Molecular basis of size and antigenic variation of a Mycoplasma hominis adhesin encoded by divergent vaa genes

Unraveling the adaptive strategies of Mycoplasma hominis through proteogenomic profiling of clinical isolates

Introduction

Mycoplasma hominis (M. hominis) belongs to the class Mollicutes, characterized by a very small genome size, reduction of metabolic pathways, including transcription factors, and the absence of a cell wall. Despite this, they adapt well not only to specific niches within the host organism but can also spread throughout the body, colonizing various organs and tissues. The adaptation mechanisms of M. hominis, as well as their regulatory pathways, are poorly understood. It is known that, when adapting to adverse conditions, Mycoplasmas can undergo phenotypic switches that may persist for several generations.

Methods

To investigate the adaptive properties of M. hominis related to survival in the host, we conducted a comparative phenotypic and proteogenomic analysis of eight clinical isolates of M. hominis obtained from patients with urogenital infections and the laboratory strain H-34.

Results

We have shown that clinical isolates differ in phenotypic features from the laboratory strain, form biofilms more effectively and show resistance to ofloxacin. The comparative proteogenomic analysis revealed that, unlike the laboratory strain, the clinical isolates possess several features related to stress survival: they switch carbon metabolism, activating the energetically least advantageous pathway of nucleoside utilization, which allows slowing down cellular processes and transitioning to a starvation state; they reconfigure the repertoire of membrane proteins; they have integrative conjugative elements in their genomes, which are key mediators of horizontal gene transfer. The upregulation of the methylating subunit of the restriction-modification (RM) system type I and the additional components of RM systems found in clinical isolates suggest that DNA methylation may play a role in regulating the adaptation mechanisms of M. hominis in the host organism. It has been shown that based on the proteogenomic profile, namely the genome sequence, protein content, composition of the RM systems and additional subunits HsdM, HsdS and HsdR, composition and number of transposable elements, as well as the sequence of the main variable antigen Vaa, we can divide clinical isolates into two phenotypes: typical colonies (TC), which have a high growth rate, and atypical (aTC) mini-colonies, which have a slow growth rate and exhibit properties similar to persisters.

Discussion

We believe that the key mechanism of adaptation of M. hominis in the host is phenotypic restructuring, leading to a slowing down cellular processes and the formation of small atypical colonies. This is due to a switch in carbon metabolism and activation the pathway of nucleoside utilization. We hypothesize that DNA methylation may play a role in regulating this switch.

Molecular Bases of Protein Antigenicity and Determinants of Immunogenicity, Anergy, and Mitogenicity

BACKGROUND

The immune system is able to recognize substances that originate from inside or outside the body and are potentially harmful. Foreign substances that bind to immune system components exhibit antigenicity and are defined as antigens. The antigens exhibiting immunogenicity can induce innate or adaptive immune responses and give rise to humoral or cell-mediated immunity. The antigens exhibiting mitogenicity can cross-link cell membrane receptors on B and T lymphocytes leading to cell proliferation. All antigens vary greatly in physicochemical features such as biochemical nature, structural complexity, molecular size, foreignness, solubility, and so on.

OBJECTIVE

Thus, this review aims to describe the molecular bases of protein-antigenicity and those molecular bases that lead to an immune response, lymphocyte proliferation, or unresponsiveness.

CONCLUSION

The epitopes of an antigen are located in surface areas; they are about 880-3,300 Da in size. They are protein, carbohydrate, or lipid in nature. Soluble antigens are smaller than 1 nm and are endocytosed less efficiently than particulate antigens. The more the structural complexity of an antigen increases, the more the antigenicity increases due to the number and variety of epitopes. The smallest immunogens are about 4,000-10,000 Da in size. The more phylogenetically distant immunogens are from the immunogen-recipient, the more immunogenicity increases. Antigens that are immunogens can trigger an innate or adaptive immune response. The innate response is induced by antigens that are pathogen-associated molecular patterns. Exogenous antigens, T Dependent or T Independent, induce humoral immunogenicity. TD protein-antigens require two epitopes, one sequential and one conformational to induce antibodies, whereas, TI non-protein-antigens require only one conformational epitope to induce low-affinity antibodies. Endogenous protein antigens require only one sequential epitope to induce cell-mediated immunogenicity.

SARS-CoV-2, Zika viruses and mycoplasma: Structure, pathogenesis and some treatment options in these emerging viral and bacterial infectious diseases

The molecular evolution of life on earth along with changing environmental, conditions has rendered mankind susceptible to endemic and pandemic emerging infectious diseases. The effects of certain systemic viral and bacterial infections on morbidity and mortality are considered as examples of recent emerging infections. Here we will focus on three examples of infections that are important in pregnancy and early childhood: SARS-CoV-2 virus, Zika virus, and Mycoplasma species. The basic structural characteristics of these infectious agents will be examined, along with their general pathogenic mechanisms. Coronavirus infections, such as caused by the SARS-CoV-2 virus, likely evolved from zoonotic bat viruses to infect humans and cause a pandemic that has been the biggest challenge for humanity since the Spanish Flu pandemic of the early 20th century. In contrast, Zika Virus infections represent an expanding infectious threat in the context of global climate change. The relationship of these infections to pregnancy, the vertical transmission and neurological sequels make these viruses highly relevant to the topics of this special issue. Finally, mycoplasmal infections have been present before mankind evolved, but they were rarely identified as human pathogens until recently, and they are now recognized as important coinfections that are able to modify the course and prognosis of various infectious diseases and other chronic illnesses. The infectious processes caused by these intracellular microorganisms are examined as well as some general aspects of their pathogeneses, clinical presentations, and diagnoses. We will finally consider examples of treatments that have been used to reduce morbidity and mortality of these infections and discuss briefly the current status of vaccines, in particular, against the SARS-CoV-2 virus. It is important to understand some of the basic features of these emerging infectious diseases and the pathogens involved in order to better appreciate the contributions of this special issue on how infectious diseases can affect human pregnancy, fetuses and neonates.

Planctomycetes attached to algal surfaces: Insight into their genomes

Planctomycetes are bacteria with complex molecular and cellular biology. They have large genomes, some over 7Mb, and complex life cycles that include motile cells and sessile cells. Some live on the complex biofilm of macroalgae. Factors governing their life in this environment were investigated at the genomic level. We analyzed the genomes of three planctomycetes isolated from algal surfaces. The genomes were 6.6Mbp to 8.1Mbp large. Genes for outer-membrane proteins, peptidoglycan and lipopolysaccharide biosynthesis were present. Rubripirellula obstinata LF1T, Roseimaritima ulvae UC8T and Mariniblastus fucicola FC18T shared with Rhodopirellula baltica and R. rubra SWK7 unique proteins related to metal binding systems, phosphate metabolism, chemotaxis, and stress response. These functions may contribute to their ecological success in such a complex environment. Exceptionally huge proteins (6000 to 10,000 amino-acids) with extracellular, periplasmic or membrane-associated locations were found which may be involved in biofilm formation or cell adhesion.

Production of a chimeric protein and its potential application in sero-diagnosis of Mycoplasma hominis infection

INTRODUCTION

Mycoplasma hominis is an opportunistic pathogen of the human genital tract. Detection of antibodies against this organism in human serum or plasma is theoretically unreliable because of high variation in bacterial surface antigens. In this study, we applied the bioinformatics tools to design a chimeric protein constructed of specific, conserved and predicted immuno-dominant epitopes from two different membrane proteins, P120 and P80.

MATERIAL AND METHODS

Linear B-cell epitopes of P120 and P80 were predicted and evaluated by bioinformatics tools and the designed chimeric protein was expressed in Escherichia coli. The chimeric protein, Mh128, was further analyzed in terms of immuno-reactivity by western blotting and enzyme immuno-sorbent assay (ELISA).

RESULTS

We found eight specific, conserved and immuno-dominant epitopes within P120 and P80 based on the bioinformatic studies. The constructed chimeric protein showed immuno-reaction in both western-blotting and ELISA tests.

DISCUSSION

Because of extensive variation of genomic and antigenic structure, diagnosis of M. hominis infection is difficult. Mh128 as a predicted specific and conserved recombinant protein can be potentially used for sero-diagnosis of M. hominis infection. We plan to develop an immuno-assay based on Mh128 and further evaluate the clinical specificity and sensitivity of the method.

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.

Cloning, Stability, and Modification of Mycoplasma hominis Genome in Yeast

Mycoplasma hominis is a minimal human pathogen that is responsible for genital and neonatal infections. Despite many attempts, there is no efficient genetic tool to manipulate this bacterium, limiting most investigations of its pathogenicity and its uncommon energy metabolism that relies on arginine. The recent cloning and subsequent engineering of other mycoplasma genomes in yeast opens new possibilities for studies of the genomes of genetically intractable organisms. Here, we report the successful one-step cloning of the M. hominis PG21 genome in yeast using the transformation-associated recombination (TAR) cloning method. At low passages, the M. hominis genome cloned into yeast displayed a conserved size. However, after ∼60 generations in selective media, this stability was affected, and large degradation events were detected, raising questions regarding the stability of large heterologous DNA molecules cloned in yeast and the need to minimize host propagation. Taking these results into account, we selected early passage yeast clones and successfully modified the M. hominis PG21 genome using the CRISPR/Cas9 editing tool, available in Saccharomyces cerevisiae. Complete M. hominis PG21 genomes lacking the adhesion-related vaa gene were efficiently obtained.

Cardiothoracic Transplant Recipient Mycoplasma hominis: An Uncommon Infection with Probable Donor Transmission

The role of infection with Mycoplasma hominis following cardiothoracic organ transplantation and its source of transmission have not been well-defined. Here, we identify and describe infection with M. hominis in patients following cardiothoracic organ transplantation after reviewing all cardiothoracic transplantations performed at our center between 1998 and July 2015. We found seven previously unreported cases of M. hominis culture positive infection all of whom presented with pleuritis, surgical site infection, and/or mediastinitis. PCR was used to establish the diagnosis in four cases. In two instances, paired single lung transplant recipients manifested infection, and in one of these pairs, isolates were indistinguishable by multilocus sequence typing (MLST). To investigate the prevalence of M. hominis in the lower respiratory tract, we tested 178 bronchoalveolar lavage (BAL) fluids collected from immunocompromised subjects for M. hominis by PCR; all were negative. Review of the literature revealed an additional 15 cases of M. hominis in lung transplant recipients, most with similar clinical presentations to our cases. We recommend that M. hominis should be considered in post-cardiothoracic transplant infections presenting with pleuritis, surgical site infection, or mediastinitis. M. hominis PCR may facilitate early diagnosis and prompt therapy. Evaluation for possible donor transmission should be considered.

Repetitive Elements in Mycoplasma hyopneumoniae Transcriptional Regulation

Transcriptional regulation, a multiple-step process, is still poorly understood in the important pig pathogen Mycoplasma hyopneumoniae. Basic motifs like promoters and terminators have already been described, but no other cis-regulatory elements have been found. DNA repeat sequences have been shown to be an interesting potential source of cis-regulatory elements. In this work, a genome-wide search for tandem and palindromic repetitive elements was performed in the intergenic regions of all coding sequences from M. hyopneumoniae strain 7448. Computational analysis demonstrated the presence of 144 tandem repeats and 1,171 palindromic elements. The DNA repeat sequences were distributed within the 5' upstream regions of 86% of transcriptional units of M. hyopneumoniae strain 7448. Comparative analysis between distinct repetitive sequences found in related mycoplasma genomes demonstrated different percentages of conservation among pathogenic and nonpathogenic strains. qPCR assays revealed differential expression among genes showing variable numbers of repetitive elements. In addition, repeats found in 206 genes already described to be differentially regulated under different culture conditions of M. hyopneumoniae strain 232 showed almost 80% conservation in relation to M. hyopneumoniae strain 7448 repeats. Altogether, these findings suggest a potential regulatory role of tandem and palindromic DNA repeats in the M. hyopneumoniae transcriptional profile.

Identification of a gene in Mycoplasma hominis associated with preterm birth and microbial burden in intraamniotic infection

OBJECTIVE

Microbial invasion of the amniotic cavity is associated with spontaneous preterm labor and adverse pregnancy outcome, and Mycoplasma hominis often is present. However, the pathogenic process by which M hominis invades the amniotic cavity and gestational tissues, often resulting in chorioamnionitis and preterm birth, remains unknown. We hypothesized that strains of M hominis vary genetically with regards to their potential to invade and colonize the amniotic cavity and placenta.

STUDY DESIGN

We sequenced the entire genomes of 2 amniotic fluid isolates and a placental isolate of M hominis from pregnancies that resulted in preterm births and compared them with the previously sequenced genome of the type strain PG21. We identified genes that were specific to the amniotic fluid/placental isolates. We then determined the microbial burden and the presence of these genes in another set of subjects from whom samples of amniotic fluid had been collected and were positive for M hominis.

RESULTS

We identified 2 genes that encode surface-located membrane proteins (Lmp1 and Lmp-like) in the sequenced amniotic fluid/placental isolates that were truncated severely in PG21. We also identified, for the first time, a microbial gene of unknown function that is referred to in this study as gene of interest C that was associated significantly with bacterial burden in amniotic fluid and the risk of preterm delivery in patients with preterm labor.

CONCLUSION

A gene in M hominis was identified that is associated significantly with colonization and/or infection of the upper reproductive tract during pregnancy and with preterm birth.

A potential pathogenic factor from Mycoplasma hominis is a TLR2-dependent, macrophage-activating, P50-related adhesin

PROBLEM

Mycoplasma hominis has been implicated in many inflammatory conditions of the human urogenital tract in particular amniotic infections that lead to fetal and neonatal disease and pre-term labor. The mechanisms responsible are poorly defined.

METHOD OF STUDY

Biochemical and immunological methods were used to extract, purify, and characterize an inflammatory component present in M. hominis.

RESULTS

We isolated and purified to homogeneity a 40-kDa bioactive lipoprotein from M. hominis that was a potent TLR2-dependent, CD14-independent activator of the human THP-1 macrophage cell line. Homology searches of the N-terminal sequence revealed that 22 of the first 23 residues were identical to those seen for the phase-variable M. hominis p50 adhesin. The truncated P50t lipoprotein importantly retained its adhesive properties for human macrophages.

CONCLUSION

The unique adhesin/macrophage activator may play a key role in M. hominis infections by triggering an inflammatory cytokine cascade.

Protein domain repetition is enriched in Streptococcal cell-surface proteins

Tandem repetition of domain in protein sequence occurs in all three domains of life. It creates protein diversity and adds functional complexity in organisms. In this work, we analyzed 52 streptococcal genomes and found 3748 proteins contained domain repeats. Proteins not harboring domain repeats are significantly enriched in cytoplasm, whereas proteins with domain repeats are significantly enriched in cytoplasmic membrane, cell wall and extracellular locations. Domain repetition occurs most frequently in S. pneumoniae and least in S. thermophilus and S. pyogenes. DUF1542 is the highest repeated domain in a single protein, followed by Rib, CW_binding_1, G5 and HemolysinCabind. 3D structures of 24 repeat-containing proteins were predicted to investigate the structural and functional effect of domain repetition. Several repeat-containing streptococcal cell surface proteins are known to be virulence-associated. Surface-associated tandem domain-containing proteins without experimental functional characterization may be potentially involved in the pathogenesis of streptococci and deserve further investigation.

Mycoplasma pulmonis Vsa proteins and polysaccharide modulate adherence to pulmonary epithelial cells

The Mycoplasma pulmonis Vsa proteins are a family of size- and phase-variable lipoproteins that shield the mycoplasmas from complement and modulate attachment to abiotic surfaces. Mycoplasmas producing a long Vsa protein hemadsorb poorly and yet are proficient at colonizing rats and mice. The effect of the length of the Vsa protein on the attachment of mycoplasmas to epithelial cells has not been previously explored. We find that independent of Vsa isotype, mycoplasmas producing a long Vsa protein with many tandem repeats adhere poorly to murine MLE-12 cells compared with mycoplasmas producing a short Vsa. We also find that mutants lacking the EPS-I polysaccharide of M. pulmonis exhibited decreased adherence to MLE-12 cells, even though it has been shown previously that such mutants have an enhanced ability to form a biofilm.

In Mycoplasma hominis the OppA-mediated cytoadhesion depends on its ATPase activity

Background

In Mycoplasma hominis, a facultative human pathogen of the human genital tract, OppA, the substrate-binding domain of the oligopeptide permease, is a multifunctional protein involved in nutrition uptake, cytoadhesion and hydrolysis of extracellular ATP.

Results

To map the function-related protein regions the ATPase activity and adhesive behavior of OppA mutants were analyzed. Mutations of the Walker BA motifs resulted in an inhibition of up to 8% of the OppA ATPase activity, whereas deletion of the N-terminal CS1 or the CS2 region, structural motifs that are conserved in bacterial OppA proteins, reduced ATPase activity to 60% and deletion of CS3, the third conserved region adjacent to the Walker B motif led to a reduction to 42% ATPase activity.

Interestingly, adhesion of the OppA mutants to immobilized HeLa cells demonstrated that two distal regions are mainly involved in adherence of OppA: the CS1 region, deletion of which led to 35% of the cytoadhesion, and the Walker BA with the adjacent upstream region CS3, deletion of which led to 25% of the cytoadhesion. The influence of the ATPase activity on the adherence of M. hominis to HeLa cells was confirmed by the use of ATPase inhibitors which reduced mycoplasmal cytoadhesion to 50%.

Conclusions

These findings suggest that the OppA-mediated cytoadherence of Mycoplasma hominis depends on both, the topology of the neighbouring CS1 and ATPase domain regions and the functionality of the ecto-ATPase activity in addition.

Adhesive activity of the haemophilus cryptic genospecies cha autotransporter is modulated by variation in tandem Peptide repeats

The Haemophilus cryptic genospecies is an important cause of maternal genital tract and neonatal systemic infections and initiates infection by colonizing the genital or respiratory epithelium. In recent work, we identified a unique Haemophilus cryptic genospecies protein called Cha, which mediates efficient adherence to genital and respiratory epithelia. The Cha adhesin belongs to the trimeric autotransporter family and contains an N-terminal signal peptide, an internal passenger domain that harbors adhesive activity, and a C-terminal membrane anchor domain. The passenger domain in Cha contains clusters of YadA-like head domains and neck motifs as well as a series of tandem 28-amino-acid peptide repeats. In the current study, we report that variation in peptide repeat number gradually modulates Cha adhesive activity, associated with a direct effect on the length of Cha fibers on the bacterial cell surface. The N-terminal 404 residues of the Cha passenger domain mediate binding to host cells and also facilitate bacterial aggregation through intermolecular Cha-Cha binding. As the tandem peptide repeats expand, the Cha fiber becomes longer and Cha adherence activity decreases. The expansion and contraction of peptide repeats represent a novel mechanism for modulating adhesive capacity, potentially balancing the need of the organism to colonize the genital and respiratory tracts with the ability to attach to alternative substrates, disperse within the host, or evade the host immune system.

Genetic variability of the P120' surface protein gene of Mycoplasma hominis isolates recovered from Tunisian patients with uro-genital and infertility disorders

Background

Among the surface antigens of Mycoplasma hominis, the P120' protein was previously shown to elicit a subtle antibody response and appears to be relatively conserved. To get better insight into the evolution of this protein, we analysed the genetic variability of its surface exposed region in 27 M. hominis isolates recovered from the genital tract of Tunisian patients with infertility disorders.

Methods

All specimens were processed for culture and PCR amplification of the N-terminal surface exposed region of p120' gene. PCR products were sequenced to evaluate the genetic variability, to test for adaptive selection, and to infer the phylogenetic relationship of the M. hominis isolates.

Results

Sequence analysis showed a total of 25 single nucleotide polymorphisms distributed through 23 polymorphic sites, yielding 13 haplotypes. All but one mutation were confined within three distinct regions. Analysis of the amino acid-based phylogenetic tree showed a predominant group of 17 closely related isolates while the remaining appear to have significantly diverged.

Conclusion

By analysing a larger sample of M. hominis recovered from patients with urogenital infections, we show here that the P120' protein undergoes substantial level of genetic variability at its surface exposed region.

Array-based genomic comparative hybridization analysis of field strains of Mycoplasma hyopneumoniae

Mycoplasma hyopneumoniae is the causative agent of porcine enzootic pneumonia and a major factor in the porcine respiratory disease complex. A clear understanding of the mechanisms of pathogenesis does not exist, although it is clear that M. hyopneumoniae adheres to porcine ciliated epithelium by action of a protein called P97. Previous studies have shown variation in the gene encoding the P97 cilium adhesin in different strains of M. hyopneumoniae, but the extent of genetic variation among field strains across the genome is not known. Since M. hyopneumoniae is a worldwide problem, it is reasonable to expect that a wide range of genetic variability may exist given all of the different breeds and housing conditions. This variation may impact the overall virulence of a single strain. Using microarray technology, this study examined the potential variation of 14 field strains compared to strain 232, on which the array was based. Genomic DNA was obtained, amplified with TempliPhi, and labeled indirectly with Alexa dyes. After genomic hybridization, the arrays were scanned and data were analyzed using a linear statistical model. The results indicated that genetic variation could be detected in all 14 field strains but across different loci, suggesting that variation occurs throughout the genome. Fifty-nine percent of the variable loci were hypothetical genes. Twenty-two percent of the lipoprotein genes showed variation in at least one field strain. A permutation test identified a location in the M. hyopneumoniae genome where there is spatial clustering of variability between the field strains and strain 232.

Distinctive repertoire of contingency genes conferring mutation- based phase variation and combinatorial expression of surface lipoproteins in Mycoplasma capricolum subsp. capricolum of the Mycoplasma mycoides phylogenetic cluster

The generation of surface variation among many divergent species of Mollicutes (mycoplasmas) occurs through stochastic expression patterns of diverse lipoprotein genes. The size and wide distribution of such variable gene sets in minimal (approximately 0.6- to 1.4-Mb) mycoplasmal genomes suggest their key role in the adaptation and survival of these wall-less monoderms. Diversity through variable genes is less clearly established among phylogenetically similar mycoplasmas, such as the Mycoplasma mycoides cluster of ruminant pathogens, which vary widely in host range and pathobiology. Using (i) genome sequences from two members of this clade, Mycoplasma capricolum subsp. capricolum and M. mycoides subsp. mycoides small colony biotype (SC), (ii) antibodies to specific peptide determinants of predicted M. capricolum subsp. capricolum gene products, and (iii) analysis of the membrane-associated proteome of M. capricolum subsp. capricolum, a novel set of six genes (vmcA to vmcF) expressing distinct Vmc (variable M. capricolum subsp. capricolum) lipoproteins is demonstrated. These occur at two separate loci in the M. capricolum subsp. capricolum genome, which shares striking overall similarity and gene synteny with the M. mycoides subsp. mycoides SC genome. Collectively, Vmc expression is noncoordinate and combinatorial, subject to a single-unit insertion/deletion in a 5' flanking dinucleotide repeat that governs expression of each vmc gene. All vmc genes share modular regions affecting expression and membrane translocation. In contrast, vmcA to vmcD genes at one locus express surface proteins with highly structured size-variable repeating domains, whereas vmcE to vmcF genes express products with short repeats devoid of predicted structure. These genes confer a distinctive, dynamic surface architecture that may represent adaptive differences within this important group of pathogens as well as exploitable diagnostic targets.

Characterization and Partial Purification of a Macrophage-Stimulating Factor from Mycoplasma hominis

PROBLEM

Mycoplasma hominis is one of the most common pathogens of the genital tract and is associated with increased production of proinflammatory cytokines in reproductive tissues during preterm labor. The mechanism by which M. hominis, an organism lacking cell walls, increases the production of proinflammatory cytokines is unknown.

METHOD OF STUDY

We characterized and purified a macrophage-activating factor from this organism.

RESULTS

Extraction of whole organisms with Triton-X-114 demonstrated that the activity was primarily associated with the detergent phase. Macrophage-stimulating activity (MSA) of detergent extracts of M. hominis was not inhibited by polymyxin B or heating but was completely abrogated by alkaline hydrolysis and partially reduced by proteinase K digestion. Further experiments that utilized Toll-like receptor (TLR)-2- and TLR-4-transfected cells, revealed that the detergent extracts activate TLR-2 but not TLR-4 signal transduction. Purification of the activity using preparative SDS-PAGE and reverse phase chromatography experiments led to the isolation of a 29-kDa protein.

CONCLUSIONS

These experiments suggest that the MSA of M. hominis is due to a lipophillic factor that interacts with TLR-2 rather than TLR-4 (as does lipopolysaccharide), to increase tumor necrosis factor (TNF)-alpha by macrophages. It is known that TNF-alpha can cause preterm labor and intrauterine fetal death and that it is upregulated in amniotic fluid samples infected with M. hominis.

Mycoplasmas and ureaplasmas as neonatal pathogens

The genital mycoplasmas represent a complex and unique group of microorganisms that have been associated with a wide array of infectious diseases in adults and infants. The lack of conclusive knowledge regarding the pathogenic potential of Mycoplasma and Ureaplasma spp. in many conditions is due to a general unfamiliarity of physicians and microbiology laboratories with their fastidious growth requirements, leading to difficulty in their detection; their high prevalence in healthy persons; the poor design of research studies attempting to base association with disease on the mere presence of the organisms in the lower urogenital tract; the failure to consider multifactorial aspects of diseases; and considering these genital mycoplasmas only as a last resort. The situation is now changing because of a greater appreciation of the genital mycoplasmas as perinatal pathogens and improvements in laboratory detection, particularly with regard to the development of powerful molecular nucleic acid amplification tests. This review summarizes the epidemiology of genital mycoplasmas as causes of neonatal infections and premature birth; evidence linking ureaplasmas with bronchopulmonary dysplasia; recent changes in the taxonomy of the genus Ureaplasma; the neonatal host response to mycoplasma and ureaplasma infections; advances in laboratory detection, including molecular methods; and therapeutic considerations for treatment of systemic diseases.

Association of a major protein antigen of Mycoplasma arthritidis with virulence

Mycoplasma arthritidis causes acute polyarthritis in rats and chronic proliferative arthritis in mice. M. arthritidis-induced arthritis serves as a model for arthritis caused by infectious agents and as a model for examining the role of the superantigen MAM (M. arthritidis T-cell mitogen) in the development of autoimmunity. M. arthritidis strain 158-1 is a spontaneous mutant of strain 158 that has a drastic reduction in virulence. We show that the mutant is missing a major antigen of 47 kDa (P47) and has acquired a protein of 67 kDa (P67). P47 and P67 partitioned into the detergent phase by extraction with Triton X-114. Coomassie blue staining of sodium dodecyl sulfate-polyacrylamide gels show that P67 is produced in abundance. Analysis of gel-purified P67 by mass spectrometry led to its identification as a lipoprotein (the open reading frame [ORF] 619 gene product) predicted from the genome sequence of M. arthritidis. PCR analysis of genomic DNA from 158 and 158-1 indicates that P47 and P67 are encoded by the same ORF 619 gene and differ only in the number of repeats in a tandem repeat region. By two-dimensional polyacrylamide gel analysis, no protein differences were detectable between 158 and 158-1 other than P47 and P67. Collectively, the data suggest that the tandem repeat region of P47 and P67 influences disease outcome.

The vaa locus of Mycoplasma hominis contains a divergent genetic islet encoding a putative membrane protein

BACKGROUND

The Mycoplasma hominis vaa gene encodes a highly variable, surface antigen involved in the adhesion to host cells. We have analysed the structure of the vaa locus to elucidate the genetic basis for variation of vaa.

RESULTS

Mapping of vaa on existing physical maps of five M. hominis isolates by pulsed field gel electrophoresis revealed that vaa is located in a genomic region containing the majority of other characterized membrane protein genes of M. hominis. Sequencing of an 11 kb region containing the vaa locus of M. hominis isolate 132 showed the presence of conserved housekeeping genes at the borders of the region, uvrA upstream and the hitABL operon downstream to vaa. Analysis of 20 M. hominis isolates revealed that the vaa upstream region was conserved whereas the downstream region was highly variable. In isolate 132 this region contained an open reading frame (ORF) encoding a putative 160 kDa membrane protein. Homologous ORFs were present in half of the isolates, whereas this ORF, termed vmp (variable membrane protein), was deleted from the locus in the remaining isolates. Compellingly, the conserved upstream region and variable downstream region of vaa correlates with the genetic structure of vaa itself which consists of a conserved 5' end and a variable 3' end containing a variable number of exchangeable sequence cassettes.

CONCLUSION

Our data demonstrate that the vaa locus contains a divergent genetic islet, and indicate pronounced intraspecies recombination. The high variability level of the locus indicate that it is a chromosomal 'hot spot', presumably important for sustaining diversity and a high adaptation potential of M. hominis.

Phenotypic variation of Pseudomonas brassicacearum as a plant root-colonization strategy

Pseudomonas brassicacearum was isolated as a major root-colonizing population from Arabidopsis thaliana. The strain NFM421 of P. brassicacearum undergoes phenotypic variation during A. thaliana and Brassica napus root colonization in vitro as well as in soil, resulting in different colony appearance on agar surfaces. Bacteria forming translucent colonies (phase II cells) essentially were localized at the surface of young roots and root tips, whereas wild-type cells (phase I cells) were localized at the basal part of roots. The ability of phase II cells to spread and colonize new sites on root surface correlates with over-production of flagellin as evidenced by sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis of surface proteins and microsequencing. Moreover, phase II cells showed a higher ability to swim and to swarm on semisolid agar medium. Phase I and phase II cells of P. brassicacearum NFM421 were tagged genetically with green fluorescent protein and red fluorescent protein. Confocal scanning laser microscopy was used to localize phase II cells on secondary roots and root tips of A. thaliana, whereas phase I cells essentially were localized at the basal part of roots. These experiments were conducted in vitro and in soil. Phenotypic variation on plant roots is likely to be a colonization strategy that may explain the high colonization power of P. brassicacearum.

Identification of a 349-kilodalton protein (Gli349) responsible for cytadherence and glass binding during gliding of Mycoplasma mobile

Several mycoplasma species are known to glide in the direction of the membrane protrusion (head-like structure), but the mechanism underlying this movement is entirely unknown. To identify proteins involved in the gliding mechanism, protein fractions of Mycoplasma mobile were analyzed for 10 gliding mutants isolated previously. One large protein (Gli349) was observed to be missing in a mutant m13 deficient in hemadsorption and glass binding. The predicted amino acid sequence indicated a 348,758-Da protein that was truncated at amino acid residue 1257 in the mutant. Immunofluorescence microscopy with a monoclonal antibody showed that Gli349 is localized at the head-like protrusion's base, which we designated the cell neck, and immunoelectron microscopy established that the Gli349 molecules are distributed all around this neck. The number of Gli349 molecules on a cell was estimated by immunoblot analysis to be 450 +/- 200. The antibody inhibited both the hemadsorption and glass binding of M. mobile. When the antibody was used to treat gliding mycoplasmas, the gliding speed and the extent of glass binding were inhibited to similar extents depending on the concentration of the antibody. This suggested that the Gli349 molecule is involved not only in glass binding for gliding but also in movement. To explain the present results, a model for the mechanical cycle of gliding is discussed.

Divergence and transcriptional analysis of the division cell wall (dcw) gene cluster in Neisseria spp

Three of the 18 open reading frames in the division and cell wall synthesis cluster of the pathogenic Neisseria spp. are not present in the clusters of other bacterial species. The region containing two of these, dcaB and dcaC, displays interstrain and interspecies variability uncharacteristic of such clusters. 3' of dcaB is a Correia repeat enclosed element (CREE), which is only present in some strains. It has been suggested that this CREE is a transcriptional terminator, although we demonstrate otherwise. A gearbox-like promoter within this CREE is active in Escherichia coli but not in Neisseria meningitidis. There is an active promoter 5' of dcaC, although its sequence is not conserved. The presence of similarly located promoters has not been demonstrated in other species. In Neisseria lactamica, this promoter involves another dcw-associated CREE, the first demonstration of active promoter generation at the 5' end of this common intergenic, apparently mobile, element. Upstream of this promoter is an inverted pair of neisserial uptake signal sequences, which are commonly considered to be transcriptional terminators. It has been proposed to terminate transcription in this location, although we have demonstrated transcript extending through this uptake signal sequence. dcaC contains a 108 bp tandem repeat, which is present in different copy numbers in the neisserial strains examined. This investigation reveals extensive sequence variation, disputes the presence of transcriptional terminators and identifies active internal promoters in this normally highly conserved cluster of essential genes, and addresses the transcriptional activity of two common neisserial intergenic components.

Molecular heterogeneity of Ehrlichia chaffeensis isolates determined by sequence analysis of the 28-kilodalton outer membrane protein genes and other regions of the genome

Ehrlichia chaffeensis, a tick-transmitted rickettsial agent, is responsible for human monocytic ehrlichiosis (HME). In this study, we genetically mapped 10 isolates obtained from HME patients. Sequence analysis of the 28-kDa outer membrane protein (OMP) multigene locus spanning 6 of the 22 tandemly arranged genes identified three distinct genetic groups with shared homology among isolates within each group. Isolates in Groups I and III contained six genes each, while Group II isolates had a gene deletion. There were two regions on the locus where novel gene deletion or insertion mutations occurred, resulting in the net loss of one gene in Group II isolates. Numerous nucleotide differences among genes in isolates of each group also were detected. The shared homology among isolates in each group for the 28-kDa OMP locus suggests the derivation of clonal lineages. Transcription and translation analysis of the locus revealed differences in the expressed genes of different group isolates. Analysis of the 120-kDa OMP gene and variable-length PCR target gene showed size variations resulting from loss or gain of long, direct repeats within the protein coding sequences. To our knowledge this is the first study that looked at several regions of the genome simultaneously, and we provide the first evidence of heterogeneity resulting from gene deletion and insertion mutations in the E. chaffeensis genome. Diversity in different genomic regions could be the result of a selection process or of independently evolved genes.

Multiple promoter inversions generate surface antigenic variation in Mycoplasma penetrans

Mycoplasma penetrans is a newly identified species of the genus MYCOPLASMA: It was first isolated from a urine sample from a human immunodeficiency virus (HIV)-infected patient. M. penetrans changes its surface antigen profile with high frequency. The changes originate from ON<==>OFF phase variations of the P35 family of surface membrane lipoproteins. The P35 family lipoproteins are major antigens recognized by the human immune system during M. penetrans infection and are encoded by the mpl genes. Phase variations of P35 family lipoproteins occur at the transcriptional level of mpl genes; however, the precise genetic mechanisms are unknown. In this study, the molecular mechanisms of surface antigen profile change in M. penetrans were investigated. The focus was on the 46-kDa protein that is present in M. penetrans strain HF-2 but not in the type strain, GTU. The 46-kDa protein was the product of a previously reported mpl gene, pepIMP13, with an amino-terminal sequence identical to that of the P35 family lipoproteins. Nucleotide sequencing analysis of the pepIMP13 gene region revealed that the promoter-containing 135-bp DNA of this gene had the structure of an invertible element that functioned as a switch for gene expression. In addition, all of the mpl genes of M. penetrans HF-2 were identified using the whole-genome sequence data that has recently become available for this bacterium. There are at least 38 mpl genes in the M. penetrans HF-2 genome. Interestingly, most of these mpl genes possess invertible promoter-like sequences, similar to those of the pepIMP13 gene promoter. A model for the generation of surface antigenic variation by multiple promoter inversions is proposed.

Surface diversity in Mycoplasma agalactiae is driven by site-specific DNA inversions within the vpma multigene locus

The ruminant pathogen Mycoplasma agalactiae possesses a family of abundantly expressed variable surface lipoproteins called Vpmas. Phenotypic switches between Vpma members have previously been correlated with DNA rearrangements within a locus of vpma genes and are proposed to play an important role in disease pathogenesis. In this study, six vpma genes were characterized in the M. agalactiae type strain PG2. All vpma genes clustered within an 8-kb region and shared highly conserved 5' untranslated regions, lipoprotein signal sequences, and short N-terminal sequences. Analyses of the vpma loci from consecutive clonal isolates showed that vpma DNA rearrangements were site specific and that cleavage and strand exchange occurred within a minimal region of 21 bp located within the 5' untranslated region of all vpma genes. This process controlled expression of vpma genes by effectively linking the open reading frame (ORF) of a silent gene to a unique active promoter sequence within the locus. An ORF (xer1) immediately adjacent to one end of the vpma locus did not undergo rearrangement and had significant homology to a distinct subset of genes belonging to the lambda integrase family of site-specific xer recombinases. It is proposed that xer1 codes for a site-specific recombinase that is not involved in chromosome dimer resolution but rather is responsible for the observed vpma-specific recombination in M. agalactiae.

Cloning and analysis of the gene for a major surface antigen of Mycoplasma gallisepticum

Myplasma gallisepticum infects a wide variety of gallineaceous birds including chickens, turkeys, and pheasants. Infection occurs both horizontally and vertically. Thus, control of the spread of M. gallisepticum to noninfected flocks is difficult. Continual monitoring is necessary to identify infected flocks even under the most stringent infectious control practices. Monitoring, however, is usually performed by measuring hemagglutination activity (HA) in serum, an insensitive and variable test. Variability in the HA test arises differences in agglutination antigen, changes in antigenic profiles of the M. gallisepticum strain, and variability in reading the agglutination reaction. Enzyme-linked immunosorbent assays (ELISAs) are the preferred method of testing because of the ease in obtaining sera and the sensitivity and reproducibility of the assays, but the ELISA suffers from a lack of standardization in the test antigen. The ELISA test will be more easily accepted once the test antigen has been standardized. To this end, we have identified, cloned, and characterized the gene for an antigen that has potential as a species-specific antigen for M. gallisepticum The gene codes for a 75-kD protein, P75, that is recognized during natural infections. Recombinant P75 is not recognized in immunoblots by convalescent sera produced in chickens infected with Mycoplasma synoviae, Mycoplasma gallinarum, and Mycoplasma gallinaceum or in turkeys infected with Mycoplasma meleagridis.

Identification and functional mapping of the Mycoplasma fermentans P29 adhesin

Initial adherence interactions between mycoplasmas and mammalian cells are important for host colonization and may contribute to subsequent pathogenic processes. Despite significant progress toward understanding the role of specialized, complex tip structures in the adherence of some mycoplasmas, particularly those that infect humans, less is known about adhesins through which other mycoplasmas of this host bind to diverse cell types, even though simpler surface components are likely to be involved. We show by flow cytometric analysis that a soluble recombinant fusion protein (FP29), representing the abundant P29 surface lipoprotein of Mycoplasma fermentans, binds human HeLa cells and inhibits M. fermentans binding to these cells, in both a quantitative and a saturable manner, whereas analogous fusion proteins representing other mycoplasma surface proteins did not. Constructs representing nested N- or C-terminal truncations of FP29 allowed initial mapping of this specific adherence function to a central region of the P29 sequence containing a 36-amino-acid disulfide loop. A derivative of FP29 containing a mutation converting one participating Cys to Ser, precluding intrachain disulfide bond formation, retained full activity. Together these results suggest that the direct interaction of M. fermentans with a ligand on the HeLa cell surface involves a limited segment of the P29 surface lipoprotein and requires neither the disulfide bond nor the contribution of adjacent portions of the protein. Earlier results indicating phase-variable display of monoclonal antibody surface epitopes on P29, now recognized to be outside this ligand binding region, raise the possibility that variation of mycoplasma surface architecture might alter the presentation of the binding region and the adherence phenotype. Preliminary results further indicated that FP29 could inhibit binding to HeLa cells by Mycoplasma hominis, a distinct human mycoplasma species displaying the phase-variable adhesin Vaa, but not that by Mycoplasma capricolum, an organism infecting caprine species. This result raises the additional, testable possibility that a common host cell ligand for two human mycoplasma species may be recognized through structurally dissimilar adhesins that undergo phase variation by two distinct mechanisms, governing protein expression (Vaa) or surface masking (P29).

Variable surface protein Vmm of Mycoplasma mycoides subsp. mycoides small colony type

A variable surface protein, Vmm, of the bovine pathogen Mycoplasma mycoides subsp. mycoides small colony type (M. mycoides SC) has been identified and characterized. Vmm was specific for the SC biotype and was expressed by 68 of 69 analyzed M. mycoides SC strains. The protein was found to undergo reversible phase variation at a frequency of 9 x 10(-4) to 5 x 10(-5) per cell per generation. The vmm gene was present in all of the 69 tested M. mycoides SC strains and encodes a lipoprotein precursor of 59 amino acids (aa), where the mature protein was predicted to be 36 aa and was anchored to the membrane by only the lipid moiety, as no transmembrane region could be identified. DNA sequencing of the vmm gene region from ON and OFF clones showed that the expression of Vmm was regulated at the transcriptional level by dinucleotide insertions or deletions in a repetitive region of the promoter spacer. Vmm-like genes were also found in four closely related mycoplasmas, Mycoplasma capricolum subsp. capricolum, M. capricolum subsp. capripneumoniae, Mycoplasma sp. bovine serogroup 7, and Mycoplasma putrefaciens. However, Vmm could not be detected in whole-cell lysates of these species, suggesting that the proteins encoded by the vmm-like genes lack the binding epitope for the monoclonal antibody used in this study or, alternatively, that the Vmm-like proteins were not expressed.

Site-specific proteolysis of the MALP-404 lipoprotein determines the release of a soluble selective lipoprotein-associated motif-containing fragment and alteration of the surface phenotype of Mycoplasma fermentans

The mature MALP-404 surface lipoprotein of Mycoplasma fermentans comprises a membrane-anchored N-terminal lipid-modified region responsible for macrophage activation (P. F. Mühlradt, M. Kiess, H. Meyer, R. Süssmuth, and G. Jung, J. Exp. Med. 185:1951-1958, 1997) and an external hydrophilic region that contains the selective lipoprotein-associated (SLA) motif defining a family of lipoproteins from diverse but selective prokaryotes, including mycoplasmas (M. J. Calcutt, M. F. Kim, A. B. Karpas, P. F. Mühlradt, and K. S. Wise, Infect. Immun. 67:760-771, 1999). This family generally corresponds to a computationally defined group of orthologs containing the basic membrane protein (BMP) domain. Two discrete lipid-modified forms of the abundant MALP product which vary dramatically in ratio among isolates of M. fermentans occur on the mycoplasma surface: (i) MALP-404, the full-length mature product, and (ii) MALP-2, the Toll-like receptor 2-mediated macrophage-activating lipopeptide containing the N-terminal 14 residues of the mature lipoprotein. The role of posttranslational processing in the biogenesis of MALP-2 from the prototype MALP-404 SLA-containing lipoprotein was investigated. Detergent phase fractionation of cell-bound products and N-terminal sequencing of a newly discovered released fragment (RF) demonstrated that MALP-404 was subject to site-specific proteolysis between residues 14 and 15 of the mature lipoprotein, resulting in the cell-bound MALP-2 and soluble RF products. This previously unknown mechanism of posttranslational processing among mycoplasmas suggests that specific cleavage of some surface proteins may confer efficient "secretion" of extracellular products by these organisms, with concurrent changes in the surface phenotype. This newly identified form of variation may have significant implications for host adaptation by mycoplasmas, as well as other pathogens expressing lipoproteins of the SLA (BMP) family.

Mapping antigenic sites of an immunodominant surface lipoprotein of Mycoplasma agalactiae, AvgC, with the use of synthetic peptides

As a first step toward the design of an epitope vaccine to prevent contagious agalactia, the strongly immunogenic 55-kDa protein of Mycoplasma agalactiae was studied and found to correspond to the AvgC protein encoded by the avgC gene. The avg genes of M. agalactiae, which encode four variable surface lipoproteins, display a significant homology to the vsp (variable membrane surface lipoproteins) genes of the bovine pathogen Mycoplasma bovis at their promoter region as well as their N-terminus-encoding regions. Some members of the Vsp family are known to be involved in cytoadhesion to host cells. In order to localize immunogenic peptides in the AvgC antigen, the protein sequence was submitted to epitope prediction analysis, and five sets of overlapping peptides, corresponding to five selected regions, were synthesized by Spot synthesis. Reactive peptides were selected by immunobinding assay with sera from infected sheep. The three most immunogenic epitopes were shown to be surface exposed by immunoprecipitation assays, and one of these was specifically recognized by all tested sera. Our study indicates that selected epitopes of the AvgC lipoprotein may be used to develop a peptide-based vaccine which is effective against M. agalactiae infection.

Molecular design of Mycoplasma hominis Vaa adhesin

The variable adherence-associated (Vaa) adhesin of the opportunistic human pathogen Mycoplasma hominis is a surface-exposed, membrane-associated protein involved in the attachment of the bacterium to host cells. The molecular masses of recombinant 1 and 2 cassette forms of the protein determined by a light-scattering (LS) method were 23.9 kD and 36.5 kD, respectively, and corresponded to their monomeric forms. Circular dichroism (CD) spectroscopy of the full-length forms indicated that the Vaa protein has an alpha-helical content of approximately 80%. Sequence analysis indicates the presence of coiled-coil domains in both the conserved N-terminal and antigenic variable C-terminal part of the Vaa adhesin. Experimental results obtained with recombinant proteins corresponding to the N- or C-terminal parts of the shortest one-cassette form of the protein were consistent with the hypothesis of two distinct coiled-coil regions. The one-cassette Vaa monomer appears to be an elongated protein with a axial shape ratio of 1:10. Analysis of a two-cassette Vaa type reveals a similar axial shape ratio. The results are interpreted in terms of the topological organization of the Vaa protein indicating the localization of the adherence-mediating structure.

Mycoplasma pneumoniae P1 type 1- and type 2-specific sequences within the P1 cytadhesin gene of individual strains

Mycoplasma pneumoniae strains traditionally are divided into two types, based on sequence variation in the P1 gene. Recently, however, we have identified 8 P1 subtypes by restriction fragment length polymorphism analysis. In the present study the P1 gene sequences of three P1 type 1 and two P1 type 2 M. pneumoniae strains were analyzed. A new P1 gene sequence in a type 1 strain with partial similarity to a recently reported variable region in the P1 gene of an M. pneumoniae type 2 strain (T. Kenri, R. Taniguchi, Y. Sasaki, N. Okazaki, M. Narita, K. Izumikawa, M. Umetsu, and T.Sasaki, Infect. Immun. 67:4557-4562, 1999) was identified. In addition, the P1 gene of the type 1 strain contained another region with nucleotide polymorphisms identical to a stretch in the P1 gene of one of our type 2 strains. These findings indicate that recombination between sequences specific for P1 type 1 and type 2 had occurred and that P1 type 1 and type 2 hybrid sequences can be present within the P1 gene of an individual strain. Identical or nearly identical variable P1 gene sequences were present in several repetitive regions outside the P1 gene locus in the genome of M. pneumoniae strain M129, implying recombination as a mechanism for generation of the P1 gene variation. Additionally, in the P1 gene sequences of four of the five strains studied, single-nucleotide polymorphisms different from the previously reported P1 type 1 and 2 characteristic sequences were identified. The polymorphic sites are candidate targets for genotyping of M. pneumoniae by direct sequencing of amplicons from clinical specimens.

Coupled phase-variable expression and epitope masking of selective surface lipoproteins increase surface phenotypic diversity in Mycoplasma hominis

A new mechanism expanding mycoplasmal surface diversity is described. Exposure of surface epitopes on a constitutively expressed membrane protein (P56) of Mycoplasma hominis was subject to high-frequency phase variation due to phase-variable expression of the P120 antigen and its selective masking of P56 epitopes. Phase-variable masking may confer previously unrealized adaptive capabilities on mycoplasmas.

Sequence polymorphism, predicted secondary structures, and surface-exposed conformational epitopes of Campylobacter major outer membrane protein

The major outer membrane protein (MOMP), a putative porin and a multifunction surface protein of Campylobacter jejuni, may play an important role in the adaptation of the organism to various host environments. To begin to dissect the biological functions and antigenic features of this protein, the gene (designated cmp) encoding MOMP was identified and characterized from 22 strains of C. jejuni and one strain of C. coli. It was shown that the single-copy cmp locus encoded a protein with characteristics of bacterial outer membrane proteins. Prediction from deduced amino acid sequences suggested that each MOMP subunit consisted of 18 beta-strands connected by short periplasmic turns and long irregular external loops. Alignment of the amino acid sequences of MOMP from different strains indicated that there were seven localized variable regions dispersed among highly conserved sequences. The variable regions were located in the putative external loop structures, while the predicted beta-strands were formed by conserved sequences. The sequence homology of cmp appeared to reflect the phylogenetic proximity of C. jejuni strains, since strains with identical cmp sequences had indistinguishable or closely related macrorestriction fragment patterns. Using recombinant MOMP and antibodies recognizing linear or conformational epitopes of the protein, it was demonstrated that the surface-exposed epitopes of MOMP were predominantly conformational in nature. These findings are instrumental in the design of MOMP-based diagnostic tools and vaccines.

Characterization of a multigene family undergoing high-frequency DNA rearrangements and coding for abundant variable surface proteins in Mycoplasma agalactiae

A family of abundant surface proteins (Vpmas [variable proteins of Mycoplasma agalactiae]) undergoing phase variation in M. agalactiae has been characterized using monoclonal antibodies and specific polyclonal sera. Two expressed members of 39 kDa (Vpma39) and 34 kDa (Vpma34), which varied in expression between clones of a lineage, shared a common amino-terminal sequence but were immunologically distinct. An amino-terminal oligonucleotide probe identified multiple vpma genes which were clustered within a 14-kb ClaI genomic fragment. Rearrangements were found to have occurred within the vpma locus between clones which correlated with changes in their Vpma phenotype. Two neighboring vpma genes were cloned and sequenced from one M. agalactiae clonal variant expressing Vpma39. The two genes, vpmaX and vpmaY, were orientated divergently and shared highly homologous 5' untranslated regions, 25-amino-acid (aa) lipoprotein leader sequences, and amino-terminal sequences. The vpmaY gene coded for 346 aa and 84% of the open reading frame, comprised of 1.5 units of a large repeat of 186 aa. Although the sequence for an entire second vpmaY repeat was present, it was prematurely terminated by insertion of two nucleotides. The vpmaX gene encoded 221 aa and possessed 102 aa of the 186-aa repeat of vpmaY. Many of the features in common between the vpma genes were also found to be shared by the vsp genes of M. bovis, which also undergo DNA rearrangements concomitant with phenotypic changes. Since M. bovis is the closest phylogenetic relative to M. agalactiae, the vpma and vsp gene families most probably represent homologous systems.

Molecular characterization of the Mycoplasma gallisepticum pvpA gene which encodes a putative variable cytadhesin protein

A putative cytadhesin-related protein (PvpA) undergoing variation in its expression was identified in the avian pathogen Mycoplasma gallisepticum. The pvpA gene was cloned, expressed in Escherichia coli, and sequenced. It exhibits 54 and 52% homology with the P30 and P32 cytadhesin proteins of the human pathogens Mycoplasma pneumoniae and Mycoplasma genitalium, respectively. In addition, 50% homology was found with the MGC2 cytadhesin of M. gallisepticum and 49% homology was found with a stretch of 205 amino acids of the cytadherence accessory protein HMW3 of M. pneumoniae. The PvpA molecule possesses a proline-rich carboxy-terminal region (28%) containing two identical directly repeated sequences of 52 amino acids and a tetrapeptide motif (Pro-Arg-Pro-X) which is repeated 14 times. Genetic analysis of several clonal isolates representing different expression states of the PvpA product ruled out chromosomal rearrangement as the mechanism for PvpA phase variation. The molecular basis of PvpA variation was revealed in a short tract of repeated GAA codons, encoding five successive glutamate resides, located in the N-terminal region and subject to frequent mutation generating an in-frame UAA stop codon. Size variation of the PvpA protein was observed among M. gallisepticum strains, ranging from 48 to 55 kDa and caused by several types of deletions occurring at the PvpA C-terminal end and within the two directly repeated sequences. By immunoelectron microscopy, the PvpA protein was localized on the mycoplasma cell surface, in particular on the terminal tip structure. Collectively, these findings suggest that PvpA is a newly identified variable surface cytadhesin protein of M. gallisepticum.

Gene rearrangements in the vsa locus of Mycoplasma pulmonis

The vsa genes of Mycoplasma pulmonis encode the V-1 lipoproteins. Most V-1 proteins contain repetitive domains and are thought to be involved in mycoplasma-host cell interactions. Previously, we have reported the isolation and characterization of six vsa genes comprising a 10-kb region of the genome of M. pulmonis strain KD735-15. In the current study, vsa-specific probes were used to clone several fragments from a genomic library of KD735-15 DNA and assemble a single 20-kb contig containing 11 vsa genes. The middle region of the vsa locus contains a large open reading frame (ORF) that is not a vsa gene and has undergone an internal deletion in some strains. The ORF is predicted to encode a membrane protein that may have a role in disease pathogenesis. To examine vsa genes in a strain of M. pulmonis that is unrelated to KD735-15, strain CT was studied. Through Southern hybridization and genomic cloning analyses, CT was found to possess homologs of the KD735-15 vsaA, -C, -E, and -F genes and two unique genes (vsaG and vsaH) that were not found in KD735-15. High-frequency, site-specific DNA inversions serve to regulate the phase-variable production of individual V-1 proteins. As a result of the sequence analysis of vsa recombination products, a model in which DNA inversion arises from strand exchange involving at least six nucleotides of the vrs box is proposed.

Host-pathogen interactions in mycoplasma pathogenesis: virulence and survival strategies of minimalist prokaryotes

Despite their very small genomes mycoplasmas are successful pathogens of man and a wide range of animal hosts. Because of the lack of effective therapeutics and vaccines, mycoplasma diseases continue to be a significant problem for public health as well as livestock production with major socio-economic consequences worldwide. Recent outbreaks and epidemiological studies predict that the incidence of human and animal mycoplasma diseases might increase which indicates the urgent need to develop new approaches for prevention and therapy. Development of such reagents, however, requires a solid understanding of the molecular biology of mycoplasma infections. Knowledge in this field has considerably increased during the past decade since new techniques have been developed and adapted to mycoplasmas that allow these organisms to be studied at the molecular level. Research on the two human pathogens Mycoplasma pneumoniae and Mycoplasma genitalium of which the genome sequences have recently been completed as well as the substantial number of studies carried out on the AIDS-associated mycoplasmas, Mycoplasma penetrans and Mycoplasma fermentans, has led the way, but a number of animal mycoplasmas are becoming increasingly appreciated as models for the study of the molecular basis of mycoplasma diseases. This review summarizes and highlights some of the recent findings concerning the molecular interactions that occur between pathogenic mycoplasmas and their hosts, both the common strategies as well as some unique approaches evolved by particular mycoplasma pathogens, including adherence to and uptake into non-phagocytic host cells, as well as mechanisms of escaping the host immune system.

Epitope mapping of immunogenic and adhesive structures in repetitive domains of Mycoplasma bovis variable surface lipoproteins

The family of variable surface lipoproteins (Vsps) of the bovine pathogen Mycoplasma bovis includes some of the most immunogenic antigens of this microorganism. Vsps were shown to undergo high-frequency phase and size variations and to possess extensive reiterated coding sequences extending from the N-terminal end to the C-terminal end of the Vsp molecule. In the present study, mapping experiments were conducted to detect regions with immunogenicity and/or adhesion sites in repetitive domains of four Vsp antigens of M. bovis, VspA, VspB, VspE, and VspF. In enzyme-linked immunosorbent assay experiments, sera obtained from naturally infected cattle showed antibodies to different repeating peptide units of the Vsps, particularly to units R(A)1, R(A)2, R(A)4.1, R(B)2.1, R(E)1, and R(F)1, all of which were found to contain immunodominant epitopes of three to seven amino acids. Competitive adherence trials revealed that a number of oligopeptides derived from various repeating units of VspA, VspB, VspE, and VspF partially inhibited cytoadhesion of M. bovis PG45 to embryonic bovine lung cells. Consequently, putative adherence sites were identified in the same repeating units (R(A)1, R(A)2, R(A)4.1, R(B)2.1, R(E)1, and R(F)1) and in R(F)2. The positions and lengths of the antigenic determinants were mostly identical to those of adhesion-mediating sites in all short repeating units, whereas in the considerably longer R(F)1 unit (84 amino acid residues), there was only one case of identity among four immunogenic epitopes and six adherence sites. The identification of epitopes and adhesive structures in repetitive domains of Vsp molecules is consistent with the highly immunogenic nature observed for several members of the Vsp family and suggests a possible function for these Vsp molecules as complex adherence-mediating regions in pathogenesis.

Molecular comparison of Mycoplasma hominis strains isolated from colonized women and women with various urogenital infections

Twenty Mycoplasma hominis strains isolated from colonized women and women with various urogenital infections were investigated for genetic and antigenic homogeneity by different methods. Restriction fragment length polymorphism analysis demonstrated heterogeneity for all strains, with one exception. Two strains sequentially isolated from one patient showed identical patterns. Otherwise, no clonal clustering could be detected within the strains isolated from either of the diagnostic groups. In contrast, SDS-PAGE analysis and the comparison of the immunoblot pattern revealed antigenic similarities of strains isolated from patients with bacterial vaginosis, chorioamnionitis, premature rupture of membranes and preterm delivery as well as endometritis but showed obvious differences in comparison to strains isolated from colonized women.

Life-threatening Mycoplasma hominis mediastinitis

Mycoplasma hominis infections are easily missed because conventional methods for bacterial detection may fail. Here, 8 cases of septic mediastinitis due to M. hominis are reported and reviewed in the context of previously reported cases of mediastinitis, sternum wound infection, pleuritis, or pericarditis caused by M. hominis. All 8 patients had a predisposing initial condition related to poor cardiorespiratory function, aspiration, or complications related to coronary artery surgery or other thoracic surgeries. Mediastinitis was associated with purulent pleural effusion and acute septic symptoms requiring inotropic medication and ventilatory support. Later, the patients had a tendency for indolent chronic courses with pleuritis, pericarditis, or open sternal wounds that lasted for several months. M. hominis infections may also present as mild sternum wound infection or as chronic local pericarditis or pleuritis without septic mediastinitis. Treatment includes surgical drainage and debridement. Antibiotics effective against M. hominis should be considered when treating mediastinitis of unknown etiology.

P48 major surface antigen of Mycoplasma agalactiae is homologous to a malp product of Mycoplasma fermentans and belongs to a selected family of bacterial lipoproteins

A major surface antigenic lipoprotein of Mycoplasma agalactiae, promptly recognized by the host's immune system, was characterized. The mature product, P48, showed significant similarity and shared conserved amino acid motifs with lipoproteins or predicted lipoproteins from Mycoplasma fermentans, Mycoplasma hyorhinis, relapsing fever Borrelia spp., Bacillus subtilis, and Treponema pallidum.

The vsp locus of Mycoplasma bovis: gene organization and structural features

Major lipoprotein antigens, known as variable membrane surface lipoproteins (Vsps), on the surface of the bovine pathogen Mycoplasma bovis were shown to spontaneously undergo noncoordinate phase variation between ON and OFF expression states. The high rate of Vsp phenotypic switching was also shown to be linked with DNA rearrangements that occur at high frequency in the M. bovis chromosome (I. Lysnyansky, R. Rosengarten, and D. Yogev, J. Bacteriol. 178:5395-5401, 1996). In the present study, 13 single-copy vsp genes organized in a chromosomal cluster were identified and characterized. All vsp genes encode highly conserved N-terminal domains for membrane insertion and lipoprotein processing but divergent mature Vsp proteins. About 80% of each vsp coding region is composed of reiterated coding sequences that create a periodic polypeptide structure. Eighteen distinct repetitive domains of different lengths and amino acid sequences are distributed within the products of the various vsp genes that are subject to size variation due to spontaneous insertions or deletions of these periodic units. Some of these repeats were found to be present in only one Vsp family member, whereas other repeats recurred at variable locations in several Vsps. Each vsp gene is also 5' linked to a highly homologous upstream region composed of two internal cassettes. The findings that rearrangement events are associated with Vsp phenotypic switching and that multiple regions of high sequence similarity are present upstream of the vsp genes and within the vsp coding regions suggest that modulation of the Vsp antigenic repertoire is determined by recombination processes that occur at a high frequency within the vsp locus of M. bovis.

Differential posttranslational processing confers intraspecies variation of a major surface lipoprotein and a macrophage-activating lipopeptide of Mycoplasma fermentans

The malp gene of Mycoplasma fermentans is shown to occur in single copy but to encode two discrete translated forms of lipid-modified surface protein that can be differentially expressed on isolates within this species: MALP-2, a 14-amino-acid (2-kDa) lipopeptide with potent macrophage-stimulatory activity (P. F. Mühlradt, M. Kiess, H. Meyer, R. Süssmuth, and G. Jung, J. Exp. Med. 185:1951-1958, 1997), and MALP-404, an abundant, full-length (404-amino-acid) surface lipoprotein of 41 kDa, previously designated P41 (K. S. Wise, M. F. Kim, P. M. Theiss, and S.-C. Lo, Infect. Immun. 61:3327-3333, 1993). The sequences, transcripts, and translation products of malp were compared between clonal isolates of strains PG18 (known to express P41) and II-29/1 (known to express high levels of MALP-2). Despite conserved malp DNA sequences containing full-length open reading frames and expression of full-length monocistronic transcripts in both isolates, Western blotting using a monoclonal antibody (MAb) to the N-terminal MALP-2 peptide revealed marked differences in the protein products expressed. Whereas PG18 expressed abundant MALP-404 with detectable MALP-2, II-29/1 revealed no MALP-404 even in samples containing a large comparative excess of MALP-2. Colony immunoblots with the MAb showed uniform surface expression of MALP-2 in II-29/1 populations. A second MAb to an epitope of MALP-404 outside the MALP-2 sequence predictably failed to stain II-29/1 colonies but uniformly stained PG18 populations. Collectively, these results provide evidence for novel posttranscriptional (probably posttranslational) processing pathways leading to differential intraspecies expression of a major lipoprotein, and a potent macrophage-activating lipopeptide, on the surface of M. fermentans. In the course of this study, a striking conserved motif (consensus, TD-G--DDKSFNQSAWE--), designated SLA, was identified in MALP-404; this motif is also distributed among selected lipoproteins and species from diverse bacterial genera, including Bacillus, Borrelia, Listeria, Mycoplasma, and Treponema. In addition, malp was shown to flank a chromosomal polymorphism. In eight isolates of M. fermentans examined, malp occurred upstream of an operon encoding the phase-variable P78 ABC transporter; but, in three of these isolates, a newly discovered insertion sequence, IS1630 (of the IS30 class), was located between these genes.