Observation of a single protein by ultrafast X-ray diffraction

The idea of using ultrashort X-ray pulses to obtain images of single proteins frozen in time has fascinated and inspired many. It was one of the arguments for building X-ray free-electron lasers. According to theory, the extremely intense pulses provide sufficient signal to dispense with using crystals as an amplifier, and the ultrashort pulse duration permits capturing the diffraction data before the sample inevitably explodes. This was first demonstrated on biological samples a decade ago on the giant mimivirus. Since then, a large collaboration has been pushing the limit of the smallest sample that can be imaged. The ability to capture snapshots on the timescale of atomic vibrations, while keeping the sample at room temperature, may allow probing the entire conformational phase space of macromolecules. Here we show the first observation of an X-ray diffraction pattern from a single protein, that of Escherichia coli GroEL which at 14 nm in diameter is the smallest biological sample ever imaged by X-rays, and demonstrate that the concept of diffraction before destruction extends to single proteins. From the pattern, it is possible to determine the approximate orientation of the protein. Our experiment demonstrates the feasibility of ultrafast imaging of single proteins, opening the way to single-molecule time-resolved studies on the femtosecond timescale.

Structural Analysis of Strigolactone-Related Gene Products

Structural knowledge of biological macromolecules is essential for understanding their function and for modifying that function by engineering. Protein crystallography is a powerful method for elucidating molecular structures of proteins, but it is essential that the investigator has a basic knowledge of good practices and of the major pitfalls in the technique. Here we describe issues specific for the case of structural studies of strigolactone (SL) receptor structure and function, and in particular the difficulties associated with capturing complexes of SL receptors with the SL hormone ligand in the crystal.

Inactivation of bacterial endospores on surfaces by plasma processed air

AIMS

In case of biological hazards and pandemics, personal protective equipment of rescue forces is currently manually decontaminated with harmful disinfectants, primarily peracetic acid. To overcome current drawbacks regarding supply, handling and disposal of chemicals, the use of plasma processed air (PPA) represents a promising alternative for surface decontamination on site. In this study, the sporicidal efficiency of a portable plasma system, designed for field applications, was evaluated.

METHODS AND RESULTS

The developed plasma device is based on a dielectric barrier discharge (DBD) and operated with ambient air as process gas. PPA from the plasma nozzle was flushed into a treatment chamber (volume: 300 l) and bacterial endospores (Bacillus subtilis and Bacillus atrophaeus) dried on different surfaces were treated under variable conditions. Reductions in spores by more than 4 log₁₀ were found within 3 min of PPA exposure. However, the presence of endospores in agglomerates or in an organic matrix as well as the complexity of the respective surface microstructure negatively affected the inactivation efficiency. When endospores were embedded in a dried protein matrix, mechanical wiping with swabs during exposure to PPA increased the inactivation effect significantly. Gaseous ozone alone did not provide a sporicidal effect. Significant spore inactivation was only obtained when water vapour was injected into the PPA stream.

CONCLUSION

The results show that endospores dried on surfaces can be reduced by several orders of magnitude within few minutes in a treatment chamber which is flushed with PPA from of a DBD plasma nozzle.

SIGNIFICANCE AND IMPACT OF THE STUDY

Plasma processed air generated on site by DBD plasma nozzles could be a suitable alternative for the disinfection of various surfaces in closed rooms.

Structure and mechanism of piperideine-6-carboxylate dehydrogenase from Streptomyces clavuligerus

The core of β-lactam antibiotics originates from amino acids of primary metabolism in certain microorganisms. β-Lactam-producing bacteria, including Streptomyces clavuligerus, synthesize the precursor of the amino acid α-aminoadipic acid by the catabolism of lysine in two steps. The second reaction, the oxidation of piperideine-6-carboxylate (or its open-chain form α-aminoadipate semialdehyde) to α-aminoadipic acid, is catalysed by the NAD⁺-dependent enzyme piperideine-6-carboxylate dehydrogenase (P6CDH). This structural study, focused on ligand binding and catalysis, presents structures of P6CDH from S. clavuligerus in its apo form and in complexes with the cofactor NAD⁺, the product α-aminoadipic acid and a substrate analogue, picolinic acid. P6CDH adopts the common aldehyde dehydrogenase fold, consisting of NAD-binding, catalytic and oligomerization domains. The product binds in the oxyanion hole, close to the catalytic residue Cys299. Clear density is observed for the entire cofactor, including the nicotinamide riboside, in the binary complex. NAD⁺ binds in an extended conformation with its nicotinamide ring overlapping with the binding site of the carboxylate group of the product, implying that the conformation of the cofactor may change during catalysis. The binding site of the substrate analogue overlaps with that of the product, suggesting that the cyclic form of the substrate, piperideine-6-carboxylate, may be accepted as a substrate by the enzyme. The catalytic mechanism and the roles of individual residues are discussed in light of these results.

Erratum: Experimental strategies for imaging bioparticles with femtosecond hard X-ray pulses. Corrigendum

[This corrects the article DOI: 10.1107/S2052252517003591.].

Electrospray sample injection for single-particle imaging with x-ray lasers

The possibility of imaging single proteins constitutes an exciting challenge for x-ray lasers. Despite encouraging results on large particles, imaging small particles has proven to be difficult for two reasons: not quite high enough pulse intensity from currently available x-ray lasers and, as we demonstrate here, contamination of the aerosolized molecules by nonvolatile contaminants in the solution. The amount of contamination on the sample depends on the initial droplet size during aerosolization. Here, we show that, with our electrospray injector, we can decrease the size of aerosol droplets and demonstrate virtually contaminant-free sample delivery of organelles, small virions, and proteins. The results presented here, together with the increased performance of next-generation x-ray lasers, constitute an important stepping stone toward the ultimate goal of protein structure determination from imaging at room temperature and high temporal resolution.

Considerations for three-dimensional image reconstruction from experimental data in coherent diffractive imaging

Diffraction before destruction using X-ray free-electron lasers (XFELs) has the potential to determine radiation-damage-free structures without the need for crystallization. This article presents the three-dimensional reconstruction of the Melbournevirus from single-particle X-ray diffraction patterns collected at the LINAC Coherent Light Source (LCLS) as well as reconstructions from simulated data exploring the consequences of different kinds of experimental sources of noise. The reconstruction from experimental data suffers from a strong artifact in the center of the particle. This could be reproduced with simulated data by adding experimental background to the diffraction patterns. In those simulations, the relative density of the artifact increases linearly with background strength. This suggests that the artifact originates from the Fourier transform of the relatively flat background, concentrating all power in a central feature of limited extent. We support these findings by significantly reducing the artifact through background removal before the phase-retrieval step. Large amounts of blurring in the diffraction patterns were also found to introduce diffuse artifacts, which could easily be mistaken as biologically relevant features. Other sources of noise such as sample heterogeneity and variation of pulse energy did not significantly degrade the quality of the reconstructions. Larger data volumes, made possible by the recent inauguration of high repetition-rate XFELs, allow for increased signal-to-background ratio and provide a way to minimize these artifacts. The anticipated development of three-dimensional Fourier-volume-assembly algorithms which are background aware is an alternative and complementary solution, which maximizes the use of data.

The elusive ligand complexes of the DWARF14 strigolactone receptor

Strigolactones, a group of terpenoid lactones, control many aspects of plant growth and development, but the active forms of these plant hormones and their mode of action at the molecular level are still unknown. The strigolactone protein receptor is unusual because it has been shown to cleave the hormone and supposedly forms a covalent bond with the cleaved hormone fragment. This interaction is suggested to induce a conformational change in the receptor that primes it for subsequent interaction with partners in the signalling pathway. Substantial efforts have been invested into describing the interaction of synthetic strigolactone analogues with the receptor, resulting in a number of crystal structures. This investigation combines a re-evaluation of models in the Protein Data Bank with a search for new conditions that may permit the capture of a receptor-ligand complex. While weak difference density is frequently observed in the binding cavity, possibly due to a low-occupancy compound, the models often contain features not supported by the X-ray data. Thus, at this stage, we do not believe that any detailed deductions about the nature, conformation, or binding mode of the ligand can be made with any confidence.

Structure of Rubisco from Arabidopsis thaliana in complex with 2-carboxyarabinitol-1,5-bisphosphate

The crystal structure of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) from Arabidopsis thaliana is reported at 1.5 Å resolution. In light of the importance of A. thaliana as a model organism for understanding higher plant biology, and the pivotal role of Rubisco in photosynthetic carbon assimilation, there has been a notable absence of an A. thaliana Rubisco crystal structure. A. thaliana Rubisco is an L8S8 hexadecamer comprising eight plastome-encoded catalytic large (L) subunits and eight nuclear-encoded small (S) subunits. A. thaliana produces four distinct small-subunit isoforms (RbcS1A, RbcS1B, RbcS2B and RbcS3B), and this crystal structure provides a snapshot of A. thaliana Rubisco containing the low-abundance RbcS3B small-subunit isoform. Crystals were obtained in the presence of the transition-state analogue 2-carboxy-D-arabinitol-1,5-bisphosphate. A. thaliana Rubisco shares the overall fold characteristic of higher plant Rubiscos, but exhibits an interesting disparity between sequence and structural relatedness to other Rubisco isoforms. These results provide the structural framework to understand A. thaliana Rubisco and the potential catalytic differences that could be conferred by alternative A. thaliana Rubisco small-subunit isoforms.

Crystal structures of β-carboxysome shell protein CcmP: ligand binding correlates with the closed or open central pore

Cyanobacterial CO2 fixation is promoted by encapsulating and co-localizing the CO2-fixing enzymes within a protein shell, the carboxysome. A key feature of the carboxysome is its ability to control selectively the flux of metabolites in and out of the shell. The β-carboxysome shell protein CcmP has been shown to form a double layer of pseudohexamers with a relatively large central pore (~13 Å diameter), which may allow passage of larger metabolites such as the substrate for CO2 fixation, ribulose 1,5-bisphosphate, through the shell. Here we describe two crystal structures, at 1.45 Å and 1.65 Å resolution, of CcmP from Synechococcus elongatus PCC7942 (SeCcmP). The central pore of CcmP is open or closed at its ends, depending on the conformation of two conserved residues, Glu69 and Arg70. The presence of glycerol resulted in a pore that is open at one end and closed at the opposite end. When glycerol was omitted, both ends of the barrel became closed. A binding pocket at the interior of the barrel featured residual density with distinct differences in size and shape depending on the conformation, open or closed, of the central pore of SeCcmP, suggestive of a metabolite-driven mechanism for the gating of the pore.

Experimental strategies for imaging bioparticles with femtosecond hard X-ray pulses

This study explores the capabilities of the Coherent X-ray Imaging Instrument at the Linac Coherent Light Source to image small biological samples. The weak signal from small samples puts a significant demand on the experiment. Aerosolized Omono River virus particles of ∼40 nm in diameter were injected into the submicrometre X-ray focus at a reduced pressure. Diffraction patterns were recorded on two area detectors. The statistical nature of the measurements from many individual particles provided information about the intensity profile of the X-ray beam, phase variations in the wavefront and the size distribution of the injected particles. The results point to a wider than expected size distribution (from ∼35 to ∼300 nm in diameter). This is likely to be owing to nonvolatile contaminants from larger droplets during aerosolization and droplet evaporation. The results suggest that the concentration of nonvolatile contaminants and the ratio between the volumes of the initial droplet and the sample particles is critical in such studies. The maximum beam intensity in the focus was found to be 1.9 × 10¹² photons per µm² per pulse. The full-width of the focus at half-maximum was estimated to be 500 nm (assuming 20% beamline transmission), and this width is larger than expected. Under these conditions, the diffraction signal from a sample-sized particle remained above the average background to a resolution of 4.25 nm. The results suggest that reducing the size of the initial droplets during aerosolization is necessary to bring small particles into the scope of detailed structural studies with X-ray lasers.

Open data set of live cyanobacterial cells imaged using an X-ray laser

Structural studies on living cells by conventional methods are limited to low resolution because radiation damage kills cells long before the necessary dose for high resolution can be delivered. X-ray free-electron lasers circumvent this problem by outrunning key damage processes with an ultra-short and extremely bright coherent X-ray pulse. Diffraction-before-destruction experiments provide high-resolution data from cells that are alive when the femtosecond X-ray pulse traverses the sample. This paper presents two data sets from micron-sized cyanobacteria obtained at the Linac Coherent Light Source, containing a total of 199,000 diffraction patterns. Utilizing this type of diffraction data will require the development of new analysis methods and algorithms for studying structure and structural variability in large populations of cells and to create abstract models. Such studies will allow us to understand living cells and populations of cells in new ways. New X-ray lasers, like the European XFEL, will produce billions of pulses per day, and could open new areas in structural sciences.

A data set from flash X-ray imaging of carboxysomes

Ultra-intense femtosecond X-ray pulses from X-ray lasers permit structural studies on single particles and biomolecules without crystals. We present a large data set on inherently heterogeneous, polyhedral carboxysome particles. Carboxysomes are cell organelles that vary in size and facilitate up to 40% of Earth's carbon fixation by cyanobacteria and certain proteobacteria. Variation in size hinders crystallization. Carboxysomes appear icosahedral in the electron microscope. A protein shell encapsulates a large number of Rubisco molecules in paracrystalline arrays inside the organelle. We used carboxysomes with a mean diameter of 115±26 nm from Halothiobacillus neapolitanus. A new aerosol sample-injector allowed us to record 70,000 low-noise diffraction patterns in 12 min. Every diffraction pattern is a unique structure measurement and high-throughput imaging allows sampling the space of structural variability. The different structures can be separated and phased directly from the diffraction data and open a way for accurate, high-throughput studies on structures and structural heterogeneity in biology and elsewhere.

Structure of Arabidopsis thaliana Rubisco activase

The CO2-fixing enzyme ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) is inactivated by the formation of dead-end complexes with inhibitory sugar phosphates. In plants and green algae, the ATP-dependent motor protein Rubisco activase restores catalytic competence by facilitating conformational changes in Rubisco that promote the release of the inhibitory compounds from the active site. Here, the crystal structure of Rubisco activase from Arabidopsis thaliana is presented at 2.9 Å resolution. The structure reveals an AAA+ two-domain structure. More than 100 residues in the protein were not visible in the electron-density map owing to conformational disorder, but were verified to be present in the crystal by mass spectrometry. Two sulfate ions were found in the structure. One was bound in the loop formed by the Walker A motif at the interface of the domains. A second sulfate ion was bound at the N-terminal end of the first helix of the C-terminal domain. The protein packs in a helical fashion in the crystal, as observed previously for Rubisco activase, but differences in the helical pitch indicate flexibility in the packing of the protein.

Imaging single cells in a beam of live cyanobacteria with an X-ray laser

There exists a conspicuous gap of knowledge about the organization of life at mesoscopic levels. Ultra-fast coherent diffractive imaging with X-ray free-electron lasers can probe structures at the relevant length scales and may reach sub-nanometer resolution on micron-sized living cells. Here we show that we can introduce a beam of aerosolised cyanobacteria into the focus of the Linac Coherent Light Source and record diffraction patterns from individual living cells at very low noise levels and at high hit ratios. We obtain two-dimensional projection images directly from the diffraction patterns, and present the results as synthetic X-ray Nomarski images calculated from the complex-valued reconstructions. We further demonstrate that it is possible to record diffraction data to nanometer resolution on live cells with X-ray lasers. Extension to sub-nanometer resolution is within reach, although improvements in pulse parameters and X-ray area detectors will be necessary to unlock this potential.

Explosion dynamics of sucrose nanospheres monitored by time of flight spectrometry and coherent diffractive imaging at the split-and-delay beam line of the FLASH soft X-ray laser

We use a Mach-Zehnder type autocorrelator to split and delay XUV pulses from the FLASH soft X-ray laser for triggering and subsequently probing the explosion of aerosolised sugar balls. FLASH was running at 182 eV photon energy with pulses of 70 fs duration. The delay between the pump-probe pulses was varied between zero and 5 ps, and the pulses were focused to reach peak intensities above 10¹⁶W/cm² with an off-axis parabola. The direct pulse triggered the explosion of single aerosolised sucrose nano-particles, while the delayed pulse probed the exploding structure. The ejected ions were measured by ion time of flight spectrometry, and the particle sizes were measured by coherent diffractive imaging. The results show that sucrose particles of 560-1000 nm diameter retain their size for about 500 fs following the first exposure. Significant sample expansion happens between 500 fs and 1 ps. We present simulations to support these observations.

Structure of the homodimeric glycine decarboxylase P-protein from Synechocystis sp. PCC 6803 suggests a mechanism for redox regulation

Glycine decarboxylase, or P-protein, is a pyridoxal 5'-phosphate (PLP)-dependent enzyme in one-carbon metabolism of all organisms, in the glycine and serine catabolism of vertebrates, and in the photorespiratory pathway of oxygenic phototrophs. P-protein from the cyanobacterium Synechocystis sp. PCC 6803 is an α2 homodimer with high homology to eukaryotic P-proteins. The crystal structure of the apoenzyme shows the C terminus locked in a closed conformation by a disulfide bond between Cys(972) in the C terminus and Cys(353) located in the active site. The presence of the disulfide bridge isolates the active site from solvent and hinders the binding of PLP and glycine in the active site. Variants produced by substitution of Cys(972) and Cys(353) by Ser using site-directed mutagenesis have distinctly lower specific activities, supporting the crucial role of these highly conserved redox-sensitive amino acid residues for P-protein activity. Reduction of the 353-972 disulfide releases the C terminus and allows access to the active site. PLP and the substrate glycine bind in the active site of this reduced enzyme and appear to cause further conformational changes involving a flexible surface loop. The observation of the disulfide bond that acts to stabilize the closed form suggests a molecular mechanism for the redox-dependent activation of glycine decarboxylase observed earlier.

Crystallization and preliminary X-ray diffraction analyses of the homodimeric glycine decarboxylase (P-protein) from the cyanobacterium Synechocystis sp. PCC 6803

Glycine decarboxylase, or P-protein, is a major enzyme that is involved in the C(1) metabolism of all organisms and in the photorespiratory pathway of plants and cyanobacteria. The protein from Synechocystis sp. PCC 6803 is a homodimer with a mass of 215 kDa. Recombinant glycine decarboxylase was expressed in Escherichia coli and purified by metal-affinity, ion-exchange and gel-filtration chromatography. Crystals of P-protein that diffracted to a resolution of 2.1 A were obtained using the hanging-drop vapour-diffusion method at 291 K. X-ray diffraction data were collected from cryocooled crystals using synchrotron radiation. The crystals belonged to space group P2(1)2(1)2(1), with unit-cell parameters a = 96.30, b = 135.81, c = 179.08 A.

Alternative splicing produces an H-protein with better substrate properties for the P-protein of glycine decarboxylase

Several thousand plant genes are known to produce multiple transcripts, but the precise function of most of the alternatively encoded proteins is not known. Alternative splicing has been reported for the H-protein subunit of glycine decarboxylase in the genus Flaveria. H-protein has no catalytic activity itself but is a substrate of the three enzymatically active subunits, P-, T- and L-protein. In C(4) species of Flaveria, two H-proteins originate from single genes in an organ-dependent manner. Here, we report on differences between the two alternative H-protein variants with respect to their interaction with the glycine-decarboxylating subunit, P-protein. Steady-state kinetic analyses of the alternative Flaveria H-proteins and artificially produced 'alternative' Arabidopsis H-proteins, using either pea mitochondrial matrix extracts or recombinant cyanobacterial P-protein, consistently demonstrate that the alternative insertion of two alanine residues at the N-terminus of the H-protein elevates the activity of P-protein by 20%in vitro, and could promote glycine decarboxylase activity in vivo.

Properties of recombinant glycine decarboxylase P- and H-protein subunits from the cyanobacterium Synechocystis sp. strain PCC 6803

The multi-enzyme complex glycine decarboxylase is important for one-carbon metabolism, essential for the photorespiratory glycolate cycle of plants, and comprises four different polypeptides, P-, H-, T-, and L-protein. We report on the production and properties of recombinant P-protein from the cyanobacterium Synechocystis and also describe features of recombinant H-protein from the same organism. The P-protein shows enzymatic activity with lipoylated H-protein and very low activity with H-apoprotein or lipoate as artificial cofactors. Its affinity towards glycine is unaffected by the presence and nature of the methyleneamine acceptor molecule. The cyanobacterial H-protein apparently forms stable dimers.

The plant-like C2 glycolate cycle and the bacterial-like glycerate pathway cooperate in phosphoglycolate metabolism in cyanobacteria

The occurrence of a photorespiratory 2-phosphoglycolate metabolism in cyanobacteria is not clear. In the genome of the cyanobacterium Synechocystis sp. strain PCC 6803, we have identified open reading frames encoding enzymes homologous to those forming the plant-like C2 cycle and the bacterial-type glycerate pathway. To study the route and importance of 2-phosphoglycolate metabolism, the identified genes were systematically inactivated by mutagenesis. With a few exceptions, most of these genes could be inactivated without leading to a high-CO(2)-requiring phenotype. Biochemical characterization of recombinant proteins verified that Synechocystis harbors an active serine hydroxymethyltransferase, and, contrary to higher plants, expresses a glycolate dehydrogenase instead of an oxidase to convert glycolate to glyoxylate. The mutation of this enzymatic step, located prior to the branching of phosphoglycolate metabolism into the plant-like C2 cycle and the bacterial-like glycerate pathway, resulted in glycolate accumulation and a growth depression already at high CO(2). Similar growth inhibitions were found for a single mutant in the plant-type C2 cycle and more pronounced for a double mutant affected in both the C2 cycle and the glycerate pathway after cultivation at low CO(2). These results suggested that cyanobacteria metabolize phosphoglycolate by the cooperative action of the C2 cycle and the glycerate pathway. When exposed to low CO(2), glycine decarboxylase knockout mutants accumulated far more glycine and lysine than wild-type cells or mutants with inactivated glycerate pathway. This finding and the growth data imply a dominant, although not exclusive, role of the C2 route in cyanobacterial phosphoglycolate metabolism.

Detection of a Phage Genome Carrying a Zonula Occludens like Toxin Gene (zot) in clinical isolates of Stenotrophomonas maltophilia

During a study of the genetic diversity of Stenotrophomonas strains, we found an autonomous replicating DNA molecule in chromosomal DNA preparations of the clinical Stenotrophomonas maltophilia strain c5. The entire sequence of 6,907 bp of the isolated DNA molecule was determined, which was called phiSMA9. Seven ORFs, which code for proteins with considerable similarity to proteins in databases, were identified in the DNA sequence. The largest ORF shows high sequence similarities to the pI protein of the filamentous phage phiLf, which was later shown to be identical to toxin Zot of Vibrio cholerae. Beside the Zot-like protein, six other proteins with similarities to known phage proteins such as a phage replication protein RstA and phage absorption or coat protein are encoded on phiSMA9, which indicate that this circular DNA molecule represents the replicative form of a linear phage genome. A PCR-based screening showed that only five from the totally investigated 47 Stenotrophomonas strains of clinical and environmental origin harbor these genes. Altogether, we describe the first genome of a phage for the nosocomial pathogen Stenotrophomonas, which contains a Zot toxin like gene and might be regarded as the first Stenotrophomonas virulence factor.

A molecular biological protocol to distinguish potentially human pathogenic Stenotrophomonas maltophilia from plant-associated Stenotrophomonas rhizophila

In recent years, the importance of the Gram-negative bacterium Stenotrophomonas as an opportunistic pathogen as well as in biotechnology has increased. The aim of the present study was to develop new methods for distinguishing between strains closely related to the potentially human pathogenic Stenotrophomonas maltophilia and those closely related to the plant-associated Stenotrophomonas rhizophila. To accomplish this, 58 strains were characterized by 16S rDNA sequencing and amplified ribosomal DNA restriction analysis (ARDRA), and the occurrence of specific functional genes. Based on 16S rDNA sequences, an ARDRA protocol was developed which allowed differentiation between strains of the S. maltophilia and the S. rhizophila group. As it was known that only salt-treated cells of S. rhizophila were able to synthesize the compatible solute glucosylglycerol (GG), the ggpS gene responsible for GG synthesis was used for differentiation between both species and it was confirmed that it only occurred in S. rhizophila strains. As a further genetic marker the smeD gene, which is part of the genes coding for the multidrug efflux pump SmeDEF from S. maltophilia, was used. Based on the results we propose a combination of fingerprinting techniques using the 16S rDNA and the functional genes ggpS and smeD to distinguish both Stenotrophomonas species.

Analysis of developmentally regulated genes of the parasite Haemonchus contortus

Differential regulation of gene expression in the development of Haemonchus contortus was analysed using RNA arbitrarily-primed PCR. A study of third-stage larval and adult H. contortus revealed large differences between the two stages; 32 and 30% unique third-stage larval and adult RNA arbitrarily-primed PCR products, respectively. This finding is consistent with a high degree of differential gene expression between these developmental stages. A number of adult products were sequenced, revealing 11 molecules to be similar to deposits within sequence databases. Four other molecules that did not have significant similarity to sequences in the databases may represent developmentally regulated genes specific to H. contortus. Northern analysis of the putative adult-expressed molecules with homologues in the databases confirmed that four were expressed only in adults, while four were expressed in both stages, but had different sized transcripts. This may reflect differential splicing, or expression of closely related but different molecules at different life cycle stages. Two molecules were present in mRNA populations from both stages, suggesting these were false stage-associated molecules. No transcript was detected for one molecule by Northern analysis, probably due to low level of expression. In situ hybridisation analysis was used to localise expression of transcripts in the adult parasite, in particular, to gain some insight into the nature of those molecules with no known predicted function.

Detection of ileal symbiont intracellularis in porcine faecal samples by polymerase chain reaction

Ileal Symbiont Intracellularis (ISI), the organism causing proliferative enteritis (PE) in pigs was detected in faeces by the application of polymerase chain reaction (PCR). The assay based on a 319 base pair DNA fragment was used on faecal and mucosal samples derived from pigs either affected or unaffected with PE. As few as 10(3) ISI could be detected in pig faeces spiked with ISI. No amplification product was detected in the faeces of unaffected pigs but faeces of confirmed clinical cases were positive. This method offers an accurate, sensitive, easy to perform alternative to monoclonal antibody tests or histological examination post-mortem for the presence of ISI in pig herds.

The prevalence of F107 fimbriae and their association with Shiga-like toxin II in Escherichia coli strains from weaned Australian pigs

A total of 480 haemolytic Escherichia coli (HEC) strains from weaned pigs were tested using an oligonucleotide probe to determine the prevalence of F107 fimbriae in Australia. Of these, 62% were positive. F107 was detected in serogroups O141, O138, O8, O45, O139, O157 and O98 but not in O149 nor O147. 81% of E. coli strains not producing other fimbriae (K88, 987P, K99 or F41) were positive for F107; 5% of strains with K88 fimbriae also had F107. Serological investigation of the expression of F107 fimbriae indicated that serogroups O141, O138, O8, O45 and O157 produced variant F107ac. Variant F107ab was found on O139 strains only. The F107 fimbrial subunits of both variants had a molecular weight of approximately 16 kDa. A total of 350 of the HEC strains were tested to determine the prevalence of the Shiga-like toxin II (SLT II) gene. 29.0% of these strains were positive. SLT II was detected in serogroups O141, O138, O149, O98, O45, O8 and O157 but not in O139. 25% of these strains were positive for both F107 and SLT II.

Plasma renin activity and sleep-wake structure of narcoleptic patients and control subjects under continuous bedrest

In order to determine if renin release would be affected by a dysfunction of the circadian and ultradian organization of sleep, 24-hour profiles of plasma renin activity (PRA) concomitant with sleep stages were established in 10 normal subjects and nine narcoleptic patients, with 10-minute blood sampling intervals. Mean PRA levels were similar in control subjects and narcoleptic patients. Individual 24-hour profiles revealed that the previously described association between renin oscillations and sleep stage alternations was preserved. Increased PRA release was observed during the transition from rapid eye movement (REM) sleep or waking periods to nonrapid eye movement (NREM) sleep, and REM sleep occurred as PRA levels were decreasing. Thus, PRA curves exactly reflected the irregularities and disturbances in the sleep structure of the narcoleptic patients. The 24-hour PRA profiles of the patients did not show the general upward trend during nighttime sleep, which is probably induced in the control subjects by the repetitive recurrence of longer episodes of undisturbed NREM sleep. Because of marked sleep fragmentation in the patients, the duration of NREM sleep was often insufficient to allow for the occurrence of a significant PRA increase. Because sleep onset REM (SOREM) episodes, characteristic of narcolepsy, are not preceded by NREM sleep and its associated increase in PRA, no relative PRA decline occurred during this type of REM sleep. In conclusion, the 24-hour PRA profiles of the narcoleptic patients reflected exactly their sleep stage distribution, confirming previous findings that PRA oscillations appear to be inseparable from the NREM-REM sleep cycle.(ABSTRACT TRUNCATED AT 250 WORDS)

Detection of enterotoxigenic Escherichia coli in piggeries in Victoria by DNA hybridisation using K88, K99, LT, ST1 and ST2 probes

Rectal swabs collected from piglets with diarrhoea from commercial pig farms were examined for the presence of enterotoxigenic Escherichia coli (ETEC) using DNA hybridisation methods. The probes specifically detected genes for the K88 and K99 fimbrial antigens and the heat-labile and heat-stable enterotoxins. DNA hybridisation methods detected more ETEC than could be detected by either enzyme-linked immunosorbent assay (ELISA) or slide agglutination methods, and also offered the opportunity to test for fimbrial antigens and toxins concurrently. The DNA hybridization method was shown to be applicable to ETEC detection in mixed growths cultured directly from rectal swabs to filters. The method eliminates the need for toxin tests using animals and enables very large numbers of samples to be investigated. The use of toxin probes has revealed large numbers of ETEC with uncharacterized fimbrial antigens.

Prolonged neuromuscular blockade associated with trimethaphan: a case report

A case of prolonged neuromuscular blockade associated with the administration of trimethaphan to a neurosurgical patient aged 29 is believed to be the possible result of interaction between trimethaphan, a ganglionic-blocking drug, and muscle relaxant. This possibility should be kept in mind when the administration of trimethaphan is being considered.