A metabolic enzyme as a primary virulence factor of Mycoplasma mycoides subsp. mycoides small colony

Genes required for survival and proliferation of Mycoplasma bovis in association with host cells

Mycoplasma bovis is an important emerging pathogen of cattle and bison, but our understanding of the genetic basis of its interactions with its host is limited. The aim of this study was to identify genes of M. bovis required for interaction and survival in association with host cells. One hundred transposon-induced mutants of the type strain PG45 were assessed for their capacity to survive and proliferate in Madin-Darby bovine kidney cell cultures. The growth of 19 mutants was completely abrogated, and 47 mutants had a prolonged doubling time compared to the parent strain. All these mutants had a similar growth pattern to the parent strain PG45 in the axenic media. Thirteen genes previously classified as dispensable for the axenic growth of M. bovis were found to be essential for the growth of M. bovis in association with host cells. In most of the mutants with a growth-deficient phenotype, the transposon was inserted into a gene involved in transportation or metabolism. This included genes coding for ABC transporters, proteins related to carbohydrate, nucleotide and protein metabolism, and membrane proteins essential for attachment. It is likely that these genes are essential not only in vitro but also for the survival of M. bovis in infected animals.

IMPORTANCE

Mycoplasma bovis causes chronic bronchopneumonia, mastitis, arthritis, keratoconjunctivitis, and reproductive tract disease in cattle around the globe and is an emerging pathogen in bison. Control of mycoplasma infections is difficult in the absence of appropriate antimicrobial treatment or effective vaccines. A comprehensive understanding of host-pathogen interactions and virulence factors is important to implement more effective control methods against M. bovis. Recent studies of other mycoplasmas with in vitro cell culture models have identified essential virulence genes of mycoplasmas. Our study has identified genes of M. bovis required for survival in association with host cells, which will pave the way to a better understanding of host-pathogen interactions and the role of specific genes in the pathogenesis of disease caused by M. bovis.

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.

Genomic characterization of a novel, widely distributed Mycoplasma species "Candidatus Mycoplasma mahonii" associated with the brittlestar Gorgonocephalus chilensis

Symbiotic relationships are ubiquitous throughout the world's oceans, yet for many marine organisms, including those in the high latitudes, little is understood about symbiotic associations and functional relationships. From a recently determined genome sequence of a filter-feeding basket star from Argentina, Gorgonocephalus chilensis, we discovered a novel Mycoplasma species with a 796Kb genome (CheckM completeness of 97.9%, G+C content = 30.1%). Similar to other Mycoplasma spp. within Mycoplasmatota, genomic analysis of the novel organism revealed reduced metabolic pathways including incomplete biosynthetic pathways, suggesting an obligate association with their basket star host. Results of 16S rRNA and multi-locus phylogenetic analyses revealed that this organism belonged to a recently characterized non-free-living lineage of Mycoplasma spp. specifically associated with marine invertebrate animals. Thus, the name "Candidatus Mycoplasma mahonii" is proposed for this novel species. Based on 16S rRNA PCR-screening, we found that Ca. M. mahonii also occurs in Gorgonocephalus eucnemis from the Northwest Pacific and other Gorgonocephalus chilensis from Argentinian waters. The level of sequence conservation within Ca. M. mahonii is considerable between widely disparate high-latitude Gorgonocephalus species, suggesting that oceanic dispersal of this microbe may be greater than excepted.

Genome Editing of Veterinary Relevant Mycoplasmas Using a CRISPR-Cas Base Editor System

Mycoplasmas are minimal bacteria that infect humans, wildlife, and most economically relevant livestock species. Mycoplasma infections cause a large range of chronic inflammatory diseases, eventually leading to death in some animals. Due to the lack of efficient recombination and genome engineering tools for most species, the production of mutant strains for the identification of virulence factors and the development of improved vaccine strains is limited. Here, we demonstrate the adaptation of an efficient Cas9-Base Editor system to introduce targeted mutations into three major pathogenic species that span the phylogenetic diversity of these bacteria: the avian pathogen Mycoplasma gallisepticum and the two most important bovine mycoplasmas, Mycoplasma bovis and Mycoplasma mycoides subsp. mycoides. As a proof of concept, we successfully used an inducible SpdCas9-pmcDA1 cytosine deaminase system to disrupt several major virulence factors in these pathogens. Various induction times and inducer concentrations were evaluated to optimize editing efficiency. The optimized system was powerful enough to disrupt 54 of 55 insertion sequence transposases in a single experiment. Whole-genome sequencing of the edited strains showed that off-target mutations were limited, suggesting that most variations detected in the edited genomes are Cas9-independent. This effective, rapid, and easy-to-use genetic tool opens a new avenue for the study of these important animal pathogens and likely the entire class Mollicutes.

IMPORTANCE Mycoplasmas are minimal pathogenic bacteria that infect a wide range of hosts, including humans, livestock, and wild animals. Major pathogenic species cause acute to chronic infections involving still poorly characterized virulence factors. The lack of precise genome editing tools has hampered functional studies of many species, leaving multiple questions about the molecular basis of their pathogenicity unanswered. Here, we demonstrate the adaptation of a CRISPR-derived base editor for three major pathogenic species: Mycoplasma gallisepticum, Mycoplasma bovis, and Mycoplasma mycoides subsp. mycoides. Several virulence factors were successfully targeted, and we were able to edit up to 54 target sites in a single step. The availability of this efficient and easy-to-use genetic tool will greatly facilitate functional studies of these economically important bacteria.

The first Mycoplasma ovipneumoniae recovered from a sheep with respiratory disease in Brazil - draft genome and genomic analysis

Mycoplasma ovipneumoniae is an important etiological agent of sheep respiratory disease worldwide. Here, we describe the first isolation and draft genome sequence of M. ovipneumoniae strain USP-BR2017 retrieved from tracheobronchial lavage of a sheep showing clinical signs of respiratory disease in the Rio de Janeiro State, Brazil. The culture of tracheobronchial lavage resulted in glucose-fermenting fried egg colonies, which were identified as M. ovipneumoniae by polymerase chain reaction. The genome was sequenced using the Illumina NextSeq 2000 and de novo assembled using SPAdes. The genome of the sequenced organism presented an approximate size of 1,122,253 bp. The annotation revealed 773 coding DNA sequences (CDSs), 806 genes, three rRNAs, and 30 tRNAs. Data analysis revealed M. ovipneumoniae strain USP-BR2017 contains a few virulence genes, including the hemolysing C gene (hlyC). In addition, strain USP-BR2017 showed high identity over the 16S rRNA gene with other sheep isolates from China and United States. This first description of M. ovipneumoniae in diseased Brazilian sheep demonstrates the importance of continuous surveillance and diagnostics of pathogens causing respiratory disease in sheep in Brazil.

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.

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.

Beware of Mycoplasma Anti-immunoglobulin Strategies

Mycoplasmas are small, genome-reduced bacteria. They are obligate parasites that can be found in a wide range of host species, including the majority of livestock animals and humans. Colonization of the host can result in a wide spectrum of outcomes. In many cases, these successful parasites are considered commensal, as they are found in the microbiota of asymptomatic carriers. Conversely, mycoplasmas can also be pathogenic, as they are associated with a range of both acute and chronic inflammatory diseases which are problematic in veterinary and human medicine. The chronicity of mycoplasma infections and the ability of these bacteria to infect even recently vaccinated individuals clearly indicate that they are able to successfully evade their host’s humoral immune response. Over the years, multiple strategies of immune evasion have been identified in mycoplasmas, with a number of them aimed at generating important antigenic diversity. More recently, mycoplasma-specific anti-immunoglobulin strategies have also been characterized. Through the expression of the immunoglobulin-binding proteins protein M or mycoplasma immunoglobulin binding (MIB), mycoplasmas have the ability to target the host’s antibodies and to prevent them from interacting with their cognate antigens. In this review, we discuss how these discoveries shed new light on the relationship between mycoplasmas and their host’s immune system. We also propose that these strategies should be taken into consideration for future studies, as they are key to our understanding of mycoplasma diseases' chronic and inflammatory nature and are probably a contributing factor to reduce vaccine efficacy.

Nicotinamide Adenine Dinucleotide-Dependent Flavin Oxidoreductase of Mycoplasma hyopneumoniae Functions as a Potential Novel Virulence Factor and Not Only as a Metabolic Enzyme

Mycoplasma hyopneumoniae (Mhp) is the main pathogen that causes enzootic pneumonia, a disease that has a significant impact on the pig industry worldwide. The pathogenesis of enzootic pneumonia, especially possible virulence factors of Mhp, has still not been fully elucidated. The transcriptomic and proteomic analyses of different Mhp strains reported in the literature have revealed differences in virulence, and differences in RNA transcription levels between high- and low-virulence strains initially indicated that nicotinamide adenine dinucleotide (NADH)-dependent flavin oxidoreductase (NFOR) was related to Mhp pathogenicity. Prokaryotic expression and purification of the NFOR protein from Mhp were performed, a rabbit-derived polyclonal antibody against NFOR was prepared, and multiple sequence alignment and evolutionary analyses of Mhp NFOR were performed. For the first time, it was found that the NFOR protein was conserved among all Mhp strains, and NFOR was localized to the cell surface and could adhere to immortalized porcine bronchial epithelial cells (hTERT-PBECs). Adhesion to hTERT-PBECs could be specifically inhibited by an anti-NFOR polyclonal antibody, and the rates of adhesion to both high- and low-virulence strains, 168 and 168L, significantly decreased by more than 40%. Moreover, Mhp NFOR not only recognized and interacted with host fibronectin and plasminogen but also induced cellular oxidative stress and apoptosis in hTERT-PBECs. The release of lactate dehydrogenase by hTERT-PBECs incubated with Mhp NFOR was significantly positively correlated with the virulence of Mhp. Overall, in addition to being a metabolic enzyme related to oxidative stress, NFOR may also function as a potential novel virulence factor of Mhp, thus contributing to the pathogenesis of Mhp; these findings provide new ideas and theoretical support for studying the pathogenic mechanisms of other mycoplasmas.

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.

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.

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.

Contagious Bovine and Caprine Pleuropneumonia: a research community's recommendations for the development of better vaccines

Contagious bovine pleuropneumonia (CBPP) and contagious caprine pleuropneumonia (CCPP) are major infectious diseases of ruminants caused by mycoplasmas in Africa and Asia. In contrast with the limited pathology in the respiratory tract of humans infected with mycoplasmas, CBPP and CCPP are devastating diseases associated with high morbidity and mortality. Beyond their obvious impact on animal health, CBPP and CCPP negatively impact the livelihood and wellbeing of a substantial proportion of livestock-dependent people affecting their culture, economy, trade and nutrition. The causative agents of CBPP and CCPP are Mycoplasma mycoides subspecies mycoides and Mycoplasma capricolum subspecies capripneumoniae, respectively, which have been eradicated in most of the developed world. The current vaccines used for disease control consist of a live attenuated CBPP vaccine and a bacterin vaccine for CCPP, which were developed in the 1960s and 1980s, respectively. Both of these vaccines have many limitations, so better vaccines are urgently needed to improve disease control. In this article the research community prioritized biomedical research needs related to challenge models, rational vaccine design and protective immune responses. Therefore, we scrutinized the current vaccines as well as the challenge-, pathogenicity- and immunity models. We highlight research gaps and provide recommendations towards developing safer and more efficacious vaccines against CBPP and CCPP.

Contagious Bovine Pleuropneumonia: A Comprehensive Overview

Contagious bovine pleuropneumonia (CBPP) is a respiratory disease of cattle that is listed as notifiable by the World Organization for Animal Health. It is endemic in sub-Saharan Africa and causes important productivity losses due to the high mortality and morbidity rates. CBPP is caused by Mycoplasma mycoides subsp. mycoides (Mmm) and is characterized by severe fibrinous bronchopneumonia and pleural effusion during the acute to subacute stages and by pulmonary sequestra in chronic cases. Additional lesions can be detected in the kidneys and in the carpal and tarsal joints of calves. Mmm infection occurs through the inhalation of infected aerosol droplets. After the colonization of bronchioles and alveoli, Mmm invades blood and lymphatic vessels and causes vasculitis. Moreover, Mmm can be occasionally demonstrated in blood and in a variety of other tissues. In the lung, Mmm antigen is commonly detected on bronchiolar and alveolar epithelial cells, in lung phagocytic cells, within the wall of blood and lymphatic vessels, inside necrotic areas, and within tertiary lymphoid follicles. Mmm antigen can also be present in the cytoplasm of macrophages within lymph node sinuses, in the germinal center of lymphoid follicles, in glomerular endothelial cells, and in renal tubules. A complete pathological examination is of great value for a rapid presumptive diagnosis, but laboratory investigations are mandatory for definitive diagnosis. The purpose of this review is to describe the main features of CBPP including the causative agent, history, geographic distribution, epidemiology, clinical course, diagnosis, and control. A special focus is placed on gross and microscopic lesions in order to familiarize veterinarians with the pathology and pathogenesis of CBPP.

Pro-Inflammatory Response of Bovine Polymorphonuclear Cells Induced by Mycoplasma mycoides subsp. mycoides

Mycoplasma mycoides subsp. mycoides (Mmm) is the etiological agent of contagious bovine pleuropneumonia (CBPP), one of the major diseases affecting cattle in sub-Saharan Africa. Some evidences suggest that the immune system of the host (cattle) plays an important role in the pathogenic mechanism of CBPP, but the factors involved in the process remain largely unknown. The present study aimed to investigate the cell response of bovine polymorphonuclear neutrophils (PMNs) after Mmm in vitro exposure using one step RT-qPCR and Western blotting. Data obtained indicate that gene and protein expression levels of some pro-inflammatory factors already change upon 30 min of PMNs exposure to Mmm. Of note, mRNA expression level in Mmm exposed PMNs increased in a time-dependent manner and for all time points investigated; targets expression was also detected by Western blotting in Mmm exposed PMNs only. These data demonstrate that when bovine PMN cells are triggered by Mmm, they undergo molecular changes, upregulating mRNA and protein expression of specific pro-inflammatory factors. These results provide additional information on host-pathogen interaction during CBPP infection.

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.

Extracellular DNA: A Nutritional Trigger of Mycoplasma bovis Cytotoxicity

Microbial access to host nutrients is a key factor of the host-pathogen interplay. With their nearly minimal genome, wall-less bacteria of the class Mollicutes have limited metabolic capacities and largely depend on host nutrients for their survival. Despite these limitations, host-restricted mycoplasmas are widely distributed in nature and many species are pathogenic for humans and animals. Yet, only partial information is available regarding the mechanisms evolved by these minimal pathogens to meet their nutrients and the contribution of these mechanisms to virulence. By using the ruminant pathogen Mycoplasma bovis as a model system, extracellular DNA (eDNA) was identified as a limiting nutrient for mycoplasma proliferation under cell culture conditions. Remarkably, the growth-promoting effect induced by supplementation with eDNA was associated with important cytotoxicity for actively dividing host cells, but not confluent monolayers. To identify biological functions mediating M. bovis cytotoxicity, we produced a library of transposon knockout mutants and identified three critical genomic regions whose disruption was associated with a non-cytopathic phenotype. The coding sequences (CDS) disrupted in these regions pointed towards pyruvate metabolism as contributing to M. bovis cytotoxicity. Hydrogen peroxide was found responsible for eDNA-mediated M. bovis cytotoxicity, and non-cytopathic mutants were unable to produce this toxic metabolic compound. In our experimental conditions, no contact between M. bovis and host cells was required for cytotoxicity. Further analyses revealed important intra-species differences in eDNA-mediated cytotoxicity and H₂O₂ production, with some strains displaying a cytopathic phenotype despite no H₂O₂ production. Interestingly, the genome of strains PG45 and HB0801 were characterized by the occurrence of insertion sequences (IS) at close proximity to several CDSs found disrupted in non-cytopathic mutants. Since PG45 and HB0801 produced no or limited amount of H₂O₂, IS-elements might influence H₂O₂ production in M. bovis. These results confirm the multifaceted role of eDNA in microbial communities and further identify this ubiquitous material as a nutritional trigger of M. bovis cytotoxicity. M. bovis may thus take advantage of the multiple sources of eDNA in vivo to modulate its interaction with host cells, a way for this minimal pathogen to overcome its limited coding capacity.

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.

Tn-sequencing of Mycoplasma hyopneumoniae and Mycoplasma hyorhinis mutant libraries reveals non-essential genes of porcine mycoplasmas differing in pathogenicity

Mycoplasma hyopneumoniae and Mycoplasma hyorhinis are two phylogenetically related species colonizing the respiratory tract of pigs but differing in pathogenicity, the basis of which is not well resolved. We hypothesize that genes belonging to the species-specific portion of the genome and being non-essential during ideal laboratory growth conditions encode possible virulent determinants and are the driver of interspecies differences. To investigate this, transposon mutant libraries were generated for both species and a transposon sequencing (Tn-seq) method for mycoplasmas was established to identify non-essential genes. Tn-seq datasets combined with bidirectional Blastp analysis revealed that 101 out of a total 678 coding sequences (CDS) are species-specific and non-essential CDS of M. hyopneumoniae strain F7.2C, while 96 out of a total 751 CDS are species-specific and non-essential CDS in the M. hyorhinis strain JF5820. Among these species-specific and non-essential CDS were genes involved in metabolic pathways. In particular, the myo-inositol and the sialic acid pathways were found to be non-essential and therefore could be considered important to the specific pathogenicity of M. hyopneumoniae and M. hyorhinis, respectively. Such pathways could enable the use of an alternative energy source providing an advantage in their specific niche and might be interesting targets to knock out in order to generate attenuated live vaccines.

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.

Attenuation of a Pathogenic Mycoplasma Strain by Modification of the obg Gene by Using Synthetic Biology Approaches

Animal diseases due to mycoplasmas are a major cause of morbidity and mortality associated with economic losses for farmers all over the world. Currently used mycoplasma vaccines exhibit several drawbacks, including low efficacy, short time of protection, adverse reactions, and difficulty in differentiating infected from vaccinated animals. Therefore, there is a need for improved vaccines to control animal mycoplasmoses. Here, we used genome engineering tools derived from synthetic biology approaches to produce targeted mutations in the essential GTPase-encoding obg gene of Mycoplasma mycoides subsp. capri. Some of the resulting mutants exhibited a marked temperature-sensitive phenotype. The virulence of one of the obg mutants was evaluated in a caprine septicemia model and found to be strongly reduced. Although the obg mutant reverted to a virulent phenotype in one infected animal, we believe that these results contribute to a strategy that should help in building new vaccines against animal mycoplasmoses.

Mycoplasma species are responsible for several economically significant livestock diseases for which there is a need for new and improved vaccines. Most of the existing mycoplasma vaccines are attenuated strains that have been empirically obtained by serial passages or by chemical mutagenesis. The recent development of synthetic biology approaches has opened the way for the engineering of live mycoplasma vaccines. Using these tools, the essential GTPase-encoding gene obg was modified directly on the Mycoplasma mycoides subsp. capri genome cloned in yeast, reproducing mutations suspected to induce a temperature-sensitive (TS⁺) phenotype. After transplantation of modified genomes into a recipient cell, the phenotype of the resulting M. mycoides subsp. capri mutants was characterized. Single-point obg mutations did not result in a strong TS⁺ phenotype in M. mycoides subsp. capri, but a clone presenting three obg mutations was shown to grow with difficulty at temperatures of ≥40°C. This particular mutant was then tested in a caprine septicemia model of M. mycoides subsp. capri infection. Five out of eight goats infected with the parental strain had to be euthanized, in contrast to one out of eight goats infected with the obg mutant, demonstrating an attenuation of virulence in the mutant. Moreover, the strain isolated from the euthanized animal in the group infected with the obg mutant was shown to carry a reversion in the obg gene associated with the loss of the TS⁺ phenotype. This study demonstrates the feasibility of building attenuated strains of mycoplasma that could contribute to the design of novel vaccines with improved safety.

IMPORTANCE Animal diseases due to mycoplasmas are a major cause of morbidity and mortality associated with economic losses for farmers all over the world. Currently used mycoplasma vaccines exhibit several drawbacks, including low efficacy, short time of protection, adverse reactions, and difficulty in differentiating infected from vaccinated animals. Therefore, there is a need for improved vaccines to control animal mycoplasmoses. Here, we used genome engineering tools derived from synthetic biology approaches to produce targeted mutations in the essential GTPase-encoding obg gene of Mycoplasma mycoides subsp. capri. Some of the resulting mutants exhibited a marked temperature-sensitive phenotype. The virulence of one of the obg mutants was evaluated in a caprine septicemia model and found to be strongly reduced. Although the obg mutant reverted to a virulent phenotype in one infected animal, we believe that these results contribute to a strategy that should help in building new vaccines against animal mycoplasmoses.

Mycoplasma hyopneumoniae Mhp597 is a cytotoxicity, inflammation and immunosuppression associated nuclease

Nucleases are ubiquitously recognized as essential proteins in mycoplasmas because these organisms lack most capacities for de novo synthesis of nucleotides. Some of these proteins were proved to be important pathogenic factors during the infection of mycoplasms. In this study, the protein Mhp597 from M. hyopneumoniae was expressed and purified in Escherichia coli. Analysis of nuclease activity showed that recombinant Mhp597 (rMhp597) was a Ca₂₊ or Mg₂₊ dependent thermostable nuclease with very high activity and neutrophil extracellular traps (NETs) induced by M. hyopneumoniae were completely degraded by this nuclease. In addition, when PK15 cells were incubated with different concentrations of rMhp597, their viability was reduced and cell apoptosis was observed in a dose-dependent manner. To further investigate the host immune system response, we report that rMhp597 up-regulated the exression of inflammatory genes showing that TLR4/MyD88/NF-κB signal pathway was involved. On the other hand, rMhp597 down-regulated the expression of type I IFN (IFN-α/β) and promoted the multiplication of porcine reproductive and respiratory syndrome virus (PRRSV). Recombinant rMhp597δ^315-377 lacking C-terminal 63 amino acids exhibited all biological functions mentioned above except for nuclease activity. In summary, Mhp597 is a dynamic secreted nuclease involved in cytotoxicity, inflammation and immunosuppression.

Comparative genomics analysis of Mycoplasma capricolum subsp. capripneumoniae 87001

Mycoplasma capricolum subsp. capripneumoniae (Mccp), belongs to Mycoplasma mycoides cluster and is a causal pathogen of contagious caprine pleuropneumonia (CCPP). This paper presents the complete annotated genome sequence of Mccp Strain 87001-a strain that was isolated from pneumonia affected goats on a farm in China, and comparative genomics analysis of five Mccp genomes in addition to comparative genomics within Mycoplasma mycoides cluster. The Mccp strain 87001 genome consists of a single circular chromosome 1017333 bp in length and encodes 898 open reading frames (orfs) averaging 944 bp in length. Fifty eight potential virulence genes were identified, including variable surface lipoproteins, hemolysin A, and P60 surface lipoprotein. Comparative genomic analysis revealed eight virulence genes and four extracellular genes which remained unchanged in five Mccp genomes for forty years, which can be used as potential target for drug development and vaccine design. We revealed 183 Mccp unique genes as markers to distinguish Mccp with other mycoplasma strains from goats, and different virulence factors contributing to host specificity and different syndrome of bovine pathogens and caprine pathogens.

Direct Transfer of a Mycoplasma mycoides Genome to Yeast Is Enhanced by Removal of the Mycoides Glycerol Uptake Factor Gene glpF

We previously discovered that intact bacterial chromosomes can be directly transferred to a yeast host cell where they can propagate as centromeric plasmids by fusing bacterial cells with S accharomyces cerevisiae spheroplasts. Inside the host any desired number of genetic changes can be introduced into the yeast centromeric plasmid to produce designer genomes that can be brought to life using a genome transplantation protocol. Earlier research demonstrated that the removal of restriction-systems from donor bacteria, such as Mycoplasma mycoides, Mycoplasma capricolum, or Haemophilus influenzae increased successful genome transfers. These findings suggested that other genetic factors might also impact the bacteria-to-yeast genome transfer process. In this study, we demonstrated that the removal of a particular genetic factor, the glycerol uptake facilitator protein gene glpF from M. mycoides, significantly increased direct genome transfer by up to 21-fold. Additionally, we showed that intact bacterial cells were endocytosed by yeast spheroplasts producing organelle-like structures within these yeast cells. These might lead to the possibility of creating novel synthetic organelles.

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.

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.

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.

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.

Respiratory explants as a model to investigate early events of contagious bovine pleuropneumonia infection

Contagious bovine pleuropneumonia (CBPP) is a severe disease caused by Mycoplasma mycoides subsp. mycoides (Mmm). Knowledge on CBPP pathogenesis is fragmented and hampered by the limited availability of laboratory animal and in vitro models of investigation. The purpose of the present study is to assess respiratory explants as useful tools to study the early stages of CBPP. Explants were obtained from trachea, bronchi and lungs of slaughtered cattle, tested negative for Mycoplasma spp. and for the major bacterial and viral respiratory pathogens. The interaction of Mmm with explant cells was studied by immunohistochemistry (IHC), double-labelling indirect immunofluorescence (DLIIF) and laser scanning confocal microscopy (LSCM). Mmm capability to survive and proliferate within the explants was evaluated by standard microbiological procedures. Finally, the putative cellular internalization of Mmm was further investigated by the gentamicin invasion assay. IHC and DLIIF indicated that Mmm can colonize explants, showing a marked tropism for lower airways. Specifically, Mmm was detected on/inside the bronchiolar and alveolar epithelial cells, the alveolar macrophages and the endothelial cells. The interaction between Mmm and explant cells was abolished by the pre-incubation of the pathogen with bovine anti-Mmm immune sera. Mmm was able to survive and proliferate in all tracheal, bronchial and lung explants, during the entire time course of the experiments. LSCM and gentamicin invasion assay both confirmed that Mmm can enter non-phagocytic host cells. Taken together, our data supports bovine respiratory explants as a promising tool to investigate CBPP, alternative to cattle experimental infection.

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.

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.

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.

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.

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.

Genetic loci of Mycoplasma agalactiae involved in systemic spreading during experimental intramammary infection of sheep

Mycoplasmas are amongst the most successful pathogens of both humans and animals yet the molecular basis of mycoplasma pathogenesis is poorly understood. This is partly due to the lack of classical virulence factors and little similarity to common bacterial pathogenic determinants. Using Mycoplasma agalactiae as a model we initiated research in this direction by screening a transposon mutant library in the natural sheep host using a negative selection method. Having successfully identified putative factors involved in the colonization of local infection and lymphogenic sites, the current study assessed mutants unable to spread systemically in sheep after experimental intramammary infection. Analysis of distant body sites for complete absence of mutants via SSM PCR revealed that additional set of genes, such as pdhB, oppC, oppB, gtsB, MAG1890, MAG5520 and MAG3650 are required for systemic spreading apart from those that were necessary for initial colonization. Additional in vitro studies with the mutants absent at these systemic sites confirmed the potential role of some of the respective gene products concerning their interaction with host cells. Mutants of pdhB, oppC and MAG4460 exhibited significantly slower growth in the presence of HeLa cells in MEM medium. This first attempt to identify genes exclusively required for systemic spreading provides a basis for further in-depth research to understand the exact mechanism of chronicity and persistence of M. agalactiae.

Transcriptome analysis of Cronobacter sakazakii ATCC BAA-894 after interaction with human intestinal epithelial cell line HCT-8

Cronobacter spp. are opportunistic pathogens that are responsible for infections including severe meningitis, septicemia, and necrotizing enterocolitis in neonates and infants. To date, questions still remain regarding the mechanisms of pathogenicity and virulence determinants for each bacterial strain. In this study, we established an in vitro model for Cronobacter sakazakii ATCC BAA-894 infection of HCT-8 human colorectal epithelial cells. The transcriptome profile of C. sakazakii ATCC BAA-894 after interaction with HCT-8 cells was determined using high-throughput whole-transcriptome sequencing (RNA sequencing (RNA-seq)). Gene expression profiles indicated that 139 genes were upregulated and 72 genes were downregulated in the adherent C. sakazakii ATCC BAA-894 strain on HCT-8 cells compared to the cultured bacteria in the cell-free medium. Expressions of some flagella genes and virulence factors involved in adherence were upregulated. High osmolarity and osmotic stress-associated genes were highly upregulated, as well as genes responsible for the synthesis of lipopolysaccharides and outer membrane proteins, iron acquisition systems, and glycerol and glycerophospholipid metabolism. In sum, our study provides further insight into the mechanisms underlying C. sakazakii pathogenesis in the human gastrointestinal tract.

Capsular polysaccharide from Mycoplasma mycoides subsp. mycoides shows potential for protection against contagious bovine pleuropneumonia

Contagious Bovine Pleuropneumonia (CBPP) is a severe respiratory disease caused by Mycoplasma mycoides subsp. mycoides (Mmm) which is widespread in Africa. The capsule polysaccharide (CPS) of Mmm is one of the few identified virulence determinants. In a previous study, immunization of mice against CPS generated antibodies, but they were not able to prevent multiplication of Mmm in this model animal. However, mice cannot be considered as a suitable animal model, as Mmm does not induce pathology in this species. Our aim was to induce antibody responses to CPS in cattle, and challenge them when they had specific CPS antibody titres similar or higher than those from cattle vaccinated with the live vaccine. The CPS was linked to the carrier protein ovalbumin via a carbodiimide-mediated condensation with 1-ethyl-3(3-imethylaminopropyl) carbodiimide (EDC). Ten animals were immunized twice and challenged three weeks after the booster inoculation, and compared to a group of challenged non-immunized cattle. When administered subcutaneously to adult cattle, the vaccine elicited CPS-specific antibody responses with the same or a higher titre than animals vaccinated with the live vaccine. Pathology in the group of immunized animals was significantly reduced (57%) after challenge with Mmm strain Afadé compared to the non-immunized group, a figure in the range of the protection provided by the live vaccine.

Chronic Infection and Severe Asthma

Chronic bacterial infection is implicated in both the development and severity of asthma. The atypical bacteria Mycoplasma pneumoniae and Chlamydophila pneumoniae have been identified in the airways of asthmatics and correlated with clinical features such as adult onset, exacerbation risks, steroid sensitivity, and symptom control. Asthmatic patients with evidence of bacterial infection may benefit from antibiotic treatment directed towards these atypical organisms. Examination of the airway microbiome may identify microbial communities that confer risk for or protection from severe asthma.

Hydrogen sulfide is a novel potential virulence factor of Mycoplasma pneumoniae: characterization of the unusual cysteine desulfurase/desulfhydrase HapE

Mycoplasma pneumoniae is a human pathogen causing atypical pneumonia with a minimalized and highly streamlined genome. So far, hydrogen peroxide production, cytadherence, and the ADP-ribosylating CARDS toxin have been identified as pathogenicity determinants. We have studied haemolysis caused by M. pneumoniae, and discovered that hydrogen peroxide is responsible for the oxidation of heme, but not for lysis of erythrocytes. This feature could be attributed to hydrogen sulfide, a compound that has previously not been identified as virulence factor in lung pathogens. Indeed, we observed hydrogen sulfide production by M. pneumoniae. The search for a hydrogen sulfide-producing enzyme identified HapE, a protein with similarity to cysteine desulfurases. In contrast to typical cysteine desulfurases, HapE is a bifunctional enzyme: it has both the cysteine desulfurase activity to produce alanine and the cysteine desulfhydrase activity to produce pyruvate and hydrogen sulfide. Experiments with purified HapE showed that the enzymatic activity of the protein is responsible for haemolysis, demonstrating that HapE is a novel potential virulence factor of M. pneumoniae.

In-Yeast Engineering of a Bacterial Genome Using CRISPR/Cas9

One remarkable achievement in synthetic biology was the reconstruction of mycoplasma genomes and their cloning in yeast where they can be modified using available genetic tools. Recently, CRISPR/Cas9 editing tools were developed for yeast mutagenesis. Here, we report their adaptation for the engineering of bacterial genomes cloned in yeast. A seamless deletion of the mycoplasma glycerol-3-phosphate oxidase-encoding gene (glpO) was achieved without selection in one step, using 90 nt paired oligonucleotides as templates to drive recombination. Screening of the resulting clones revealed that more than 20% contained the desired deletion. After manipulation, the overall integrity of the cloned mycoplasma genome was verified by multiplex PCR and PFGE. Finally, the edited genome was back-transplanted into a mycoplasma recipient cell. In accordance with the deletion of glpO, the mutant mycoplasma was affected in the production of H2O2. This work paves the way to high-throughput manipulation of natural or synthetic genomes in yeast.

Changes in pathogenicity and immunogenicity of Mycoplasma mycoides subsp. mycoides strains revealed by comparative genomics analysis

Mycoplasma mycoides subsp. mycoides is the causative agent of contagious bovine pleuropneumonia. A pathogenic strain BEN-1 was isolated from bovine lung and underwent continuous passages in rabbits for 468 generations. During this process, the strain's strong virulence became weak and, gradually, it lost the ability to confer protective immunity in cattle but developed virulence in rabbits. In order to gain insight into the mechanisms behind the reduction in virulence and the loss of immunogenicity, we sequenced five representative strains of the BEN series, including the original strain (BEN-1), the strain generation that first acquired virulence in rabbits (BEN-50), the two vaccine strain generations (BEN-181 and BEN-326), and the strain generation showing the greatest loss of immunogenicity (BEN-468). The gene mutation rate in the four different propagation stages varied greatly, and over half of variations observed in each generation were removed during the propagation process. However, the variation maintained in the BEN-468 generation might contribute to its changes in virulence and immunogenicity. We thus identified 18 genes associated with host adaptation, six genes contributing to virulence in cattle, and 35 genes participating in conferring immunity in cattle. These findings might help us optimize the vaccine to obtain more effective immunization results.

Proteomic characterization of pleural effusion, a specific host niche of Mycoplasma mycoides subsp. mycoides from cattle with contagious bovine pleuropneumonia (CBPP)

Mycoplasma mycoides subsp. mycoides (Mmm) is the causative agent of contagious bovine pleuropneumonia (CBPP), a severe pleuropneumonia in cattle. The abnormal accumulation of pleural fluid, called pleural effusion (PE), is one of the characteristics of this disease. We performed a proteomic analysis of seven PE samples from experimentally infected cattle and characterized their composition with respect to bovine and Mmm proteins. We detected a total of 963 different bovine proteins. Further analysis indicated a strong enrichment of proteins involved in antigen processing, platelet activation and degranulation and apoptosis and an increased abundance of acute phase proteins.With regard to the pathogen, up to 108 viable mycoplasma cells per ml were detected in the PE supernatant. The proteomic analysis revealed 350 mycoplasma proteins, including proteins involved in virulence-associated processes like hydrogen peroxide (H2O2) production and capsule synthesis. The bovine proteins detected will aid to characterize the inflammasome during an acute pleuropneumonia in cattle and the identified mycoplasma proteins will serve as baseline data to be compared with in vitro studies to improve our understanding of pathogenicity mechanisms. Based on our results, we named the pleural effusion an “in vivo niche” of Mmm during the acute phase of CBPP. Biological significance: This is the first study on bovine pleural effusions derived from an infectious disease and the first approach to characterize the proteome of Mycoplasma mycoides in vivo. This study revealed a high number of viable Mmm cells in the pleural effusion. The bovine pleural effusion proteome during Mmm infection is qualitatively similar to plasma, but differs with respect to high abundance of acute phase proteins. On the other hand,Mmm in its natural host produces proteins involved in capsule synthesis, H2O2 production and induction of inflammatory response, supporting previous knowledge on mechanisms underlying the survival and virulence of this pathogen while inside the natural host. This knowledge forms a profound basis for testing the identified protein candidates for diagnostics or vaccines.

Free exopolysaccharide from Mycoplasma mycoides subsp. mycoides possesses anti-inflammatory properties

In this study we explored the immunomodulatory properties of highly purified free galactan, the soluble exopolysaccharide secreted by Mycoplasma mycoides subsp. mycoides (Mmm). Galactan was shown to bind to TLR2 but not TLR4 using HEK293 reporter cells and to induce the production of the anti-inflammatory cytokine IL-10 in bovine macrophages, whereas low IL-12p40 and no TNF-α, both pro-inflammatory cytokines, were induced in these cells. In addition, pre-treatment of macrophages with galactan substantially reduced lipopolysaccharide (LPS)-induced production of pro-inflammatory cytokines TNF- and IL-12p40 while increasing LPS-induced secretion of immunosuppressive IL-10. Also, galactan did not activate naïve lymphocytes and induced only low production of the Th1 cytokine IFN-γ in Mmm-experienced lymphocytes. Finally, galactan triggered weak recall proliferation of CD4+ T lymphocytes from contagious bovine pleuropneumonia-infected animals despite having a positive effect on the expression of co-stimulatory molecules on macrophages. All together, these results suggest that galactan possesses anti-inflammatory properties and potentially provides Mmm with a mechanism to evade host innate and adaptive cell-mediated immune responses.

Cellular metabolic network analysis: discovering important reactions in Treponema pallidum

T. pallidum, the syphilis-causing pathogen, performs very differently in metabolism compared with other bacterial pathogens. The desire for safe and effective vaccine of syphilis requests identification of important steps in T. pallidum's metabolism. Here, we apply Flux Balance Analysis to represent the reactions quantitatively. Thus, it is possible to cluster all reactions in T. pallidum. By calculating minimal cut sets and analyzing topological structure for the metabolic network of T. pallidum, critical reactions are identified. As a comparison, we also apply the analytical approaches to the metabolic network of H. pylori to find coregulated drug targets and unique drug targets for different microorganisms. Based on the clustering results, all reactions are further classified into various roles. Therefore, the general picture of their metabolic network is obtained and two types of reactions, both of which are involved in nucleic acid metabolism, are found to be essential for T. pallidum. It is also discovered that both hubs of reactions and the isolated reactions in purine and pyrimidine metabolisms play important roles in T. pallidum. These reactions could be potential drug targets for treating syphilis.