\u3cem\u3eRhizobium leguminosarum\u3c/em\u3e CFN42 Genetic Regions Encoding Lipopolysaccharide Structures Essential for Complete Nodule Development on Bean Plants

Eight symbiotic mutants defective in lipopolysaccharide (LPS) synthesis were isolated from Rhizobium leguminosarum biovar phaseoli CFN42. These eight strains elicited small white nodules lacking infected cells when inoculated onto bean plants. The mutants had undetectable or greatly diminished amounts of the complete LPS (LPS I), whereas amounts of an LPS lacking the O antigen (LPS II) greatly increased. Apparent LPS bands that migrated between LPS I and LPS II on sodium dodecyl sulfate-polyacrylamide gels were detected in extracts of some of the mutants. The mutant strains were complemented to wild-type LPS I content and antigenicity by DNA from a cosmid library of the wild-type genome. Most of the mutations were clustered in two genetic regions; one mutation was located in a third region. Strains complemented by DNA from two of these regions produced healthy nitrogen-fixing nodules. Strains complemented to wild-type LPS content by the other genetic region induced nodules that exhibited little or no nitrogenase activity, although nodule development was obviously enhanced by the presence of this DNA. The results support the idea that complete LPS structures, in normal amounts, are necessary for infection thread development in bean plants

Computational simulations demonstrate altered wall shear stress in aortic coarctation patients previously treated by resection with end-to-end anastomosis

Background.  Atherosclerotic plaque in the descending thoracic aorta (dAo) is related to altered wall shear stress (WSS) for normal patients. Resection with end-to-end anastomosis (RWEA) is the gold standard for coarctation of the aorta (CoA) repair, but may lead to altered WSS indices that contribute to morbidity. Methods.  Computational fluid dynamics (CFD) models were created from imaging and blood pressure data for control subjects and age- and gender-matched CoA patients treated by RWEA (four males, two females, 15 ± 8 years). CFD analysis incorporated downstream vascular resistance and compliance to generate blood flow velocity, time-averaged WSS (TAWSS), and oscillatory shear index (OSI) results. These indices were quantified longitudinally and circumferentially in the dAo, and several visualization methods were used to highlight regions of potential hemodynamic susceptibility. Results.  The total dAo area exposed to subnormal TAWSS and OSI was similar between groups, but several statistically significant local differences were revealed. Control subjects experienced left-handed rotating patterns of TAWSS and OSI down the dAo. TAWSS was elevated in CoA patients near the site of residual narrowings and OSI was elevated distally, particularly along the left dAo wall. Differences in WSS indices between groups were negligible more than 5 dAo diameters distal to the aortic arch. Conclusions.  Localized differences in WSS indices within the dAo of CoA patients treated by RWEA suggest that plaque may form in unique locations influenced by the surgical repair. These regions can be visualized in familiar and intuitive ways allowing clinicians to track their contribution to morbidity in longitudinal studies

Including Aortic Valve Morphology in Computational Fluid Dynamics Simulations: Initial Findings and Application to Aortic Coarctation

Computational fluid dynamics (CFD) simulations quantifying thoracic aortic flow patterns have not included disturbances from the aortic valve (AoV). 80% of patients with aortic coarctation (CoA) have a bicuspid aortic valve (BAV) which may cause adverse flow patterns contributing to morbidity. Our objectives were to develop a method to account for the AoV in CFD simulations, and quantify its impact on local hemodynamics. The method developed facilitates segmentation of the AoV, spatiotemporal interpolation of segments, and anatomic positioning of segments at the CFD model inlet. The AoV was included in CFD model examples of a normal (tricuspid AoV) and a post-surgical CoA patient (BAV). Velocity, turbulent kinetic energy (TKE), time-averaged wall shear stress (TAWSS), and oscillatory shear index (OSI) results were compared to equivalent simulations using a plug inlet profile. The plug inlet greatly underestimated TKE for both examples. TAWSS differences extended throughout the thoracic aorta for the CoA BAV, but were limited to the arch for the normal example. OSI differences existed mainly in the ascending aorta for both cases. The impact of AoV can now be included with CFD simulations to identify regions of deleterious hemodynamics thereby advancing simulations of the thoracic aorta one step closer to reality

Genetic analysis of lipopolysaccharide and purine biosynthesis and their requirement for nodulation in Rhizobium leguminosarum strain CFN42

Bacteria of the genus Rhizobium establish a nitrogen-fixing symbiosis with leguminous plants. Rhizobia elicit the formation of root nodules and enter the nodules by way of an infection thread. Wild-type R. leguminosarum biovar phaseoli strain CFN42 nodulates bean. Two classes of symbiotically-defective mutants derived from CFN42 were studied. Symbiosis was blocked at different stages of infection in the two classes. Each class involved chromosomally-located mutations. Mutants of the first class, characterized by eliciting abortive infection threads, were altered in lipopolysaccharide (LPS) synthesis. These mutants had undetectable or greatly diminished amounts of LPS molecules containing the O-antigen polysaccharide portion of LPS. Three genetic regions required for LPS biosynthesis were found to be necessary for complete nodulation. The three regions were represented on eight cloned DNA inserts isolated from a cosmid library of the wild-type strain. When the Lps mutants were complemented to Lps+ by the appropriate cloned DNA, the ability to elicit complete nodules was restored. This restoration showed that the ability to synthesize O-antigen containing LPS was required for infection thread development in bean. Most of the lps mutations clustered in two of the genetic regions; one mutation was located in the third region. Additional mutations were induced in the first two lps regions by transposon Tn5 insertion mutagenesis of cloned DNA. A number of these mutations caused incomplete LPS synthesis. Complementation analysis with strains carrying a plasmid-borne lps mutation has identified at least thirteen of the approximately thirty genes required for complete LPS synthesis. The biochemical and immunological characterization of the LPS from two mutant strains suggested that O-antigen containing LPS, besides being present, must be in sufficient quantities as well for infection to continue. In addition, the O-antigen need not be structurally identical as the wild-type O-antigen in order to serve its function in symbiosis. The second class of symbiotically-defective mutants consists of purine (pur) auxotrophs. These strains do not initiate infection thread formation. Complementation of the purine auxotrophs by cloned DNA has shown that the failure to initiate infection was the direct result of the pur mutations. Complementation and hybridization studies indicated that most of the pur alleles were not closely linked

Mapping of Complementation Groups Within a \u3cem\u3eRhizobium leguminosarum\u3c/em\u3e CFN42 Chromosomal Region Required for Lipopolysaccharide Synthesis

A major genetic region specifying portions of the carbohydrate structure of Rhizobium leguminosarum CFN42 lipopolysaccharide was analyzed by Tn5 mutagenesis, constructing deletions in cloned DNA, restriction mapping, and complementation analysis. Mutations affecting lipopolysaccharide synthesis were arranged in nine complementation groups spanning 18 kb of DNA. One mutation resulted in O-polysaccharide-containing lipopolysaccharide having a slightly increased mobility in gel electrophoresis. This mutation did not affect the symbiosis with bean plants. The other mutations eliminated the 0-polysaccharide-containing lipopolysaccharide and resulted in strains defective in eliciting bean nodule development

Rhizobial Purine and Pyrimidine Auxotrophs: Nutrient Supplementation, Genetic Analysis, and the Symbiotic Requirement for the Novo Purine Biosynthesis

Previously described Rhizobium leguminosarum bv. phaseoli mutants elicit nodules on bean without infection thread formation. These mutants were shown to be purine or, in one case, pyrimidine auxotrophs. Each of the seven purine auxotrophs grew normally when supplied the penultimate precursor of inosine, 5-aminoimidazole-4-carboxamide riboside. Four seemed blocked early in the purine pathway, because they were also thiamine auxotrophs. Reversion analysis and genetic complementation using cloned wild-type DNA showed that in each mutant a single mutation was responsible for both the symbiotic defect and purine or pyrimidine auxotrophy. The mutations were mapped to five dispersed chromosomal locations. The previously reported weak Calcofluor staining of these mutants on minimal agar appeared to be caused by partial growth on contaminating nutrients in the agar, rather than deficient exopolysaccharide production. Nodulation by the mutants was not enhanced by supplying purine or pyrimidine compounds exogenously. Furthermore, with or without added purine, the purine auxotrophs grew in the root environment as well as the wild type. However, nodulation by the purine auxotrophs was enhanced greatly in the presence of 5-aminoimidazole-4-carboxamide riboside. The results suggest that undiminished metabolic flow through de novo purine biosynthesis, or a particular intermediate in the pathway, is essential in early symbiotic interactions

Retinal alterations in patients with Lafora disease

Purpose: Lafora disease is a genetic neurodegenerative metabolic disorder caused by insoluble polyglucosan aggregate accumulation throughout the central nervous system and body. The retina is an accessible neural tissue, which may offer alternative methods to assess neurological diseases quickly and noninvasively. In this way, noninvasive imaging may provide a means to characterize neurodegenerative disease, which enables earlier identification and diagnosis of disease and the ability to monitor disease progression. In this study, we sought to characterize the retina of individuals with Lafora disease using non-invasive retinal imaging. Methods: One eye of three individuals with genetically confirmed Lafora disease were imaged with optical coherence tomography (OCT) and adaptive optics scanning light ophthalmoscopy (AOSLO). When possible, OCT volume and line scans were acquired to assess total retinal thickness, ganglion cell-inner plexiform layer thickness, and outer nuclear layer + Henle fiber layer thickness. OCT angiography (OCTA) scans were acquired in one subject at the macula and optic nerve head (ONH). AOSLO was used to characterize the photoreceptor mosaic and examine the retinal nerve fiber layer (RNFL). Results: Two subjects with previous seizure activity demonstrated reduced retinal thickness, while one subject with no apparent symptoms had normal retinal thickness. All other clinical measures, as well as parafoveal cone density, were within normal range. Nummular reflectivity at the level of the RNFL was observed using AOSLO in the macula and near the ONH in all three subjects. Conclusions: This multimodal retinal imaging approach allowed us to observe a number of retinal structural features in all three individuals. Most notably, AOSLO revealed nummular reflectivity within the inner retina of each subject. This phenotype has not been reported previously and may represent a characteristic change produced by the neurodegenerative process

Quasiparticle interference, quasiparticle interactions, and the origin of the charge density wave in 2H-NbSe2

Physical Review Letters. Volume 114, Issue 3, 21 January 2015, Article number 037001.We show that a small number of intentionally introduced defects can be used as a spectroscopic tool to amplify quasiparticle interference in 2H-NbSe2 that we measure by scanning tunneling spectroscopic imaging. We show, from the momentum and energy dependence of the quasiparticle interference, that Fermi surface nesting is inconsequential to charge density wave formation in 2H-NbSe2. We demonstrate that, by combining quasiparticle interference data with additional knowledge of the quasiparticle band structure from angle resolved photoemission measurements, one can extract the wave vector and energy dependence of the important electronic scattering processes thereby obtaining direct information both about the fermiology and the interactions. In 2H-NbSe2, we use this combination to confirm that the important near-Fermi-surface electronic physics is dominated by the coupling of the quasiparticles to soft mode phonons at a wave vector different from the charge density wave ordering wave vector. © 2015 American Physical Society

The Herschel-SPIRE Legacy Survey (HSLS): the scientific goals of a shallow and wide submillimeter imaging survey with SPIRE

A large sub-mm survey with Herschel will enable many exciting science opportunities, especially in an era of wide-field optical and radio surveys and high resolution cosmic microwave background experiments. The Herschel-SPIRE Legacy Survey (HSLS), will lead to imaging data over 4000 sq. degrees at 250, 350, and 500 micron. Major Goals of HSLS are: (a) produce a catalog of 2.5 to 3 million galaxies down to 26, 27 and 33 mJy (50% completeness; 5 sigma confusion noise) at 250, 350 and 500 micron, respectively, in the southern hemisphere (3000 sq. degrees) and in an equatorial strip (1000 sq. degrees), areas which have extensive multi-wavelength coverage and are easily accessible from ALMA. Two thirds of the of the sources are expected to be at z > 1, one third at z > 2 and about a 1000 at z > 5. (b) Remove point source confusion in secondary anisotropy studies with Planck and ground-based CMB data. (c) Find at least 1200 strongly lensed bright sub-mm sources leading to a 2% test of general relativity. (d) Identify 200 proto-cluster regions at z of 2 and perform an unbiased study of the environmental dependence of star formation. (e) Perform an unbiased survey for star formation and dust at high Galactic latitude and make a census of debris disks and dust around AGB stars and white dwarfs