Expected resolution limits of x-ray free-electron laser single-particle imaging for realistic source and detector properties

The unprecedented intensity of x-ray free-electron laser sources has enabled single-particle x-ray diffraction imaging (SPI) of various biological specimens in both two-dimensional projection and three dimensions (3D). The potential of studying protein dynamics in their native conditions, without crystallization or chemical staining, has encouraged researchers to aim for increasingly higher resolutions with this technique. The currently achievable resolution of SPI is limited to the sub-10 nanometer range, mainly due to background effects, such as instrumental noise and parasitic scattering from the carrier gas used for sample delivery. Recent theoretical studies have quantified the effects of x-ray pulse parameters, as well as the required number of diffraction patterns to achieve a certain resolution, in a 3D reconstruction, although the effects of detector noise and the random particle orientation in each diffraction snapshot were not taken into account. In this work, we show these shortcomings and address limitations on achievable image resolution imposed by the adaptive gain integrating pixel detector noise.

Time-Resolved XUV Opacity Measurements of Warm Dense Aluminum

The free-free opacity in plasmas is fundamental to our understanding of energy transport in stellar interiors and for inertial confinement fusion research. However, theoretical predictions in the challenging dense plasma regime are conflicting and there is a dearth of accurate experimental data to allow for direct model validation. Here we present time-resolved transmission measurements in solid-density Al heated by an XUV free-electron laser. We use a novel functional optimization approach to extract the temperature-dependent absorption coefficient directly from an oversampled pool of single-shot measurements, and find a pronounced enhancement of the opacity as the plasma is heated to temperatures of order of the Fermi energy. Plasma heating and opacity enhancement are observed on ultrafast timescales, within the duration of the femtosecond XUV pulse. We attribute further rises in the opacity on ps timescales to melt and the formation of warm dense matter.

A versatile liquid-jet setup for the European XFEL

The SPB/SFX instrument of the European XFEL provides unique possibilities for high-throughput serial femtosecond crystallography. This publication presents the liquid-jet sample delivery setup of this instrument. The setup is compatible with state-of-the-art gas dynamic virtual nozzle systems as well as high-viscosity extruders and provides space and flexibility for other liquid injection devices and future upgrades. The liquid jets are confined in a differentially pumped catcher assembly and can be replaced within a couple of minutes through a load-lock. A two-microscope imaging system allows visual control of the jets from two perspectives.

EXPERIMENTAL AND MONTE CARLO INVESTIGATIONS OF BCF-12 SMALL‑AREA PLASTIC SCINTILLATION DETECTORS FOR NEUTRON PINHOLE CAMERA

Plastic organic scintillators such as the blue-emitting BCF-12 are versatile and inexpensive tools. Recently, BCF-12 scintillators have been foreseen for investigation of the spatial distribution of neutrons emitted from dense magnetized plasma. For this purpose, small-area (5 mm × 5 mm) detectors based on BCF-12 scintillation rods and Hamamatsu photomultiplier tubes were designed and constructed at the Institute of Nuclear Physics. They will be located inside the neutron pinhole camera of the PF-24 plasma focus device. Two different geometrical layouts and approaches to the construction of the scintillation element were tested. The aim of this work was to determine the efficiency of the detectors. For this purpose, the experimental investigations using a neutron generator and a Pu-Be source were combined with Monte Carlo computations using the Geant4 code.

Phillips-Tikhonov regularization with a priori information for neutron emission tomographic reconstruction on Joint European Torus

A method of tomographic reconstruction of the neutron emissivity in the poloidal cross section of the Joint European Torus (JET, Culham, UK) tokamak was developed. Due to very limited data set (two projection angles, 19 lines of sight only) provided by the neutron emission profile monitor (KN3 neutron camera), the reconstruction is an ill-posed inverse problem. The aim of this work consists in making a contribution to the development of reliable plasma tomography reconstruction methods that could be routinely used at JET tokamak. The proposed method is based on Phillips-Tikhonov regularization and incorporates a priori knowledge of the shape of normalized neutron emissivity profile. For the purpose of the optimal selection of the regularization parameters, the shape of normalized neutron emissivity profile is approximated by the shape of normalized electron density profile measured by LIDAR or high resolution Thomson scattering JET diagnostics. In contrast with some previously developed methods of ill-posed plasma tomography reconstruction problem, the developed algorithms do not include any post-processing of the obtained solution and the physical constrains on the solution are imposed during the regularization process. The accuracy of the method is at first evaluated by several tests with synthetic data based on various plasma neutron emissivity models (phantoms). Then, the method is applied to the neutron emissivity reconstruction for JET D plasma discharge #85100. It is demonstrated that this method shows good performance and reliability and it can be routinely used for plasma neutron emissivity reconstruction on JET.

Human lymphocytic B-leukemia cell line treatment with the bacterial toxin listeriolysin O and rituximab (anti-CD20 antibody): Effects of similar localization of their receptors

Small B-cell lymphocytic lymphoma/chronic lymphocytic leukemia, which typically affects elderly people, is a group of conditions that are not clinically uniform. It has been suggested that using the combined activity of the monoclonal antibody anti-CD20 (rituximab) and Listeria monocytogenes toxin listeriolysin O (LLO) for this condition could produce an enhanced treatment effect. Here, we tested the effect of the joint activity of rituximab and LLO, which is a cell membrane toxin, in human leukemia cell lines. The human B-leukemia Raji cell line, which expresses CD20, and the T-cell Jurkat cell line, which does not express CD20, for comparison were used in model tests. Cell cytotoxicity of rituximab or LLO and both applied jointly to the cell lines was compared in the presence of human plasma complement. Optimal cytotoxic effects dependent on rituximab or LLO concentration were tested separately. LD50 values were determined and used for optimal application of a mixture of the two factors. The cytotoxic effect on Raji cells of both rituximab and LLO was more than 2.5 times that of LLO alone and 1.5 times that of rituximab alone. At the highest tested concentrations, a mixture of the tested factors had a non-specific cytotoxic effect on the Jurkat cell line, as well. The rituximab and LLO binding sites appear to be in a similar region of the Raji leukemia cell membrane, suggesting an effective interaction of both factors. The joint interaction of these compounds in cell membrane pore formation suggests an explanation for the more effective cytotoxic activity that their combination was observed in this experiment.

Cytotoxicity of listeriolysin O produced by membrane-encapsulated Bacillus subtilis on leukemia cells

Encapsulation of biological material in the permiselective membrane allows to construct a system separating cells from their products, which may find biotechnological as well as biomedical applications in biological processes regulation. Application of a permiselective membrane allows avoiding an attack of the implanted microorganisms on the host. Our aim was to evaluate the performance of Bacillus subtilis encapsulated in an elaborate membrane system producing listeriolysin O, a cytolysin from Listeria monocytogenes, with chosen eukaryotic cells for future application in anticancer treatment. The system of encapsulating in membrane live Bacillus subtilis BR1-S secreting listeriolysin O was proven to exert the effective cytotoxic activity on eukaryotic cells. Interestingly, listeriolysin O showed selective cytotoxic activity on eukaryotic cells: more human leukemia Jurkat T cells were killed than human chronic lymphocytic B cells leukemia at similar conditions in vitro. This system of encapsulated B. subtilis, continuously releasing bacterial products, may affect selectively different types of cells and may have future application in local anticancer treatment.

Opposite patterns of diurnal activity in the box jellyfish Tripedalia cystophora and Copula sivickisi

Cubozoan medusae have a stereotypic set of 24 eyes, some of which are structurally similar to vertebrate and cephalopod eyes. Across the approximately 25 described species, this set of eyes varies surprisingly little, suggesting that they are involved in an equally stereotypic set of visual tasks. During the day Tripedalia cystophora is found at the edge of mangrove lagoons where it accumulates close to the surface in sun-lit patches between the prop roots. Copula sivickisi (formerly named Carybdea sivickisi) is associated with coral reefs and has been observed to be active at night. At least superficially, the eyes of the two species are close to identical. We studied the diurnal activity pattern of these two species both in the wild and under controlled conditions in laboratory experiments. Despite the very similar visual systems, we found that they display opposite patterns of diurnal activity. T. cystophora is active exclusively during the day, whereas C. sivickisi is actively swimming at night, when it forages and mates. At night T. cystophora is found on the muddy bottom of the mangrove lagoon. C. sivickisi spends the day attached to structures such as the underside of stones and coral skeletons. This species difference seems to have evolved to optimize foraging, since the patterns of activity follow those of the available prey items in their respective habitats.

Modulation of inv gene expression by the OmpR two-component response regulator protein of Yersinia enterocolitica

To elucidate the physiological meaning of OmpR-dependent expression of invasin gene (inv) inhibition in Yersinia enterocolitica, the function of the EnvZ/OmpR regulatory pathway in osmoregulation of inv expression was analyzed in detail. The osmoregulation of inv expression was found to be a multifaceted process involving both OmpR-dependent and -independent mechanisms. Analysis of inv transcription in strains lacking OmpR or EnvZ proteins indicated that kinase EnvZ is not the only regulator of OmpR phosphorylation. Using the transcriptional inv::lacZ fusion in a heterologous system (Escherichia coli) we tried to clarify the role of OmpR in the inv regulatory circuit composed of negative (H-NS) and positive (RovA) regulators of inv gene transcription. We were able to show a significant increase in inv expression in E. coli ompR background under H-NS( Ecoli )-repressed condition. Moreover, H-NS-mediated inv repression was relieved when RovA of Y. enterocolitica was expressed from a plasmid. Furthermore, we showed that RovA may activate inv expression irrespective on the presence of H-NS protein. Using this strategy we showed that OmpR of Y. enterocolitica decrease RovA-mediated inv activation.

Swim pacemakers in box jellyfish are modulated by the visual input

A major part of the cubozoan central nervous system is situated in the eye-bearing rhopalia. One of the neuronal output channels from the rhopalia carries a swim pacemaker signal, which has a one-to-one relation with the swim contractions of the bell shaped body. Given the advanced visual system of box jellyfish and that the pacemaker signal originates in the vicinity of these eyes, it seems logical to assume that the pacemakers are modified by the visual input. Here, the firing frequency and distribution of inter-signal intervals (ISIs) of single pacemakers are examined in the Caribbean box jellyfish, Tripedalia cystophora. It is shown that the absolute ambient light intensity, if kept constant, has no influence on the signal, but if the intensity changes, it has a major impact on both frequency and ISIs. If the intensity suddenly drops there is an increase in firing frequency, and the ISIs become more homogeneously distributed. A rise in intensity, on the other hand, produces a steep decline in the frequency and makes the ISIs highly variable. These electrophysiological data are correlated with behavioral observations from the natural habitat of the medusae.

Listeria monocytogenes protein p60 affects hemolytic activity and uptake of bacteria by macrophages

Bacillus subtilis strains expressing listeriolysin O (LLO) and simultaneously LLO and p60 protein were constructed. The effect of p60 protein on hemolytic activity and on the invasion of professional phagocytes was demonstrated in the absence of other virulence factors of L. monocytogenes. The hemolytic activity of LLO in the presence of p60 protein decreased which indicates that p60 promoted adhesion and subsequent invasion of professional phagocytes.

Contribution of hemolysin and phospholipase activity to cytolytic properties and viability of Listeria monocytogenes

The life cycle of Listeria monocytogenes strongly depends on cytolysin which facilitates the pathogen's escape from the endosome. This process is very ineffective in the absence of phospholipases. In this study we investigated the molecular mechanism of cooperation between hemolysin and phospholipases. We propose a model involving interactions between proteins that increase the affinity of cytolysins for the membrane as well direct enzymatic enhancement of lysis.

Insertional knock-out of protein translocation systems common for Yersinia enterocolitica and Listeria monocytogenes

To carry out efficient insertional mutagenesis in Listeria monocytogenes and to facilitate the characterisation of disrupted genes, a novel derivative of plasmid pACYC 184 was constructed, pLIV virA3, carrying a fragment from the virA region of the of Y. enterocolitica plasmid pYVe 0:9. After transformation of this plasmid into L. monocytogenes it was possible to select for its integration into the host DNA at 42 degrees C. Insertional mutants of L. monocytogenes obtained by using pLIV vector containing plasmid DNA fragments from Y. enterocolitica were constructed and are described.

Psychopharmacology and mental retardation: a 10 year review (1990-1999)

We conducted a 10 year review of the literature pertaining to psychopharmacology and mental retardation. Studies were included or excluded from the review based on meeting one or more of the methodological criteria normally considered fundamental for sound scientific research. The vast majority of studies conducted in the last 10 years in this area had major methodological flaws. While a large number of medications were prescribed for various psychological disorders and behavior problems, most drug administrations were not based in science, were not evaluated appropriately, and generally did not follow best practices for treatment of persons with mental retardation. Very few medications prescribed were behavior or psychiatric symptom specific; that is, most medications were given to suppress a myriad of aberrant behaviors thus chemically restraining the individual in question. Practices such as these present serious problems for service providers due to the deleterious side effects of many psychotropic medications and the federal government's intervention into the care-provision practices of developmental centers, community homes, and other living arrangements for persons with mental retardation. Implications of our review are discussed.

The development of a reinforcer choice assessment scale for persons with severe and profound mental retardation

Reinforcement is a cornerstone for treating adaptive skills and eliminating problem behaviors for persons evincing mental retardation. To effectively use reinforcement, professionals must find reinforcers that are most effective for each individual. Establishing reinforcers is particularly important for persons functioning in the severe and profound ranges of mental retardation as reinforcers are often difficult to identify in this population. The current study aimed at developing a reinforcer rating scale that-would have applicability on a broad clinical basis, looking specifically at the psychometric properties of the scale.

Reliability of the Matson Evaluation of Drug Side Effects Scale (MEDS)

The potential negative effects of psychoactive medication are well documented. Given the high rate of their use in persons with mental retardation, the need to assess and identify these negative effects is great. The Matson Evaluation of Drug Side Effects (MEDS) was designed to evaluate commonly identified side effects with a psychometrically sound checklist. The initial psychometric properties of this scale are presented and discussed. An examination of interrater reliability and internal consistency revealed that the MEDS has excellent consistency across raters and good internal consistency. Potential uses for the scale and directions for future research are reviewed as well.

Capacity of listeriolysin O, streptolysin O, and perfringolysin O to mediate growth of Bacillus subtilis within mammalian cells

The Listeria monocytogenes hemolysin listeriolysin O (LLO) plays a major role in mediating the escape of L. monocytogenes from a vacuolar compartment. In a previous report, it was shown that Bacillus subtilis expressing LLO could escape from a host vacuolar compartment and grow in the cytoplasm (J. Bielecki, P. Youngman, P. Connelly, and D. A. Portnoy, Nature [London] 345:175-176, 1990). In the present study, two related thiol-activated hemolysins, streptolysin O (SLO) and perfringolysin O (PFO), were expressed in B. subtilis and their ability to mediate intracellular growth was monitored by visual inspection and by assaying for CFU. Like LLO, PFO was active within the vacuolar environment, whereas SLO showed negligible activity. However, expression of PFO seemed to damage the host cells. The pH of the vacuole probably had little to do with these results, since all three hemolysins showed full or enhanced activity at pH 5.5, although LLO showed greatly reduced activity at pH 7. In addition, neutralization of the pH within host vacuoles by using weak bases had little effect on the lysis of the vacuole. The lack of SLO activity is probably caused by its lower specific activity; the purified protein had 10-fold less activity on a molar basis. These results suggest that LLO is not unique in its capacity to mediate intracellular growth of B. subtilis.

Changes in murein composition during the cell cycle of Caulobacter crescentus

The amino acid and muropeptide compositions of murein (peptidoglycan) isolated from populations of Caulobacter crescentus predominantly composed of swarmer or stalked cells were determined and compared with the structure of murein sacculi obtained from a population of unsegregated cells. It appears that in spite of vast morphological alterations in the course of the cell cycle, the murein composition of the various cell types is not markedly different.

Bacillus subtilis expressing a haemolysin gene from Listeria monocytogenes can grow in mammalian cells

Intracellular parasites can be classified into those that reside within a host vacuole and those which grow directly in the host cytoplasm. Members of the latter group, which includes Rickettsia, Shigellae, Trypanosoma cruzi, and Listeria monocytogenes, possess haemolytic activity associated with the ability to enter the host cytoplasm. Therefore mutants of L. monocytogenes lacking a pore-forming haemolysin, listeriolysin O, do not escape from the endosomal compartment and consequently fail to become established in the cytoplasm. To examine the role of listeriolysin O, we cloned the structural gene for the L. monocytogenes haemolysin, hlyA, into an asporogenic mutant of Bacillus subtilis under the control of an IPTG-inducible promoter. After being internalized by the macrophage-like cell line J774, haemolytic B. subtilis disrupted the phagosomal membrane and grew rapidly within the macrophage cytoplasm. These results show that a single gene product is sufficient to convert a common soil bacterium into a parasite that can grow in the cytoplasm of a mammalian cell.

Mutation affecting resistance of Escherichia coli K12 to nalidixic acid

A new mutation, nalD, determining resistance of Escherichia coli to nalidixic acid (NAL) is reported. The nalD mutant described is resistant to NAL at 37 degrees C but sensitive at 30 degrees C. It is defective in penetration of NAL and glycerol through the outer membrane at 37 degrees C. The nalD mutation is located half-way between 89 and 89.5 min on the E. coli genetic map.

[Centers and consultation in the field of nutritional hygiene: medicosocial structures in the control of alcoholism in France]

In France, an original approach to the prevention of alcoholism has been developed and implemented. It is based on a network of medico-social centres, called "Centres of Nutritional Hygiéne". These centres are the basic elements of the medico-social health services dealing with alcoholism. They are designed to receive, listen to and provide emergency support to any person faced with alcohol problems, as well as to detect and treat heavy drinkers. They are animated by a multidisciplinary team which consists of a doctor, a nurse, a psychologist, a dieteticien, a social worker and a medical secretary. The doctor, who is a specialist in alcohology, usually, though not always, plays the most important role in the team work. The main purpose of the centre of nutritional hygiene is the secondary prevention of alcoholism, implying early case finding and early treatment of heavy drinkers before they become alcohol-dependent. This approach to the prevention of alcoholism was conceived in France by Dr Le Go in 1950. The first centres of nutritional hygiene were created in 1970-1975. The results obtained so far are encouraging. More than half the patients seen in these centres have reduced their alcohol intake. There are good reasons to believe that these results could be improved by developing a better coordination with general practitioners and follow-up support. Better detection of heavy drinkers could be achieved by diversifying the sources of recruitment.(ABSTRACT TRUNCATED AT 250 WORDS)

Mutants of Escherichia coli K12 sensitive to acidic pH

Four mutants of Escherichia coli K12 were isolated on the basis of their sensitivity to pH 5.4. Under non-permissive conditions their growth was reversibly inhibited. At pH 7.0 these mutants showed a highly pleiotropic phenotype, which included altered phage and detergent sensitivities and leakage of periplasmic proteins. The findings suggest a defect in the outer membrane, perhaps in lipopolysaccharide. Two mutants mapped in or near the rfa locus, while the other two were removed from this region.