Phase variation among major surface antigens of Mycoplasma penetrans

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

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

The Variable Internal Structure of the Mycoplasma penetrans Attachment Organelle Revealed by Biochemical and Microscopic Analyses: Implications for Attachment Organelle Mechanism and Evolution

Although mycoplasmas have small genomes, many of them, including the HIV-associated opportunist Mycoplasma penetrans, construct a polar attachment organelle (AO) that is used for both adherence to host cells and gliding motility. However, the irregular phylogenetic distribution of similar structures within the mycoplasmas, as well as compositional and ultrastructural differences among these AOs, suggests that AOs have arisen several times through convergent evolution. We investigated the ultrastructure and protein composition of the cytoskeleton-like material of the M. penetrans AO with several forms of microscopy and biochemical analysis, to determine whether the M. penetrans AO was constructed at the molecular level on principles similar to those of other mycoplasmas, such as Mycoplasma pneumoniae and Mycoplasma mobile We found that the M. penetrans AO interior was generally dissimilar from that of other mycoplasmas, in that it exhibited considerable heterogeneity in size and shape, suggesting a gel-like nature. In contrast, several of the 12 potential protein components identified by mass spectrometry of M. penetrans detergent-insoluble proteins shared certain distinctive biochemical characteristics with M. pneumoniae AO proteins, although not with M. mobile proteins. We conclude that convergence between M. penetrans and M. pneumoniae AOs extends to the molecular level, leading to the possibility that the less organized material in both M. pneumoniae and M. penetrans is the substance principally responsible for the organization and function of the AO.IMPORTANCEMycoplasma penetrans is a bacterium that infects HIV-positive patients and may contribute to the progression of AIDS. It attaches to host cells through a structure called an AO, but it is not clear how it builds this structure. Our research is significant not only because it identifies the novel protein components that make up the material within the AO that give it its structure but also because we find that the M. penetrans AO is organized unlike AOs from other mycoplasmas, suggesting that similar structures have evolved multiple times. From this work, we derive some basic principles by which mycoplasmas, and potentially all organisms, build structures at the subcellular level.

Mycoplasma agassizii strain variation and distinct host antibody responses explain differences between enzyme-linked immunosorbent assays and Western blot assays

The precarious status of desert (Gopherus agassizii) and gopher (G. polyphemus) tortoises has resulted in conservation efforts that now include health assessment as an important component of management decision-making. Mycoplasmal upper respiratory tract disease (URTD) is one of very few diseases in chelonians for which comprehensive and rigorously validated diagnostic tests exist. In this study, serum samples obtained from eight Gopherus tortoises documented at necropsy to (i) be enzyme-linked immunosorbent assay (ELISA) seropositive using the PS6 antigen, (ii) be infected with Mycoplasma agassizii as indicated by direct isolation of the pathogen from the respiratory surfaces, and (iii) have histological lesions of mycoplasmal URTD were used to evaluate four distinct clinical isolates of M. agassizii as antigens for ELISA and Western blot analyses. Each animal sample reacted in the Western blot with its homologous M. agassizii strain, but recognition of heterologous M. agassizii strains was variable. Further, individual animals varied significantly with respect to the specific proteins recognized by the humoral immune response. An additional 114 Gopherus serum samples were evaluated using ELISA antigens prepared from the four distinct M. agassizii strains; A₄₀₅ values were significantly correlated (r² goodness of fit range, 0.708 to 0.771; P < 0.0001) for all antigens tested. The results confirm that strain variation is responsible for the observed differences between Western blot binding patterns. Thus, reliance on a single M. agassizii strain as an antigen in Western blot assays may provide false-negative results. This could have adverse consequences for the well-being of these environmentally sensitive hosts if false-negative animals were relocated to sites consisting of true-negative populations.

Phase and antigenic variation in mycoplasmas

With their reduced genome bound by a single membrane, bacteria of the Mycoplasma species represent some of the simplest autonomous life forms. Yet, these minute prokaryotes are able to establish persistent infection in a wide range of hosts, even in the presence of a specific immune response. Clues to their success in host adaptation and survival reside, in part, in a number of gene families that are affected by frequent, stochastic genotypic changes. These genetic events alter the expression, the size and the antigenic structure of abundant surface proteins, thereby creating highly versatile and dynamic surfaces within a clonal population. This phenomenon provides these wall-less pathogens with a means to escape the host immune response and to modulate surface accessibility by masking and unmasking stably expressed components that are essential in host interaction and survival.

Common strategies for antigenic variation by bacterial, fungal and protozoan pathogens

The complex relationships between infectious organisms and their hosts often reflect the continuing struggle of the pathogen to proliferate and spread to new hosts, and the need of the infected individual to control and potentially eradicate the infecting population. This has led, in the case of mammals and the pathogens that infect them, to an 'arms race', in which the highly adapted mammalian immune system has evolved to control the proliferation of infectious organisms and the pathogens have developed correspondingly complex genetic systems to evade this immune response. We review how bacterial, protozoan and fungal pathogens from distant evolutionary lineages have evolved surprisingly similar mechanisms of antigenic variation to avoid eradication by the host immune system and can therefore maintain persistent infections and ensure their transmission to new hosts.

Identification of a site-specific tyrosine recombinase that mediates promoter inversions of phase-variable mpl lipoprotein genes in Mycoplasma penetrans

Mycoplasma penetrans has the ability to change its surface lipoprotein profiles frequently. The P35 family lipoproteins encoded by the mpl genes are key players in this profile variation. The M. penetrans HF-2 genome has 38 mpl genes that form three gene clusters. Most of these mpl genes have an invertible promoter sequence that is responsible for the ON/OFF switching of individual mpl gene expression. Here, we identified the recombinase that catalyses inversions of the mpl gene promoters. We focused on two open reading frames of the M. penetrans HF-2 genome, namely MYPE2900 and MYPE8180, which show significant homology to the tyrosine site-specific recombinase (Tsr) family proteins. Since genetic tools for M. penetrans are still not developed, we cloned the MYPE2900 and MYPE8180 genes and expressed them in Mycoplasma pneumoniae and Escherichia coli. The promoter regions of the mpl genes [p35 (MYPE6810) or p42 (MYPE6630) genes] were also introduced into M. pneumoniae and E. coli cells expressing MYPE2900 or MYPE8180. Inversion of these promoters occurred in the presence of the MYPE2900 gene but not in the presence of the MYPE8180 gene, indicating that the MYPE2900 gene product is the recombinase that catalyses mpl gene promoter inversions. We used a PCR-based method to detect mpl promoter inversion. This method also enabled us to detect inversions of 10 mpl gene promoters in M. penetrans HF-2 cells. All these promoter inversions occurred at the 12 bp inverted repeat (IR) sequences flanking the promoter sequence. The consensus sequence of these IRs was proposed as TAAYNNNDATTA (Y=C or T; D=A, G or T).

Occurrence, plasticity, and evolution of the vpma gene family, a genetic system devoted to high-frequency surface variation in Mycoplasma agalactiae

Mycoplasma agalactiae, an important pathogen of small ruminants, exhibits a very versatile surface architecture by switching multiple, related lipoproteins (Vpmas) on and off. In the type strain, PG2, Vpma phase variation is generated by a cluster of six vpma genes that undergo frequent DNA rearrangements via site-specific recombination. To further comprehend the degree of diversity that can be generated at the M. agalactiae surface, the vpma gene repertoire of a field strain, 5632, was analyzed and shown to contain an extended repertoire of 23 vpma genes distributed between two loci located 250 kbp apart. Loci I and II include 16 and 7 vpma genes, respectively, with all vpma genes of locus II being duplicated at locus I. Several Vpmas displayed a chimeric structure suggestive of homologous recombination, and a global proteomic analysis further indicated that at least 13 of the 16 Vpmas can be expressed by the 5632 strain. Because a single promoter is present in each vpma locus, concomitant Vpma expression can occur in a strain with duplicated loci. Consequently, the number of possible surface combinations is much higher for strain 5632 than for the type strain. Finally, our data suggested that insertion sequences are likely to be involved in 5632 vpma locus duplication at a remote chromosomal position. The role of such mobile genetic elements in chromosomal shuffling of genes encoding major surface components may have important evolutionary and epidemiological consequences for pathogens, such as mycoplasmas, that have a reduced genome and no cell wall.

Binding of IgA by Mycoplasma penetrans

The current study shows that Mycoplasma penetrans strain GTU binds human serum immunoglobulin A (IgA) and secretory IgA but not IgG. Binding of IgA was associated almost exclusively with the lipoprotein fraction obtained by Triton X-114 fractionation of isolated M. penetrans membranes. Western immunoblot analysis of isolated membranes of M. penetrans strain GTU and of the Triton X-114 fraction showed that the major IgA-binding component was a lipoprotein with a molecular mass of 38 kDa, one of the major lipoproteins of this organism. The authors suggest that the high IgA-binding capacity of M. penetrans strain GTU may serve as a defense mechanism, conferring on this microorganism the ability to evade clearance mediated by specific IgA antibodies.

Long simple sequence repeats in host-adapted pathogens localize near genes encoding antigens, housekeeping genes, and pseudogenes

Simple sequence repeats (SSRs) in DNA sequences are tandem iterations of a single nucleotide or a short oligonucleotide. SSRs are subject to slipped-strand mutations and a common source of phase variation in bacteria and antigenic variation in pathogens. Significantly long SSRs are generally rare in prokaryotic genomes, and long SSRs composed of iterations of mono-, di-, tri-, and tetranucleotides are mostly restricted to host-adapted pathogens. We present new results concerning associations between long SSRs and genes related to different cellular functions in genomes of host-adapted pathogens. We found that in the majority of the analyzed genomes, at least some of the genes associated with SSRs encode potential antigens, which is expected if the primary function of SSRs is their contribution to antigenic variation. However, we also found a number of long SSRs associated with housekeeping genes, including rRNA and tRNA genes, genes encoding ribosomal proteins, amino acyl-tRNA synthetases, chaperones, and important metabolic enzymes. Many of these genes are probably essential and it is unlikely that they are phase-variable. Few statistically significant associations between SSRs and gene functional classifications were detected, suggesting that most long SSRs are not related to a particular cellular function or process. Long SSRs in Mycobacterium leprae are mostly associated with pseudogenes and may be contributing to gene loss following the adaptation to an obligate pathogenic lifestyle. We speculate that LSSRs may have played a similar role in genome reduction of other host-adapted pathogens.

Molecular mechanisms of pathogenicity of Mycoplasma mycoides subsp. mycoides SC

Mycoplasma mycoides subsp. mycoides SC, the aetiological agent of contagious bovine pleuropneumonia (CBPP), is considered the most pathogenic of the Mycoplasma species. Its virulence is probably the result of a coordinated action of various components of an antigenically and functionally dynamic surface architecture. The different virulence attributes allow the pathogen to evade the host's immune defence, adhere tightly to the host cell surface, persist and disseminate in the host causing mycoplasmaemia, efficiently import energetically valuable nutrients present in the environment, and release and simultaneously translocate toxic metabolic pathway products to the host cell where they cause cytotoxic effects that are known to induce inflammatory processes and disease. This strategy enables the mycoplasma to exploit the minimal genetic information in its small genome, not only to fulfil the basic functions for its replication but also to damage host cells in intimate proximity thereby acquiring the necessary bio-molecules, such as amino acids and nucleic acid precursors, for its own biosynthesis and survival.

Rapid and efficient preparation of monoclonal antibodies against 35 kDa lipoprotein of Mycoplasma penetrans

To develop a rapid and efficient method for preparing monoclonal antibodies (MAb) against 35 kDa lipoprotein of Mycoplasma penetrans, BALB/c mice were injected into the footpads for immunization, and the popliteal lymph nodes were isolated 19 days later for MAb-producing hybridomas, from which the mAbs against the 35 kDa lipoprotein were screened. The identification of the mAb against the 35 kDa lipoprotein was performed using indirect enzyme-linked immunosorbent assay (ELISA) and immunoblotting. Using popliteal lymph node procedures, we generated several positive clones, one of which we characterized by ELISA and immunoblot. The clone 1D41B8 was identified as the immunoglobulin G1 (IgG1) isotype, kappa chain with affinity constants (Ka) of 2.95 x 10(9) M(-1). The MAbs did not cross-react with a number of control bacteria, which included Mycoplasma fermentans, Mycoplasma hominis, and Mycoplasma genitalium. This is the first report on the preparation of mAbs against M. penetrans that is specific to 35 kDa lipoprotein using popliteal lymph nodes. The high-specificity and high-affinity MAbs produced by two methodologies used of hybridomas provide a basis for further research on the pathogenesis and early diagnosis of M. penetrans. This simple approach may become a method of choice for the generation and production of MAbs in a short period of time.

Interactions between mycoplasma lipid-associated membrane proteins and the host cells

Mycoplamas are a group of wall-less prokaryotes widely distributed in nature, some of which are pathogenic for humans and animals. There are many lipoproteins anchored on the outer face of the plasma membrane, called lipid-associated membrane proteins (LAMPs). LAMPs are highly antigenic and could undergo phase and size variation, and are recognized by the innate immune system through Toll-like receptors (TLR) 2 and 6. LAMPs can modulate the immune system, and could induce immune cells apoptosis or death. In addition, they may associate with malignant transformation of host cells and are also considered to be cofactors in the progression of AIDS.

Mycoplasma penetrans infections and seroconversion in patients with AIDS: identification of major mycoplasmal antigens targeted by host antibody response

We examined Mycoplasma penetrans-specific antibodies in sera of five male homosexual AIDS patients from whom M. penetrans was isolated during the disease process. No consistent immune reaction pattern could be recognized in Western blot using whole cell proteins. Serum samples obtained prior to M. penetrans isolation reacted with a number of M. penetrans proteins, most likely due to non-specific cross-reactions. Further analysis revealed that patients produced prominent antibody reaction to lipid-associated membrane proteins (LAMPs) of M. penetrans at the time of mycoplasma isolation, which could not be observed for serum samples obtained prior to M. penetrans isolation. The positive antibody reaction was mainly directed against two major LAMPs of M. penetrans with molecular mass of 35 and 38 kDa and produced a distinctive pattern of positive immunoreaction bands. Our observation suggested that, comparing with whole mycoplasmal proteins, LAMPs were more specific target antigens in serological assays for M. penetrans infection.

The frequency and rate of pilin antigenic variation in Neisseria gonorrhoeae

The pilin antigenic variation (Av) system of Neisseria gonorrhoeae (Gc) mediates unidirectional DNA recombination from silent gene copies into the pilin expression locus. A DNA sequencing assay was developed to accurately measure pilin Av in a population of Gc strain FA1090 arising from a defined pilin progenitor under non-selective culture conditions. This assay employs a piliated parental Gc variant with a recA allele whose promoter is replaced by lac-regulatory elements, allowing for controlled induction of pilin Av. From this assay, the frequency of pilin Av was measured as 0.13 recombination events per cell, with a corresponding rate of pilin Av of 4x10(-3) events per cell per generation. Most pilin variants retained the parental piliation phenotype, providing the first comprehensive analysis of piliated variants arising from a piliated progenitor. Sequence analysis of pilin variants revealed that a subset of possible recombination events predominated, which differed between piliated and non-piliated progeny. Pilin Av exhibits the highest reported frequency of any pathogenic gene conversion system and can account for the extensive pilin variation detected during human infection.

The diversity of Mycoplasma hyopneumoniae within and between herds using pulsed-field gel electrophoresis

Over the years, pulsed-field gel electrophoresis (PFGE) has been proven a robust technique to type isolates with a high resolution and a good reproducibility. In this study, a PFGE protocol is described for the typing of Mycoplasma hyopneumoniae isolates. The potential of this technique was demonstrated by comparing M. hyopneumoniae isolates obtained from the same as well as from different herds. The use of two different restriction enzymes, SalI and ApaI, was evaluated. For each enzyme, the resulting restriction profiles were clustered using the unweighted pair group method with arithmetic means (UPGMA). For both obtained dendrograms, the included isolates of the related M. flocculare species clustered separately from all M. hyopneumoniae isolates, forming the root of the dendrograms. The PFGE patterns of the M. hyopneumoniae isolates of different herds were highly diverse and clustered differently in both dendrograms, illustrated by a Pearson's correlation coefficient of only 0.33. A much higher similarity was observed with isolates originating from different pigs of a same herd. The PFGE patterns of these isolates always clustered according to their herd and this for both dendrograms. In conclusion, the results indicate a closer relationship of M. hyopneumoniae isolates within a herd compared to isolates from different herds and this for both restriction enzymes used. Since the described PFGE technique was shown to be highly discriminative and reproducible, it will be a helpful tool to further elucidate the epidemiology of M. hyopneumoniae.

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 Mycoplasma fermentans prophage φMFV1: genome organization, mobility and variable expression of an encoded surface protein

The approximately 16 kb genome of the Mycoplasma fermentans phiMFV1 prophage is described, and its mobility, replication and effect on the mycoplasma surface phenotype are demonstrated. In various M. fermentans strains, phiMFV1 was either absent or integrated at diverse (and sometimes multiple) chromosomal sites, each marked by a conserved TTTTTA target sequence that is duplicated upon integration. Precise excision, replication of an extrachromosomal form and loss of phiMFV1 from the mycoplasmal genome were documented in a series of clonal derivatives of M. fermentans propagated in culture. Of 18 open reading frames (ORFs) encoded by phiMFV1, most can be ascribed functions related to phage biology, whereas one encodes a unique coiled-coil membrane surface protein, Mem, that was confirmed to be expressed in propagating populations of M. fermentans. With the exception of Mem and other minor ORFs, the striking similarity between the deduced proteomes of phiMFV1 and the recently described phiMAV1 of arthritogenic strains of Mycoplasma arthritidis, along with the prominent gene synteny between these elements, provides the taxonomic basis for a new family of prophage. Their coding features are consistent with long-term residence in mycoplasma genomes and the divergence of species within a phylogenetic clade of mycoplasmas. The unique Mem protein expressed from phiMFV1 and the unique hypothetical surface lipoproteins encoded by phiMAV1 and phiMFV1 also suggest that prophage-associated genes may provide specific, selectable phenotypic traits during co-evolution of mycoplasma species with their respective mammalian hosts. Retention of these labile prophage elements in organisms with such drastically reduced genome sizes implies a significant role in adaptation and survival.

Multiple promoter inversions generate surface antigenic variation in Mycoplasma penetrans

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

The complete genomic sequence of Mycoplasma penetrans, an intracellular bacterial pathogen in humans

The complete genomic sequence of an intracellular bacterial pathogen, Mycoplasma penetrans HF-2 strain, was determined. The HF-2 genome consists of a 1 358 633 bp single circular chromosome containing 1038 predicted coding sequences (CDSs), one set of rRNA genes and 30 tRNA genes. Among the 1038 CDSs, 264 predicted proteins are common to the Mycoplasmataceae sequenced thus far and 463 are M.penetrans specific. The genome contains the two-component system but lacks the essential cellular gene, uridine kinase. The relatively large genome of M.penetrans HF-2 among mycoplasma species may be accounted for by both its rich core proteome and the presence of a number of paralog families corresponding to 25.4% of all CDSs. The largest paralog family is the p35 family, which encodes surface lipoproteins including the major antigen, P35. A total of 44 genes for p35 and p35 homologs were identified and 30 of them form one large cluster in the chromosome. The genetic tree of p35 paralogs suggests the occurrence of dynamic chromosomal rearrangement in paralog formation during evolution. Thus, M.penetrans HF-2 may have acquired diverse repertoires of antigenic variation-related genes to allow its persistent infection in humans.