. In mycoplasmal infections, adhesion to the host cell is of the utmost importance. In this study, the amino acid sequence of NOX was predicted to have enzymatic domains. The nox gene was then cloned and expressed in Escherichia coli. The enzymatic activity of recombinant NOX (rNOX) was confirmed based on its capacity to oxidize NADH to NAD⁺ and reduce O₂ to H₂O₂. The adherence of rNOX to embryonic bovine lung (EBL) cells was confirmed with confocal laser scanning microscopy, enzyme-linked immunosorbent assay, and flow cytometry. Both preblocking EBL cells with purified rNOX and preneutralizing M. bovis with polyclonal antiserum to rNOX significantly reduced the adherence of M. bovis to EBL cells. Mycoplasma bovis^NOX–expressed a truncated NOX protein at a level 10-fold less than that of the wild type. The capacities of M. bovis^NOX– for cell adhesion and H₂O₂ production were also significantly reduced. The rNOX was further used to pan phage displaying lung cDNA library and fibronectin was determined to be potential ligand. In conclusion, M. bovis NOX functions as both an active NADH oxidase and adhesin, and is therefore a potential virulence factor.

Identification of genes involved in Mycoplasma gallisepticum biofilm formation using mini-Tn4001-SGM transposon mutagenesis

Mycoplasma gallisepticum (MG) is an important pathogen that can cause chronic respiratory disease in chickens and infectious sinusitis in turkeys. MG has the ability to form biofilms. The molecular mechanisms underlying MG biofilm formation are complex and poorly understood. To better understand the mechanisms involved in biofilm formation, mini-Tn4001-SGM, a novel transposon vector containing the gentamicin gene was constructed and electroporated into MG strain R_low. Of the 738 mutants obtained, 12 had significantly reduced capacity to form biofilms in a polystyrene microtiter-plate biofilm assay. Ten different genes were identified as disrupted in these mutants using genomic walking from the transposon insertion sites and Southern bolt hybridization with a transposon-based probe. Four genes were associated with cellular processes, especially synthesis of extracellular polysaccharide and several lipoproteins encoded. Other genes were associated with translation, metabolism and gene regulation, and one had unknown function. Seven genes identified in this study have been previously associated with biofilm formation in MG or other bacterial species. The other three have not been previously reported to play a role in biofilm formation in MG. In conclusion, a new transposon vector was shown to be a powerful tool for future studies of MG pathogenesis. This study adds to our understanding of the molecular mechanisms involved in MG biofilm formation and may shed light on the persistence of MG infections.

Rhamnose Links Moonlighting Proteins to Membrane Phospholipid in Mycoplasmas

Many proteins that have a primary function as a cytoplasmic protein are known to have the ability to moonlight on the surface of nearly all organisms. An example is the glycolytic enzyme enolase, which can be found on the surface of many types of cells from bacteria to human. Surface enolase is not enzymatic because it is monomeric and oligomerization is required for glycolytic activity. It can bind various molecules and activate plasminogen. Enolase lacks a signal peptide and the mechanism by which it attaches to the surface is unknown. We found that treatment of whole cells of the murine pathogen Mycoplasma pulmonis with phospholipase D released enolase and other common moonlighting proteins. Glycostaining suggested that the released proteins were glycosylated. Cytoplasmic and membrane-bound enolase was isolated by immunoprecipitation. No post-translational modification was detected on cytoplasmic enolase, but membrane enolase was associated with lipid, phosphate and rhamnose. Treatment with phospholipase released the lipid and phosphate from enolase but not the rhamnose. The site of rhamnosylation was identified as a glutamine residue near the C-terminus of the protein. Rhamnose has been found in all species of mycoplasma examined but its function was previously unknown. Mycoplasmas are small bacteria with have no peptidoglycan, and rhamnose in these organisms is also not associated with polysaccharide. We suggest that rhamnose has a central role in anchoring proteins to the membrane by linkage to phospholipid, which may be a general mechanism for the membrane association of moonlighting proteins in mycoplasmas and perhaps other bacteria.

Interactions of surface-displayed glycolytic enzymes of Mycoplasma pneumoniae with components of the human extracellular matrix

Mycoplasma pneumoniae is a major cause of community-acquired respiratory infections worldwide. Due to the strongly reduced genome, the number of virulence factors expressed by this cell wall-less pathogen is limited. To further understand the processes during host colonization, we investigated the interactions of the previously confirmed surface-located glycolytic enzymes of M. pneumoniae (pyruvate dehydrogenase A-C [PdhA-C], glyceraldehyde-3-phosphate dehydrogenase [GapA], lactate dehydrogenase [Ldh], phosphoglycerate mutase [Pgm], pyruvate kinase [Pyk] and transketolase [Tkt]) to the human extracellular matrix (ECM) proteins fibrinogen (Fn), fibronectin (Fc), lactoferrin (Lf), laminin (Ln) and vitronectin (Vc), respectively. Concentration-dependent interactions between Fn and Vc and all eight recombinant proteins derived from glycolytic enzymes, between Ln and PdhB-C, GapA, Ldh, Pgm, Pyk and Tkt, between Lf and PdhA-C, GapA and Pyk, and between Fc and PdhC and GapA were demonstrated. In most cases, these associations are significantly influenced by ionic forces and by polyclonal sera against recombinant proteins. In immunoblotting, the complex of human plasminogen, activator (tissue-type or urokinase plasminogen activator) and glycolytic enzyme was not able to degrade Fc, Lf and Ln, respectively. In contrast, degradation of Vc was confirmed in the presence of all eight enzymes tested. Our data suggest that the multifaceted associations of surface-localized glycolytic enzymes play a potential role in the adhesion and invasion processes during infection of human respiratory mucosa by M. pneumoniae.

Mycoplasma bovis-derived lipid-associated membrane proteins activate IL-1β production through the NF-κB pathway via toll-like receptor 2 and MyD88

Mycoplasma bovis causes pneumonia, otitis media, and arthritis in young calves, resulting in economic losses to the cattle industry worldwide. M. bovis pathogenesis results in part from excessive immune responses. Lipid-associated membrane proteins (LAMPs) can potently induce host innate immunity. However, interactions between M. bovis-derived LAMPs and Toll-like receptors (TLRs), or signaling pathways eliciting active inflammation and NF-κB activation, are incompletely understood. Here, we found that IL-1β expression was induced in embryonic bovine lung (EBL) cells stimulated with M. bovis-derived LAMPs. Subcellular-localization analysis revealed nuclear p65 translocation following EBL cell stimulation with M. bovis-derived LAMPs. An NF-κB inhibitor reversed M. bovis-derived LAMP-induced IL-1β expression. TLR2 and myeloid differentiation primary response gene 88 (MyD88) overexpression increased LAMP-dependent IL-1β induction. TLR2-neutralizing antibodies reduced IL-1β expression during LAMP stimulation. LAMPs also inhibited IL-1β expression following overexpression of a dominant-negative MyD88 protein. These results suggested that M. bovis-derived LAMPs activate IL-1β production through the NF-κB pathway via TLR2 and MyD88.

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

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

Network of Surface-Displayed Glycolytic Enzymes in Mycoplasma pneumoniae and Their Interactions with Human Plasminogen

In different bacteria, primarily cytosolic and metabolic proteins are characterized as surface localized and interacting with different host factors. These moonlighting proteins include glycolytic enzymes, and it has been hypothesized that they influence the virulence of pathogenic species. The presence of surface-displayed glycolytic enzymes and their interaction with human plasminogen as an important host factor were investigated in the genome-reduced and cell wall-less microorganism Mycoplasma pneumoniae, a common agent of respiratory tract infections of humans. After successful expression of 19 glycolytic enzymes and production of polyclonal antisera, the localization of proteins in the mycoplasma cell was characterized using fractionation of total proteins, colony blot, mild proteolysis and immunofluorescence of M. pneumoniae cells. Eight glycolytic enzymes, pyruvate dehydrogenases A to C (PdhA-C), glyceraldehyde-3-phosphate dehydrogenase (GapA), lactate dehydrogenase (Ldh), phosphoglycerate mutase (Pgm), pyruvate kinase (Pyk), and transketolase (Tkt), were confirmed as surface expressed and all are able to interact with plasminogen. Plasminogen bound to recombinant proteins PdhB, GapA, and Pyk was converted to plasmin in the presence of urokinase plasminogen activator and plasmin-specific substrate d-valyl-leucyl-lysine-p-nitroanilide dihydrochloride. Furthermore, human fibrinogen was degraded by the complex of plasminogen and recombinant protein PdhB or Pgm. In addition, surface-displayed proteins (except PdhC) bind to human lung epithelial cells, and the interaction was reduced significantly by preincubation of cells with antiplasminogen. Our results suggest that plasminogen binding and activation by different surface-localized glycolytic enzymes of M. pneumoniae may play a role in successful and long-term colonization of the human respiratory tract.