Cloning and sequence analysis of cytadhesin P1 gene from Mycoplasma pneumoniae

Development of a Rapid and Efficient RPA-CRISPR/Cas12a Assay for Mycoplasma pneumoniae Detection

Mycoplasma pneumoniae (MP) is a one of most common pathogen in causing respiratory infection in children and adolescents. Rapid and efficient diagnostic methods are crucial for control and treatment of MP infections. Herein, we present an operationally simple, rapid and efficient molecular method for MP identification, which eliminates expensive instruments and specialized personnel. The method combines recombinase polymerase amplification (RPA) with clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR associated proteins (Cas) 12a-based detection, with an optimal procedure less than 1 h from sample to result including DNA extraction (25 min), RPA reaction (39°C for 15-20 min), CRISPR/Cas12a detection (37°C for 10 min) and visual detection by naked eyes (2 min). This diagnostic method shows high sensitivity (two copies per reaction) and no cross-reactivity against other common pathogenic bacteria. Preliminary evaluation using 201 clinical samples shows sensitivity of 99.1% (107/108), specificity of 100% (93/93) and consistency of 99.5% (200/201), compared with real-time PCR method. The above data demonstrate that our developed method is reliable for rapid diagnosis of MP. In conclusion, the RPA-CRISPR/Cas12a has a great potential to be as a useful tool for reliable and quick diagnosis of MP infection, especially in primary hospitals with limited conditions.

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

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

Molecular Typing of Mycoplasma pneumoniae Strains in Sweden from 1996 to 2017 and the Emergence of a New P1 Cytadhesin Gene, Variant 2e

Mycoplasma pneumoniae causes respiratory infections, such as community-acquired pneumonia (CAP), with epidemics recurring every 3 to 7 years. In 2010 and 2011, many countries experienced an extraordinary epidemic peak.

Mycoplasma pneumoniae causes respiratory infections, such as community-acquired pneumonia (CAP), with epidemics recurring every 3 to 7 years. In 2010 and 2011, many countries experienced an extraordinary epidemic peak. The cause of these recurring epidemics is not understood, but decreasing herd immunity and shifts in the strains’ antigenic properties have been suggested as contributing factors. M. pneumoniae PCR-positive samples were collected between 1996 and 2017 from four neighboring counties inhabited by 12% of Sweden’s population. A total of 578 isolates were characterized directly from 624 clinical samples using P1 typing by sequencing and multilocus variable number tandem repeat analysis (MLVA). A fluorescence resonance energy transfer (FRET)-PCR approach was also used to detect mutations associated with macrolide resistance in the 23S rRNA gene. Through P1 typing, the strains were classified into type 1 and type 2, as well as variants 2a, 2b, 2c, and a new variant found in nine of the strains, denoted variant 2e. Twelve MLVA types were distinguished, and 3-5-6-2 (42.4%), 4-5-7-2 (37.4%), and 3-6-6-2 (14.9%) predominated. Several P1 and MLVA types cocirculated each year, but type 2/variant 2 strains and MLVA types 3-5-6-2 and 4-5-7-2 predominated during the epidemic period comprising the peak of 2010 and 2011. In 2016 and 2017, type 1 became more common, and MLVA type 4-5-7-2 predominated. We also found that 0.2% (1/578) of the strains carried a macrolide resistance-associated mutation, indicating a very low prevalence of macrolide resistance in this region of Sweden.

P40 and P90 from Mpn142 are Targets of Multiple Processing Events on the Surface of Mycoplasma pneumoniae

Mycoplasma pneumoniae is a significant cause of community acquired pneumonia globally. Despite having a genome less than 1 Mb in size, M. pneumoniae presents a structurally sophisticated attachment organelle that (i) provides cell polarity, (ii) directs adherence to receptors presented on respiratory epithelium, and (iii) plays a major role in cell motility. The major adhesins, P1 (Mpn141) and P30 (Mpn453), are localised to the tip of the attachment organelle by the surface accessible cleavage fragments P90 and P40 derived from Mpn142. Two events play a defining role in the formation of P90 and P40; removal of a leader peptide at position 26 (²³SLA↓NTY²⁸) during secretion to the cell surface and cleavage at amino acid 455 (⁴⁵²GPL↓RAG⁴⁵⁷) generating P40 and P90. Liquid Chromatography Tandem Mass Spectrometry (LC-MS/MS) analysis of tryptic peptides generated by digesting size-fractionated cell lysates of M. pneumoniae identified 15 cleavage fragments of Mpn142 ranging in mass from 9–84 kDa. Further evidence for the existence of cleavage fragments of Mpn142 was generated by mapping tryptic peptides to proteins recovered from size fractionated eluents from affinity columns loaded with heparin, fibronectin, fetuin, actin, plasminogen and A549 surface proteins as bait. To define the sites of cleavage in Mpn142, neo-N-termini in cell lysates of M. pneumoniae were dimethyl-labelled and characterised by LC-MS/MS. Our data suggests that Mpn142 is cleaved to generate adhesins that are auxiliary to P1 and P30.

Delineation of immunodominant and cytadherence segment(s) of Mycoplasma pneumoniae P1 gene

BACKGROUND

Adhesion of Mycoplasma pneumoniae (M. pneumoniae) to host epithelial cells requires several adhesin proteins like P1, P30 and P116. Among these proteins, P1 protein has been inedited as one of the major adhesin and immunogenic protein present on the attachment organelle of M. pneumoniae. In the present study, we scanned the entire sequence of M. pneumoniae P1 protein to identify the immunodominant and cytadherence region(s). M. pneumoniae P1 gene was synthesized in four segments replacing all the UGA codons to UGG codons. Each of the four purified P1 protein fragment was analyzed for its immunogenicity with anti-M. pneumoniae M129 antibodies (Pab M129) and sera of M. pneumoniae infected patients by western blotting and ELISA. Antibodies were produced against all the P1 protein fragments and these antibodies were used for M. pneumoniae adhesion, M. pneumoniae adhesion inhibition and M. pneumoniae surface exposure assays using HEp-2 cells lines.

RESULTS

Our results show that the immunodominant regions are distributed throughout the entire length of P1 protein, while only the N- and C- terminal region(s) of P1 protein are surface exposed and block cytadhesion to HEp-2 cells, while antibodies to two middle fragments failed to block cytadhesion.

CONCLUSIONS

These results have important implications in designing strategies to block the attachment of M. pneumoniae to epithelial cells, thus preventing the development of atypical pneumonia.

Mycoplasma pneumoniae large DNA repetitive elements RepMP1 show type specific organization among strains

Mycoplasma pneumoniae is the smallest self-replicating bacterium with a streamlined genome of 0.81 Mb. Complete genome analysis revealed the presence of multiple copies of four large repetitive elements (designated RepMP1, RepMP2/3, RepMP4 and RepMP5) that are implicated in creating sequence variations among individual strains. Recently, we described RepMP1-associated sequence variations between reference strain M129 and clinical isolate S1 that involved three RepMP1-genes (i.e. mpn130, mpn137 and mpn138). Using PCR and sequencing we analyze 28 additional M. pneumoniae strains and demonstrate the existence of S1-like sequence variants in nine strains and M129-like variants in the remaining nineteen strains. We propose a series of recombination steps that facilitates transition from M129- to S1-like sequence variants. Next we examined the remaining RepMP1-genes and observed no other rearrangements related to the repeat element. The only other detected difference was varying numbers of the 21-nucleotide tandem repeats within mpn127, mpn137, mpn501 and mpn524. Furthermore, typing of strains through analysis of large RepMPs localized within the adhesin P1 operon revealed that sequence divergence involving RepMP1-genes mpn130, mpn137 and mpn138 is strictly type-specific. Once more our analysis confirmed existence of two highly conserved groups of M. pneumoniae strains.

Protective immune responses in mice induced by intramuscular and intranasal immunization with a Mycoplasma pneumoniae P1C DNA vaccine

Mycoplasma pneumoniae is an important causative agent of atypical pneumonia. This study was to determine the ability of a DNA expression vector, which encodes the carboxy terminal region of the M. pneumoniae P1 protein (P1C), to induce humoral and cellular immune responses and to protect against M. pneumoniae infection in BALB/c mice. Mice were immunized with pcDNA3.1/P1C by either intramuscular injection (i.m.) or intranasal inoculation (i.n.). Our results showed that p1c DNA immunization generates detectable antibodies specific to M. pneumoniae, and elicits high levels of IgG1, IgG2a, and IgG2b isotypes (P < 0.01). The levels of IFN-γ and IL-4 in spleen cells of the immunized mice were significantly elevated by immunization via both the i.m. and i.n. methods. Moreover, p1c DNA-immunized mice exhibited detectable protection against M. pneumoniae infection. The lung tissue inflammation was relieved and the histopathologic score (HPS) of pcDNA3.1/P1C-immunized mice was significantly decreased than those in phosphate-buffed saline (PBS) or vaccine-vector-immunized mice (P < 0.01), whereas there were no significant differences in HPS between i.m. and i.n. vaccination (P > 0.05). Our results suggest that pcDNA3.1/P1C could be useful for developing a vaccine against M. pneumoniae infection.

Processing is required for a fully functional protein P30 in Mycoplasma pneumoniae gliding and cytadherence

The cell wall-less prokaryote Mycoplasma pneumoniae causes bronchitis and atypical pneumonia in humans. Mycoplasma attachment to the host respiratory epithelium is required for colonization and mediated largely by a differentiated terminal organelle. P30 is an integral membrane protein located at the distal end of the terminal organelle. The P30 null mutant II-3 is unable to attach to host cells and nonmotile and has a branched cellular morphology compared to the wild type, indicating an important role for P30 in M. pneumoniae biology. P30 is predicted to have an N-terminal signal sequence, but the presence of such a motif has not been confirmed experimentally. In the current study we analyzed P30 derivatives having epitope tags engineered at various locations to demonstrate that posttranslational processing occurred in P30. Several potential cleavage sites predicted in silico were examined, and a processing-defective mutant was created to explore P30 maturation further. Our results suggested that signal peptide cleavage occurs between residues 52 and 53 to yield mature P30. The processing-defective mutant exhibited reduced gliding velocity and cytadherence, indicating that processing is required for fully functional maturation of P30. We speculate that P30 processing may trigger a conformational change in the extracellular domain or expose a binding site on the cytoplasmic domain to allow interaction with a binding partner as a part of functional maturation.

Isolation and characterization of P1 adhesin, a leg protein of the gliding bacterium Mycoplasma pneumoniae

Mycoplasma pneumoniae, a pathogen causing human pneumonia, binds to solid surfaces at its membrane protrusion and glides by a unique mechanism. In this study, P1 adhesin, which functions as a "leg" in gliding, was isolated from mycoplasma culture and characterized. Using gel filtration, blue-native polyacrylamide gel electrophoresis (BN-PAGE), and chemical cross-linking, the isolated P1 adhesin was shown to form a complex with an accessory protein named P90. The complex included two molecules each of P1 adhesin and P90 (protein B), had a molecular mass of about 480 kDa, and was observed by electron microscopy to form 20-nm-diameter spheres. Partial digestion of isolated P1 adhesin by trypsin showed that the P1 adhesin molecule can be divided into three domains, consistent with the results from trypsin treatment of the cell surface. Sequence analysis of P1 adhesin and its orthologs showed that domain I is well conserved and that a transmembrane segment exists near the link between domains II and III.

Genomic analysis reveals Mycoplasma pneumoniae repetitive element 1-mediated recombination in a clinical isolate

Mycoplasmas are cell wall-less bacteria that evolved by drastic reduction of the genome size. Complete genome analysis of Mycoplasma pneumoniae revealed the presence of numerous copies of four distinct large M. pneumoniae repetitive elements (RepMPs). One copy each of RepMP2/3, RepMP4, and RepMP5 are localized within the P1 operon (MPN140 to MPN142 loci), and their involvement in sequence variation in adhesin P1 and adherence-related protein B/C has been documented. Here we analyzed a clinical strain of M. pneumoniae designated S1 isolated from a 1993 outbreak of respiratory infections in San Antonio, TX. Based on the type of RepMPs within the P1 operon, we classified clinical isolate S1 as type 2 with unique minor sequence variations. Hybridization with oligonucleotide arrays revealed sequence divergence in two previously unsuspected hypothetical genes (MPN137 and MPN138 loci). Closer inspection of this region revealed that the MPN137 and MPN138 loci harbored previously unrecognized unique RepMP1 sequences found only in M. pneumoniae. PCR and sequence analyses revealed a recombination event involving three RepMP1-containing genes that resulted in fusion of MPN137 and MPN138 reading frames and loss of all but a short fragment of another RepMP1-containing locus, MPN130. The multiple copies of unique RepMP1 elements spread throughout the chromosome could allow vast numbers of sequence variations in clinical strains. Comparisons of amino acid sequences showed the presence of leucine zipper motifs in MPN130 and MPN138 proteins in reference strain M129 and the absence of these motifs in the fused protein of S1. The presence of tandem leucine and other repeats points to possible regulatory functions of proteins encoded by RepMP1-containing genes.

Beta-D-glucoside utilization by Mycoplasma mycoides subsp. mycoides SC: possible involvement in the control of cytotoxicity towards bovine lung cells

Background

Contagious bovine pleuropneumonia (CBPP) caused by Mycoplasma mycoides subsp. mycoides small-colony type (SC) is among the most serious threats for livestock producers in Africa. Glycerol metabolism-associated H₂O₂ production seems to play a crucial role in virulence of this mycoplasma. A wide number of attenuated strains of M. mycoides subsp. mycoides SC are currently used in Africa as live vaccines. Glycerol metabolism is not affected in these vaccine strains and therefore it does not seem to be the determinant of their attenuation. A non-synonymous single nucleotide polymorphism (SNP) in the bgl gene coding for the 6-phospho-β-glucosidase (Bgl) has been described recently. The SNP differentiates virulent African strains isolated from outbreaks with severe CBPP, which express the Bgl isoform Val₂₀₄, from strains to be considered less virulent isolated from CBPP outbreaks with low mortality and vaccine strains, which express the Bgl isoform Ala₂₀₄.

Results

Strains of M. mycoides subsp. mycoides SC considered virulent and possessing the Bgl isoform Val₂₀₄, but not strains with the Bgl isoform Ala₂₀₄, do trigger elevated levels of damage to embryonic bovine lung (EBL) cells upon incubation with the disaccharides (i.e., β-D-glucosides) sucrose and lactose. However, strains expressing the Bgl isoform Val₂₀₄ show a lower hydrolysing activity on the chromogenic substrate p-nitrophenyl-β-D-glucopyranoside (pNPbG) when compared to strains that possess the Bgl isoform Ala₂₀₄. Defective activity of Bgl in M. mycoides subsp. mycoides SC does not lead to H₂O₂ production. Rather, the viability during addition of β-D-glucosides in medium-free buffers is higher for strains harbouring the Bgl isoform Val₂₀₄ than for those with the isoform Ala₂₀₄.

Conclusion

Our results indicate that the studied SNP in the bgl gene is one possible cause of the difference in bacterial virulence among strains of M. mycoides subsp. mycoides SC. Bgl does not act as a direct virulence factor, but strains possessing the Bgl isoform Val₂₀₄ with low hydrolysing activity are more prone to survive in environments that contain high levels of β-D-glucosides, thus contributing in some extent to mycoplasmaemia.

Real-time detection of Mycoplasma pneumoniae in respiratory samples with an internal processing control

Real-time PCR was employed to detect a region of the P1 cytadhesin gene of Mycoplasma pneumoniae in clinical samples. An internal processing control was included that could be co-amplified simultaneously in the same reaction tube. The assay could reproducibly detect 1 x 10(3) M. pneumoniae organisms ml(-1) in clinical samples. There was no amplification of DNA or signal production from 15 other species of human mycoplasmas and 19 other bacterial species. Using a panel of 175 respiratory samples taken from patients with pneumonia of proven aetiology, the sensitivity was found to be 60 % and the specificity of the assay 96.7 % when compared with serology. This assay is suitable for same-day diagnosis of M. pneumoniae infection and batch processing of respiratory samples for clinical screening.

Experimental proof for a signal peptidase I like activity in Mycoplasma pneumoniae, but absence of a gene encoding a conserved bacterial type I SPase

Although the annotation of the complete genome sequence of Mycoplasma pneumoniae did not reveal a bacterial type I signal peptidase (SPase I) we showed experimentally that such an activity must exist in this bacterium, by determining the N-terminus of the N-terminal gene product P40 of MPN142, formerly called ORF6 gene. Combining mass spectrometry with a method for sulfonating specifically the free amino terminal group of proteins, the cleavage site for a typical signal peptide was located between amino acids 25 and 26 of the P40 precursor protein. The experimental results were in agreement with the cleavage site predicted by computational methods providing experimental confirmation for these theoretical analyses.

Amplification of P1 and 16S rRNA genes by nested PCR for detection of Mycoplasma pneumoniae in paediatric patients

Mycoplasma (M.) pneumoniae is the most frequent atypical pathogen responsible for community-acquired respiratory infection in children and adults. The etiologic diagnosis of these infections still remains difficult. This is mainly due to the absence of characteristic clinical findings, and to the available detection methods (serology and culture) which are time consuming, insensitive and non-specific. To improve the detection of this infectious agent, nested polymerase chain reaction (PCR) analysis was developed. A total of 46 nasal aspirates, from children hospitalised with severe lower respiratory tract infection and in whom M. pneumoniae was suspected, were analysed for the presence of M. pneumoniae DNA by PCR. Routine microbiological investigations revealed no virus in these 46 samples. Using nested PCR, two targets were amplified: the sequences of 16S ribosomal (r) RNA gene (rDNA) and P1 adhesin gene. Evidence of M. pneumoniae infection was identified in four paediatric patients. The amplification of 16S rDNA was found to be more sensitive for the detection of M. pneumoniae. Our results suggest that amplification of the 16S rDNA by nested PCR and detection of the amplification products by visual inspection of the polyacrylamide gel should allow the rapid diagnosis of M. pneumoniae in respiratory tract infection in paediatric patients.

Expression and immunological characterization of the carboxy-terminal region of the P1 adhesin protein of Mycoplasma pneumoniae

Mycoplasma pneumoniae is the causative agent of primary atypical pneumonia in humans. Adherence of M. pneumoniae to host cells requires several adhesin proteins, such as P1, P30, and P116. A major limitation in developing a specific diagnostic test for M. pneumoniae is the inability to express adhesin proteins in heterologous expression systems due to unusual usage of the UGA stop codon, leading to premature termination of these proteins in Escherichia coli. In the present study, we successfully expressed the C-terminal (P1-C1) and N-terminal (P1-N1) regions of the P1 protein in E. coli. On screening these recombinant proteins with sera from M. pneumoniae-infected patients, only the P1-C1 protein was found to be immunogenic. This protein can be used as an antigen for immunodiagnosis of M. pneumoniae infection, as well as in adherence inhibition studies to understand the pathophysiology of the disease.

Detection of Mycoplasma pneumoniae in respiratory samples by real-time PCR using an inhibition control

Polymerase chain reaction (PCR) with real-time detection using two adjacent fluorescent probes in a Lightcycler instrument was applied for detection of the Mycoplasma pneumoniae P1 protein gene. To monitor inhibition in each sample an internal control was constructed that can be amplified by the same primers but detected by different probes and dual color detection. The real-time PCR was applied on 115 respiratory samples from 82 patients and compared to a conventional PCR. There was 100% agreement between the assays, but the real-time PCR proved to be highly superior in speed with a much lower risk of false positives by laboratory contamination.

Surface localized glyceraldehyde-3-phosphate dehydrogenase of Mycoplasma genitalium binds mucin

Mycoplasma genitalium is the smallest known self-replicating cell. It was first isolated from urethral specimens in individuals with non-gonococcal urethritis and, more recently, from respiratory and synovial sites. Our laboratory has been interested in defining the mechanisms by which M. genitalium adheres to and colonizes host cell surfaces. In order to determine potential targets of adherence, we examined the interaction of M. genitalium with a primary component of the mucosal epithelial lining, mucin (Mn). Three Mn-binding proteins (MnBPs) of M. genitalium were isolated by affinity chromatography. One of these proteins was identified by N-terminal sequencing as glyceraldehyde-3-phosphate dehy-drogenase (GAPDH). Antiserum raised against recombinant GAPDH blocked binding of intact biosynthetically labelled mycoplasmas to mucin by approximately 70%. Whole cell radioimmunoprecipitation indicated that GAPDH was surface-accessible and surface localization of GAPDH was further verified by membrane fractionation and immunoelectron microscopy. The role of GAPDH as an adhesin to Mn not only provides insights into the organism's mechanisms of adherence and colonization but also into its ability to maximize its limited genome.

Prospective epidemiologic survey of patients with community-acquired pneumonia requiring hospitalization in Switzerland

BACKGROUND

Community-acquired pneumonia (CAP) is a common problem and the principal infection requiring hospitalization, but its treatment is complicated by the difficulty in microbiological diagnosis and the increasing incidence of antibiotic resistance among respiratory pathogens. The purpose of this paper is to present the main epidemiologic features of patients with CAP requiring hospitalization in our country.

METHODS

We enrolled three hundred and eighteen adult patients with CAP requiring hospitalization in seven large medical centers in Switzerland during two winter periods. The patients' mean age was 70.4 years. This study describes the epidemiology of these patients. Clinical, radiologic and microbiological evaluations were performed at study entry during treatment, and at 4 weeks post-therapy. For microbiological diagnostic purposes, sputum culture, throat swab culture, PCR, blood cultures, Legionella urinary antigen and serologic evaluations were also performed.

RESULTS

Despite the higher mean age, the overall mortality rate was 8%, lower than in other comparable studies. The most common underlying diseases present at study entry were cardiac failure (23%), chronic obstructive pulmonary disease (20%), renal failure (15%), and diabetes (12%); 40% of the patients were smokers. Although dyspnea, cough and positive pulmonary auscultation findings were present in about 90% of patients, fever >38 degrees C was present in only 64%. The most frequently isolated respiratory pathogens were Streptococcus pneumoniae (12.6%), Haemophilus influenzae (6%), Staphylococcus aureus (1.6%), and Moraxella catarrhalis (1.6%). Atypical pathogens were frequently found, with the following distribution: Mycoplasma pneumoniae, 7.5%; Chlamydia pneumoniae, 5.3%; and Legionella pneumophila, 4.4%. The mean duration between onset of symptoms and hospital admission was 4.8 days, and the mean treatment duration was 12.1 days. Two weeks after the start of therapy, although clinical symptoms were absent, radiologic infiltrates were still present in 24% of patients.

CONCLUSIONS

The microbiological diagnosis in CAP can be established in only about 50% of cases with the combination of several diagnostic tools. Epidemiologic surveys of CAP should be performed on a regular basis, regionally, as a way to improve the management of these infections.

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.

Structure, function, and assembly of the terminal organelle of Mycoplasma pneumoniae

Mycoplasmas are cell wall-less bacteria at the low extreme in genome size in the known prokaryote world, and the minimal nature of their genomes is clearly reflected in their metabolic and regulatory austerity. Despite this apparent simplicity, certain species such as Mycoplasma pneumoniae possess a complex terminal organelle that functions in cytadherence, gliding motility, and cell division. The attachment organelle is a membrane-bound extension of the cell and is characterized by an electron-dense core that is part of the mycoplasma cytoskeleton, defined here for working purposes as the protein fraction that remains after extraction with the detergent Triton X-100. This review focuses on the architecture and assembly of the terminal organelle of M. pneumoniae. Characterizing the downstream consequences of defects involving attachment organelle components has made it possible to begin to elucidate the probable sequence of certain events in the biogenesis of this structure.

Defining the mycoplasma 'cytoskeleton': the protein composition of the Triton X-100 insoluble fraction of the bacterium Mycoplasma pneumoniae determined by 2-D gel electrophoresis and mass spectrometry

After treating Mycoplasma pneumoniae cells with the nonionic detergent Triton X-100, an undefined, structured protein complex remains that is called the 'Triton X-100 insoluble fraction' or 'Triton shell'. By analogy with eukaryotic cells and supported by ultrastructural analyses it is supposed that this fraction contains the components of a bacterial cytoskeleton-like structure. In this study, the composition of the Triton X-100 insoluble fraction was defined by electron microscopic screening for possible structural elements, and by two-dimensional (2-D) gel electrophoresis and MS to identify the proteins present. Silver staining of 2-D gels revealed about 100 protein spots. By staining with colloidal Coomassie blue, about 50 protein spots were visualized, of which 41 were identified by determining the mass and partial sequence of tryptic peptides of individual proteins. The identified proteins belonged to several functional categories, mainly energy metabolism, translation and heat-shock response. In addition, lipoproteins were found and most of the proteins involved in cytadherence that were previously shown to be components of the Triton X-100 insoluble fraction. There were also 11 functionally unassigned proteins. Based on sequence-derived predictions, some of these might be potential candidates for structural components. Quantitatively, the most prevalent proteins were the heat-shock protein DnaK, elongation factor Tu and subunits alpha and beta of the pyruvate dehydrogenase complex (PdhA, PdhB), but definite conclusions regarding the composition of the observed structures can only be drawn after specific proteins are assigned to them, for example by immunocytochemistry.

Development of a genomics-based PCR assay for detection of Mycoplasma pneumoniae in a large outbreak in New York State

A genomics-based PCR method was developed and used to test specimens from patients involved in a large outbreak of Mycoplasma pneumoniae in a closed religious community in New York State. New P1 adhesin gene primers were designed to bind to 9 of 10 target sequences in the repetitive-element sequences obtained from the whole genome sequence of M. pneumoniae. This PCR method had a sensitivity of 0.006 CFU and a specificity of 100% for M. pneumoniae. The PCR was validated by testing a subset of patient samples by culture and comparing the results to those obtained by PCR. Of the initial 280 samples tested, 73 were positive by PCR and 22 were positive by culture. All samples positive by culture were also positive by PCR. Follow-up testing of selected patients 3 to 6 weeks after antibiotic treatment revealed that eight samples remained positive by PCR and that three samples remained positive by culture. Additionally, no nonspecific PCR inhibition was detected as a result of the specimen type, transport medium, or sample preparation methodology. The study demonstrates that the PCR described here is a rapid, sensitive, and specific method for the identification of M. pneumoniae and was helpful for the detection and monitoring of the outbreak.

Expression of UGA-containing Mycoplasma genes in Bacillus subtilis

We used Bacillus subtilis to express UGA-containing Mycoplasma genes encoding the P30 adhesin (one UGA) of Mycoplasma pneumoniae and methionine sulfoxide reductase (two UGAs) of Mycoplasma genitalium. Due to natural UGA suppression, these Mycoplasma genes were expressed as full-length protein products, but at relatively low efficiency, in recombinant wild-type Bacillus. The B. subtilis-expressed Mycoplasma proteins appeared as single bands and not as multiple bands compared to expression in recombinant Escherichia coli. Bacillus mutants carrying mutations in the structural gene (prfB) for release factor 2 markedly enhanced the level of readthrough of UGA-containing Mycoplasma genes.

Identification of a new variable sequence in the P1 cytadhesin gene of Mycoplasma pneumoniae: evidence for the generation of antigenic variation by DNA recombination between repetitive sequences

A Mycoplasma pneumoniae cytadhesin P1 gene with novel nucleotide sequence variation has been identified. Four clinical strains of M. pneumoniae were found to carry this type of P1 gene. This new P1 gene is similar to the known group II P1 genes but possesses novel sequence variation of approximately 300 bp in the RepMP2/3 region. The position of the new variable region is distant from the previously reported variable regions known to differ between group I and II P1 genes. Two sequences closely homologous to this new variable region were found within the repetitive sequences outside the P1 gene of the M. pneumoniae M129 genome. This suggests that the new P1 gene was generated by DNA recombination between repetitive sequences and the P1 gene locus. The finding of this new type of P1 gene supports the hypothesis that the repetitive sequences of the M. pneumoniae genome serve as a reservoir to generate antigenic variation of the cytadhesin P1 gene.

Mycoplasma pneumoniae protein P30 is required for cytadherence and associated with proper cell development

The attachment organelle of Mycoplasma pneumoniae is a polar, tapered cell extension containing an intracytoplasmic, electron-dense core. This terminal structure is the leading end in gliding motility, and its duplication is thought to precede cell division, raising the possibility that mutations affecting cytadherence also confer a defect in motility or cell development. Mycoplasma surface protein P30 is associated with the attachment organelle, and P30 mutants II-3 and II-7 do not cytadhere. In this study, the recombinant wild-type but not the mutant II-3 p30 allele restored cytadherence when transformed into P30 mutants by recombinant transposon delivery. The mutations associated with loss of P30 in mutant II-3 and reacquisition of P30 in cytadhering revertants thereof were identified by nucleotide sequencing of the p30 gene. Morphological abnormalities that included ovoid or multilobed cells having a poorly defined tip structure were associated with loss of P30. Digital image analysis confirmed quantitatively the morphological differences noted visually. Transformation of the P30 mutants with the wild-type p30 allele restored a normal morphology, as determined both visually and by digital image analysis, suggesting that P30 plays a role in mycoplasma cell development. Finally, the P30 mutants localized the adhesin protein P1 to the terminal organelle, indicating that P30 is not involved in P1 trafficking but may be required for its receptor-binding function.

Molecular and biochemical analysis of a 105 kDa Mycoplasma gallisepticum cytadhesin (GapA)

The identification of a gene (gapA) from Mycoplasma gallisepticum with homology to the P1 cytadherence gene of Mycoplasma pneumoniae is reported. The gapA gene is a 2895 bp ORF encoding a protein with a molecular mass of 105 kDa. Nucleotide sequence analysis of the gapA gene revealed 45% homology to the M. pneumoniae P1 gene, 46% homology to the Mycoplasma genitalium MgPa gene and 47% homology to the Mycoplasma pirum P1-like protein gene. It has a 64 mol % A+T content compared to 46, 60 and 72 mol % respectively for the P1, MgPa and the P1-like protein genes. As with the P1 and MgPa genes, gapA is a central gene in a multi-gene operon, but unlike the P1 and MgPa genes, there is only a single copy of gapA in the genome. GapA is a trypsin-sensitive surface-exposed protein. Chicken tracheal-ring inhibition-of-attachment assays, using anti-GapA Fab fragments, resulted in 64% inhibition of attachment. These results indicated that GapA plays a role in cytadherence of M. gallisepticum to host cells.

Multigene families encoding the major hemagglutinins in phylogenetically distinct mycoplasmas

Mycoplasma synoviae has two major membrane antigens, MSPA and MSPB, both of which are phase variable and which may be coordinately involved in adhesion of the organism to erythrocytes. A single gene (vlhA) from M. synoviae was characterized, and polypeptides were expressed from nonoverlapping 5' and 3' regions in Escherichia coli. The expression product of the vlhA 5' region reacted with specific reagents against MSPB, while that of the 3' region reacted with specific reagents against MSPA. Analysis of the predicted amino acid sequence showed a characteristic signal peptidase II cleavage site, and the presence of the acylation site was confirmed by identification of a lipid-associated membrane protein, similar in molecular mass to MSPB, in [3H]palmitate-labelled membrane proteins. Further sequence analysis of the vlhA gene revealed a high identity with the Mycoplasma gallisepticum pMGA1.7 gene, a member of a large translated family. The vlhA gene was shown to hybridize to multiple restriction fragments of the M. synoviae genome, suggesting that it was also a member of a multigene family. These findings indicate that coordinate phase variation of the two major surface antigens of M. synoviae WVU may be due to their expression from the same gene and that homologous gene families encode the major hemagglutinins of two phylogenetically distinct mycoplasmas. The presence of homologous multigene families in such phylogenetically distinct species, but not in the genomes of more closely related species, suggests that the families may have been transferred horizontally.

Mycoplasma pneumoniae cytadherence: organization and assembly of the attachment organelle

Mycoplasma pneumoniae has no cell wall but possesses a complex terminal structure that is required for polar localization of adhesins and is thought to participate in cell division. Several protein components of this structure have been identified by analysis of non-cytadhering mutants. Genetic manipulation of mycoplasmas now allows elucidation of the assembly and regulation of the terminal organelle.

Loss of HMW1 and HMW3 in noncytadhering mutants of Mycoplasma pneumoniae occurs post-translationally

The genomic sequence of Mycoplasma pneumoniae establish this cell-wall-less prokaryote as among the smallest known microorganisms capable of self-replication. However, this genomic simplicity and corresponding biosynthetic austerity are sharply contrasted by the complex terminal structure found in this species. This tip structure (attachment organelle) directs colonization of the human respiratory mucosa, leading to bronchitis and atypical pneumonia. Furthermore, formation of a second tip structure appears to precede cell division, implying temporal regulation. However, the organization, regulation, and assembly of the attachment organelle in M. pneumoniae are poorly understood, and no counterparts have been identified among the walled bacteria. M. pneumoniae possesses a cytoskeleton-like structure required to localize adhesin proteins to the attachment organelle. The cytadherence-associated proteins HMW1, HMW2, and HMW3 are components of the mycoplasma cytoskeleton, with HMW1 localizing strictly along the filamentous extensions from the cell body and HMW3 being a key structural element of the terminal organelle. Disruptions in hmw2 result in the loss of HMW1 and HMW3. However, the hmw1 and hmw3 genes were transcribed and translated at wild-type levels in hmw2 mutants. HMW1 and HMW3 were relatively stable in the wild-type background over 8 h but disappeared in the mutants over this time period. Evaluation of recombinant HMW1 levels in mycoplasma mutants suggested a requirement for the C-terminal domain of HMW1 for turnover. Finally, an apparent defect in the processing of the precursor for the adhesin protein P1 was noted in the HMW- mutants.

Sialic acids in molecular and cellular interactions

Sialic acids (Sias) are terminal components of many glycoproteins and glycolipids especially of higher animals. In this exposed position they contribute significantly to the structural properties of these molecules, both in solution and on cell surfaces. Therefore, it is not surprising that Sias are important regulators of cellular and molecular interactions, in which they play a dual role. They can either mask recognition sites or serve as recognition determinants. Whereas the role of Sias in masking and in binding of pathogens to host cells has been documented over many years, their role in nonpathological cellular interaction has only been shown recently. The aim of this chapter is to summarize our knowledge about Sias in masking, for example, galactose residues, and to review the progress made during the past few years with respect to Sias as recognition determinants in the adhesion of pathogenic viruses, bacteria, and protozoa, and particularly as binding sites for endogenous cellular interaction molecules. Finally, perspectives for future research on these topics are discussed.

Mycoplasmas: sophisticated, reemerging, and burdened by their notoriety

Mycoplasmas are most unusual self-replicating bacteria, possessing very small genomes, lacking cell wall components, requiring cholesterol for membrane function and growth, using UGA codon for tryptophan, passing through "bacterial-retaining" filters, and displaying genetic economy that requires a strict dependence on the host for nutrients and refuge. In addition, many of the mycoplasmas pathogenic for humans and animals possess extraordinary specialized tip organelles that mediate their intimate interaction with eucaryotic cells. This host-adapted survival is achieved through surface parasitism of target cells, acquisition of essential biosynthetic precursors, and in some cases, subsequent entry and survival intracellularly. Misconceptions concerning the role of mycoplasmas in disease pathogenesis can be directly attributed to their biological subtleties and to fundamental deficits in understanding their virulence capabilities. In this review, we highlight the biology and pathogenesis of these procaryotes and provide new evidence that may lead to increased appreciation of their role as human pathogens.

Interplay between mycoplasma surface proteins, airway cells, and the protean manifestations of mycoplasma-mediated human infections

Adherence of mycoplasmas to specific tissue surfaces is a crucial step in the establishment of infection. Several pathogenic mycoplasmas are flask-shaped and possess specialized tips that permit a highly oriented surface parasitism of host target cells. Mycoplasma pneumoniae, which causes primary atypical pneumonia in humans, requires a network of interactive adhesins and accessory proteins to cytadhere. The adhesins must cluster at the mycoplasma tip organelle in close association with cytadherence-related accessory proteins and a naplike structure, which together appear to comprise a primitive cytoskeleton-like system. Proline-rich regions associated with these proteins play critical roles in the maintenance of the structural and functional integrity of the tip. Mycoplasma genitalium, originally isolated from the human urogenital tract of patients with nongonococcal urethritis, also colonizes airway cells along with M. pneumoniae. The molecular basis for cytadherence of these mycoplasmas is discussed in terms of the identification, cloning, and sequencing of the implicated mycoplasma genes, their common DNA and amino acid homologies and structural and functional domains, and the organizational similarities in their cytadherence-related operons. In addition, the multiorgan protean manifestations of mycoplasma infection are discussed in terms of the role that mycoplasma adhesins may play in molecular mimicry, postinfectious autoimmunity, and immune-mediated damage.

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.

Isotype-specific antibody responses to acute Mycoplasma pneumoniae infection

BACKGROUND

Mycoplasma pneumoniae-induced respiratory infections affect millions of patients and have been implicated in exacerbation of bronchial asthma. IgE may be involved in such exacerbations. While specific IgG and IgM responses to Mycoplasma pneumoniae are well described, the response of other isotypes is less known.

PURPOSE

To determine whether specific IgE and what subclasses of IgG are formed in response to Mycoplasma pneumoniae infection.

METHODS

We studied 20 patients with acute Mycoplasma pneumoniae infection, in whom the diagnosis was confirmed by a 16-fold increase in complement fixation titer between acute and convalescent serum samples. We developed an enzyme-linked immunosorbent assay (ELISA) for the determination of IgG, IgA, and IgM antibodies specific for Mycoplasma pneumoniae protein antigens. We used Western blotting to confirm the results of the ELISA and to detect Mycoplasma-specific IgG subclasses and IgE.

RESULTS

Changes in Mycoplasma pneumoniae-specific IgG, IgA, and IgM were significant. Western blots of Mycoplasma pneumoniae antigens in 13 convalescent sera showed specific IgG in all, IgM in 11, IgA in 6, and IgE in 10. The IgG response consisted mainly of IgG1 and IgG3, and to a lesser degree of IgG2 and IgG4.

CONCLUSIONS

We conclude that Mycoplasma pneumoniae infection is associated with a significant specific IgA and IgE response, in addition to the well-known responses of IgG and IgM. As IgE is involved in allergic reactions, the production of Mycoplasma pneumoniae-specific IgE may have a role in exacerbation of bronchial asthma.

Biofunctional domains of the Mycoplasma pneumoniae P30 adhesin

The P30 adhesin genes of spontaneous, hemadsorption-negative (HA-) class II Mycoplasma pneumoniae mutants that displayed P30 adhesin-deficient protein profiles were analyzed. One subclass of P30-deficient mutants possessed the entire p3O structural gene without alterations (825 nucleotides, encoding 275 amino acids with a predicted molecular mass of 29,743 Da [S. F. Dallo, A. Chavoya, and J. B. Baseman, Infect. Immun. 58:4163-4165, 1990]). However, the second mutant subclass contained a deletion in p3O resulting in the expression of a 25-kDa peptide (681 nucleotides, encoding 227 amino acids with a calculated molecular mass of 24,823 Da). This P25-truncated peptide lacked 8 of the 13 proline-rich amino acid repeat sequences at the carboxy terminus. Whole-cell radioimmunoprecipitation of M. pneumoniae with antibodies directed against the proline-rich repeat sequences located in the carboxy terminus demonstrated their surface accessibility. In contrast, antibodies generated against N-terminal amino acid sequences upstream of the repeats did not bind to intact mycoplasmas. The amino acid sequence homologies exhibited by the P30 adhesin and eucaryotic structural proteins were corroborated by cross-reactive epitopes shared between the P30 adhesin and fibrinogen, keratin, and myosin. These data reinforce the importance of the P30 protein in cytadherence and virulence and provide a molecular basis for postinfectious autoimmunity associated with M. pneumoniae-mediated pathologies.

Cloning and characterization of a putative cytadhesin gene (mgc1) from Mycoplasma gallisepticum

A 150-kDa cytadhesin-like protein from Mycoplasma gallisepticum has been identified. A previously described 583-bp fragment (J.E. Dohms, L.L. Hnatow, P. Whetzel, R. Morgan and C.L. Keeler, Jr., Avian Dis. 37:380-388, 1993) was used to probe a genomic library of M. gallisepticum DNA. An 8.0-kb SacI fragment was identified, cloned, and partially sequenced. Analysis of the resulting 3,750-bp sequence revealed the presence of a 3,366-nucleotide open reading frame, mgc1. The 1,122-amino-acid protein encoded by this open reading frame, MGC1, has characteristics of a class I membrane protein and has homology with the MgPa cytadhesin of Mycoplasma genitalium (26.3%) and the P1 cytadhesin of Mycoplasma pneumoniae (28.7%). A portion of MGC1 was expressed as a glutathione S-transferase fusion protein and used to produce antiserum in rabbits. The antiserum recognizes a 150-kDa protein from M. gallisepticum. The protein is sensitive to trypsin, confirming that it is surface exposed. Primer extension analysis indicates that the mgc1 RNA starts within an upstream open reading frame, suggesting complex control of its expression. This is the first description of a functional gene from M. gallisepticum showing homology to cytadhesin genes from human mycoplasmas.

Sequence analysis of 56 kb from the genome of the bacterium Mycoplasma pneumoniae comprising the dnaA region, the atp operon and a cluster of ribosomal protein genes

To sequence the entire 800 kilobase pair genome of the bacterium Mycoplasma pneumoniae, a plasmid library was established with contained the majority of the EcoR1 fragments from M.pneumoniae. The EcoR1 fragments were subcloned from an ordered cosmid library comprising the complete M.pneumoniae genome. Individual plasmid clones were sequenced in an ordered fashion mainly by primer walking. We report here the initial results from the sequence analysis of -56 kb comprising the dnaA region as a potential origin of replication, the ATPase operon and a region coding for a cluster of ribosomal protein genes. The data were compared with the corresponding genes/operons from Bacillus subtilis, Escherichia coli, Mycoplasma capricolum and Mycoplasma gallisepticum.

Diagnosis of Legionella pneumophila, Mycoplasma pneumoniae, or Chlamydia pneumoniae lower respiratory infection using the polymerase chain reaction on a single throat swab specimen

Diagnosis of Mycoplasma pneumoniae and Chlamydia pneumoniae lower respiratory infections using DNA amplification by polymerase chain reaction (PCR) on throat swab specimens has been reported. In this study we determined the sensitivity of the detection of Legionella pneumophila in simulated throat swab specimens by PCR. Next, we compared the sensitivity and specificity of a single throat swab PCR with the current tests for diagnosis of Legionella spp., M. pneumoniae, and C. pneumoniae in patients with lower respiratory tract infections. Patients' work-up included: (a) throat swab specimen for Legionella spp., M. pneumoniae, and C. pneumoniae PCR; (b) throat swab specimen for C. pneumoniae culture; (c) sputum specimen for L. pneumophila direct fluorescent antibody and culture; (d) urine specimen for L. pneumophila serogroup 1 antigen detection; and (e) serum specimen for L. pneumophila, M. pneumoniae, and C. pneumoniae acute and convalescent antibody titers. A total of 155 patients with lower respiratory infection were enrolled in this prospective study. Throat swab PCR was positive for Legionella spp. in five of the six patients with legionellosis, indicating the presence of this organism in the oropharynx of patients with Legionnaires disease. Mycoplasma pneumoniae PCR was positive in eight of the nine patients with mycoplasma infection. Chlamydia pneumoniae PCR was positive in the two patients with C. pneumoniae infection. None of the other 138 patients with negative PCR had other positive confirmatory tests for respiratory infection by these three organisms (100% specificity). PCR was able to detect 15 of the 17 infected (88.2%). Results of this investigation indicate that PCR on a single throat swab specimen is a rapid, sensitive, and specific test that may greatly simplify the diagnosis of lower respiratory infection caused by Legionella spp., Mycoplasma pneumoniae, or C. pneumoniae.

A spontaneous hemadsorption-negative mutant of Mycoplasma pneumoniae exhibits a truncated adhesin-related 30-kilodalton protein and lacks the cytadherence-accessory protein HMW1

A spontaneous, hemadsorption-negative mutant of Mycoplasma pneumoniae lacks the cytoskeleton-forming HMW1 protein and exhibits a truncated adhesin-related 30-kDa protein. Genetic analyses revealed deletion of one nucleotide in the hmw1 gene and loss of eight repeated sequences comprising 144 nucleotides in the gene for the adhesin-related 30-kDa protein.

Physical mapping of the Mycoplasma gallisepticum S6 genome with localization of selected genes

We report the construction of a physical map of the Mycoplasma gallisepticum S6 genome by field-inversion gel electrophoresis of DNA fragments generated by digestion of genomic DNA with rare-cutting restriction endonucleases. The size of the M. gallisepticum S6 genome was calculated to be approximately 1,054 kb. The loci of several genes have been assigned to the map by Southern hybridization utilizing specific gene probes.

Typing of Mycoplasma pneumoniae by PCR-mediated DNA fingerprinting

PCR fingerprinting was used to characterize clinical isolates of Mycoplasma pneumoniae. Among 24 strains tested, two types were distinguished. Nineteen strains belonged to type 1, whereas only 5 strains belonged to type 2. The majority of strains isolated since 1991 in Belgium belong to type 1. No variations in fingerprinting patterns were observed within each group, confirming the highly conserved nature of the M. pneumoniae genome.

Sequence divergence in the ORF6 gene of Mycoplasma pneumonia

The ORF6 gene product of Mycoplasma pneumoniae is involved in a yet-unknown manner in the adhesion of the bacterium to its host cell. Part of the ORF6 gene is a repetitive DNA sequence (RepMP5), about 1,900 bp long. Seven additional similar copies of RepMP5 are dispersed on the genome. In the independently isolated strains M. pneumoniae M129 and FH, the RepMP5 copies residing in the ORF6 gene are not identical. Two conserved regions, ranging from nucleotides 1 to 799 and from nucleotide 1795 to the end of the gene, border a variable region, ranging from nucleotides 800 to 1794. This variable region differs in DNA sequence and by 201 bp. Analysis of RepMP5 copies outside the ORF6 gene showed that both M. pneumoniae M129 and M. pneumoniae FH carry a RepMP5 copy on a 6-kbp EcoRI fragment which has the same DNA sequence as the variable region of RepMP5 in the M. pneumoniae FH ORF6 gene. According to these data, a switch from the M. pneumoniae M129 ORF6 gene to the M. pneumoniae FH ORF6 gene could take place by gene conversion.

Identification and characterization of hitherto unknown Mycoplasma pneumoniae proteins

Eleven hitherto unknown Mycoplasma pneumoniae proteins were identified and characterized with respect to their size and subcellular location. This was carried out through the construction of in vitro gene fusions between a modified mouse dehydrofolate reductase (dhfr) gene and selected regions (cosmid clones) of the M. pneumoniae genome and expressing them in Escherichia coli. Positive clones were identified using antibodies against specific fractions of M. pneumoniae. The deduced protein sequences of 11 out of 30 clones did not show significant homologies to known proteins in protein data-bank searches. Monospecific antibodies against these 11 fusion proteins were used to determine the size and cellular location of the corresponding M. pneumoniae proteins by immunoscreening Western blots of SDS-acrylamide gels from M. pneumoniae cell extracts.

Spatial arrangement of gene products of the P1 operon in the membrane of Mycoplasma pneumoniae

The spatial arrangement of three P1 operon-encoded proteins--attachment protein P1 (ORF5 gene product) and the ORF6-derived proteins of 40 and 90 kDa--in the membrane of Mycoplasma pneumoniae M129 was investigated by nearest-neighbor analysis. For these studies, the homobivalent, thiol-cleavable, and nonmembrane-permeating cross-linking reagent 3,3'-dithiobis(sulfosuccinimidylpropionate) (DTSSP) was used. The cross-linked proteins were isolated by immunoprecipitation with antibodies directed against fusion proteins of selected regions of the 40-kDa, the 90-kDa, or the P1 protein. The individual components of the immunoprecipitated protein complexes were identified by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, autoradiography, and immunoblot analysis. This study showed that the P1 protein, the ORF6 gene product, and an unidentified 30-kDa protein were linked to each other in the intact bacterial membrane by the reagent DTSSP, indicating that these proteins are located at a maximal distance of 12 A (1 A = 0.1 nm) on the tip structure of M. pneumoniae.

Molecular characterization of the P1-like adhesin gene from Mycoplasma pirum

A DNA fragment has been isolated from the genome of Mycoplasma pirum by use of a genetic probe derived from the conserved region within the genes for the major adhesins of Mycoplasma genitalium and Mycoplasma pneumoniae. A gene encoding an adhesin-like polypeptide was localized, and sequence analysis indicated a G + C content of only 28%, with A- and T-rich codons being preferentially used. A total of 91% of positions 3 were either A or T. The deduced polypeptide is 1,144 amino acids long (126 kDa) and shows 26% identity with the adhesins of M. genitalium and M. pneumoniae. Other features in common with these two membrane proteins include a similar hydropathic profile and a proline-rich C terminus. Antibodies were prepared by using as an immunogen a peptide derived from the C terminus of the M. pirum adhesin-like polypeptide and were found to recognize on immunoblots a 126-kDa polypeptide from an M. pirum cellular extract. The characterization of the adhesin-like gene is a first step toward a better understanding of the mechanisms allowing this human mycoplasma to attach to host cells.