Mycoplasma pneumoniae induces airway epithelial cell expression of MUC5AC in asthma

As excess mucin expression can contribute to the exacerbation of asthma, the present authors hypothesised that Mycoplasma pneumoniae significantly induces MUC5AC (the major airway mucin) expression in airway epithelial cells isolated directly from asthmatic subjects. A total of 11 subjects with asthma and six normal controls underwent bronchoscopy with airway brushing. Epithelial cells were cultured at an air-liquid interface and incubated with and without M. pneumoniae for 48 h, and in the presence and absence of nuclear factor (NF)-kappaB and a toll-like receptor (TLR)2 inhibitor. Quantitative PCR was performed for MUC5AC and TLR2 mRNA. MUC5AC protein and total protein were determined by ELISA. M. pneumoniae exposure significantly increased MUC5AC mRNA and protein expression after 48 h in epithelial cells isolated from asthmatic, but not from normal control subjects, at all concentrations as compared to unexposed cells. TLR2 mRNA expression was significantly increased in asthmatic epithelial cells at 4 h compared with unexposed cells. NF-kappaB and TLR2 inhibition reduced MUC5AC expression to the level of the unexposed control in both groups. Mycoplasma pneumoniae exposure significantly increased MUC5AC mRNA and protein expression preferentially in airway epithelial cells isolated from asthmatic subjects. The toll-like receptor 2 pathway may be involved in this process.

Growth characteristics of Bartonella henselae in a novel liquid medium: primary isolation, growth-phase-dependent phage induction, and metabolic studies

Bartonella henselae is a zoonotic pathogen that usually causes a self-limiting infection in immunocompetent individuals but often causes potentially life-threatening infections, such as bacillary angiomatosis, in immunocompromised patients. Both diagnosis of infection and research into the molecular mechanisms of pathogenesis have been hindered by the absence of a suitable liquid growth medium. It has been difficult to isolate B. henselae directly from the blood of infected humans or animals or to grow the bacteria in liquid culture media under laboratory conditions. Therefore, we have developed a liquid growth medium that supports reproducible in vitro growth (3-h doubling time and a growth yield of approximately 5 x 10(8) CFU/ml) and permits the isolation of B. henselae from the blood of infected cats. During the development of this medium, we observed that B. henselae did not derive carbon and energy from the catabolism of glucose, which is consistent with genome nucleotide sequence data suggesting an incomplete glycolytic pathway. Of interest, B. henselae depleted amino acids from the culture medium and accumulated ammonia in the medium, an indicator of amino acid catabolism. Analysis of the culture medium throughout the growth cycle revealed that oxygen was consumed and carbon dioxide was generated, suggesting that amino acids were catabolized in a tricarboxylic acid (TCA) cycle-dependent mechanism. Additionally, phage particles were detected in the culture supernatants of stationary-phase B. henselae, but not in mid-logarithmic-phase culture supernatants. Enzymatic assays of whole-cell lysates revealed that B. henselae has a complete TCA cycle. Taken together, these data suggest B. henselae may catabolize amino acids but not glucose to derive carbon and energy from its host. Furthermore, the newly developed culture medium should improve isolation of B. henselae and basic research into the pathogenesis of the bacterium.

Stability and subcellular localization of cytadherence-associated protein P65 in Mycoplasma pneumoniae

The surface protein P65 is a constituent of the Mycoplasma pneumoniae cytoskeleton and is present at reduced levels in mutants lacking the cytadherence accessory protein HMW2. Pulse-chase studies demonstrated that P65 is subject to accelerated turnover in the absence of HMW2. P65 was also less abundant in noncytadhering mutants lacking HMW1 or P30 but was present at wild-type levels in mutants lacking proteins A, B, C, and P1. P65 exhibited a polar localization like that in wild-type M. pneumoniae in all mutants having normal levels of HMW1 and HMW2. Partial or complete loss of these proteins, however, correlated with severe reduction in the P65 level and the inability to localize P65 properly.

Stability of Mycoplasma pneumoniae cytadherence-accessory protein HMW1 correlates with its association with the triton shell

Mycoplasma pneumoniae adsorbs to host respiratory epithelium primarily by its attachment organelle, the proper function of which depends upon mycoplasma adhesin and cytoskeletal proteins. Among the latter are the cytadherence-associated proteins HMW1 and HMW2, whose specific roles in this process are unknown. In the M. pneumoniae cytadherence mutant I-2, loss of HMW2 results in accelerated turnover of HMW1 and other cytadherence-accessory proteins, probably by proteolysis. However, both the mechanism of degradation and the means by which these proteins are rendered susceptible to it are not understood. In this study, we addressed whether HMW1 degradation is a function of its presence among specific subcellular fractions and established that HMW1 is a peripheral membrane protein that is antibody accessible on the outer surfaces of both wild-type and mutant I-2 M. pneumoniae but to a considerably lesser extent in the mutant. Quantitation of HMW1 in Triton X-100-fractionated extracts from cells pulse-labeled with [(35)S]methionine indicated that HMW1 is synthesized in a Triton X-100-soluble form that exists in equilibrium with an insoluble (cytoskeletal) form. Pulse-chase analysis demonstrated that over time, HMW1 becomes stabilized in the cytoskeletal fraction and associated with the cell surface in wild-type M. pneumoniae. The less efficient transition to the cytoskeleton and mycoplasma cell surface in mutant I-2 leads to accelerated degradation of HMW1. These data suggest a role for HMW2 in promoting export of HMW1 to the cell surface, where it is stable and fully functional.

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

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

Transcriptional analysis of the hmw gene cluster of Mycoplasma pneumoniae

Mycoplasma pneumoniae adherence to host cells is a multifactorial process that requires the cytadhesin P1 and additional accessory proteins. The hmw gene cluster consists of the genes p30, hmw3, and hmw1, the products of which are known to be essential for cytadherence, the rpsD gene, and six open reading frames of unknown function. Putative transcriptional terminators flank this locus, raising the possibility that these genes are expressed as a single transcriptional unit. However, S1 nuclease protection and primer extension experiments identified probable transcriptional start sites upstream of the p32, p21, p50, and rpsD genes. Each was preceded at the appropriate spacing by the -10-like sequence TTAAAATT, but the -35 regions were not conserved. Analysis of the M. pneumoniae genome sequence indicated that this promoter-like sequence is found upstream of only a limited number of open reading frames, including the genes for P65 and P200, which are structurally related to HMW1 and HMW3. Promoter deletion studies demonstrated that the promoter-like region upstream of p21 was necessary for the expression of p30 and an hmw3-cat fusion in M. pneumoniae, while deletion of the promoter-like region upstream of p32 had no apparent effect. Analysis by reverse transcription-PCR confirmed transcriptional linkage of all the open reading frames in the hmw gene cluster. Taken together, these findings suggest that the genes of this locus constitute an operon expressed from overlapping transcripts.

Identification and complementation of frameshift mutations associated with loss of cytadherence in Mycoplasma pneumoniae

Mycoplasma pneumoniae cytadherence is mediated by a specialized, polar attachment organelle. Certain spontaneously arising cytadherence mutants (designated class I) lack HMW2, fail to localize the adhesin protein P1 to the attachment organelle, and exhibit accelerated turnover of proteins HMW1, HMW3, and P65. Insertional inactivation of hmw2 by Tn4001 results in a phenotype nearly identical to that of the class I mutants, suggesting that the latter may result from a defect in hmw2. In this study, the recombinant wild-type hmw2 allele successfully complemented a class I mutant when introduced by transposon delivery. Synthesis of recombinant HMW2 at wild-type levels resulted in reacquisition of hemadsorption and normal levels of HMW1, HMW3, and P65. Low-level production of HMW2 in some transformants resulted in only an intermediate capacity to hemadsorb. Furthermore, full restoration of HMW1 and P65, but not that of HMW3, was directly proportional to the amount of recombinant HMW2 produced, reflecting the importance of proper stoichiometry for certain cytadherence-associated proteins. The recombinant class I hmw2 allele did not restore cytadherence, consistent with a defect in hmw2 in this mutant. A frameshift was discovered in different oligoadenine tracts in hmw2 from two independent class I mutants. Finally, protein P28 is thought to be the product of internal translation initiation in hmw2. A transposon excision-deletion mutant produced a truncated HMW2 but no P28, consistent with this conclusion. However, this deletion mutant was hemadsorption positive, indicating that P28 may not be required for cytadherence.

Construction and analysis of a modified Tn4001 conferring chloramphenicol resistance in Mycoplasma pneumoniae

The Staphylococcus aureus transposon Tn4001 and derivatives thereof have been transformed successfully in several mycoplasma species. In order to expand the versatility of Tn4001 for other genetic manipulations and for use in mycoplasma species resistant to gentamicin (Gm), chloramphenicol acetyltransferase (Cat) from S. aureus was evaluated as a selectable marker. The cat gene was cloned in both orientations into a modified Tn4001 and transformed into Mycoplasma pneumoniae, conferring resistance to Cm and Gm. Replacement of the gene for GmR in Tn4001 with cat likewise conferred CmR when transformed into M. pneumoniae. The minimum inhibitory concentration to Cm in transformants with cat derivatives of Tn4001 was 300-500 microg/ml, and Cat enzyme activity was demonstrated by using a fluorescent substrate.

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

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

Bartonella henselae invasion of feline erythrocytes in vitro

Bartonella henselae, the causative agent of cat scratch disease, establishes long-term bacteremia in cats, in which it attaches to and invades feline erythrocytes (RBC). Feline RBC invasion was assessed in vitro, based on gentamicin selection for intracellular bacteria or by laser confocal microscopy and digital sectioning. Invasion rates ranged from 2 to 20% of the inoculum, corresponding to infection of less than 1% of the RBC. Invasion was a slow process, requiring >8 h before significant numbers of intracellular bacteria were detected. Pretreatment of the bacteria with trypsin, or of the RBC with trypsin or neuraminidase, had no effect, but pronase pretreatment of RBC resulted in a slight increase in invasion frequency. The ability to model B. henselae invasion of feline RBC in vitro should permit identification of bacterial surface components involved in this process and elucidate the significance of RBC invasion to transmission and infection in cats.

HMW1 is required for cytadhesin P1 trafficking to the attachment organelle in Mycoplasma pneumoniae

Mycoplasma pneumoniae proteins HMW1-HMW3 collectively are essential for cytadherence, but the function or requirement for each has not been defined. Cytadherence mutant M6 lacks HMW1 because of a frameshift in hmw1 and produces a truncated adherence-associated protein P30 because of a deletion at the 3' end of p30. Genetic manipulation of this mutant was used to evaluate the role of HMW1 in cytadherence. Mutant M6 was transformed with a recombinant transposon containing a wild-type p30 allele. Transformants synthesized both truncated and full-length P30, from the resident and recombinant alleles, respectively. However, these transformants remained hemadsorption negative, suggesting that HMW1 is required for cytadherence. Wild-type M. pneumoniae cells are generally elongated, tapering to form the attachment organelle at one end of the cell. The cytadhesin protein P1 is normally densely clustered on the mycoplasma surface at this differentiated terminal structure. However, both mutant M6 and M6 transformed with recombinant p30 had a striking ovoid morphology with no tapering at the tip structure, making the attachment organelle indistinguishable. Furthermore, protein P1 was randomly distributed on the mycoplasma surface rather than clustered at a polar location. In contrast, mutant M6 transformed with a recombinant transposon expressing the wild-type hmw1 allele exhibited a near-normal morphology and localized P1 to the attachment organelle. Significantly, M6 transformed with an hmw1 gene truncated slightly at the 3' end failed to restore proper morphology or P1 localization to the attachment organelle, suggesting a functional importance to the C-terminal domain of HMW1.

Mycoplasma pneumoniae cytadherence: organization and assembly of the attachment organelle

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

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

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

Transposon mutagenesis reinforces the correlation between Mycoplasma pneumoniae cytoskeletal protein HMW2 and cytadherence

A new genetic locus associated with Mycoplasma pneumoniae cytadherence was previously identified by transposon mutagenesis with Tn4001. This locus maps approximately 160 kbp from the genes encoding cytadherence-associated proteins HMW1 and HMW3, and yet insertions therein result in loss of these proteins and a hemadsorption-negative (HA-) phenotype, prompting the designation cytadherence-regulatory locus (crl). In the current study, passage of transformants in the absence of antibiotic selection resulted in loss of the transposon, a wild-type protein profile, and a HA+ phenotype, underscoring the correlation between crl and M. pneumoniae cytadherence. Nucleotide sequence analysis of crl revealed open reading frames (ORFs) orfp65, orfp216, orfp41, and orfp24, arranged in tandem and flanked by a promoter-like and a terminator-like sequence, suggesting a single transcriptional unit, the P65 operon. The 5' end of orfp65 mRNA was mapped by primer extension, and a likely promoter was identified just upstream. The product of each ORF was identified by using antisera prepared against fusion proteins. The previously characterized surface protein P65 is encoded by orfp65, while the 190,000 Mr cytadherence-associated protein HMW2 is a product of orfp216. Proteins with sizes of 47,000 and 41,000 Mr and unknown function were identified for orfp41 and orfp24, respectively. Structural analyses of HMW2 predict a periodicity highly characteristic of a coiled-coil conformation and five leucine zipper motifs, indicating that HMW2 probably forms dimers in vivo, which is consistent with a structural role in cytadherence. Each transposon insertion mapped to orfp216 but affected the levels of all products of the P65 operon. HMW2 is thought to form a disulfide-linked dimer, formerly designated HMW5, and examination of an hmw2 deletion mutant confirms that HMW5 is a product of the hmw2 gene.

Sequence analysis and characterization of the hmw gene cluster of Mycoplasma pneumoniae

Mycoplasma pneumoniae (Mp) cytadherence requires the proper anchoring of cytadhesin proteins in the mycoplasmal membrane at an attachment organelle through their interaction with a cytoskeleton-like network of accessory proteins that includes HMW1 and HMW3. Approximately 8.25 kb of Mp DNA was sequenced, beginning at the 3' end of the hmw3 gene and continuing through hmw1. Comparison of the resulting deduced amino acid (aa) sequence with N terminus and internal peptide aa sequences from purified HMW1 permitted definitive identification of hmw1. HMW1 was characterized with respect to structure, hydrophobicity, possible phosphoacceptor sites and expression of the Mp recombinant protein in Escherichia coli. In addition, HMW1 membrane topography was examined for antibody accessibility on the mycoplasmal surface. hmw3 and hmw1 flank four open reading frames (ORFs) spanning approximately 4.3 kb and in the same orientation as the hmw genes. The sequences of their deduced products were evaluated for likely structural features and comparison with protein data banks. Finally, the Mp rpsD analog was identified immediately downstream from hmw1.

Mycoplasma pneumoniae cytadherence: unravelling the tie that binds

Mycoplasma pneumoniae is the leading cause of pneumonia in older children and young adults. Mycoplasma adherence to the respiratory epithelium (cytadherence) is required for colonization and pathogenesis. Although considered to be among the smallest and simplest known prokaryotes, this cell-wall-less bacterium possesses a highly differentiated terminal structure that is thought to be functional in mycoplasma cell division, gliding motility, and cytadherence. Mutant analysis has identified mycoplasma proteins associated with cytadherence, and revealed novel regulatory features. Ultrastructural and biochemical studies have established the subcellular location and interaction of key components, several of which are phosphorylated by ATP-dependent kinase(s) in a manner that is responsive to changing nutritional conditions. This review summarizes recent progress in defining the composition, organization and regulation of the attachment organelle. What emerges is a picture of M. pneumoniae cytadherence as a multifactorial process that extends well beyond adhesin-receptor recognition.

Expression in Mycoplasma pneumoniae of the recombinant gene encoding the cytadherence-associated protein HMW1 and identification of HMW4 as a product

Mycoplasma pneumoniae is a major cause of tracheobronchitis and pneumonia in older children and young adults. The lack of adequate tools for genetic analysis has hindered the elucidation of function and regulation of mycoplasma virulence determinants. We describe here the use of a transposon vector to deliver the cloned gene for the cytadherence-associated protein HMW1 in M. pneumoniae. A 4.95 kbp BamHI fragment encoding all but the C-terminal end of HMW1 was cloned into a modified Tn4001 and transformed into wild-type M. pneumoniae and into a non-cytadhering mutant lacking HMW1-HMW5. Southern blot hybridizations confirmed insertion of the transposon and the presence of both the resident and recombinant hmw1 alleles. Analysis by Western immunoblotting revealed a truncated HMW1 (HMW1') in the transformants, the level of HMW1' being dependent upon the orientation of the hmw1 gene in the transposon and the site of insertion. Similar expression patterns were noted in wild-type and mutant backgrounds. However, expression of wild-type levels of HMW1' in the mutant did not restore adherence. Finally, HMW4 and HMW1 were shown to be products of the same gene, HMW4 being a heat-modified derivative of HMW1.

Identification of a possible cytadherence regulatory locus in Mycoplasma pneumoniae

Transposon mutagenesis was used to analyze Mycoplasma pneumoniae cytadherence. Mycoplasmas were electroporated with Tn4001, and transformants were identified by antibiotic selection using gentamicin. The resulting colonies were screened for hemadsorption (HA) as an indicator for cytadherence. Six HA- colonies from independent transformations were isolated, filter cloned, and characterized in more detail. Southern hybridization analysis revealed that all six transposon insertions mapped to the same 252-kbp ApaI fragment and 19.5-kbp XhoI fragment. More detailed analysis localized the insertion to two adjacent EcoRI fragments. This site is distinct from the locus containing the genes for the high-molecular weight cytadherence-accessory proteins HMW1 and HMW3, and yet these proteins were absent from the protein profiles of all six transformants. To determine if transposon insertion was responsible for the HA- phenotype, reversion frequencies of the transformants were assessed after passage in the presence of antibiotic selection. In contrast to a spontaneously arising HMW-deficient variant, which reverted to an HA+ phenotype readily, no HA+ revertants were identified for any of the six transformants. These observations suggest that a potential regulatory locus that may be important in the expression of the HMW cytadherence-accessory proteins has been identified.

Phosphorylation of Mycoplasma pneumoniae cytadherence-accessory proteins in cell extracts

A cell-free system was used to characterize the phosphorylation of Mycoplasma pneumoniae proteins HMW1 and HMW2, which are involved in the adherence of this organism to human tracheal epithelium during infection. The pH and cation requirements for phosphorylation of HMW1 and HMW2 were determined, and the effects of glycolytic intermediates, cyclic AMP, and eukaryotic kinase-phosphatase inhibitors and stimulators on this process were examined. Phosphoamino acid analysis identified serine as the major phosphate acceptor for both HMW1 and HMW2 in this system.

Differentiation of Bartonella-like isolates at the species level by PCR-restriction fragment length polymorphism in the citrate synthase gene

The citrate synthase gene (gltA) of Bartonella henselae was cloned and sequenced to compare genetic divergence among alpha and gamma branches of the class Proteobacteria and to develop enhanced genotypic reagents for B. henselae identification. B. henselae gltA is 1,293 nucleotides in length and 63 to 66% homologous with corresponding gene sequences of Rickettsia prowazekii, Escherichia coli, and Coxiella burnetii. The observed genetic variability suggests that gltA sequences can provide a useful means for studying moderate divergence among related bacteria. Oligonucleotides specific for B. henselae gltA were evaluated for the ability to prime PCR amplification within the alpha and gamma branches of the proteobacteria. Under the conditions used, only B. henselae, Bartonella quintana, and R. prowazekii template DNAs yielded amplification products (approximately 380 bp). DNAs from 28 Bartonella-like isolates of feline origin were amplified by B. henselae primers and analyzed for restriction fragment length polymorphism. The resulting patterns for all 28 isolates were similar or identical to that of the recognized B. henselae strain. Current studies are aimed at optimization of PCR conditions for specificity and sensitivity of amplification of Bartonella sequences from clinical isolates.

Phosphorylation of cytadherence-accessory proteins in Mycoplasma pneumoniae

Attachment to host cells of the respiratory epithelium by Mycoplasma pneumoniae is a complex, multicomponent process, requiring a number of accessory proteins in addition to adhesins directly involved in receptor binding. In this study, protein phosphorylation of the cytadherence-accessory proteins HMW1, HMW2, and HMW4 of M. pneumoniae was examined using biochemical and immunological techniques. The initial indication of protein modification came from Western immunoblot analysis of the two-dimensional polyacrylamide gel electrophoresis (PAGE) profile of M. pneumoniae proteins, revealing multiple spots for both HMW1 and HMW4 that varied in pI but not in size. M. pneumoniae cultured in the presence of H3(32)PO4 exhibited numerous phosphorylated proteins as detected by sodium dodecyl sulfate-PAGE and autoradiography. These included proteins corresponding to HMW1, HMW2, and HMW4 in electrophoretic mobility. The Triton X-100 partitioning characteristics of these phosphorylated proteins was identical to that described previously for HMW1, -2, and -4. Furthermore, these protein bands were absent when a noncytadhering variant deficient in HMW1-5 was examined in the same manner. Finally, the availability of antiserum to HMW1 and -4 enabled us to confirm by radioimmunoprecipitation that HMW1 and HMW4 are phosphoproteins. Phosphoamino acid analysis of acid-hydrolyzed HMW1 and HMW2 identified primarily phosphothreonine and, to a lesser extent, phosphoserine in HMW1 and predominantly phosphoserine, with a trace of phosphothreonine, in HMW2. Neither protein contained phosphotyrosine. HMW1-HMW5 are components of a cytoskeleton-like structure in M. pneumoniae that is thought to function in cell division, changes in cell morphology, gliding motility, and the localization of adhesins in the mycoplasma membrane. Phosphorylation may regulate cytoskeleton dynamics involving these cytadherence-accessory proteins.

Transformation of Mycoplasma pneumoniae with Tn4001 by electroporation

Mycoplasma pneumoniae was transformed with the Staphylococcus aureus transposon Tn4001 by electroporation. A transformation frequency of 10(-3) to 10(-5)/colony-forming unit was observed using 30.0 microgram plasmid DNA and 10(7)-10(8) M. pneumoniae colony-forming units. DNA hybridization analyses using standard and pulsed field agarose gel electrophoresis confirmed chromosomal insertion of the transposon, apparently by a transpositional mechanism into random sites. These studies demonstrate the functionality of Tn4001 in M. pneumoniae and suggest its potential as a genetic tool in this mycoplasma.

Mycoplasma pneumoniae cytadherence phase-variable protein HMW3 is a component of the attachment organelle

The subcellular location of the phase-variable cytadherence-accessory protein HMW3 in Mycoplasma pneumoniae has been examined by biochemical and immunoelectron microscopic techniques. Analysis by Western blot (immunoblot) with HMW3-specific antiserum established the presence of this protein within the M. pneumoniae Triton X-100-insoluble fraction or triton shell. Immunogold labeling of Triton-extracted mycoplasmas with affinity-purified antibodies localized HMW3 to the terminal knob on the rodlike extensions of the triton shell, a location that would correspond to the adherence organelle in whole mycoplasmas. Treatment of triton shells with KI resulted in the selective removal of the adherence-accessory proteins HMW1 to HMW4. Analysis of these triton shells by transmission electron microscopy revealed dramatic ultrastructural changes in the filamentous network and core structure. Immunogold labeling of KI-extracted shells reflected the removal of HMW3 from the disrupted tip structure. An examination of ultrathin sections of wild-type cells by transmission electron microscopy following labeling with HMW3-specific antibodies provided further evidence for the nonrandom distribution of HMW3 and its localization to the terminal portion of filamentous cell extensions. Most colloidal gold molecules were associated with the cell interior, but limited peripheral labeling of the terminal region was also observed. Postfixation antibody labeling of whole cells suggested limited exposure of HMW3 on the mycoplasma surface at the tip structure. However, prefixation antibody labeling failed to indicate surface exposure, raising some uncertainty regarding the relationship of HMW3 with the mycoplasma membrane.

Nucleotide sequence analysis reveals novel features of the phase-variable cytadherence accessory protein HMW3 of Mycoplasma pneumoniae

The Mycoplasma pneumoniae hmw3 gene was sequenced and its gene product was characterized with the goal of elucidating the functional role of HMW3 as an accessory component in cytadherence. A total of 2,016 bp of the hmw3 locus was sequenced, revealing an open reading frame large enough to encode a 672-amino-acid protein with a molecular weight of 73,725. No consensuslike ribosome binding or promoter sequences were identified. However, hmw3 was flanked by upstream and downstream open reading frames. Gene identity was confirmed by comparing the deduced amino acid sequence with the amino acid sequence obtained directly from N-terminal amino acid sequencing of HMW3. Analysis of the deduced amino acid sequence indicated an acidic pI (4.4), an unusual distribution of charged residues, a high degree of hydrophilicity, and a high proline content for HMW3. M. pneumoniae protein profiles obtained by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) following culturing in the presence of [3H]Pro were consistent with the high Pro content predicted for HMW3 and indicated the same for cytadherence accessory protein HMW1. A discrepancy existed between the predicted size of HMW3 (Mr, 73,725) and the size of HMW3 obtained by SDS-PAGE (Mr, 140,000). Variable electrophoretic mobility in SDS-PAGE was observed at different acrylamide concentrations for HMW3, indicating that anomalous migration might account for the size discrepancy. The relative mobility of HMW3 was enhanced only slightly in the presence of magnesium acetate, suggesting that the unusual charge distribution might only be partially responsible for the anomalous migration. Secondary structure predictions were dominated by beta-sheets and nonrepetitive turns or coils, suggesting a probable extended, rigid conformation for HMW3. Finally, an unusual, highly acidic domain (residues 180 to 280) which might have particular functional significance relative to the role of HMW3 as a cytadherence accessory protein was identified.

Juxtaposition of the genes encoding Mycoplasma pneumoniae cytadherence-accessory proteins HMW1 and HMW3

The loss and reacquisition of high-Mr (HMW) proteins, HMW1, 2, 3, 4 and 5, by Mycoplasma pneumoniae correlates with cytadherence phase variation. We are cloning and characterizing the genes encoding HMW1-5 to understand the mechanism regulating their coordinate expression. HMW1 was purified by polyacrylamide-gel electrophoresis. Amino acid (aa) sequence data were obtained from enzymatically generated peptide fragments from HMW1. A degenerate 17-mer probe synthesized based upon the aa sequence of one peptide clearly identified a single 4.75-kb BamHI fragment of M. pneumoniae DNA under stringent hybridization conditions. This fragment was cloned into pUC19 to generate pKV16. Restriction mapping of the 4.75-kb BamHI fragment in pKV16 revealed a possible overlap with the 9.4-kb EcoRI fragment containing the gene encoding protein HMW3. Southern blotting and reciprocal hybridization studies confirmed this overlap, establishing the juxtaposition of the genes encoding HMW1 and HMW3. Finally, physical mapping analysis by probing restriction fragments of M. pneumoniae DNA resolved by pulsed-field gel electrophoresis with the cloned genes encoding HMW1 and HMW3 revealed definitively that the hmw locus maps to a 106.8-kb ApaI fragment, rather than a 117.5-kb ApaI fragment, as had been reported previously for hmw3 [Krause and Mawn, J. Bacteriol. 172 (1990) 4790-4797].

A spectrophotometric analysis of dentinal leakage in the resected root

The purpose of this study was to compare dye leakage in the dentin of resected and nonresected roots. Fifty-four single rooted extracted teeth were used. The two groups were subdivided into young, middle age, and old age samples. Each sample was biomechanically prepared in a standard fashion and obturated using lateral condensation with sealer and gutta-percha. All root surfaces were sealed with nail polish, leaving the apical portion exposed. The apical portion of the roots were placed in 2% methylene blue dye for 72 h, rinsed, and placed in 15 ml of 35% HNO3 for 72 h. The supernatant was analyzed at 640 nm using a visible light spectrophotometer. The amount of leakage was extrapolated from a standard linear regression curve constructed from the stock 2% methylene blue dye solution. The percentage of concentration leakage in all samples ranged from less than 0.0600 to 0.1658. It was concluded that there is a greater amount of leakage in resected versus nonresected extracted teeth. The data also suggest that older teeth exhibit less leakage than younger teeth.

Localization of the Mycoplasma pneumoniae cytadherence-accessory proteins HMW1 and HMW4 in the cytoskeletonlike Triton shell

The location of the cytadherence-accessory high-molecular weight proteins 1 and 4 (HMW1/4) within Mycoplasma pneumoniae cells has been studied by both biochemical and electron microscopic techniques. Peptide mapping studies demonstrated that HMW1/4 share almost identical peptide profiles, suggesting that the two proteins are structurally related. Examination of thin sections of M. pneumoniae with antibodies to HMW1/4 and colloidal gold particles revealed distinct labeling of the filamentous extensions of the mycoplasma cells. Labeling was absent on thin sections of a cytadherence-deficient variant lacking HMW1/4. HMW1/4 partitioned in the detergent-insoluble fraction following Triton X-100 extraction, and analysis by sucrose density gradient centrifugation suggested that HMW1/4 are part of a high-molecular-weight, multiprotein complex. These results were confirmed by immunogold labeling of Triton X-100-extracted M. pneumoniae cells incubated with antibodies to HMW1/4: gold particles bound in specific clusters to detergent-insoluble filaments. Finally, immunogold labeling of whole cells revealed that HMW1/4 are exposed on the cell surface, although to a lesser degree than on the cell interior. These findings indicate that HMW1/4 are membrane proteins associated with the cytoskeletonlike triton shell of M. pneumoniae and localized primarily in the filamentous extensions of the mycoplasma cells.

Cloning and analysis of the gene encoding the cytadherence phase-variable protein HMW3 from Mycoplasma pneumoniae

We have cloned the gene encoding the Mycoplasma pneumoniae cytadherence-accessory protein HMW3 into Escherichia coli to study its phase-variable expression. A truncated HMW3 protein (HMW3'; 113 kDa), identified using HMW3-specific, affinity-purified antibodies, was expressed under the control of the lacZ promoter in lambda gt11. The protein did not react with beta-galactosidase (beta Gal)-specific antibodies, however, indicating that HMW3' was not a beta Gal fusion protein. The direction of transcription was determined by examining gene expression from inserts in opposite orientations with respect to the lacZpo in pUC18 and pUC19, to generate pKV5 and pKV6. Amino acid sequence data were obtained from an enzymatically generated HMW3 peptide fragment and used to create a degenerate 17-mer probe. The degenerate 17-mer hybridized to the mycoplasma DNA insert in pKV6; both the 17-mer and the pKV6 insert hybridized to a 9.4-kb EcoRI fragment from wild-type (wt) M. pneumoniae chromosomal DNA. This EcoRI fragment was cloned from wt M. pneumoniae and an HMW3-deficient variant in both orientations into pUC18. The HMW3'-encoding region was localized to the center of the 9.4-kb EcoRI fragment, and no differences were observed in restriction patterns between the wt and variant. Although the 9.4-kb EcoRI fragment included the DNA segment encoding HMW3', neither this protein, nor derivatives thereof, were detected in IPTG-induced E. coli containing the EcoRI fragment from either wt or variant M. pneumoniae, in either orientation in pUC18.

Disulfide-linked protein associated with Mycoplasma pneumoniae cytadherence phase variation

Wild-type Mycoplasma pneumoniae possessed a protein with a very high molecular weight under nonreducing conditions (greater than 340,000; designated HMW5); this protein was absent from a noncytadhering phase variant lacking HMW1, 2, 3, and 4. When examined by two-dimensional nonreducing-reducing gel electrophoresis, HMW5 dissociated to yield a single polypeptide spot of molecular weight 190,000 that comigrated with cytadherence phase-variable protein HMW2. Extraction of wild-type mycoplasmas with Triton X-100 revealed the exclusive partitioning of HMW5 with the detergent-insoluble cytoskeletonlike triton shell.

Physical analysis and mapping of the Mycoplasma pneumoniae chromosome

Field inversion gel electrophoresis was used for analysis of the chromosome of Mycoplasma pneumoniae. The restriction endonuclease SfiI (5'-GGCCNNNNNGGCC-3') generated 2 M. pneumoniae DNA fragments of approximately 437 and 357.5 kilobase pairs (kbp), whereas 13 restriction fragments ranging in size from 2.4 to 252.0 kbp resulted from digestion with ApaI (5'-GGGCCC-3'). Totaling the sizes of the individual restriction fragments from digestion with SfiI or ApaI yielded a genome size of 794.5 or 775.4 kbp, respectively. A physical map of the M. pneumoniae chromosome was constructed by using a combination of techniques that included analysis by sequential or partial restriction endonuclease digestions and use as hybridization probes of cloned M. pneumoniae DNA containing ApaI sites and hence overlapping adjacent ApaI fragments. Genetic loci for deoC, rrn, hmw3, and the P1 gene were identified by using cloned DNA to probe ApaI restriction fragment profiles.

Cloning and expression in Escherichia coli of Mycoplasma gallisepticum antigens recognized by sera from infected chickens

A clone bank of Mycoplasma gallisepticum (MG) strain A5969 DNA was prepared in the expression vector phage lambda gt11. Approximately 75% of the resulting phages were recombinants, based upon the insertional inactivation of the lacZ gene of the vector. Clones were screened immunologically with serum prepared from specific-pathogen-free white leghorn chickens that had been infected with aerosolized MG. Approximately 250 clones, or less than 1% of the recombinant phage, reacted positively to various degrees with the test serum and failed to react with serum from uninfected specific-pathogen-free control chickens. A single clone was chosen at random for comparison with a vector control by western immunoblot, revealing a polypeptide of 140,000 molecular weight in the clone profile but not the control profile that reacted with immune serum. Clones expressing MG antigens recognized during infection may provide an improved means for antigen preparation for serologic diagnosis of mycoplasmosis.

Nucleotide sequence of the Rickettsia prowazekii ATP/ADP translocase-encoding gene

The Rickettsia prowazekii ATP/ADP translocase (Tlc) gene (tlc), previously cloned in Escherichia coli was localized to a 1.6-kb chromosomal fragment. Nucleotide sequence analysis of this fragment revealed an open reading frame of 1494 bp that could encode a hydrophobic protein of 497 amino acids (aa) with an Mr of 56,668. Analysis of the deduced aa sequence revealed that it contained twelve potential membrane-spanning regions. Comparisons between the deduced aa sequence of the R. prowazekii ATP/ADP Tlc and the sequences of mitochondrial (mt) Tlc revealed no detectable homologies between the rickettsial and mt sequences. The major protein synthesized in E. coli minicells containing the rickettsial gene exhibited and Mr of approx. 34,000.

Interaction of Mycoplasma pneumoniae with HeLa cells

The susceptibility of HeLa cells to Mycoplasma pneumoniae-induced injury was examined. Infections were initiated with relatively low mycoplasma doses, carried out in a culture medium incapable of supporting M. pneumoniae replication in the absence of host cells, and monitored for up to 10 days. Under these conditions, a time- and dose-dependent decline in the number of viable host cells compared with that of uninfected controls was observed. The effect of M. pneumoniae infection on host cell macromolecular synthesis was also evaluated. At high doses of infection, synthesis of both protein and RNA declined rapidly relative to that in control cells. At lower doses there was a biphasic response in protein synthesis, which was substantially lower than that in the uninfected control by day 1 postinfection, returned to control levels by day 4 postinfection, and was again less than that in control cells by day 7 postinfection. In contrast, no transient recovery was observed in RNA synthesis, which declined very gradually over 7 days in infected HeLa cells compared with that in uninfected control cells. The ability of HeLa cells to support the proliferation of M. pneumoniae under these experimental conditions was demonstrated by quantitation of mycoplasma CFU in the nonpermissive medium in the presence or absence of HeLa cells. A negligible increase in the number of M. pneumoniae was observed over 4 days when HeLa cells were absent, while CFU increased by almost 20-fold when M. pneumoniae was cultured in the presence of HeLa cells. The susceptibility and response in macromolecular synthesis in M. pneumoniae-infected HeLa cells differed from that recently described for a nontransformed culture of hamster trachea epithelial cells under the same experimental conditions (Y.-Y. Chen and D.C. Krause, Infect. Immun. 56: 570-576, 1988), underscoring the importance of the choice of host cell for in vitro modeling of M. pneumoniae pathogenesis.

Parasitism of hamster trachea epithelial cells by Mycoplasma pneumoniae

Hamster trachea epithelial (HTE) cells were employed as a model system for Mycoplasma pneumoniae pathogenesis. To more closely mimic natural infection, M. pneumoniae was forced to rely upon host cells (as opposed to the growth medium) for nutrients, and infections were initiated with relatively low mycoplasma doses and monitored for extended time periods. A time- and dose-dependent decline in the viability of infected cells was observed; however, viability never declined below 50% of that in uninfected controls. Protein and RNA synthesis actually increased above control levels in infected cells, despite a concomitant decrease in viability. This response was pronounced at higher multiplicities of infection but was only transient at lower doses. In parallel studies in which a culture medium capable of supporting M. pneumoniae growth was used, loss of viability was accelerated. With a low-dose infection a transient increase followed by a precipitous decline in macromolecular synthesis was observed, relative to that in uninfected controls. At higher doses, however, macromolecular synthesis decreased dramatically and in proportion to the loss of viability. The requirement for HTE cells for mycoplasma growth under the experimental culture conditions was demonstrated by quantitating viable mycoplasmas in the culture medium in the presence or absence of HTE cells over 4 days. The increase in mycoplasma number was negligible in the absence of HTE cells, while a 30-fold increase was observed in the presence of HTE cells. These findings demonstrate the feasibility of long-term, low-dose studies of M. pneumoniae pathogenesis with trachea epithelial cells and a nonpermissive culture medium. This experimental system should facilitate the elucidation of the mechanism(s) responsible for host cell injury, and perhaps reveal how host cells respond to infection.

Nucleotide sequence of the Rickettsia prowazekii citrate synthase gene

The Rickettsia prowazekii citrate synthase (gltA) gene, previously cloned in Escherichia coli, was localized to a 2.0-kilobase chromosomal fragment. DNA sequence analysis of a portion of this fragment revealed an open reading frame of 1,308 base pairs that encodes a protein of 435 amino acids with a molecular weight of 49,171. This translation product is comparable in size to both the E. coli and pig heart citrate synthase monomers and to the protein synthesized in E. coli minicells containing the rickettsial gene. Comparisons between the deduced amino acid sequence of R. prowazekii citrate synthase and those of the E. coli and pig heart enzymes revealed extensive homology (59%) between the two bacterial proteins. In contrast, only 20% of the rickettsial enzyme residues were shared with the functionally similar pig heart enzyme residues. Upstream from the open reading frame and in close proximity to one another, sequences with homology to E. coli consensus sequences for RNA polymerase and ribosome binding were identified. S1 nuclease mapping experiments demonstrated that the start of transcription for this gene in E. coli was located in the upstream region. Codon usage in the rickettsial gltA gene was found to be very biased and differed from the pattern observed in E. coli. Adenine and uracil were used preferentially in the third base position of rickettsial codons.

Inhibition of mycoplasma pneumoniae hemadsorption and adherence to respiratory epithelium by antibodies to a membrane protein

Antiserum and purified immunoglobulin directed against Mycoplasma pneumoniae membrane protein P1 were examined for their influence on mycoplasma viability, metabolism, and cytadsorption. Anti-P1 immunoglobulin inhibited adherence of M. pneumoniae to hamster tracheal rings in vitro by up to 80% and inhibited hemadsorption by greater than 90%. Cytadsorption was also inhibited by anti-P1 Fab fragments. Anti-P1 antibodies had no effect on M. pneumoniae viability or metabolism. The data indicate that anti-P1 antibody obstructs the interaction of M. pneumoniae adhesin P1 with its host receptors.

Hemadsorption and virulence are separable properties of Mycoplasma pneumoniae

A selective enrichment technique was used to isolate a hemadsorption-positive revertant of a hemadsorption-negative mutant strain of Mycoplasma pneumoniae. This hemadsorption-positive revertant was shown to have simultaneously regained both the ability to attach to neuraminidase-sensitive receptors on the tracheal ring respiratory epithelium in vitro and the ability to synthesize three virulent-strain-specific proteins which were not synthesized by the hemadsorption-negative mutant. Despite the persistence of the revertant in hamster lung tissue for 9 to 12 weeks postinfection, no cytopathology was observed. Intranasal inoculation of the revertant provided limited protection against a challenge dose of virulent M. pneumoniae.

Reacquisition of specific proteins confers virulence in Mycoplasma pneumoniae

Hemadsorbing revertants were isolated from spontaneous hemadsorption-negative, avirulent mutants of Mycoplasma pneumoniae. The revertants simultaneously reacquired specific proteins absent in their homologous mutants, along with neuraminidase-sensitive adherence to the respiratory epithelium and virulence. Peptide mapping and immunological analysis indicated no precursor-product relationships among certain of these proteins.

Molecular basis for cytadsorption of Mycoplasma pneumoniae

Hemadsorbing (HA+) virulent Mycoplasma pneumoniae and spontaneously derived nonhemadsorbing (HA-) avirulent mutants were compared by biochemical and ultrastructural techniques in an attempt to understand the molecular basis for cytadsorption. Lactoperoxidase-catalyzed iodination of intact mycoplasmas indicated that both virulent and avirulent mycoplasmas displayed similar surface protein patterns. A specific external protein, P1 (molecular weight, 165,000), previously implicated as a major ligand mediating attachment, was readily detected in HA+ and HA- mycoplasma strains. However, immunoferritin electron microscopy, with monospecific antibody against P1, revealed that differences in P1 topography existed among these strains. Only virulent mycoplasmas exhibited high concentrations of P1 at the terminal organelle. Avirulent mycoplasmas which possessed P1 showed no P1 clustering at the terminus. Both virulent M. pneumoniae and avirulent P1-containing mutants possessed numerous less dense P1 regions along the mycoplasma surface. Not surprisingly, an HA- mutant lacking P1 exhibited only background immunoferritin labeling. Negative staining of intact mycoplasmas revealed a well-defined, naplike terminus (associated with P1 clusters) confined at the tip of virulent M. pneumoniae. Previous characterization of HA+ virulent and HA- avirulent strains of M. pneumoniae by one- and two-dimensional polyacrylamide gel electrophoresis suggests that identified groups of mycoplasma proteins, lacking in specific HA- mycoplasmas, regulate the physical arrangement of P1 and the ultrastructure of the terminus, thus influencing adherence to the respiratory epithelium and virulence.

Mycoplasma pneumoniae proteins that selectively bind to host cells

Mycoplasma pneumoniae proteins that bind to hamster trachea epithelial cells were identified by incubating 125I-labeled, detergent-solubilized mycoplasmas with glutaraldehyde-fixed host cells. Analysis of the bound fraction by gel electrophoresis and autoradiography revealed that proteins P1, P2, and HMW3 (molecular weights, 165,000, 110,000, and 140,000, respectively), previously implicated in attachment, were among the predominant species. Unlabeled mycoplasma preparations competed with the binding of radiolabeled proteins, suggesting the involvement of a limited number of receptor sites on the host cells.

Identification of Mycoplasma pneumoniae proteins associated with hemadsorption and virulence

Twenty-two mutants of Mycoplasma pneumoniae spontaneously deficient in hemadsorption were isolated. Examination of mutant protein profiles by one- and two-dimensional polyacrylamide gel electrophoresis permitted the grouping of these mutants into four classes. The largest class of mutants was deficient in four high-molecular-weight proteins (215,000, 210,000, 190,000, and 140,000). A second class of mutants lacked three proteins previously designated A, B, and C (72,000, 85,000, and 37,000, respectively). A single mutant, in addition to lacking proteins A, B, and C, was missing a fourth protein of 165,000 molecular weight. The remaining mutants exhibited protein profiles apparently identical to that of the wild-type strain. All mutant strains attached to the respiratory epithelium of hamster tracheal rings in vitro at reduced levels; however, mutants lacking proteins A, B, and C recognized only neuraminidase-insensitive receptors. None of the mutants tested produced detectable pneumonia in intranasally inoculated hamsters, although one mutant class demonstrated low-level survival in vivo.

Magnetic Polarity of Pillow Basalts from Reykjanes Ridge

A first attempt to measure directly the magnetic polarity of submarine basalts dredged from the Reykjanes Ridge indicates that the first two magnetic anomalies over the ridge resulted from a reversal of the earth's magnetic field. Volcanic criteria were used to determine the orientation the samples had before they were dredged from the sea floor.

Guinea Fracture Zone in the Equatorial Atlantic

The east-west Guinea fracture zone is situated off Sierra Leone, West Africa. The estimated topographic left lateral displacement is about 230 kilometers. This fracture zone is the eastern analog of the Vema fracture zone, with its associated troughs, and of the Barracuda Fault. The Guinea fracture zone marks the northern boundary on the African coast of a wide zone of left lateral shear in the equatorial Atlantic.