A surface epitope undergoing high-frequency phase variation is shared by Mycoplasma gallisepticum and Mycoplasma bovis

Avian safety guardian: Luteolin restores Mycoplasma gallisepticum-induced immunocompromise to improve production performance via inhibiting the IL-17/NF-kB pathway

Mycoplasma gallisepticum (MG) is a major pathogen causing chronic respiratory disease (CRD) in chickens. Exposure to MG poses a constant threat to chicken health and causes substantial economic losses. Antibiotics are the main treatment for MG infections, but have to struggle with antibiotic residues and MG resistance. To date, no safe and more effective prevention or treatment for MG infections has been identified. Luteolin (Lut) is a natural flavonoid compound known for its excellent anti-viral, anti-bacterial, immunoregulatory, and anti-inflammatory pharmacological activities. Herein, we established an MG-infected model using partridge shank chickens and chicken-like macrophages (HD11 cells) to investigate the effect and potential mechanism of Lut against MG-induced immune damage. According to our findings, Lut significantly inhibited the expression of MG adhesion protein (pMGA1.2) in vivo and in vitro. Lut effectively mitigated the MG-induced decrease in body weight gain, feed conversion ratio, survival rate, and serum IgG and IgA levels. Lut directly repaired MG-induced spleen and thymus damage by histopathological analysis. Furthermore, network pharmacology analysis revealed that Lut most probably resisted MG infection through the IL-17/NF-kB pathway. In vivo and in vitro experiments, Lut significantly suppressed the increase in key protein IL-17A, TRAF6, p-p65, and p-IkBα in the IL-17/NF-kB pathway. Meanwhile, Lut markedly alleviated MG-induced the increase of pro-inflammatory cytokines TNF-α, IL-6, IL-1β, pro-apoptotic genes caspase3 and caspase9, while promoting the expression of anti-apoptotic genes Bcl-2 and Bcl-XL. In summary, Lut effectively suppressed MG colonization, alleviated MG-induced the production performance degradation, inflammatory responses, and immune damage by inhibiting the IL-17/ NF-kB pathway. This study indicates Lut can serve as a safe and effective antibiotic alternative drug for preventing and treating MG-induced CRD. It also provides new evidence to explore the molecular mechanisms of MG infection.

Infection, Transmission, Pathogenesis and Vaccine Development against Mycoplasma gallisepticum

Mycoplasma sp. comprises cell wall-less bacteria with reduced genome size and can infect mammals, reptiles, birds, and plants. Avian mycoplasmosis, particularly in chickens, is primarily caused by Mycoplasma gallisepticum (MG) and Mycoplasma synoviae. It causes infection and pathology mainly in the respiratory, reproductive, and musculoskeletal systems. MG is the most widely distributed pathogenic avian mycoplasma with a wide range of host susceptibility and virulence. MG is transmitted both by horizontal and vertical routes. MG infection induces innate, cellular, mucosal, and adaptive immune responses in the host. Macrophages aid in phagocytosis and clearance, and B and T cells play critical roles in the clearance and prevention of MG. The virulent factors of MG are adhesion proteins, lipoproteins, heat shock proteins, and antigenic variation proteins, all of which play pivotal roles in host cell entry and pathogenesis. Prevention of MG relies on farm and flock biosecurity, management strategies, early diagnosis, use of antimicrobials, and vaccination. This review summarizes the vital pathogenic mechanisms underlying MG infection and recapitulates the virulence factors of MG-host cell adhesion, antigenic variation, nutrient transport, and immune evasion. The review also highlights the limitations of current vaccines and the development of innovative future vaccines against MG.

Designing of novel chimeric PvpA-pMGA protein of Mycoplasma gallisepticum, applicable for indirect ELISA

Background

Mycoplasma gallisepticum is the primary agent of chronic respiratory disease in chickens creating important economic losses in poultry industry. pMGA and pvpA genes encode major surface proteins in M. gallisepticum containing pathogenic, antigenic, and immune evasion characteristics. The objective of the present study was to design, express, and purify the recombinant chimeric PvpA-pMGA protein from M.gallisepticum for using in serological diagnostic test.

Methods

Antigenic regions of PvpA and pMGA proteins were predicted for designing chimeric pvpA-pMGA gene construct. The codon optimized sequence was cloned into the expression vector pET32a+ and transformed into the Escherichia coli strain BL21 (DE3). The pET32a-PvpA-pMGA recombinant plasmid was expressed and confirmed by SDS-PAGE and immunoblotting. PvpA-pMGA recombinant protein (20μg and 50μg), ts-11 vaccine strain, and S6 strain that formulated by montanide adjuvant and two control groups (PBS and adjuvant) were injected subcutaneously to six groups of chickens.

Results

High yield of protein was purified amount 138 mg/L by affinity batch formation method. Indirect ELISA showed the levels of antibodies in rPvpA-pMGA was significantly higher than ts-11 and S6 groups (p<0.05). The results indicated that antigen-specific response was successfully elicited by the rpMGA-PvpA in chickens. The result of the ELISA with sera collected from ts-11 and S6 groups showed that indirect PvpA-pMGA-ELISA is appropriate candidate for detection of specific antibodies against M. gallisepticum with 100% sensitivity and specificity.

Conclusions

The rPvpA-pMGA is a highly candidate immunogenic protein which induced high amount of humoral immune response. Novel rPvpA-pMGA protein could be useful for evaluation of antibody level in vaccinated poultry flocks.

Cloning of cytadhesin protein gene (pvpA) and expression analysis of recombinant fusion protein of Mycoplasma gallisepticum

Chronic respiratory disease (CRD) caused by Mycoplasma gallisepticum (MG) is one of the major respiratory tract infections of the poultry, resulting in significant economic loss to the poultry farmers. Diagnosis of such ailment is highly necessary for effective control measures. In addition, promising molecular tools are warranted for efficient epidemiological tracing of the outbreaks. The study was focused on the elucidation of phase variable cytadhesin protein gene (pvpA) of MG through cloning and expression analysis. A set of primers targeting the pvpA gene of MG was designed. The complete pvpA gene was amplified and cloned into pUC-derived expression vector pRSETA. Finally, the recombinant clones were examined through colony PCR and restriction endonuclease (RE) analysis with EcoR1 and BamH1 enzymes followed by sequencing. The expression of the recombinant pvpA gene was optimized at 1.4mM/μl concentration of Isopropyl-β-D-thiogalactoside induction at 30°C. The recombinant fusion protein was purified by immobilized metal affinity chromatography and characterized by SDS-PAGE followed by confirmation of recombinant cytadhesin fusion protein through western blot analysis. The pvpA gene was successfully cloned and expressed. The deduced amino acid sequence analysis had shown the presence of two direct repeats (DR1 and DR2) along with predicted PRP motifs repeatedly with high proline encoding regions at the carboxy-terminal of pvpA gene indicating its scope for epidemiological studies.

The application of aptamer Apt-236 targeting PvpA protein in the detection of antibodies against Mycoplasma gallisepticum

Mycoplasma gallisepticum (M. gallisepticum) is the primary agent of chronic respiratory disease causing important economic losses in the poultry industry. Compared to antibodies, aptamers used to diagnose M. gallisepticum have many advantages, such as being chemically, animal-free produced and easily modifiable without affecting their affinity. Herein, a single-stranded DNA (ssDNA) aptamer Apt-236 which can specifically bind to PvpA protein of M. gallisepticum with a Kd of 1.30 ± 0.18 nM was selected successfully. An indirect blocking ELAA (ib-ELAA) for M. gallisepticum antibodies detection was also developed using Apt-236, in which M. gallisepticum antibodies would block the binding-position of aptamers. Therefor positive sera would prevent color development whereas negative sera will allow a strong color reaction. The ib-ELAA was consistent with other three widely used assays in terms of the growth and decline of the antibody response to M. gallisepticum, and showed substantial agreement with the results obtained using a commercial ELISA kit in clinical chicken sera samples. Therefore, the ib-ELAA developed in this study was a new format for aptamer application and would be an alternative method for the surveillance of M. gallisepticum.

Current status of vaccine research, development, and challenges of vaccines for Mycoplasma gallisepticum

Mycoplasma gallisepticum (MG) is an important avian pathogen that causes significant economic losses in the poultry industry. Surprisingly, the limited protection and adverse reactions caused by the vaccines, including live vaccines, bacterin-based (killed) vaccines, and recombinant viral vaccines is still a major concern. Mycoplasma gallisepticum strains vary in infectivity and virulence and infection may sometimes unapparent and goes undetected. Although extensive research has been carried out on the biology of this pathogen, information is lacking about the type of immune response that confers protection and selection of appropriate protective antigens and adjuvants. Regardless of numerous efforts focused on the development of safe and effective vaccine for the control of MG, the use of modern DNA vaccine technology selected in silico approaches for the use of conserved recombinant proteins may be a better choice for the preparation of novel effective vaccines. More research is needed to characterize and elucidate MG products modulating MG-host interactions. These products could be used as a reference for the preparation and development of vaccines to control MG infections in poultry flocks.

Application of high-resolution melting-curve analysis on pvpA gene for detection and classification of Mycoplasma gallisepticum strains

Mycoplasma gallisepticum (MG) is an avian species pathogen which causes heavy economic losses in the poultry industry. The purpose of this study was to determine genomic diversity of 14 MG field strains from chicken, Chuker partridge and peacock collected during 2009-2012 in Iran by polymerase chain reaction and partial sequencing of the pvpA gene. A High-Resolution Melting (HRM) technique was also developed and applied to differentiate between field and vaccine strains. Sequencing of the pvpA gene revealed a 51 nucleotide deletion, within DR-1 and DR-2, among MG strains from chicken and partridge whilst 63 nucleotides were deleted in MG strain from peacock. One nucleotide substitution was also observed among chicken MG strains. Phylogenetic analysis of the sequences clustered all of the Iranian MG strains into two clades or phylogeny groups; the strains from chicken and partridge in one group (group 1) and the strain from peacock into another group (group 4). HRM analysis has also produced comparable outcome to those of sequencing; four distinct melting curves which correspond to the three MG strains from chicken, Chukar partridge and peacock and ts-11 vaccine strain. Overall, findings of this study point towards a single source of infection for the chicken and partridge MG strains and likelihood of the strains being native and endemic in Iran. Peacock considered as an exotic species in Iran, hence the genetic distance for the pvpA gene. MG can be transmitted easily among different avian species and this distinct peacock strain may pose a threat to poultry industry. Our findings also show that molecular variation among pvpA gene of MG strains could be revealed using the relatively rapid and affordable HRM technique.

Mycoplasma gallisepticum lipid associated membrane proteins up-regulate inflammatory genes in chicken tracheal epithelial cells via TLR-2 ligation through an NF-κB dependent pathway

Mycoplasma gallisepticum-mediated respiratory inflammation in chickens is associated with accumulation of leukocytes in the tracheal submucosa. However the molecular mechanisms underpinning these changes have not been well described. We hypothesized that the initial inflammatory events are initiated upon ligation of mycoplasma lipid associated membrane proteins (LAMP) to TLRs expressed on chicken tracheal epithelial cells (TEC). To test this hypothesis, live bacteria or LAMPs isolated from a virulent (R_low) or a non-virulent (R_high) strain were incubated with primary TECs or chicken tracheae ex vivo. Microarray analysis identified up-regulation of several inflammatory and chemokine genes in TECs as early as 1.5 hours post-exposure. Kinetic analysis using RT-qPCR identified the peak of expression for most genes to be at either 1.5 or 6 hours. Ex-vivo exposure also showed up-regulation of inflammatory genes in epithelial cells by 1.5 hours. Among the commonly up-regulated genes were IL-1β, IL-6, IL-8, IL-12p40, CCL-20, and NOS-2, all of which are important immune-modulators and/or chemo-attractants of leukocytes. While these inflammatory genes were up-regulated in all four treatment groups, R_low exposed epithelial cells both in vitro and ex vivo showed the most dramatic up-regulation, inducing over 100 unique genes by 5-fold or more in TECs. Upon addition of a TLR-2 inhibitor, LAMP-mediated gene expression of IL-1β and CCL-20 was reduced by almost 5-fold while expression of IL-12p40, IL-6, IL-8 and NOS-2 mRNA was reduced by about 2–3 fold. Conversely, an NF-κB inhibitor abrogated the response entirely for all six genes. miRNA-146a, a negative regulator of TLR-2 signaling, was up-regulated in TECs in response to either R_low or R_high exposure. Taken together we conclude that LAMPs isolated from both R_high and R_low induced rapid, TLR-2 dependent but transient up-regulation of inflammatory genes in primary TECs through an NF-κB dependent pathway.

A simple agar plate preparation for effective transfer of Ureaplasma colonies onto nitrocellulose membranes for colony immunoblotting

A simple method for preparing agar plates is presented, which allows an efficient transfer of Ureaplasma colonies to nitrocellulose membranes for subsequent immunological detection. This simple and reproducible procedure was used to demonstrate antigenic variation in the phase-variable mba-locus of Ureaplasma parvum serovar 3.

A novel transposon construct expressing PhoA with potential for studying protein expression and translocation in Mycoplasma gallisepticum

BACKGROUND

Mycoplasma gallisepticum is a major poultry pathogen and causes severe economic loss to the poultry industry. In mycoplasmas lipoproteins are abundant on the membrane surface and play a critical role in interactions with the host, but tools for exploring their molecular biology are limited.

RESULTS

In this study we examined whether the alkaline phosphatase gene (phoA ) from Escherichia coli could be used as a reporter in mycoplasmas. The promoter region from the gene for elongation factor Tu (ltuf) and the signal and acylation sequences from the vlhA 1.1 gene, both from Mycoplasma gallisepticum , together with the coding region of phoA , were assembled in the transposon-containing plasmid pISM2062.2 (pTAP) to enable expression of alkaline phosphatase (AP) as a recombinant lipoprotein. The transposon was used to transform M. gallisepticum strain S6. As a control, a plasmid containing a similar construct, but lacking the signal and acylation sequences, was also produced (pTP) and also introduced into M. gallisepticum . Using a colorimetric substrate for detection of alkaline phosphatase activity, it was possible to detect transformed M. gallisepticum . The level of transcription of phoA in organisms transformed with pTP was lower than in those transformed with pTAP, and alkaline phosphatase was not detected by immunoblotting or enzymatic assays in pTP transformants, eventhough alkaline phosphatase expression could be readily detected by both assays in pTAP transformants. Alkaline phosphatase was shown to be located in the hydrophobic fraction of transformed mycoplasmas following Triton X-114 partitioning and in the membrane fraction after differential fractionation. Trypsin proteolysis confirmed its surface exposure. The inclusion of the VlhA lipoprotein signal sequence in pTAP enabled translocation of PhoA and acylation of the amino terminal cysteine moiety, as confirmed by the effect of treatment with globomycin and radiolabelling studies with [14C]palmitate. PhoA could be identified by mass-spectrometry after separation by two-dimensional electrophoresis.

CONCLUSION

This is the first study to express PhoA as a lipoprotein in mycoplasmas. The pTAP plasmid will facilitate investigations of lipoproteins and protein translocation across the cell membrane in mycoplasmas, and the ease of detection of these transformants makes this vector system suitable for the simultaneous screening and detection of cloned genes expressed as membrane proteins in mycoplasmas.

The Mycoplasma gallisepticum α-enolase is cell surface-exposed and mediates adherence by binding to chicken plasminogen

The α-enolase protein is reported to be an adhesin in several pathogenic bacterial species, but its role in Mycoplasma gallisepticum is unknown. In this study, the M. gallisepticum α-enolase gene was adapted to heterologous expression in Escherichia coli by performing overlapping polymerase chain reaction with site-directed mutagenesis to introduce A960G and A1158G mutations in the nucleotide sequence. The full-length mutated gene was cloned into a pGEM-T Easy vector and subcloned into the expression vector pET32a(+) to construct the pET-rMGEno plasmid. The expression of rMGEno in E. coli strain DE3 was confirmed by sodium dodecyl sulfate polyacrylamide gel electrophoresis with Coomassie blue staining. Purified rMGEno exhibited α-enolase catalytic activity that it could reflect the conversion of NADH to NAD(+). Mouse antiserum to α-enolase was generated by immunization with rMGEno. Immunoblotting and immunofluorescence assay with the antiserum identified α-enolase on the surface of M. gallisepticum cells. Enzyme-linked immunosorbent assay characterized rMGEno as a chicken plasminogen binding protein. An adherence inhibition assay on immortalized chicken fibroblasts (DF-1) demonstrated more than 77% inhibition of adhesion in the presence of mouse antiserum, suggesting that α-enolase of M. gallisepticum participates in bacterial adhesion to DF-1 cells.

Bi-antigenic immunoassay models based on the recombinant PvpA proteins for Mycoplasma gallisepticum diagnosis in chickens

The present study aimed to produce the relatively conserved central fragment of the Mycoplasma gallisepticum PvpA cytadhesin as recombinant antigen and to determine its species-specific diagnostic potential in comparison with the full-length recombinant rPvpA336 protein. For this purpose, a recombinant protein (rPvpA134) consisting of 134 amino acids with apparent molecular mass of 27 kD was produced and highly purified. The rPvpA134 protein was composed of the amino acid residues at positions 133-265 with respect to the wild-type PvpA. Two bi-antigenic diagnostic models based on Western blot and enzymatic rapid immunofiltration assay (ERIFA) were developed to compare simultaneously the diagnostic potential of the recombinant antigens rPvpA134 and rPvpA336. Although 40% of the confirmed rPvpA336-positive chicken sera were detected as reactive with rPvpA134, this protein would be a useful secondary diagnostic antigen with which to confirm species-specific antibody response for monitoring M. gallisepticum infections. It can be concluded from the present study that 2 bi-antigenic models were successfully adapted to the specific diagnosis of chicken M. gallisepticum. Furthermore, by virtue of its simplicity and rapidity, the ERIFA model has multi-antigenic application potential, making it an alternative field test that is widely applicable in the veterinary diagnostic field.

Comparative genomic analyses of attenuated strains of Mycoplasma gallisepticum

Mycoplasma gallisepticum is a significant respiratory and reproductive pathogen of domestic poultry. While the complete genomic sequence of the virulent, low-passage M. gallisepticum strain R (R(low)) has been reported, genomic determinants responsible for differences in virulence and host range remain to be completely identified. Here, we utilize genome sequencing and microarray-based comparative genomic data to identify these genomic determinants of virulence and to elucidate genomic variability among strains of M. gallisepticum. Analysis of the high-passage, attenuated derivative of R(low), R(high), indicated that relatively few total genomic changes (64 loci) occurred, yet they are potentially responsible for the observed attenuation of this strain. In addition to previously characterized mutations in cytadherence-related proteins, changes included those in coding sequences of genes involved in sugar metabolism. Analyses of the genome of the M. gallisepticum vaccine strain F revealed numerous differences relative to strain R, including a highly divergent complement of vlhA surface lipoprotein genes, and at least 16 genes absent or significantly fragmented relative to strain R. Notably, an R(low) isogenic mutant in one of these genes (MGA_1107) caused significantly fewer severe tracheal lesions in the natural host compared to virulent M. gallisepticum R(low). Comparative genomic hybridizations indicated few genetic loci commonly affected in F and vaccine strains ts-11 and 6/85, which would correlate with proteins affecting strain R virulence. Together, these data provide novel insights into inter- and intrastrain M. gallisepticum genomic variability and the genetic basis of M. gallisepticum virulence.

Genetic and antigenic characterization of the surface lipoprotein P48 of Mycoplasma bovis

The presence of a membrane lipoprotein homologous to the P48 of Mycoplasma agalactiae was investigated in different Mycoplasma bovis isolates selected by geographical locations and biological properties. Its potential as a diagnostic tool was also discussed. The presence of a specific signal observed in all M. bovis field isolates probed with a rabbit antiserum raised against the M. agalactiae recombinant P48 demonstrated that this protein is structurally and antigenically conserved within the M. bovis cluster. No signal was detected when testing six different mycoplasma species found in cattle. The p48 gene was identified by PCR approach and partially sequenced. Full length gene sequence was obtained by direct bacterial chromosome sequencing. Five UGAs were selectively mutated into UGG and the full length mutated gene, lacking the signal peptide, was cloned and expressed in Escherichia coli. The purified recombinant antigen (r-P48) was evaluated as a potential marker of infection using a panel of 86 well-characterized sera from experimentally and naturally infected cattle. Specific IgM antibodies were detected within 6-9 days after experimental infection followed by an IgG response lasting from the third/fourth week after contact. Although antibody titers were well below those observed in sheep or goats infected with M. agalactiae, results suggest that M. bovis r-P48 can be used as a specific marker of infection.

Avoidance of the host immune system through phase variation in Mycoplasma pulmonis

Phase-variable lipoproteins are commonly found in Mycoplasma species. Mycoplasma pulmonis contains a family of extensively studied phase- and size-variable lipoproteins encoded by the vsa locus. The Vsa surface proteins vary at a high frequency, the in vivo significance of which has yet to be determined. We investigated the role of Vsa phase variation in respect to tissue tropism and avoidance of the immune system in the mouse host. Mycoplasmas were cultured 3, 14, and 21 days postinoculation from the nose, lung, trachea, liver, and spleen of experimentally infected C57BL/6 (wild-type), C57BL/6-RAG-1-/- (RAG-/-), and C57BL/6-inducible nitric oxide synthase (iNOS)-/- (iNOS-/-) mice. In wild-type and iNOS-/- mice, a large number of Vsa variants were seen by 21 days postinoculation. In contrast, little Vsa variation occurred in all tissues of RAG-/- mice. Analysis of isolates from 14 days postinoculation revealed less variation of the Vsa proteins in iNOS-/- mice than in the wild type. Western blot analysis of isolates from each strain of mouse demonstrated that Vsa phase variation occurred independently of size variation, indicating no obvious selection pressure for size variants. Additionally, these experiments provided no evidence that mycoplasmas producing particular Vsa proteins adhered only to specific tissues. The data strongly indicate that Vsa phase variation is a mechanism for avoidance of the immune system with no obvious contribution to tissue tropism.

Phase and antigenic variation in bacteria

Phase and antigenic variation result in a heterogenic phenotype of a clonal bacterial population, in which individual cells either express the phase-variable protein(s) or not, or express one of multiple antigenic forms of the protein, respectively. This form of regulation has been identified mainly, but by no means exclusively, for a wide variety of surface structures in animal pathogens and is implicated as a virulence strategy. This review provides an overview of the many bacterial proteins and structures that are under the control of phase or antigenic variation. The context is mainly within the role of the proteins and variation for pathogenesis, which reflects the main body of literature. The occurrence of phase variation in expression of genes not readily recognizable as virulence factors is highlighted as well, to illustrate that our current knowledge is incomplete. From recent genome sequence analysis, it has become clear that phase variation may be more widespread than is currently recognized, and a brief discussion is included to show how genome sequence analysis can provide novel information, as well as its limitations. The current state of knowledge of the molecular mechanisms leading to phase variation and antigenic variation are reviewed, and the way in which these mechanisms form part of the general regulatory network of the cell is addressed. Arguments both for and against a role of phase and antigenic variation in immune evasion are presented and put into new perspective by distinguishing between a role in bacterial persistence in a host and a role in facilitating evasion of cross-immunity. Finally, examples are presented to illustrate that phase-variable gene expression should be taken into account in the development of diagnostic assays and in the interpretation of experimental results and epidemiological studies.

The complete genome sequence of the avian pathogen Mycoplasma gallisepticum strain R(low)

The complete genome of Mycoplasma gallisepticum strain R(low) has been sequenced. The genome is composed of 996,422 bp with an overall G+C content of 31 mol%. It contains 742 putative coding DNA sequences (CDSs), representing a 91 % coding density. Function has been assigned to 469 of the CDSs, while 150 encode conserved hypothetical proteins and 123 remain as unique hypothetical proteins. The genome contains two copies of the rRNA genes and 33 tRNA genes. The origin of replication has been localized based on sequence analysis in the region of the dnaA gene. The vlhA family (previously termed pMGA) contains 43 genes distributed among five loci containing 8, 2, 9, 12 and 12 genes. This family of genes constitutes 10.4% (103 kb) of the total genome. Two CDSs were identified immediately downstream of gapA and crmA encoding proteins that share homology to cytadhesins GapA and CrmA. Based on motif analysis it is predicted that 80 genes encode lipoproteins and 149 proteins contain multiple transmembrane domains. The authors have identified 75 proteins putatively involved in transport of biomolecules, 12 transposases, and a number of potential virulence factors. The completion of this sequence has spawned multiple projects directed at defining the biological basis of M. gallisepticum.

Phenotypic switching in Mycoplasma gallisepticum hemadsorption is governed by a high-frequency, reversible point mutation

Mycoplasma gallisepticum is a flask-shaped organism that commonly induces chronic respiratory disease in chickens and infectious sinusitis in turkeys. Phenotypic switching in M. gallisepticum hemadsorption (HA) was found to correlate with phase variation of the GapA cytadhesin concurrently with that of the CrmA protein, which exhibits cytadhesin-related features and is encoded by a gene located downstream of the gapA gene as part of the same transcription unit. In clones derived from strain R(low), detailed genetic analyses further revealed that on-off switching in GapA expression is governed by a reversible base substitution occurring at the beginning of the gapA structural gene. In HA(-) variants, this event generates a stop codon that results in the premature termination of GapA translation and consequently affects the expression of CrmA. Sequences flanking the mutation spot do not feature any repeated motifs that could account for error-prone mutation via DNA slippage and the exact mechanism underlying this high-frequency mutational event remains to be elucidated. An HA(-) mutant deficient in producing CrmA, mHAD3, was obtained by disrupting the crmA gene by using transposition mutagenesis. Despite a fully functional gapA gene, the amount of GapA detected in this mutant was considerably lower than in HA(+) clonal variants, suggesting that, in absence of CrmA, GapA might be subjected to a higher turnover.

Recognition of multiple Mycoplasma bovis antigens by monoclonal antibodies

To produce monoclonal antibodies (MAbs), Balb/c AnN Crl BR mice were inoculated with the cell suspension of a Hungarian Mycoplasma bovis strain designated 26034. Three days after the last immunization the spleen of the immunized mouse was removed aseptically. The fusion of spleen cells with Sp2/0-Ag14 murine myeloma cells was performed in the presence of polyethylene glycol. The obtained hybrid cells were selected with hipoxantine, aminopterine and thymidine (HAT) medium. Two weeks after the fusion, the supernatants of the grown cells were tested by a self-developed indirect enzyme-linked immunosorbent assay (ELISA). The results showed that 63 antibody-producing hybridomas had been obtained. For accurate determination of the molecular weight of antigen determinants, the supernatants giving positive reaction in the ELISA were tested by Western blotting. According to the results, the obtained MAbs recognize the antigen determinants of the following molecular weights: 1B11: 63 kDa, 1C7: 63 kDa, 2C5: 22, 25 and 27 kDa, 2C9: 69 kDa, 3G12: 67, 69 and 72 kDa, 4H9: 63 kDa, 5B8: 22, 25 and 27 kDa, 5D3: 22, 25 and 27 kDa, 5C11: 69 kDa, 5E5: 22, 25 and 27 kDa, 6F11: 63 kDa, and 6H10: 22, 25 and 27 kDa. The 12 cell groups selected on the basis of the Western blotting were cloned twice by end-point dilution method. The cloned cells were propagated, and with 5 cell lines antibodies were produced in the CELLine bioreactor (Integra Biosciences, Zurich, Switzerland). Cell line 3G12 showed the highest productivity with an average daily output of 1.5 mg immunoglobulin. Cell line 5E5 produced 1.1 mg, 6H10 0.8 mg, 2C9 0.47 mg and 6F11 0.4 mg antibody per day. The isotype of the antibodies was determined by ELISA. The antibodies produced by the 12 cell lines tested were assigned to the IgG(1) subclass according to the heavy chain. Ten cell lines produced kappa and two produced lambda light-chain antibody. Possible cross-reactions of the produced monoclonal anti-M. bovis antibodies with certain Mycoplasma, Ureaplasma and Acholeplasma species were tested by an indirect ELISA procedure. All of the 12 antibodies tested gave a reaction with the antigen of M. bovis strain designated 26034. MAbs 3G12 (67, 69, and 72 kDa) and 5B8 (22, 25, and 27 kDa) gave no cross-reaction with antigens other than strains of the homologous Mycoplasma species. The other antibodies reacted with the M. bovigenitalium F7, M. anseris 8389, M. oculi, and M. gallisepticum s6 Holland antigens. Owing to its high specificity and affinity, the antibody produced by the cell line 3G12 is primarily considered suitable for use in immunodiagnostic tests of M. bovis infections.

Haemagglutinins of pathogenic avian mycoplasmas

The pathogenic avian mycoplasmas, Mycoplasma gallisepticum, Mycoplasma synoviae, Mycoplasma meleagridis, Mycoplasma iowae and Mycoplasma imitans, synthesize haemagglutinins that are immunogenic, variably expressed, surface proteins. The haemagglutinins of M. gallisepticum (pMGA), M. synoviae (VlhA) and M. imitans are lipoproteins, encoded by related multigene families that appear to have arisen by horizontal gene transfer. M. gallisepticum also has genes encoding cytadhesins in its genome but these are present as a single copies, while the pMGA gene family contains 30 to 70 genes. The switch in expression of distinct pMGA genes (e.g. pMGA1.1 to pMGA1.9) generates antigenic variation, which is thought to be important in immune evasion but also has significance in the preparation of M. gallisepticum antigens for serological diagnosis. In the majority of M. synoviae strains, post-translational cleavage of the VlhA protein generates an amino-terminal part (the lipoprotein MSPB) and a carboxyl-terminal part (MSPA), which mediates binding to erythrocytes. The 5'vlhA gene region, which encodes proline-rich repeats in the amino-terminal part of MSPB, is highly polymorphic among M. synoviae strains. Insertions or deletions in the part of vlhA encoding the proline-rich repeats cause MSPB length variation in different M. synoviae strains. Recombination between the 5'vlhA gene and pseudogenes in the genome generates changes in antigenic determinants in the carboxyl two-thirds of the MSPB molecule, and in MSPA, resulting in changes in the domains involved in the binding of M. synoviae to erythrocytes. Variant haemagglutinins of M. gallisepticum (pMGA1.7) and M. synoviae (diverse VlhA forms) share sequences that may be responsible for antigenic cross-reactions between M. gallisepticum and M. synoviae. Shared epitopes have been demonstrated using specific antibodies against MSPB that also recognize proteins of M. gallisepticum and of M. iowae (serotype N). Size and antigenic variants have also been reported for M. meleagridis and M. iowae proteins, but it is not known if these are their haemagglutinins. Advances in the molecular characterization of M. gallisepticum (pMGA, pvpA) and M. synoviae (vlhA) genes and their sequencing in numerous strains is likely to enable significantly improved epidemiological studies and improved tracing of M. gallisepticum and M. synoviae strains in different flocks.

Juxtaposition of an active promoter to vsp genes via site-specific DNA inversions generates antigenic variation in Mycoplasma bovis

Mycoplasma bovis, the most important etiological agent of bovine mycoplasmosis, undergoes extensive antigenic variation of major and highly immunogenic surface lipoprotein antigens (Vsps). A family of 13 related but divergent vsp genes, which occur as single chromosomal copies, was recently found in the chromosome of M. bovis. In the present study, the molecular mechanism mediating the high-frequency phase variation of two Vsps (VspA and VspC) as representatives of the Vsp family was investigated. Analysis of clonal isolates exhibiting phase transitions of VspA or of VspC (i.e., ON-->OFF-->ON) has shown that DNA inversions occur during Vsp phase variation. The upstream region of each vsp gene contains two sequence cassettes. The first (cassette no. 1), a 71-bp region upstream of the ATG initiation codon, exhibits 98% homology among all vsp genes, while the second (cassette no. 2), upstream of cassette no. 1, ranges in size from 50 to 180 bp and is more divergent. Examination of the ends of the inverted fragments during VspA or VspC phase variation revealed that in both cases, a change in the organization of vsp upstream cassettes involving three vsp genes had occurred. Primer extension and Northern blot analysis have shown that a specific cassette no. 2, designated A(2), is an active promoter and that juxtaposition of this regulatory element to a silent vsp gene by DNA inversions allows transcription initiation of the recipient gene. Further genetic analysis revealed that phase variation of VspA or of VspC involves two site-specific DNA inversions occurring between inverted copies of a specific 35-bp sequence present within the conserved cassette no. 1. A model for the control of Vsp phase variation is proposed.

Characterization and analysis of a stable serotype-associated membrane protein (P30) of Mycoplasma agalactiae

The gene for a 30-kDa immunodominant antigen, P30, of Mycoplasma agalactiae was cloned from type strain PG2 and expressed in Escherichia coli. P30 is encoded on a monocistronic operon determined by two -10 boxes and a possible -35 region constituting the potential promoter, and a transcription termination site. The gene for the 266-amino-acid protein is preceded by a polypurine-rich region designed as the consensus sequence for a ribosome-binding site. Analysis of the amino acid sequence of P30 revealed the presence of a recognition site for a prokaryotic signal peptidase II at amino acid (aa) 24, indicating that P30 is a transmembrane protein. Moreover, Triton X-114 phase partitioning of M. agalactiae PG2 total antigen revealed that P30 is strongly hydrophobic and hence a possible membrane component. Immunoblot analysis using the monospecific polyclonal anti-P30-His serum indicated that P30 is specific to M. agalactiae. Furthermore, PCR amplification with specific primers for p30 and Southern blot analysis revealed the presence of the gene in all M. agalactiae strains tested and its absence in the other mycoplasma species. Among 27 strains of M. agalactiae studied, 20 strains belonging to the common serotypes A to D, including PG2, expressed P30 or part of it as detected by the monospecific polyclonal anti-P30 antibodies. The other seven strains belonging to the rarely isolated serotypes E to H were negative for P30. The p30 gene was sequenced in 15 strains of M. agalactiae, 10 of which expressed P30 or at least part of it and 5 of which did not express P30. The negative strains carried mutations in both -10 boxes of the promoters. These mutations seem to be responsible for the lack of P30 expression in these strains. Analysis of sera from sheep that were experimentally infected with M. agalactiae revealed that P30 induced a strong and persistent immune response which was still very high two months after infection. In contrast, currently used enzyme-linked immunosorbent assay serology gave only low titers.

Molecular variability of the adhesin-encoding gene pvpA among Mycoplasma gallisepticum strains and its application in diagnosis

Mycoplasma gallisepticum is an important pathogen of chickens and turkeys that causes considerable economic losses to the poultry industry worldwide. The reemergence of M. gallisepticum outbreaks among poultry, the increased use of live M. gallisepticum vaccines, and the detection of M. gallisepticum in game and free-flying song birds has strengthened the need for molecular diagnostic and strain differentiation tests. Molecular techniques, including restriction fragment length polymorphism of genomic DNA (RFLP) and PCR-based random amplification of polymorphic DNA (RAPD), have already been utilized as powerful tools to detect intraspecies variation. However, certain intrinsic drawbacks constrain the application of these methods. The main goal of this study was to determine the feasibility of using an M. gallisepticum-specific gene encoding a phase-variable putative adhesin protein (PvpA) as the target for molecular typing. This was accomplished using a pvpA PCR-RFLP assay. Size variations among PCR products and nucleotide divergence of the C-terminus-encoding region of the pvpA gene were the basis for strain differentiation. This method can be used for rapid differentiation of vaccine strains from field isolates by amplification directly from clinical samples without the need for isolation by culture. Moreover, molecular epidemiology of M. gallisepticum outbreaks can be performed using RFLP and/or sequence analysis of the pvpA gene.

A chromosomal region of Mycoplasma agalactiae containing vsp-related genes undergoes in vivo rearrangement in naturally infected animals

A Mycoplasma agalactiae genomic fragment carrying four vsp-related genes (designated avg: agalactiae variable genes) was cloned, sequenced and compared to the vspA gene of Mycoplasma bovis. The following features were revealed: (i) the presence of a highly conserved vsp 5' upstream region; (ii) a highly homologous vsp N-terminal end encoding a putative lipoprotein signal sequence; (iii) sequence divergence of the rest of the mature proteins. By using avg specific probes in Southern blot analysis of genomic DNAs of M. agalactiae strains as well as of isolates from infected animals, marked DNA polymorphism of avg fragments was demonstrated. In addition, the avg genomic fingerprints were monitored for a period of 7 months, in isolates of M. agalactiae from an individual chronically infected animal. The results provided evidence that a chromosomal region of M. agalactiae, carrying vsp-related genes, undergoes rearrangements in vivo in the natural animal host during the course of infection.

pMGA phenotypic variation in Mycoplasma gallisepticum occurs in vivo and is mediated by trinucleotide repeat length variation

Chickens were infected with a pathogenic strain of Mycoplasma gallisepticum, and the expression of pMGA, the major surface protein, was inferred by examination of colonies from ex vivo cells. Within 2 days postinfection, 40% of cells had ceased the expression of the original pMGA surface protein (pMGA1.1), and by day 6, the majority of recovered cells were in this category. The switch in pMGA phenotype which had occurred in vivo was reversible, since most colonies produced from ex vivo progenitors exhibited frequent pMGA1. 1(+) sectors. After prolonged in vivo habitation, increasing proportions of recovered cells gave rise to variant pMGA colonies which had switched from the expression of pMGA1.1 to another gene, pMGA1.2, concomitant with the acquisition of a (GAA)(12) motif 5' to its promoter. Collectively, the results suggest that changes in M. gallisepticum pMGA gene expression in vivo are normal, common, and possibly obligate events for successful colonization of the host. Surprisingly, the initial cessation of pMGA1.1 expression occurred in the absence of detectable pMGA antibodies and seemed to precede the adaptive immune response.

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.

In vitro cell invasion of Mycoplasma gallisepticum

The ability of the widespread avian pathogen Mycoplasma gallisepticum to invade cultured human epithelial cells (HeLa-229) and chicken embryo fibroblasts (CEF) was investigated by using the gentamicin invasion assay and a double immunofluorescence microscopic technique for accurate localization of cell-associated mycoplasmas. The presence of intracellular mycoplasmas in both cell lines was clearly demonstrated, with organisms entering the eukaryotic cells within 20 min. Internalized mycoplasmas have the ability to leave the cell, but also to survive within the intracellular space over a 48-h period. Frequencies of invasion were shown to differ between the two cell lines, but were also considerably dependent on the mycoplasma input population. Of the prototype strain R, a low-passage population in artificial medium, R(low), was capable of active cell invasion, while a high-passage population, R(high), showed adherence to but nearly no uptake into HeLa-229 and CEF. By passaging R(low) and R(high) multiple times through HeLa-229 cells, the invasion frequency was significantly increased. Taken together, these findings demonstrate that M. gallisepticum has the capability of entering nonphagocytic host cells that may provide this pathogen with the opportunity for resisting host defenses and selective antibiotic therapy, establishing chronic infections, and passing through the respiratory mucosal barrier to cause systemic infections.

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.

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.

Expression of the monocytic differentiation/activation factor P48 in Mycoplasma species

P48 is a 48 kd monocytic differentiation/activation factor previously purified from the conditioned medium of the Reh human pre-B cell leukemia line. It induces differentiation of HL-60 promyelocytic leukemia cells along the monocytic pathway and production of IL1, TNF-alpha and IL6 in human monocytes and monocytic cell lines. Recently our laboratory isolated cDNA clones for P48 from Reh cells and genomic clones from Mycoplasma fermentans DNA and showed that P48 is a M. fermentans gene product. In this paper we report the analysis of P48 expression at the DNA, mRNA and protein levels in different Mycoplasma species. Polymerase Chain Reaction (PCR) analysis of extracted DNA using P48-specific oligonucleotide primers revealed P48 sequences in M. fermentans but not M. hominis, M. iowae, M. genitalium or M. capricolum. Southern analysis of Mycoplasma DNAs revealed hybridizing bands in M. fermentans and M. capricolum under low stringency, but only in M. fermentans under high stringency. Consistent with this, Northern blot studies revealed a single hybridizing transcript in M. fermentans but not in other Mycoplasma species tested. However, Western blot studies with anti-P48 antibodies revealed P48 antigenic material in M. fermentans, as well as M. hominis and M. iowae. These studies demonstrate that the gene for P48 is derived from M. fermentans or a closely related species and is absent in these other species tested. However, the P48 protein exhibits shared antigenic determinants among several Mycoplasma species which presently are of unknown function or significance. P48 is a Mycoplasma -derived immunomodulatory molecule which may be important in Mycoplasma pathophysiology and may be useful in understanding human haematopoietic differentiation and the control of cytokine biosynthesis.

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.

Antigen heterogeneity among Mycoplasma mycoides subsp. mycoides SC isolates: discrimination of major surface proteins

The protein and antigen profiles of 60 isolates, strains and the type strain PG1 of Mycoplasma mycoides subsp. mycoides s.c. were compared by sodium dodecyl sulphate polyacrylamide gel electrophoresis and immunoblot analysis. Analysis using contagious bovine pleuropneumonia antisera and hyperimmune rabbit sera against several representative strains revealed some differences in protein profiles and variability in antigens among strains from different geographic regions. The most common antigenic bands had the molecular masses of 110, 95, 80, 69, 62, 60, 48, 44, 39 and 38 kDa. There were differences among European strains, where a larger group coming from Italy lacked the p98 antigen, thus, with one exception, distinguishing the Italian strains from Portuguese, French and Spanish strains. African, Australian and PG1 strains showed heterogenic profiles, with quantitative differences and in a few strains some antigenic bands were absent. The group constituting African, Australian and PG1 strains was characterised by the presence of 71.5/70 kDa antigens, which were not detected in European strains. Mycoplasma mycoides subsp. mycoides s.c. membrane proteins were characterised by Triton X-114 partitioning and p110, p98, p95, p62/60 and p48 were identified as immunogenic antigens. The simultaneous presence of these five antigens was common to all the sera examined and, therefore, indicates the diagnostic potential of immunoblotting. Most immunodominant antigens are surface-exposed proteins as determined by the trypsin treatment.

Mycoplasmas in the etiology of multifactorial respiratory disease

The avian mycoplasmas pathogenic for commercial poultry, Mycoplasma gallisepticum and Mycoplasma synoviae in chickens and turkeys, and Mycoplasma meleagridis and Mycoplasma iowae in turkeys are egg-transmitted infections and exhibit wide variations in clinical manifestations. Mycoplasma gallisepticum strains vary widely in virulence, tissue tropism, and antigenic makeup and have the ability to alter the expression of major surface antigenic proteins. Although less well studied, strains of M. synoviae, M. meleagridis, and M. iowae appear to exhibit similar variability. Intraspecies variability among mycoplasma strains and their ability to interact with other disease-producing factors explain the wide variability of clinical manifestations, difficulties in diagnosis, their ability to persist within the host for long periods of time, and many of the difficulties involved in control and eradication programs. Mycoplasmas are also well known for their interactions with other infectious agents and environmental factors in producing clinical disease. Control of the clinical manifestations of Mycoplasma infections is simplified when concurrent infections are minimized and optimum environmental conditions are provided.

Species identification of Mycoplasma bovis and Mycoplasma agalactiae based on the uvrC genes by PCR

The DNA repair genes uvrC from Mycoplasma bovis and Mycoplasma agalactiae type strains were cloned and their nucleotide sequences were established. These sequences were used to design polymerase chain reaction (PCR) primer pairs for M. bovis and M. agalactiae. Each primer pair amplified a 1-6 kb fragment of the uvrC gene in the respective species. The specificity of the primer pairs for the two species was demonstrated through the lack of cross-amplifications in heterologous PCR reactions and in reactions using DNA from other mycoplasma species. Subsequent restriction enzyme analysis of the amplified uvrC gene segments from type and field strains of M. bovis and M. agalactiae showed that the uvrC genes are well conserved in both species but differ significantly between the two species. The diagnostic PCR assay enabled unambiguous identification of M. bovis and M. agalactiae strains isolated from geographically diverse places, even in cases where 16S rRNA gene sequence analysis was unable to discriminate between the two species.

Immunoblot examination of humoral response of chickens infected with Mycoplasma gallisepticum at various ages

Mycoplasma gallisepticum- and Mycoplasma synoviae-free chickens were infected with 0.2 ml broth culture of M. gallisepticum strain 1226 intra air sac at 3, 14, 18, 28, 42, 49 and 65 days of age. Blood samples were taken 0-5 weeks before infection and 1-6 weeks after infection (depending on age of infection). The antibody response was examined by Western blot. As a control of infection, serum plate agglutination test (SPA), pathological lesions, and presence of Mycoplasma in air sacs were used. Antibodies to p64-67 kDa appeared in all groups of birds on the first week post-infection. Antibodies to p56 were detected from the second week post-challenge if infection was performed at 3 or 14 days of age, while on first week if challenge was done at 18, 28, 42, 49 or 65 days of age. Antibodies to p200, p120, p98, p80, p75, p72, p60, p50, p45, p40, p35, p33, p31, p28, p26, p24 and p22 were also detected.

Mycoplasma synoviae has two distinct phase-variable major membrane antigens, one of which is a putative hemagglutinin

Mycoplasma synoviae is a major pathogen of poultry, causing synovitis and respiratory infection. A cluster of 45- to 50-kDa membrane proteins is immunodominant in strain WVU-1853. Four distinct proteins were identified in this cluster by high-pressure liquid chromatography. Monoclonal antibodies and monospecific antisera against each established that they fell into two groups, MSPA and MSPB, each containing two members distinguishable by a difference in hydrophobicity. A 25- to 30-kDa membrane protein (MSPC) was shown to be antigenically related to the MSPB proteins. Considerable variation in the size and expression of MSPA and MSPB was observed among different strains of M. synoviae. Examination of expression in colonies of strain WVU-1853 established that both MSPA and MSPB (and MSPC) were phase variable. Immunostaining of MSPB (and MSPC) with monoclonal antibodies exhibited quantal variation, with three distinct levels observed between and within colonies. Hemadsorption by M. synoviae colonies was also found to be phase variable, with some colonies exhibiting sectorial expression of hemadsorption. Monospecific antisera against MSPA inhibited hemagglutination, but neither monoclonal antibodies nor monospecific antisera against MSPB could inhibit hemagglutination. However, loss of the capacity to hemadsorb by individual clones was associated with loss of expression of both MSPA and MSPB. These findings have elucidated the complexity of structure, function, and expression of the 45- to 50-kDa membrane protein cluster of M. synoviae, and they suggest that all members of the cluster may be involved in adhesion.

Cloning and functional analysis of the P97 swine cilium adhesin gene of Mycoplasma hyopneumoniae

Colonization of the swine respiratory tract by Mycoplasma hyopneumoniae is accomplished by specific binding to the cilia of the mucosal epithelial cells. Previous studies have implicated a 97-kDa outer membrane-associated protein, P97, that appeared to mediate this interaction. In order to further define the role of P97 in adherence to porcine cilia, the structural gene was cloned and sequenced, and the recombinant products were analyzed. Monoclonal antibodies were used to identify recombinant clones in a genomic library expressed in an opal suppressor host because of alternate codon usage by mycoplasmas. The gene coding for P97 was then identified by Tn1000 mutagenesis of recombinant clones. DNA sequence analysis revealed an open reading frame coding for a 124.9-kDa protein with a hydrophobic transmembrane spanning domain. The N-terminal sequence of purified P97 mapped at amino acid position 195 of the translated sequence, indicating that a processing event had occurred in M. hyopneumoniae. Both recombinant P97 protein expressed in an Escherichia coli opal suppressor host and M. hyopneumoniae bound specifically to swine cilia, and the binding was inhibited by heparin and fucoidan, thus supporting the hypothesis that P97 was actively involved in binding to swine cilia in vivo.

Molecular biology of mycoplasmas

Although mycoplasmas lack cell walls, they are in many respects similar to the gram-positive bacteria with which they share a common ancestor. The molecular biology of mycoplasmas is intriguing because the chromosome is uniquely small (< 600 kb in some species) and extremely A-T rich (as high as 75 mol% in some species). Perhaps to accommodate DNA with a lower G + C content, most mycoplasmas do not have the "universal" genetic code. In these species, TGA is not a stop codon; instead it encodes tryptophan at a frequency 10 times greater than TGG, the usual codon for this amino acid. Because of the presence of TGA codons, the translation of mycoplasmal proteins terminates prematurely when cloned genes are expressed in other eubacteria, such as Escherichia coli. Many mycoplasmas possess strikingly dynamic chromosomes in which high-frequency changes result from errors in DNA repair or replication and from highly active recombination systems. Often, high-frequency changes in the mycoplasmal chromosome are associated with antigenic and phase variation, which regulate the production of factors critical to disease pathogenesis.

Phenotypic switching of variable surface lipoproteins in Mycoplasma bovis involves high-frequency chromosomal rearrangements

Mycoplasma bovis, an important pathogen of cattle, was recently shown to possess a family of phase- and size-variable membrane surface lipoprotein antigens (Vsps). These proteins spontaneously undergo noncoordinate phase variation between ON and OFF expression states, generating surface antigenic variation. In the present study, we show that the spontaneously high rate of Vsp phenotypic switching involves DNA rearrangements that occur at high frequency in the M. bovis chromosome. A 1.5-kb HindIII genomic fragment carrying the vspA gene from M. bovis PG45 was cloned and sequenced. The deduced VspA amino acid sequence revealed that 80% of the VspA molecule is composed of reiterated intragenic coding sequences, creating a periodic polypeptide structure. Four distinct internal regions of repetitive sequences in the form of in-tandem blocks extending from the N-terminal to the C-terminal portion of the Vsp product were identified. Southern blot analysis of phenotypically switched isogenic lineages representing ON or OFF phase states of Vsp products suggested that changes in the Vsp expression profile were associated with detectable changes at the DNA level. By using a synthetic oligonucleotide representing a sequence complementary to the repetitive vspA gene region as a probe, we could identify the vspA-bearing restriction fragment undergoing high-frequency reversible rearrangements during oscillating phase transition of vspA. The 1.5-kb HindIII fragment carrying the vspA gene (on state) rearranged and produced a 2.3-kb HindIII fragment (OFF state) and vice versa. Two newly discovered vsp genes (vspE and vspF) were localized on two HindIII fragments flanking the vsp gene upstream and downstream. Southern blot hybridization with vspE- and vspF-specific oligonucleotides as probes against genomic DNA of VspA phase variants showed that the organization and size of the fragments adjacent to the vspA gene remained unchanged during VspA ON-OFF switching. The mechanisms regulating the vsp genes are yet unknown; our findings suggest that a recombinative mechanism possibly involving DNA inversions, DNA insertion, or mobile genetic elements may play a role in generating the observed high-frequency DNA rearrangements.

Size and genomic location of the pMGA multigene family of Mycoplasma gallisepticum

The pMGA multigene family encodes variant copies of the cell surface haemagglutinin of Mycoplasma gallisepticum. Quantitative Southern blotting, using an oligonucleotide probe complementary to a region conserved in the leader sequence of all known pMGA genes, was used to estimate the number of members of the family in the genome of seven strains of M. gallisepticum. The number of copies estimated to be present in the genome varied from 32 in strain F to 70 in strain R, indicating that the pMGA gene family may be second in size only to the tRNA family among prokaryotes. If all members of the pMGA family are of similar length to those which have been characterized, a minimum of 79 kb (7.7%) of the genome of strain S6, 82 kb (8.2%) of PG31 and 168 kb (16%) of the genome of strain R is dedicated to encoding variants of the same haemagglutinin. The GAA repeat motif identified in the intergenic region between all characterized pMGA genes appeared to be a feature common to most, if not all, pMGA genes, and furthermore probably exclusive to them. The genomic locations of members of the pMGA family were determined by PFGE and Southern blot hybridization of M. gallisepticum strain S6. The hybridizing regions were localized to four separate regions on the chromosome. The pMGA genes are likely to be predominantly arranged as tandem repeats within these regions, similar to the restricted regions for which the genomic sequence has been determined.

Variant colony surface antigenic phenotypes within mycoplasma strain populations: implications for species identification and strain standardization

Immunobinding assays with mycoplasma colonies on agar plates (immunofluorescence and immunoperoxidase techniques) or with imprints of colonies transferred to solid supports (colony immunoblotting) are widely used as standard diagnostic tests for serological species identification of mycoplasma isolates. However, in light of the high rate of variability of surface antigens in many mycoplasmas, diagnostic data obtained with these techniques require a more critical evaluation. In this report, we demonstrate with some examples that mycoplasma surface variability based on alterations in expression, in size, and in surface presentation of integral and peripheral membrane proteins may lead to misinterpretation of colony immunostaining reactions obtained by using specific monoclonal antibodies as well as conventional diagnostic hyperimmune sera. To more easily identify phenotypically mixed isolates or samples which contain more than one species, we have introduced some minor modifications of the colony immunoblot technique which provide sharp signals of positive as well as negative reactions and enable identification of cryptic epitopes. It is further demonstrated that because of the variability in colony surface antigenic phenotype, mycoplasma strains, including well-established reference and other prototype strains which are used under the same designation in many laboratories, can differ markedly in their antigen profiles and their potentially virulence-related surface properties, since they are usually purified by filter cloning and often propagated by subcultivation of randomly selected agar-grown subpopulations. We conclude from this study that because of this surface variability, the establishment of criteria for standardization of mycoplasma strains and diagnostic antisera is urgently required in order to obtain reproducible results in different laboratories.

Increased structural and combinatorial diversity in an extended family of genes encoding Vlp surface proteins of Mycoplasma hyorhinis

Variable lipoproteins (Vlp) constitute the major coat protein of Mycoplasma hyorhinis. They are products of multiple, divergent, single-copy genes organized in a chromosomal cluster. Three genes, vlpA, vlpB, and vlpC, have been previously identified in clonal isolates of M. hyorhinis SK76. Each is linked to a characteristic promoter region containing a homopolymeric tract of adenine residues [poly(A) tract], subject to hypermutation, that transcriptionally controls phase variation of vlp genes and leads to combinatorial surface mosaics of distinct Vlp products. The size of the natural vlp gene repertoire is unknown but may critically determine the degree of structural and combinatorial diversity available in this species. In this study, the vlp repertoire of M. hyorhinis GDL-1 was characterized and shown to contain three additional genes, vlpD, vlpE, and vlpF, clustered with other known vlp genes in the order 5'-vlpD-vlpE-vlpF-IS-vlpA-IS-vlpB-vlpC+ ++-3', where IS represents copies of the IS1221 element of M. hyorhinis. The 5' boundary of this expanded family was identical to that of the more limited family 5'-vlpA-IS-vlpB-vlpC-3' previously described in a clonal isolate of strain SK76. A recombinant construct containing vlpD, vlpE, and vlpF expressed antigenically distinguishable products corresponding to each gene. These genes encode characteristic C-terminal repetitive regions that are subject to size variation by insertion or deletion of intragenic repeats but maintain an extended, charged structure. Each vlp gene also contained characteristic alternative open reading frames, which provide a potential reservoir of coding sequence for Vlp diversity, possibly recruited through insertion and/or deletion mutations. These findings demonstrate a vastly expanded potential for structural diversity and combinatorial display of surface mosaics on this organism and suggest that modulation of the vlp repertoire, possibly in conjunction with mobile elements, may determine the capacity for surface variation in natural populations and laboratory strains of this mycoplasma species.

In vivo variation of Mycoplasma gallisepticum antigen expression in experimentally infected chickens

The antigen expression profiles of Mycoplasma gallisepticum isolates obtained from tracheal swabs of chickens after aerosol-inoculation with M. gallisepticum strain R or clonal variant R/E were examined in western immunoblots. A reference anti-M. gallisepticum chicken antiserum and antisera from individual infected chickens as well as monoclonal antibodies (mAbs) specific for surface proteins were used to monitor in vivo antigenic variation. mAbs 1E5 and 12D8, recognizing PvpA and p67a, recently shown to undergo high-frequency in vitro phase variation, were used for consecutive staining of colony and western immunoblots in order to distinguish between the resultant phenotypes with respect to the corresponding epitopes. Marked differences in the expression of major immunogenic proteins, including p67a, were observed between the two inocula as well as among reisolates recovered at different times of infection. Comparative western immunoblot analysis of the rapidly changing chicken serum antibody response and reisolates recovered during the course of an experimental infection with M. gallisepticum R or clonal variant R/E suggest that immune modulation may have a key role in generating surface diversity. In addition, comparison of colony immunoblots of strain R inoculum and of reisolated colonies from tracheas of birds 8 days post infection indicated an in vivo selection of the PvpA+p67a- phenotype. This study established that surface antigens of M. gallisepticum are subjected in vivo to rapid alteration in their expression. This variability may function as a crucial adaptive mechanism, enabling the organism to escape from the host immune defense and to adapt to the changing host environment at different stages of a natural infection.