The mycoplasmas

Temperature change elicits lipidome adaptation in the simple organisms Mycoplasma mycoides and JCVI-syn3B

Cell membranes mediate interactions between life and its environment, with lipids determining their properties. Understanding how cells adjust their lipidomes to tune membrane properties is crucial yet poorly defined due to the complexity of most organisms. We used quantitative shotgun lipidomics to study temperature adaptation in the simple organism Mycoplasma mycoides and the minimal cell JCVI-syn3B. We show that lipid abundances follow a universal logarithmic distribution across eukaryotes and bacteria, with comparable degrees of lipid remodeling for adaptation regardless of lipidomic or organismal complexity. Lipid features analysis demonstrates head-group-specific acyl chain remodeling as characteristic of lipidome adaptation; its deficiency in Syn3B is associated with impaired homeoviscous adaptation. Temporal analysis reveals a two-stage cold adaptation process: swift cholesterol and cardiolipin shifts followed by gradual acyl chain modifications. This work provides an in-depth analysis of lipidome adaptation in minimal cells, laying a foundation to probe the design principles of living membranes.

Marine bacteriophages disturb the associated microbiota of Aurelia aurita with a recoverable effect on host morphology

The concept of the metaorganism describes a multicellular host and its diverse microbial community, which form one biological unit with a combined genetic repertoire that significantly influences health and survival of the host. The present study delved into the emerging field of bacteriophage research within metaorganisms, focusing on the moon jellyfish Aurelia aurita as a model organism. The previously isolated Pseudomonas phage BSwM KMM1 and Citrobacter phages BSwM KMM2 - KMM4 demonstrated potent infectivity on bacteria present in the A. aurita-associated microbiota. In a host-fitness experiment, Baltic Sea subpopulation polyps were exposed to individual phages and a phage cocktail, monitoring polyp survival and morphology, as well as microbiome changes. The following effects were obtained. First, phage exposure in general led to recoverable malformations in polyps without affecting their survival. Second, analyses of the community structure, using 16S rRNA amplicon sequencing, revealed alterations in the associated microbial community in response to phage exposure. Third, the native microbiota is dominated by an uncultured likely novel Mycoplasma species, potentially specific to A. aurita. Notably, this main colonizer showed resilience through the recovery after initial declines, which aligned with abundance changes in Bacteroidota and Proteobacteria, suggesting a dynamic and adaptable microbial community. Overall, this study demonstrates the resilience of the A. aurita metaorganism facing phage-induced perturbations, emphasizing the importance of understanding host-phage interactions in metaorganism biology. These findings have implications for ecological adaptation and conservation in the rapidly changing marine environment, particularly regarding the regulation of blooming species and the health of marine ecosystems during ongoing environmental changes.

Characterization of heterologously expressed Fibril, a shape and motility determining cytoskeletal protein of the helical bacterium Spiroplasma

Fibril is a constitutive filament-forming cytoskeletal protein of unidentified fold, exclusive to members of genus Spiroplasma. It is hypothesized to undergo conformational changes necessary to bring about Spiroplasma motility through changes in cell helicity. However, the mechanism driving conformational changes in Fibril remains unknown. We expressed Fibril from S. citri in E. coli for its purification and characterization. Sodium dodecyl sulfate solubilized Fibril filaments and facilitated purification by affinity chromatography. An alternative protocol for obtaining enriched insoluble Fibril filaments was standardized using density gradient centrifugation. Electron microscopy of Fibril purified by these protocols revealed filament bundles. Probable domain boundaries of Fibril protein were identified based on mass spectrometric analysis of proteolytic fragments. Presence of α-helical and β-sheet signatures in FT-IR measurements suggests that Fibril filaments consist of an assembly of folded globular domains, and not a β-strand-based aggregation like amyloid fibrils.

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Codon-optimized Spiroplasma citri Fibril was expressed in E. coli

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SDS treatment does not denature Fibril filaments

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Fibril possesses α helices and β sheet and is not an amyloid-like protein

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Domain boundaries were predicted using mass spectrometry of proteolytic fragments

Gene Silencing through CRISPR Interference in Mycoplasmas

Mycoplasmas are pathogenic, genome-reduced bacteria. The development of such fields of science as system and synthetic biology is closely associated with them. Despite intensive research of different representatives of this genus, genetic manipulations remain challenging in mycoplasmas. Here we demonstrate a single-plasmid transposon-based CRISPRi system for the repression of gene expression in mycoplasmas. We show that selected expression determinants provide a level of dCas9 that does not lead to a significant slow-down of mycoplasma growth. For the first time we describe the proteomic response of genome-reduced bacteria to the expression of exogenous dcas9. The functionality of the resulting vector is confirmed by targeting the three genes coding transcription factors-fur, essential spxA, whiA, and histone-like protein hup1 in Mycoplasma gallisepticum. As a result, the expression level of each gene was decreased tenfold and influenced the mRNA level of predicted targets of transcription factors. To illustrate the versatility of this vector, we performed a knockdown of metabolic genes in a representative member of another cluster of the Mycoplasma genus-Mycoplasma hominis. The developed CRISPRi system is a powerful tool to discover the functioning of genes that are essential, decipher regulatory networks and that can help to identify novel drug targets to control Mycoplasma infections.

A genetic toolkit and gene switches to limit Mycoplasma growth for biosafety applications

Mycoplasmas have exceptionally streamlined genomes and are strongly adapted to their many hosts, which provide them with essential nutrients. Owing to their relative genomic simplicity, Mycoplasmas have been used to develop chassis for biotechnological applications. However, the dearth of robust and precise toolkits for genomic manipulation and tight regulation has hindered any substantial advance. Herein we describe the construction of a robust genetic toolkit for M. pneumoniae, and its successful deployment to engineer synthetic gene switches that control and limit Mycoplasma growth, for biosafety containment applications. We found these synthetic gene circuits to be stable and robust in the long-term, in the context of a minimal cell. With this work, we lay a foundation to develop viable and robust biosafety systems to exploit a synthetic Mycoplasma chassis for live attenuated vectors for therapeutic applications.

Mycoplasmas are minimal cell model organisms but lack genetic tools. Here the authors provide a robust genetic toolkit for Mycoplasma demonstrating gene circuit engineering applications.

The Genome Reduction Excludes the Ribosomal Rescue System in Acholeplasmataceae

The trans-translation process is a ribosomal rescue system for stalled ribosomes processing truncated mRNA. The genes ssrA and smpB fulfil the key functions in most bacteria, but some species have either lost these genes or the function of the ribosomal rescue system is taken over by other genes. To date, the ribosomal rescue system has not been analysed in detail for the Acholeplasmataceae. This family, in the Mollicutes class, comprises the genus Acholeplasma and the provisional taxon "Candidatus Phytoplasma". Despite their monophyletic origin, the two clades can be separated by traits such as not representing primary pathogens for acholeplasmas versus being phytopathogenic for the majority of phytoplasmas. Both taxa share reduced genomes, but only phytoplasma genomes are characterised by a remarkable level of instability and reduction. Despite the general relevance of the ribosomal rescue system, information is lacking on coding, the genomic context and pseudogenisation of smpB and ssrA and their possible application as a phylogenetic marker. Herein, we provide a comprehensive analysis of the ribosomal rescue system in members of Acholeplasmataceae. The examined Acholeplasmataceae genomes encode a ribosomal rescue system, which depends on tmRNA encoded by ssrA acting in combination with its binding protein SmpB. Conserved gene synteny is evident for smpB, while ssrA shows a less conserved genomic context. Analysis of the tmRNA sequences highlights the variability of proteolysis tag sequences and short conserved sites at the 5'- and 3'-ends. Analyses of smpB provided no hints regarding the coding of pseudogenes, but they did suggest its application as a phylogenetic marker of Acholeplasmataceae - in accordance with 16S rDNA topology. Sequence variability of smpB provides sufficient information for species assignment and phylogenetic analysis.

Identification of Mycoplasma species and related organisms from ruminants in England and Wales during 2005-2019

Background

Mycoplasma species have been associated with economically important diseases affecting ruminants worldwide and include contagious bovine pleuropneumonia (CBPP), contagious caprine pleuropneumonia (CCPP) and contagious agalactia, listed by the World Organisation for Animal Health (OIE). The Mycoplasma Team at the Animal and Plant Health Agency provides an identification service for Mycoplasma and Ureaplasma species of veterinary importance to the United Kingdom (UK), supporting the detection of new and emerging pathogens, as well as contributing to the surveillance of endemic, and the OIE listed diseases exotic to the UK. Mycoplasma and other Mollicutes species were identified from diagnostic samples from farmed ruminants in England and Wales using a combination of culture and 16S rRNA gene-based PCR-denaturing gradient gel electrophoresis, submitted between 2005 and 2019.

Results

A total of 5578 mollicutes identifications, which include mycoplasmas and the related acholeoplasmas and ureaplasmas, were made from farmed ruminant animals during the study period. Throughout the study period, the pathogen Mycoplasma bovis was consistently the most frequently identified species, accounting for 1411 (32%) of 4447 molecular identifications in cattle, primarily detected in the lungs of pneumonic calves, followed by joints and milk of cattle showing signs of arthritis and mastitis, respectively. M. bovirhinis, M. alkalescens, M. dispar, M. arginini and Ureaplasma diversum, were also common. Mixed species, principally M. bovis with M. alkalescens, M. arginini or M. bovirhinis were also prevalent, particularly from respiratory samples. The non-cultivable blood-borne haemoplasmas Candidatus ‘Mycoplasma haemobos’ and Mycoplasma wenyonii were identified from cattle, with the latter species most often associated with milk-drop. M. ovipneumoniae was the predominant species identified from sheep and goats experiencing respiratory disease, while M. conjunctivae preponderated in ocular samples. The UK remains free of the ruminant mycoplasmas listed by OIE.

Conclusions

The continued high prevalence of M. bovis identifications confirms its ongoing dominance and importance as a significant pathogen of cattle in England and Wales, particularly in association with respiratory disease. M. ovipneumoniae has seen a general increase in prevalence in recent years, notably in coughing lambs and should therefore be considered as a primary differential diagnosis of respiratory disease in small ruminants.

The Relationship between Mycoplasmas and Cancer: Is It Fact or Fiction ? Narrative Review and Update on the Situation

More than one million new cancer cases occur worldwide every year. Although many clinical trials are applied and recent diagnostic tools are employed, curing cancer disease is still a great challenge for mankind. Heredity and epigenetics are the main risk factors often related to cancer. Although, the infectious etiological role in carcinogenesis was also theorized. By establishing chronic infection and inflammation in their hosts, several microorganisms were suggested to cause cell transformation. Of these suspicious microorganisms, mycoplasmas were well regarded because of their intimate parasitism with host cells, as well as their silent and insidious role during infections. This assumption has opened many questions about the real role played by mycoplasmas in oncogenesis. Herein, we presented a sum up of many studies among the hundreds which had addressed the Mycoplasma-cancer topic over the past 50 years. Research studies in this field have first started by approving the mycoplasmas malignancy potential. Indeed, using animal models and in vitro experiments in various cell lines from human and other mammalians, many mycoplasmas were proven to cause varied modifications leading to cell transformation. Moreover, many studies have looked upon the Mycoplasma-cancer subject from an epidemiological point of view. Diverse techniques were used to assess the mycoplasmas prevalence in patients with cancer from different countries. Not less than 10 Mycoplasma species were detected in the context of at least 15 cancer types affecting the brain, the breast, the lymphatic system, and different organs in the genitourinary, respiratory, gastrointestinal, and urinary tracts. Based on these revelations, one should concede that detection of mycoplasmas often linked to ‘‘wolf in sheep's clothing” is not a coincidence and might have a role in cancer. Thorough investigations are needed to better elucidate this role. This would have a substantial impact on the improvement of cancer diagnosis and its prevention.

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.

MreB5 Is a Determinant of Rod-to-Helical Transition in the Cell-Wall-less Bacterium Spiroplasma

In most rod-shaped bacteria, the spatial coordination of cell wall synthesis machinery by MreBs is the main theme for shape determination and maintenance in cell-walled bacteria [1-9]. However, how rod or spiral shapes are achieved and maintained in cell-wall-less bacteria is currently unknown. Spiroplasma, a helical Mollicute that lacks cell wall synthesis genes, encodes five MreB paralogs and a unique cytoskeletal protein fibril [10, 11]. Here, we show that MreB5, one of the five MreB paralogs, contributes to cell elongation and is essential for the transition from rod-to-helical shape in Spiroplasma. Comparative genomic and proteomic characterization of a helical and motile wild-type Spiroplasma strain and a non-helical, non-motile natural variant helped delineate the specific roles of MreB5. Moreover, complementation of the non-helical strain with MreB5 restored its helical shape and motility by a kink-based mechanism described for Spiroplasma [12]. Earlier studies had proposed that length changes in fibril filaments are responsible for the change in handedness of the helical cell and kink propagation during motility [13]. Through structural and biochemical characterization, we identify that MreB5 exists as antiparallel double protofilaments that interact with fibril and the membrane, and thus potentially assists in kink propagation. In summary, our study provides direct experimental evidence for MreB in maintaining cell length, helical shape, and motility-revealing the role of MreB in sculpting the cell in the absence of a cell wall.

Exploring Spiroplasma Biology: Opportunities and Challenges

Spiroplasmas are cell-wall-deficient helical bacteria belonging to the class Mollicutes. Their ability to maintain a helical shape in the absence of cell wall and their motility in the absence of external appendages have attracted attention from the scientific community for a long time. In this review we compare and contrast motility, shape determination and cytokinesis mechanisms of Spiroplasma with those of other Mollicutes and cell-walled bacteria. The current models for rod-shape determination and cytokinesis in cell-walled bacteria propose a prominent role for the cell wall synthesis machinery. These models also involve the cooperation of the actin-like protein MreB and FtsZ, the bacterial homolog of tubulin. However the exact role of the cytoskeletal proteins is still under much debate. Spiroplasma possess MreBs, exhibit a rod-shape dependent helical morphology, and divide by an FtsZ-dependent mechanism. Hence, spiroplasmas represent model organisms for deciphering the roles of MreBs and FtsZ in fundamental mechanisms of non-spherical shape determination and cytokinesis in bacteria, in the absence of a cell wall. Identification of components implicated in these processes and deciphering their functions would require genetic experiments. Challenges in genetic manipulations in spiroplasmas are a major bottleneck in understanding their biology. We discuss advancements in genome sequencing, gene editing technologies, super-resolution microscopy and electron cryomicroscopy and tomography, which can be employed for addressing long-standing questions related to Spiroplasma biology.

Model-driven design allows growth of Mycoplasma pneumoniae on serum-free media

Mycoplasma pneumoniae is a slow-growing, human pathogen that causes atypical pneumonia. Because it lacks a cell wall, many antibiotics are ineffective. Due to its reduced genome and dearth of many biosynthetic pathways, this fastidious bacterium depends on rich, undefined medium for growth, which makes large-scale cultivation challenging and expensive. To understand factors limiting growth, we developed a genome-scale, constraint-based model of M. pneumoniae called iEG158_mpn to describe the metabolic potential of this bacterium. We have put special emphasis on cell membrane formation to identify key lipid components to maximize bacterial growth. We have used this knowledge to predict essential components validated with in vitro serum-free media able to sustain growth. Our findings also show that glycolysis and lipid metabolism are much less efficient under hypoxia; these findings suggest that factors other than metabolism and membrane formation alone affect the growth of M. pneumoniae. Altogether, our modelling approach allowed us to optimize medium composition, enabled growth in defined media and streamlined operational requirements, thereby providing the basis for stable, reproducible and less expensive production.

Rapid Detection of Mycoplasma-Infected Cells by an ssDNA Aptamer Probe

Mycoplasmas are unique cell wall-free bacteria. Because they lack a cell wall and have resistance to β-lactam antibiotics, mycoplasma is the major pathogen that infects cultured cells in research laboratories. For rapid detection of mycoplasma-infected cells, we developed an ssDNA aptamer sequence composed of 40 nucleotides. Flow cytometry analysis showed that the synthetic aptamer probe selectively targeted mycoplasma-infected culture cells with high specificity identical to commercially available PCR-based assays. Additionally, fluorescent microscopy studies revealed that the aptamer probe rapidly stained mycoplasma-infected cells with higher sensitivity compared to Hoechst dye-mediated cellular DNA content stains. Moreover, confocal microscopy studies of trypsin-treated cells validated that the aptamer probes selectively targeted mycoplasma components on the surface of infected cells. Finally, preclinical studies of peripheral blood cells demonstrated that the aptamer probe was able to detect in vitro mycoplasma infection of primary lymphocytes. Taken together, these findings indicate that the aptamer probe will not only allow rapid detection of mycoplasma-infected culture cells for research purposes but also provide a simple method to monitor mycoplasma infection in primary cell products for clinical use.

Detection of Mycoplasma hyopneumoniae in piglet processing fluids

Processing fluid (PF) is a sample type composed of fluids obtained from testicles and tails as the product of piglet processing. Mycoplasma hyopneumoniae is a bacterium that colonises the respiratory tract of pigs and has rarely been detected in tissues outside the respiratory system. No data exist in the literature regarding detection of M hyopneumoniae in PF or its use for herd monitoring of this pathogen. The main goal of this study was to evaluate the feasibility of detecting M hyopneumoniae in PF. Testicles and tails of 21 conveniently selected litters from a commercial sow farm were collected, by litter, and tested for M hyopneumoniae by real time-PCR. Daily aggregated processing tissues were collected for a two-month period to assess the detection of M hyopneumoniae in PF. The comparison in the percentage of positive samples in fluids from testicles (38 per cent, 8/21) or tails (4.8 per cent, 1/21) was significantly different (P=0.023). The percentage of daily aggregated PF with cycle threshold values up to 37 was 52.9 per cent (9/17) and 26.7 per cent (4/15) for December and January, respectively. Overall, these data show detection of M hyopneumoniae in PF for the first time and points at the potential use of this sample for monitoring of this bacterium in breeding farms.

Metabolic network percolation quantifies biosynthetic capabilities across the human oral microbiome

The biosynthetic capabilities of microbes underlie their growth and interactions, playing a prominent role in microbial community structure. For large, diverse microbial communities, prediction of these capabilities is limited by uncertainty about metabolic functions and environmental conditions. To address this challenge, we propose a probabilistic method, inspired by percolation theory, to computationally quantify how robustly a genome-derived metabolic network produces a given set of metabolites under an ensemble of variable environments. We used this method to compile an atlas of predicted biosynthetic capabilities for 97 metabolites across 456 human oral microbes. This atlas captures taxonomically-related trends in biomass composition, and makes it possible to estimate inter-microbial metabolic distances that correlate with microbial co-occurrences. We also found a distinct cluster of fastidious/uncultivated taxa, including several Saccharibacteria (TM7) species, characterized by their abundant metabolic deficiencies. By embracing uncertainty, our approach can be broadly applied to understanding metabolic interactions in complex microbial ecosystems.

Mycoplasma bovis: Mechanisms of Resistance and Trends in Antimicrobial Susceptibility

Mycoplasma bovis is a cell-wall-less bacterium and belongs to the class Mollicutes. It is the most important etiological agent of bovine mycoplasmoses in North America and Europe, causing respiratory disease, mastitis, otitis media, arthritis, and reproductive disease. Clinical disease associated with M. bovis is often chronic, debilitating, and poorly responsive to antimicrobial therapy, resulting in significant economic loss, the full extent of which is difficult to estimate. Until M. bovis vaccines are universally available, sanitary control measures and antimicrobial treatment are the only approaches that can be used in attempts to control M. bovis infections. However, in vitro studies show that many of the current M. bovis isolates circulating in Europe have high minimum inhibitory concentrations (MIC) for many of the commercially available antimicrobials. In this review we summarize the current MIC trends indicating the development of antimicrobial resistance in M. bovis as well as the known molecular mechanisms by which resistance is acquired.

Mm19, a Mycoplasma meleagridis Major Surface Nuclease that Is Related to the RE_AlwI Superfamily of Endonucleases

Mycoplasma meleagridis infection is widespread in turkeys, causing poor growth and feathering, airsacculitis, osteodystrophy, and reduction in hatchability. Like most mycoplasma species, M. meleagridis is characterized by its inability to synthesize purine and pyrimidine nucleotides de novo. Consistent with this intrinsic deficiency, we here report the cloning, expression, and characterization of a M. meleagridis gene sequence encoding a major surface nuclease, referred to as Mm19. Mm19 consists of a 1941-bp ORF encoding a 646-amino-acid polypeptide with a predicted molecular mass of 74,825 kDa. BLASTP analysis revealed a significant match with the catalytic/dimerization domain of type II restriction enzymes of the RE_AlwI superfamily. This finding is consistent with the genomic location of Mm19 sequence, which dispalys characteristics of a typical type II restriction-modification locus. Like intact M. meleagridis cells, the E. coli-expressed Mm19 fusion product was found to exhibit a nuclease activity against plasmid DNA, double-stranded DNA, single-stranded DNA, and RNA. The Mm19-associated nuclease activity was consistently enhanced with Mg2+ divalent cations, a hallmark of type II restriction enzymes. A rabbit hyperimmune antiserum raised against the bacterially expressed Mm19 strongly reacted with M. meleagridis intact cells and fully neutralized the surface-bound nuclease activity. Collectively, the results show that M. meleagridis expresses a strong surface-bound nuclease activity, which is the product of a single gene sequence that is related to the RE_AlwI superfamily of endonucleases.

Apoptosis in HEp-2 cells infected with Ureaplasma diversum

BACKGROUND

Bacterial pathogens have many strategies for infecting and persisting in host cells. Adhesion, invasion and intracellular life are important features in the biology of mollicutes. The intracellular location of Ureaplasma diversum may trigger disturbances in the host cell. This includes activation or inhibition of pro and anti-apoptotic factors, which facilitate the development of host damage. The aim of the present study was to associate U. diversum infection in HEp-2 cells and apoptosis induction. Cells were infected for 72hs with four U. diversum clinical isolates and an ATCC strain. The U. diversum invasion was analyzed by Confocal Laser Scanning Microscopy and gentamicin invasion assay. The apoptosis was evaluated using pro-apoptotic and anti-apoptotic gene expression, and FITC Annexin V/Dead Cell Apoptosis Kit.

RESULTS

The number of internalized ureaplasma in HEp-2 cells increased significantly throughout the infection. The flow cytometry analysis with fluorochromes to detect membrane depolarization and gene expression for caspase 2, 3 and 9 increased in infected cells after 24 hours. However, after 72 hours a considerable decrease of apoptotic cells was observed.

CONCLUSIONS

The data suggests that apoptosis may be initially induced by some isolates in association with HEp-2 cells, but over time, there was no evidence of apoptosis in the presence of ureaplasma and HEp-2 cells. The initial increase and then decrease in apoptosis could be related to bacterial pathogen-associated molecular pattern (PAMPS). Moreover, the isolates of U. diversum presented differences in the studied parameters for apoptosis. It was also observed that the amount of microorganisms was not proportional to the induction of apoptosis in HEp-2 cells.

Structural characterization of the enzymes composing the arginine deiminase pathway in Mycoplasma penetrans

The metabolism of arginine towards ATP synthesis has been considered a major source of energy for microorganisms such as Mycoplasma penetrans in anaerobic conditions. Additionally, this pathway has also been implicated in pathogenic and virulence mechanism of certain microorganisms, i.e. protection from acidic stress during infection. In this work we present the crystal structures of the three enzymes composing the gene cluster of the arginine deiminase pathway from M. penetrans: arginine deiminase (ADI), ornithine carbamoyltransferase (OTC) and carbamate kinase (CK). The arginine deiminase (ADI) structure has been refined to 2.3 Å resolution in its apo-form, displaying an "open" conformation of the active site of the enzyme in comparison to previous complex structures with substrate intermediates. The active site pocket of ADI is empty, with some of the catalytic and binding residues far from their active positions, suggesting major conformational changes upon substrate binding. Ornithine carbamoyltransferase (OTC) has been refined in two crystal forms at 2.5 Å and 2.6 Å resolution, respectively, both displaying an identical dodecameric structure with a 23-point symmetry. The dodecameric structure of OTC represents the highest level of organization in this protein family and in M.penetrans it is constituted by a novel interface between the four catalytic homotrimers. Carbamate kinase (CK) has been refined to 2.5 Å resolution and its structure is characterized by the presence of two ion sulfates in the active site, one in the carbamoyl phosphate binding site and the other in the β-phosphate ADP binding pocket of the enzyme. The CK structure also shows variations in some of the elements that regulate the catalytic activity of the enzyme. The relatively low number of metabolic pathways and the relevance in human pathogenesis of Mycoplasma penetrans places the arginine deiminase pathway enzymes as potential targets to design specific inhibitors against this human parasite.

Transmission electron microscopy reveals distinct macrophage- and tick cell-specific morphological stages of Ehrlichia chaffeensis

Background

Ehrlichia chaffeensis is an emerging tick-borne rickettsial pathogen responsible for human monocytic ehrlichiosis. Despite the induction of an active host immune response, the pathogen has evolved to persist in its vertebrate and tick hosts. Understanding how the organism progresses in tick and vertebrate host cells is critical in identifying effective strategies to block the pathogen transmission. Our recent molecular and proteomic studies revealed differences in numerous expressed proteins of the organism during its growth in different host environments.

Methodology/Principal Findings

Transmission electron microscopy analysis was performed to assess morphological changes in the bacterium within macrophages and tick cells. The stages of pathogen progression observed included the attachment of the organism to the host cells, its engulfment and replication within a morulae by binary fission and release of the organisms from infected host cells by complete host cell lysis or by exocytosis. E. chaffeensis grown in tick cells was highly pleomorphic and appears to replicate by both binary fission and filamentous type cell divisions. The presence of Ehrlichia-like inclusions was also observed within the nucleus of both macrophages and tick cells. This observation was confirmed by confocal microscopy and immunoblot analysis.

Conclusions/Significance

Morphological differences in the pathogen’s progression, replication, and processing within macrophages and tick cells provide further evidence that E. chaffeensis employs unique host-cell specific strategies in support of adaptation to vertebrate and tick cell environments.

Proteomics characterization of cytoplasmic and lipid-associated membrane proteins of human pathogen Mycoplasma fermentans M64

Mycoplasma fermentans is a potent human pathogen which has been implicated in several diseases. Notably, its lipid-associated membrane proteins (LAMPs) play a role in immunomodulation and development of infection-associated inflammatory diseases. However, the systematic protein identification of pathogenic M. fermentans has not been reported. From our recent sequencing results of M. fermentans M64 isolated from human respiratory tract, its genome is around 1.1 Mb and encodes 1050 predicted protein-coding genes. In the present study, soluble proteome of M. fermentans was resolved and analyzed using two-dimensional gel electrophoresis. In addition, Triton X-114 extraction was carried out to enrich amphiphilic proteins including putative lipoproteins and membrane proteins. Subsequent mass spectrometric analyses of these proteins had identified a total of 181 M. fermentans ORFs. Further bioinformatics analysis of these ORFs encoding proteins with known or so far unknown orthologues among bacteria revealed that a total of 131 proteins are homologous to known proteins, 11 proteins are conserved hypothetical proteins, and the remaining 39 proteins are likely M. fermentans-specific proteins. Moreover, Triton X-114-enriched fraction was shown to activate NF-kB activity of raw264.7 macrophage and a total of 21 lipoproteins with predicted signal peptide were identified therefrom. Together, our work provides the first proteome reference map of M. fermentans as well as several putative virulence-associated proteins as diagnostic markers or vaccine candidates for further functional study of this human pathogen.

Complete genome and proteome of Acholeplasma laidlawii

We present the complete genome sequence and proteogenomic map for Acholeplasma laidlawii PG-8A (class Mollicutes, order Acholeplasmatales, family Acholeplasmataceae). The genome of A. laidlawii is represented by a single 1,496,992-bp circular chromosome with an average G+C content of 31 mol%. This is the longest genome among the Mollicutes with a known nucleotide sequence. It contains genes of polymerase type I, SOS response, and signal transduction systems, as well as RNA regulatory elements, riboswitches, and T boxes. This demonstrates a significant capability for the regulation of gene expression and mutagenic response to stress. Acholeplasma laidlawii and phytoplasmas are the only Mollicutes known to use the universal genetic code, in which UGA is a stop codon. Within the Mollicutes group, only the sterol-nonrequiring Acholeplasma has the capacity to synthesize saturated fatty acids de novo. Proteomic data were used in the primary annotation of the genome, validating expression of many predicted proteins. We also detected posttranslational modifications of A. laidlawii proteins: phosphorylation and acylation. Seventy-four candidate phosphorylated proteins were found: 16 candidates are proteins unique to A. laidlawii, and 11 of them are surface-anchored or integral membrane proteins, which implies the presence of active signaling pathways. Among 20 acylated proteins, 14 contained palmitic chains, and six contained stearic chains. No residue of linoleic or oleic acid was observed. Acylated proteins were components of mainly sugar and inorganic ion transport systems and were surface-anchored proteins with unknown functions.

Role of RecJ-like protein with 5'-3' exonuclease activity in oligo(deoxy)nucleotide degradation

RecJ-like proteins belonging to the DHH family have been proposed to function as oligoribonucleases and 3'-phosphoadenosine 5'-phosphate (pAp) phosphatases in bacteria and archaea, which do not have Orn (oligoribonuclease) and CysQ (pAp phosphatase) homologs. In this study, we analyzed the biochemical and physiological characterization of the RecJ-like protein TTHA0118 from Thermus thermophilus HB8. TTHA0118 had high enzymatic activity as an oligodeoxyribonucleotide- and oligoribonucleotide-specific exonuclease and as pAp phosphatase. The polarity of degradation was 5' to 3', in contrast to previous reports about Bacillus subtilis NrnA, a RecJ-like protein. TTHA0118 preferentially hydrolyzed short oligodeoxyribonucleotides and oligoribonucleotides, whereas the RecJ exonuclease from T. thermophilus HB8 showed no such length dependence on oligodeoxyribonucleotide substrates. An insertion mutation of the ttha0118 gene led to growth reduction in minimum essential medium. Added 5'-mononucleotides, nucleosides, and cysteine increased growth of the ttha0118 mutant in minimum essential medium. The RecJ-like protein Mpn140 from Mycoplasma pneumoniae M129, which cannot synthesize nucleic acid precursors de novo, showed similar biochemical features to TTHA0118. Furthermore, B. subtilis NrnA also hydrolyzed oligo(deoxy)ribonucleotides in a 5'-3' direction. These results suggested that these RecJ-like proteins act in recycling short oligonucleotides to mononucleotides and in controlling pAp concentrations in vivo.

Nanotechnology, nanotoxicology, and neuroscience

Nanotechnology, which deals with features as small as a 1 billionth of a meter, began to enter into mainstream physical sciences and engineering some 20 years ago. Recent applications of nanoscience include the use of nanoscale materials in electronics, catalysis, and biomedical research. Among these applications, strong interest has been shown to biological processes such as blood coagulation control and multimodal bioimaging, which has brought about a new and exciting research field called nanobiotechnology. Biotechnology, which itself also dates back approximately 30 years, involves the manipulation of macroscopic biological systems such as cells and mice in order to understand why and how molecular level mechanisms affect specific biological functions, e.g., the role of APP (amyloid precursor protein) in Alzheimer's disease (AD). This review aims (1) to introduce key concepts and materials from nanotechnology to a non-physical sciences community; (2) to introduce several state-of-the-art examples of current nanotechnology that were either constructed for use in biological systems or that can, in time, be utilized for biomedical research; (3) to provide recent excerpts in nanotoxicology and multifunctional nanoparticle systems (MFNPSs); and (4) to propose areas in neuroscience that may benefit from research at the interface of neurobiologically important systems and nanostructured materials.

Adhesion of mycoplasmas to eukaryotic cells

Many pathogenic mycoplasmas are surface parasites, adhering to the epithelial linings of the respiratory and urogenital tracts. Since mycoplasmas lack cell walls their plasma membrane comes in close contact with that of their host, allowing exchange of components between the two membranes and possibly fusion. The tight association of the parasite with its host is illustrated in scanning electron micrographs of Mycoplasma pneumoniae and M. gallisepticum adhering to human red blood cells. Specialized structure at the tips of the mycoplasma cells appear to function as attachment organelles. Our main aim has been to chemically define the receptors on the host cell and the binding sites on the mycoplasma cells responsible for adhesion. Glycophorin (the major sialoglycoprotein of human red blood cells) serves as the main or sole receptor for M. gallisepticum whereas M. pneumoniae binds to additional receptors on human red blood cells. Trypsin treatment of M. pneumoniae cells abolishes their ability to attach to human red cells, suggesting the protein nature of the binding sites. M. pneumoniae membranes solubilized by detergents were subjected to affinity chromatography on glycophorin-Sepharose so that membrane components with high affinity for glycophorin could be isolated. The fraction isolated consisted of several proteins (relative molecular mass 25 000 and 45 000). The binding of this fraction to red cells was relatively low but appeared to be specific, as it was inhibited by glycophorin but not by its hydrophobic moiety. The possibility is discussed that the exposure of the binding sites on the mycoplasma cell surface is influenced by the electrochemical ion gradient across the membrane.

Mycoplasma hyopneumoniae mhp379 is a Ca2+-dependent, sugar-nonspecific exonuclease exposed on the cell surface

Mycoplasma hyopneumoniae mhp379 is a putative lipoprotein that shares significant amino acid sequence similarity with a family of bacterial thermostable nucleases. To examine the nuclease activity of mhp379, the gene was cloned and expressed in Escherichia coli following the deletion of the amino-terminal signal sequence and prokaryotic lipoprotein cleavage site and mutagenesis of the mycoplasma TGA tryptophan codons to TGG. The recombinant fusion protein yielded a 33-kDa thrombin cleavage product, corresponding in size to the mature mhp379 protein. Exonuclease activity was indicated by agarose gel electrophoresis analysis of the reaction products that were released when different nucleic acid substrates were used. Endonuclease activity was also indicated by the digestion of closed circular plasmid DNA. The recombinant mhp379 fusion protein completely digested single-stranded DNA, double-stranded DNA (dsDNA), and RNA. The optimal reaction conditions were determined with a novel nuclease assay based on the enhancement of fluorescence of SYBR green I bound to dsDNA. Optimal activity was observed in the presence of calcium ions at a concentration of 15 mM and a pH of 9.5. No nuclease activity was observed in the absence of calcium ions. Mycoplasmas do not have the ability to synthesize nucleic acid precursors, and thus, nucleases are likely to be important in the acquisition of precursors for the synthesis of nucleic acids. Homologs of an ATP-binding cassette (ABC) transport system were identified immediately downstream of the gene encoding mhp379, and two homologs of M. pneumoniae lipoprotein multigene family 2 were also identified immediately upstream. Homologs of mhp379 were identified in the sequenced genomes of a number of mycoplasma species, and in most cases the homologous ABC transport system was identified immediately downstream of the homologous gene; in several cases a homolog of M. pneumoniae lipoprotein multigene family 2 was also identified immediately upstream. These observations suggest that mhp379 comprises part of a conserved ABC transport operon in mycoplasmas and that the exonuclease activity of mhp379 may be associated with the conserved function of the ABC transport system in the import of nucleic acid precursors. This is the first study to identify the gene and characterize the activity of a mycoplasma exonuclease.

Mycoplasma hyopneumoniae colonization of pigs sired by different boars

Differences in Mycoplasma hyopneumoniae colonization were evaluated in experimentally inoculated pigs sired by 3 different boars of the same genetic line. Forty-six pigs were used, including a treatment group and positive and negative control groups. The pigs were intratracheally inoculated with an M. hyopneumoniae suspension or with Friis media as a placebo. To evaluate differences in the magnitude of colonization during a 35-day period, nasal and tracheal swabs were collected weekly and tested by nested polymerase chain reaction (N-PCR). Temperature, weight and circulating antibodies were measured for 35 days. At 11 and 35 d postinoculation the pigs were necropsied and macroscopic and microscopic lesions were determined. A section of bronchus was tested by the indirect immunofluorescence test (IFAT), scanning electron microscopy (SEM) and N-PCR. The N-PCR results from the nasal and tracheal swabs showed that the pigs sired by one boar (B3) had a distinctive colonization pattern, different from that of the pigs from the other 2 boars and from the positive controls. SEM studies demonstrated that at 35 d postinoculation a higher proportion of B3 pigs had lower numbers of mycoplasmas attached to the cilia compared with B1 and B2 offspring. No significant differences were observed in temperature and weight gain among groups by ANOVA; however, with use of a 2 x 2 table, temperature differences were observed between pigs sired by boars B1 and B2 at 4 d postinoculation. No pigs seroconverted, showed gross or microscopic lesions, or had positive IFAT results. These results provide evidence of differences in patterns of colonization between pigs sired by different boars, suggesting a possible genetic effect.

Isolation and characterization of Mycoplasma arginini from camels (Camelus dromedarius) with pneumonia

Post-mortem examinations of 100 camels with pneumonic lesions were made at a local abattoir for Mycoplasma species. Sixteen isolates with indistinguishable biochemical and immunological characters were identified. The biochemical profile of these isolates showed that they were sensitive to digitonin, negative for urease production, glucose fermentation, and phosphatase activity but were positive for arginine hydrolysis. The identity of these isolates was further confirmed by disk growth inhibition test using a panel of specific antisera against selected reference Mycoplasma spp. Based on the biochemical profile and growth inhibition results, the camel isolates were identified as M. arginini. The pathological findings associated with M. arginini isolation consisted mostly of chronic interstitial pneumonia. The isolation rate of M. arginini from these specimens was 8.8%. These results suggest that the role of M. arginini in pneumonia in camels should be explored in greater detail.

Range of phytoplasma concentrations in various plant hosts as determined by competitive polymerase chain reaction

ABSTRACT For competitive polymerase chain reaction (PCR), an internal standard DNA template was developed that consisted of a highly conserved, internally deleted 16S rDNA fragment of an aster yellows phytoplasma. The internal standard was calibrated using a quantified culture of Acholeplasma laidlawii. Serial dilutions of the internal standard and fixed amounts of target templates from infected plants were coamplified with the same primers, and the products obtained were quantified using an enzyme-linked immunosorbent assay procedure. Analysis of the data revealed that the phytoplasma concentration in the plants examined differed by a factor of about 4 x 10(6). Phytoplasma concentrations of 2.2 x 10(8) to 1.5 x 10(9) cells per g of tissue were identified in periwinkles infected with various phytoplasmas. High to moderate concentrations were detected in Malus domestica (apple) genotypes infected with the apple proliferation phytoplasma, Alnus glutinosa (alder) genotypes infected with the alder yellows phytoplasma, and most aster yellows-infected Populus (poplar) genotypes examined. Very low phytoplasma concentrations, ranging from 370 to 34,000 cells per g of tissue, were identified in proliferation-diseased apple trees on resistant rootstocks 4551 and 4608, yellows-diseased Quercus robur (oak) trees, and Carpinus betulus (hornbeam) trees. Such low concentrations, which corresponded to about 4 to 340 cells in the reaction mixture, could only be detected and quantified by nested PCR.

Role of Mycoplasma penetrans endonuclease P40 as a potential pathogenic determinant

Recently, we reported the purification to homogeneity and characterization of Ca(2+)- and Mg(2+)-dependent endonuclease P40 produced by Mycoplasma penetrans (M. Bendjennat, A. Blanchard, M. Loutfi, L. Montagnier, and E. Bahraoui, J. Bacteriol. 179; 2210-2220, 1997), a mycoplasma which was isolated for the first time from the urine of human immunodeficiency virus-infected patients. To evaluate how this nuclease could interact with host cells, we tested its effect on CEM and Molt-4 lymphocytic cell lines and on peripheral blood mononuclear cells. We observed that 10(-7) to 10(-9) M P40 is able to mediate a cytotoxic effect. We found that 100% of cells were killed after 24 h of incubation with 10(-7) M P40 while only 40% cytotoxicity was obtained after 72 h of incubation with 10(-9) M P40. Phase-contrast microscopy observations of P40-treated cells revealed morphological changes, including pronounced blebbing of the plasma membrane and cytoplasmic shrinkage characteristic of programmed cell death, which is in agreement with the internucleosomal fragmentation of P40-treated cell DNA as shown by agarose gel electrophoresis. We showed that (125)I-radiolabeled or fluorescein isothiocyanate-labeled P40 was able to bind specifically in a dose-dependent manner to the cell membrane of CEM cells, which suggested that the cytotoxicity of P40 endonuclease was mediated by its interaction with the cell surface receptor(s). The concentration of unlabeled P40 required to inhibit by 50% the formation of (125)I-P40-CEM complexes was about 3 x 10(-9) M, indicating a high-affinity interaction. Both P40 interaction and cytotoxicity are Ca(2+) dependent. Our results suggest that the cytotoxicity of M. penetrans observed in vitro is mediated at least partially by secreted P40, which, after interaction with host cells, can induce an apoptosis-like death. These results strongly suggest a major role of mycoplasmal nucleases as potential pathogenic determinants.

Cloning of mnuA, a membrane nuclease gene of Mycoplasma pulmonis, and analysis of its expression in Escherichia coli

Membrane nucleases of mycoplasmas are believed to play important roles in growth and pathogenesis, although no clear evidence for their importance has yet been obtained. As a first step in defining the function of this unusual membrane activity, studies were undertaken to clone and analyze one of the membrane nuclease genes from Mycoplasma pulmonis. A novel screening strategy was used to identify a recombinant lambda phage expressing nuclease activity, and its cloned fragment was analyzed. Transposon mutagenesis was used to identify an open reading frame of 1,410 bp, which coded for nuclease activity in Escherichia coli. This gene coded for a 470-amino-acid polypeptide of 53,739 Da and was designated mnuA (for "membrane nuclease"). The MnuA protein contained a prolipoprotein signal peptidase II recognition sequence along with an extensive hydrophobic region near the amino terminus, suggesting that the protein may be lipid modified or that it is anchored in the membrane by this membrane-spanning region. Antisera raised against two MnuA peptide sequences identified an M. pulmonis membrane protein of approximately 42 kDa by immunoblotting, which corresponded to a trypsin-sensitive nucleolytic band of the same size. Maxicell experiments with E. coli confirmed that mnuA coded for a nuclease of unknown specificity. Hybridization studies showed that mnuA sequences are found in few Mycoplasma species, suggesting that mycoplasma membrane nucleases display significant sequence variation within the genus Mycoplasma.

Molecular biology and pathogenicity of mycoplasmas

The recent sequencing of the entire genomes of Mycoplasma genitalium and M. pneumoniae has attracted considerable attention to the molecular biology of mycoplasmas, the smallest self-replicating organisms. It appears that we are now much closer to the goal of defining, in molecular terms, the entire machinery of a self-replicating cell. Comparative genomics based on comparison of the genomic makeup of mycoplasmal genomes with those of other bacteria, has opened new ways of looking at the evolutionary history of the mycoplasmas. There is now solid genetic support for the hypothesis that mycoplasmas have evolved as a branch of gram-positive bacteria by a process of reductive evolution. During this process, the mycoplasmas lost considerable portions of their ancestors' chromosomes but retained the genes essential for life. Thus, the mycoplasmal genomes carry a high percentage of conserved genes, greatly facilitating gene annotation. The significant genome compaction that occurred in mycoplasmas was made possible by adopting a parasitic mode of life. The supply of nutrients from their hosts apparently enabled mycoplasmas to lose, during evolution, the genes for many assimilative processes. During their evolution and adaptation to a parasitic mode of life, the mycoplasmas have developed various genetic systems providing a highly plastic set of variable surface proteins to evade the host immune system. The uniqueness of the mycoplasmal systems is manifested by the presence of highly mutable modules combined with an ability to expand the antigenic repertoire by generating structural alternatives, all compressed into limited genomic sequences. In the absence of a cell wall and a periplasmic space, the majority of surface variable antigens in mycoplasmas are lipoproteins. Apart from providing specific antimycoplasmal defense, the host immune system is also involved in the development of pathogenic lesions and exacerbation of mycoplasma induced diseases. Mycoplasmas are able to stimulate as well as suppress lymphocytes in a nonspecific, polyclonal manner, both in vitro and in vivo. As well as to affecting various subsets of lymphocytes, mycoplasmas and mycoplasma-derived cell components modulate the activities of monocytes/macrophages and NK cells and trigger the production of a wide variety of up-regulating and down-regulating cytokines and chemokines. Mycoplasma-mediated secretion of proinflammatory cytokines, such as tumor necrosis factor alpha, interleukin-1 (IL-1), and IL-6, by macrophages and of up-regulating cytokines by mitogenically stimulated lymphocytes plays a major role in mycoplasma-induced immune system modulation and inflammatory responses.

The pathogenicity and pathogenesis of Mycoplasma capricolum subsp. capripneumoniae (F38) in the caprine mammary gland

The right mammary gland of 12 lactating goats was inoculated intracisternally with 1 ml of Mycoplasma capricolum subsp. capripneumoniae (Mcc) containing 10(6) colony-forming units (CFU), while their left mammary halves received 1 ml of sterile PPLO broth only. Two goats served as uninfected controls. The clinical mastitis that developed in the infected mammary halves within 24 h was initially acute but became increasingly chronic by the end of the experiment at 24 days post inoculation (DPI). The disease was characterized by atrophy of the infected mammary halves, leading to marked agalactia and an increase in somatic cell counts, with a preponderance of neutrophils initially and lymphocytes later. The Mycoplasma was re-isolated from infected mammary secretions up to 16 DPI but not from blood. Histopathology revealed that the mastitis was acute and purulent initially, followed by infiltration of lymphonuclear cells and fibroplasia in the lymphomononuclear cells and fibroplasia in the interacinar tissue, and later by massive fibrosis. Immunohistology demonstrated the presence of Mycoplasma-like bodies localized mainly on the surface of acinar/duct epithelial cells. The studies showed that Mcc was highly pathogenic in the caprine mammary gland.

Purification and characterization of Mycoplasma penetrans Ca2+/Mg2+-dependent endonuclease

The major nuclease from Mycoplasma penetrans has been purified to homogeneity. The enzyme seems to be present as a membrane-associated precursor of 50 kDa and as a peripheral membrane monomeric polypeptide of 40 kDa that is easily removed by washing of cells with isotonic buffers and in the aqueous phase upon Triton partitioning of Triton X-114-solubilized protein. The 40-kDa nuclease was extracted from M. penetrans cells by Triton X-114 and phase fractionation and was further purified by chromatography on Superdex 75 and chelating Sepharose (Zn2+ form) columns. By gel filtration, the apparent molecular mass was 40 kDa. The purified enzyme exhibits both a nicking activity on superhelical and linear double-stranded DNA and a nuclease activity on RNA and single-stranded DNA. No exonuclease activity was found for this enzyme. This nuclease required both Mg2+ (optimum, 5 mM) and Ca2+ (optimum, 2 mM) for activity and exhibited a pH optimum between pH 7 and 8 for DNase activity. It was inhibited by Zn2+, Mn2+, heparin, sodium dodecyl sulfate, and chelator agents such EDTA and EGTA, but no effect was observed with ATP, 2-mercaptoethanol, N-ethylmaleimide, dithiothreitol, nonionic detergents, phenylmethylsulfonyl fluoride, and iodoacetamide. Nuclease activity was inhibited by diethylpyrocarbonate at both pH 6 and 8 and by pepstatin, suggesting the involvement of a histidine and an aspartate in the active site. When added to human lymphoblast nuclei, the purified M. penetrans endonuclease induced internucleosomal fragmentation of the chomatin into oligonucleosomal fragments. On the basis of this result, and taking into account the fact that M. penetrans has the capacity to invade eucaryotic cells, one can suggest, but not assert, that produced Ca2+/Mg2+-dependent endonuclease may alter the nucleic acid metabolism of host cells by DNA and/or RNA degradation and may act as a potential pathogenic determinant.

Molecular systematic studies of eubacteria, using sigma70-type sigma factors of group 1 and group 2

Sigma factors of the sigma70 family were used as a phylogenetic tool to compare evolutionary relationships among eubacteria. Several new sigma factor genes were cloned and sequenced to increase the variety of available sequences. Forty-two group 1 sigma factor sequences of various species were analyzed with the help of a distance matrix method to establish a phylogenetic tree. The tree derived by using sigma factors yielded subdivisions, including low-G+C and high-G+C gram-positive bacteria, cyanobacteria, and the alpha, beta, gamma, and delta subdivisions of proteobacteria, consistent with major bacterial groups found in trees derived from analyses with other molecules. However, some groupings (e.g., the chlamydiae, mycoplasmas, and green sulfur bacteria) are found in different positions than for trees obtained by using other molecular markers. A direct comparison to the most extensively used molecule in systematic studies, small-subunit rRNA, was made by deriving trees from essentially the same species set and using similar phylogenetic methods. Differences and similarities based on the two markers are discussed. Additionally, 31 group 2 sigma factors were analyzed in combination with the group 1 proteins in order to detect functional groupings of these alternative sigma factors. The data suggest that promoters recognized by the major vegetative sigma factors of eubacteria will contain sequence motifs and spacing very similar to those for the sigma70 sigma factors of Escherichia coli.

Antimycoplasma properties and application in cell culture of surfactin, a lipopeptide antibiotic from Bacillus subtilis

Surfactin, a cyclic lipopeptide antibiotic and biosurfactant produced by Bacillus subtilis, is well-known for its interactions with artificial and biomembrane systems (e.g., bacterial protoplasts or enveloped viruses). To assess the applicability of this antiviral and antibacterial drug, we determined the cytotoxicity of surfactin with a 50% cytotoxic concentration of 30 to 64 microM for a variety of human and animal cell lines in vitro. Concomitantly, we observed an improvement in proliferation rates and changes in the morphology of mycoplasma-contaminated mammalian cells after treatment with this drug. A single treatment over one passage led to complete removal of viable Mycoplasma hyorhinis cells from various adherent cell lines, and Mycoplasma orale was removed from nonadherent human T-lymphoid cell lines by double treatment. This effect was monitored by a DNA fluorescence test, an enzyme-linked immunosorbent assay, and two different PCR methods. Disintegration of the mycoplasma membranes as observed by electron microscopy indicated the mode of action of surfactin. Disintegration is obviously due to a physicochemical interaction of the membrane-active surfactant with the outer part of the lipid membrane bilayer, which causes permeability changes and at higher concentrations leads finally to disintegration of the mycoplasma membrane system by a detergent effect. The low cytotoxicity of surfactin for mammalian cells permits specific inactivation of mycoplasmas without significant deleterious effects on cell metabolism and the proliferation rate in cell culture. These results were used to develop a fast and simple method for complete and permanent inactivation of mycoplasmas in mammalian monolayer and suspension cell cultures.

New aspects on membrane lipid regulation in Acholeplasma laidlawii A and phase equilibria of monoacyldiglucosyldiacylglycerol

A new membrane lipid, monoacyldiglucosyldiacylglycerol (MADGlcDAG), was recently discovered in Acholeplasma laidlawii strain A-EF22, demanding a new study of the biosynthetic regulation, and the phase behavior, of the glucolipids in this organism. The only liquid-crystalline phase formed by MADGlcDAG is a reversed hexagonal phase. A. laidlawii A-EF22 synthesizes four lipids that have the ability to induce the formation of reversed nonlamellar phases: MADGlcDAG, monoglucosyldiacylglycerol (MGlcDAG), monoacylmonoglucosyldiacylglycerol (MAMGlcDAG), and diacylglycerol (DAG). A Cn value of approximately 16 seems to be a critical value for the fractions of these lipids in the membrane: the fractions of MADGlcDAG and MGlcDAG are largest when the Cn values are lower than 16, while the fractions of MAMGlcDAG and DAG are largest when the Cn values are higher than 16. The fraction of nonlamellar-forming lipids was 55 mol% when the Cn value was 14.8 and the degree of unsaturation was 33 mol%. This fraction was reduced to 7 mol% when the Cn value and the degree of unsaturation were increased to 17.8 and 92 mol%, respectively, i.e., at conditions that markedly favor the formation of reversed nonlamellar phases. These observations convincingly show that a balance between lamellar- and nonlamellar-forming lipids is maintained in the membrane and strongly support the validity of the lipid regulation model proposed by us. From earlier biochemical data, obtained with short acyl chains, that were difficult to reconcile with our regulation model, it could be predicted that a lipid ought to be synthesized that assists MGlcDAG to maintain the nonlamellar-forming properties with the short chains. It is shown in the present work that this lipid is MADGlcDAG and that the regulation of the balance between lamellar- and nonlamellar-forming lipids is even more complex and sophisticated in A. laidlawii A-EF22 than previously proposed.

Characterization of genes encoding topoisomerase IV of Mycoplasma genitalium

A type-II toposiomerase (Topo-IV) encoded by the parC and parE genes in Escherichia coli and Salmonella typhimurium is thought to be involved in cell septation and in the decatenation of newly replicated chromosomes. We have identified parC and parE homologs in the pleomorphic, wall-less organism Mycoplasma genitalium. Since the mechanics of cell septation in conventional eubacterial species is believed to be mediated by cell-wall constituents, there is no clear understanding of what coordinates that process in wall-less species. The presence of par genes in this bacterium, which has the smallest genome of any free-living organism, suggests that Topo-IV has been evolutionarily conserved because of an essential role in mediating cell division.

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.

Induced mouse spleen B-cell proliferation and secretion of immunoglobulin by lipid-associated membrane proteins of Mycoplasma fermentans incognitus and Mycoplasma penetrans

Mycoplasmas have been implicated as a possible cofactor in AIDS pathogenesis. Mycoplasma fermentans and M. penetrans infect human immunodeficiency virus-positive patients at a significantly higher frequency than non-human immunodeficiency virus-infected control subjects. Various mycoplasmal membrane preparations are known to affect the functions of immune cells both in vitro and in vivo. A group of lipid-associated membrane proteins (LAMPs) extracted by Triton X-114 from mycoplasmas are major antigenic targets of human host antibody responses. In this study, LAMPs prepared from both M. fermentans and M. penetrans nonspecifically stimulated spleen cells of CBA/CaH mice to proliferate. LAMPs were also stimulatory to spleen cells from athymic mice. On the other hand, enriched splenic T cells from CBA/CaH mice with or without accessory cells responded poorly. Thus, the mitogenic effect of mycoplasmal LAMPs appeared mainly on B cells. High levels of immunoglobulin (Ig) M and low but detectable amounts of IgG were found in the supernatant of LAMP-treated splenic cell culture. M. penetrans LAMPs had a much more potent effect on murine spleen cells than did M. fermentans incognitus LAMPs in inducing both B-cell proliferation and Ig secretion. In conclusion, the mycoplasmal LAMPs contained an active component(s) with T-independent B-cell mitogenic effect.

Membrane-associated nuclease activities in mycoplasmas

Membrane-associated nucleases of various mycoplasmal species were investigated by using two nuclease assays. A lambda DNA assay was developed to measure nuclease activity associated with whole-cell suspensions, activity released from intact cells, and activity associated with detergent-disrupted cells. In most species, nuclease activities were entirely membrane associated, and disruption by a detergent had a stimulatory effect on these activities. All mycoplasmal species contained nuclease activity, but Mycoplasma capricolum was unusual because its activity was dependent upon magnesium and was inhibited by calcium. We developed a sodium dodecyl sulfate-polyacrylamide gel electrophoresis system that produced reproducible nuclease patterns, and this system was used to determine the apparent molecular weights of the nuclease proteins. An examination of 20 mycoplasmal species failed to identify common bands in their nuclease patterns. An examination of 11 Mycoplasma pulmonis strains, however, indicated that nuclease patterns on polyacrylamide gels may provide a means for categorizing strains within a species. Our results suggest that nucleases are important constituents of mycoplasmal membranes and may be involved in the acquisition of host nucleic acids required for growth.

Prevalence of complement-fixing antibodies to Mycoplasma pneumoniae in the savannah and forest belts of Nigeria

A survey of complement-fixing antibodies to Mycoplasma pneumoniae in 1673 children (aged 5-13 years) was conducted in Nigeria. Although the antibodies were detected in 25.7% of the children from the savannah belt and 20.4% of those from the forest belt, only 8.9% and 7.4%, respectively, had titres considered high enough to protect them from infection. The geometric mean titres (GMT) tended to increase with age up to 8 years and then gradually fall. The age-specific differences in GMT were significant (F = 2.98; analysis of variance with x = 0.05) but those due to the child's sex (F = 2.49) and belt of origin (F = 2.61) were not. The results indicate that Nigeria is a highly endemic area for M. pneumoniae infection, with a large pool of susceptible children in which epidemic outbreaks could occur.

Identification of Mycoplasma pirum genes involved in the salvage pathways for nucleosides

Genes encoding enzymes involved in the salvage pathway for nucleosides have been cloned and sequenced from the mollicute Mycoplasma pirum. One of them, encoding deoxyriboaldolase, was functionally identified by complementation of an Escherichia coli mutant. These genes are clustered, suggesting an operon organization, and they are immediately followed by the putative gene for the triose phosphate isomerase, an enzyme used during glycolysis.

Localizing the replication origin region on the physical map of the Mycoplasma capricolum genome

Four lines of evidence argue that the replication origin of the Mycoplasma capricolum genome lies within the 46-kb BamHI fragment bordered by two BamHI sites of the total of nine BamHI sites that have been located on the physical map (M. Miyata, L. Wang, and T. Fukumura, FEMS Microbiol. Lett. 79:329-334, 1991). First, this fragment lost its labeling in preference to other fragments when log-phase cultures were incubated in the presence of chloramphenicol for various times to inhibit the initiation of new rounds of replication and then further incubated with radioactive dTMP to allow DNA elongation to continue. Second, the relative frequencies of various restriction fragments of the genome DNA from exponentially growing cells decreased with increasing distance from the putative origin. Third, preferential labeling occurred when radioactive dTMP was added to cultures of a DNA elongation-defective, temperature-sensitive mutant with a simultaneous temperature downshift. Fourth, the M. capricolum homolog of the dnaA gene, which is located near the replication origin in many other bacteria, was found in the 46-kb fragment.

Protection against airsacculitis with sequential systemic and local immunization of chickens using killed Mycoplasma gallisepticum bacterin with iota carrageenan adjuvant

The induction of protective immunity to Mycoplasma gallisepticum (MG) by bacterins containing 0.2% iota carrageenan (iCGN) as an adjuvant has been studied. Various combinations of intracoelomic (i.c.), intratracheal (i.t.), intranasal (i.n.), intravenous (i.v.), subcutaneous (s.c.) and oral immunization routes were evaluated. Vaccinated and non-vaccinated groups were compared with a group vaccinated s.c. with a commercial bacterin. Primary i.c. immunization with the bacterin was as effective as commercial bacterin and was more effective when followed by i.n. or i.t. immunization. Oral immunization was ineffective, in contrast to observations reported with mice. The i.c./i.n. and i.c./i.t. combinations were the most effective, produced the highest levels of anti-MG IgG and IgA in serum and tracheobronchial washes, and sometimes provided 100% protection against air sac lesions. Chickens vaccinated by the i.c./i.n. or i.c./i.t. routes had the fewest virulent organisms in their respiratory tract secretions. These results demonstrated that i.c. immunization followed by local immunization with the bacterin is most efficacious in protecting chickens against airsacculitis.

Nucleotide sequence, organization and characterization of the atp genes and the encoded subunits of Mycoplasma gallisepticum ATPase

The nucleotide sequence of a 7.8 kbp DNA fragment from the genome of Mycoplasma gallisepticum has been determined. The fragment contains a cluster of nine tightly linked genes coding for the subunits of the M. gallisepticum ATPase. The gene order is I (I-subunit), B (a-subunit), E (c-subunit), F (b-subunit), H (delta-subunit), A (alpha-subunit), G (gamma-subunit), D (beta-subunit) and C (epsilon-subunit). Two open reading frames were identified in the flanking regions; one (ORFU), preceding the I gene, encodes at least 110 amino acids and the other (ORFS), following the C gene, encodes at least 90 amino acids. The deduced amino acid sequences of the various subunits are presented and discussed with regard to the structure, function and differing sensitivity of the M. gallisepticum enzyme to dicyclohexylcarbodiimide and aurovertin. The alpha- and beta-subunits of the F1 portion are well conserved (51% and 65% identity with those of Escherichia coli), whereas the gamma-, delta- and epsilon-subunits, as well as the F0-subunits, show a low percentage identity. Nonetheless, the secondary structure of the F0-subunits show a high degree of similarity to the corresponding subunits of E. coli. Two very strong potential amphipathic alpha-helices are predicted in the delta-subunit and the N-terminus of the b-subunit contains two hydrophobic helical stretches. The possible roles of these structural properties in the close association of the F1 and F0 multisubunit complexes among mycoplasmas are discussed.

Role of the S layer in morphogenesis and cell division of the archaebacterium Methanocorpusculum sinense

Thin sections, freeze-etched, and negatively stained preparations of Methanocorpusculum sinense cells reveal a highly lobed cell structure with a hexagonally arranged surface layer (S layer). Digital image processing of negatively stained envelope fragments show that the S layer forms a porous but strongly interconnected network. Since the S layer is the exclusive cell envelope component outside the cytoplasmic membrane it must have a cell shape determining and maintaining function. Although lattice faults such as disclinations and dislocations are a geometrical necessity on the surface of a closed protein crystal, our data indicate that they also play important roles as sites for the incorporation of new morphological units, in the formation of the lobed cell structure, and in the cell division process. In freeze-etched preparations of intact cells numerous positive and negative 60 degree wedge disclinations can be detected which form pentagons and heptagons in the hexagonal array. Complementary pairs of pentagons and heptagons are the termination points of edge dislocations. They can be expected to function both as sites for incorporation of new morphological units into the lattice and as initiation points for the cell division process. The latter is determined by the ratio between the increase of protoplast volume and the increase in actual S-layer surface area during cell growth. We postulate that this mode of cell fission represents a common feature in lobed archaebacteria which possess an S layer as the exclusive wall component.

Interaction of chlamydiae and host cells in vitro

The obligately intracellular bacteria of the genus Chlamydia, which is only remotely related to other eubacterial genera, cause many diseases of humans, nonhuman mammals, and birds. Interaction of chlamydiae with host cells in vitro has been studied as a model of infection in natural hosts and as an example of the adaptation of an organism to an unusual environment, the inside of another living cell. Among the novel adaptations made by chlamydiae have been the substitution of disulfide-bond-cross-linked polypeptides for peptidoglycans and the use of host-generated nucleotide triphosphates as sources of metabolic energy. The effect of contact between chlamydiae and host cells in culture varies from no effect at all to rapid destruction of either chlamydiae or host cells. When successful infection occurs, it is usually followed by production of large numbers of progeny and destruction of host cells. However, host cells containing chlamydiae sometimes continue to divide, with or without overt signs of infection, and chlamydiae may persist indefinitely in cell cultures. Some of the many factors that influence the outcome of chlamydia-host cell interaction are kind of chlamydiae, kind of host cells, mode of chlamydial entry, nutritional adequacy of the culture medium, presence of antimicrobial agents, and presence of immune cells and soluble immune factors. General characteristics of chlamydial multiplication in cells of their natural hosts are reproduced in established cell lines, but reproduction in vitro of the subtle differences in chlamydial behavior responsible for the individuality of the different chlamydial diseases will require better in vitro models.

Evidence for the presence of two distinct membrane ATPases in Spiroplasma citri

Triton X-100 (TX-100) extraction of Spiroplasma citri plasma membrane solubilized two types of ATPase differing in their pH of maximum activity. The activity measured at pH 8·5 was inhibited by vanadate and the activity measured at pH 6·5 was not. The vanadate-sensitive ATPase had a relatively basic isoelectric point (8·65) and therefore could be separated from the vanadate-insensitive ATPase using chromatofocusing. Elution of the TX-100 membrane extract in a pH gradient from 9 to 6 generated two peaks of ATPase activity: one in the acidic range, composed of an F0F1-type ATPase, and one in the basic range, corresponding to the vanadate-sensitive activity. Electrophoretic analysis of proteins from the latter peak revealed one major polypeptide of 37 kDa. This peptide was shown to correspond to spot A37 in a two-dimensional protein map of S. citri. Using the gene for the kdp-operon of Escherichia coli as a probe in heterologous hybridization, sequences were detected in the genomic DNA of S. citri, suggesting that a gene coding for an enzyme related to this P-type ATPase is present in the S. citri genome. We therefore postulate the presense of two distinct kinds of ATPase in S. citri: one of the F-type which is resistant to vanadate inhibition, and one, probably of the P-type, which is vanadate-sensitive.