\u3cem\u3eRhizobium etli\u3c/em\u3e CE3 Bacteroid Lipopolysaccharides Are Structurally Similar but Not Identical to Those Produced by Cultured CE3 Bacteria

Rhizobium etli CE3 bacteroids were isolated from Phaseolus vulgaris root nodules. The lipopolysaccharide (LPS) from the bacteroids was purified and compared with the LPS from laboratory-cultured R. etli CE3and from cultures grown in the presence of anthocyanin. Comparisons were made of the O-chain polysaccharide, the core oligosaccharide, and the lipid A. Although LPS from CE3 bacteria and bacteroids are structurally similar, it was found that bacteroid LPS had specific modifications to both the O-chain polysaccharide and lipid A portions of their LPS. Cultures grown with anthocyanin contained modifications only to the O-chain polysaccharide. The changes to the O-chain polysaccharide consisted of the addition of a single methyl group to the 2-position of a fucosyl residue in one of the five O-chain trisaccharide repeat units.This same change occurred for bacteria grown in the presence of anthocyanin. This methylation change correlated with the inability of bacteroid LPS and LPS from anthocyanin-containing cultures to bind the monoclonal antibody JIM28. The coreoligosaccharide region of bacteroid LPS and from anthocyanin grown cultures was identical to that of LPS from normal laboratory-cultured CE3. The lipid A from bacteroids consisted exclusively of a tetraacylated species compared with the presence of both tetra-and pentaacylated lipid A from laboratory cultures. Growth in the presence of anthocyanin did not affect the lipid A structure. Purified bacteroids that could resume growth were also found to be more sensitive to the cationic peptides, poly-L-lysine, polymyxin-B, and melittin

Sekundäre Zellwandpolysaccharide in Bacillus anthracis und Bacillus cereus Stämmen

This thesis presents a systematic comparison of cell wall carbohydrates, in particular the non classical secondary cell wall polysaccharides from closely related strains within the Bacillus cereus group. The results suggest that the cell wall glycosyl composition of the various Bacillus cereus group strains display differences that correlate with their phylogenetic relatedness. Comparative structural analysis of polysaccharide components that were released from the cell walls of the various strains by hyrdrofluoric acid (HF) treatment and purified (then called HF-PS’s) also supported the previously observed differences in the total cell wall compositions. Imunochemical characterization of the released polysaccharides showed that they are antigenic and immunochemically as well as structurally species specific. Based on the findings described in this thesis, the HF-PS exhibits necessary properties for the development of future diagnostic applications, vaccines and possibly therapeutics for infections caused by Bacillus cereus group members.Die vorgelegte Dissertation beschreibt einen systematischen Vergleich von Zellwand Kohlenhydraten, insbesondere den, der „nicht klassischen“ Sekundärzellwandpolysacchariden isoliert von nahe verwandten Stämmen innerhalb der Bacillus cereus Gruppe. Die Ergebnisse einer Zellwandglykosylierungsanalyse von verschiedenen Stämmen aus der Bacillus cereus Gruppe zeigte, dass die beobachteten Kompositionsunterschiede mit der phylogenetischen Einordnung dieser Bakterienstämme korreliert. Die Strukturanalyse von Polysaccharidkomponenten, die von den Zellwänden der Bacillus cereus Gruppenmitglieder mittels Fluorwasserstoffsäure abgelöst und dann aufgereinigt wurden (danach HF-PS genannt), unterstützte die vorherigen Befunde der variierenden Zellwandkohlenhydratkompositionen. Weitere immunochemische Experimente zeigten ausserdem, dass das HF-PS immunogen ist. Demnach hat sich das HF-PS nicht nur immunochemisch sondern auch strukturanalytisch als stammspezifisch erwiesen und besitzt damit die erforderlichen Charakteristiken für seine mögliche Nutzung in der Entwicklung von neuen Diagnostika, Impfstoffen und anderen Therapeutika zur erfolgreiche Behandlung von Krankheiten und Infektionen, die durch Stämme der Bacillus cereus Gruppe verursacht wurden

Signal-to-noise matrix and model reduction in continuous-time hidden Markov models

Continuous-time regime-switching models are a very popular class of models for financial applications. In this work the so-called signal-to-noise matrix is introduced for hidden Markov models where the switching is driven by an unobservable Markov chain. Its relations to filtering, i.e. state estimation of the chain given the available observations, and portfolio optimization are investigated. A convergence result for the filter is derived: The filter converges to its invariant distribution if the eigenvalues of the signal-to-noise matrix converge to zero. This matrix is then also used to prove a mutual fund representation for regime-switching models and a corresponding market reduction which is consistent with filtering and portfolio optimization. Two canonical cases for the reduction are analyzed in more detail, the first based on the market regimes and the second depending on the eigenvalues. These considerations are presented both for observable and unobservable Markov chains. The results are illustrated by numerical simulations

Filterbased stochastic volatility in continuous-time hidden Markov models

Regime-switching models, in particular Hidden Markov Models (HMMs) where the switching is driven by an unobservable Markov chain, are widely-used in financial applications, due to their tractability and good econometric properties. In continuous time, properties of HMMs with constant and of HMMs with switching volatility can be quite different. To have a realistic model with unobservable Markov chain in continuous time and good econometric properties, a regime-switching model where the volatility depends on the filter for the underlying chain is introduced and the filtering equations are stated. Such models are motivated by agent based social learning models in economics. An approximation result for a fixed information filtration is proved and further motivation is provided by considering social learning arguments. The relation to the switching volatility model is analyzed in detail and a convergence result for the discretized model is given. Econometric properties are illustrated by numerical simulations

A study of John Keat's Isabella /

Originally presented as the author's thesis, Columbia University, 1968.Includes the text of the poem as found in the 2d ed. of The poetical works of John Keats published by Clarendon Press, Oxford.Bibliography: p. 215-217

A Bifunctional 3,5-Epimerase/4-Keto Reductase for Nucleotide-Rhamnose Synthesis in Arabidopsis

l-Rhamnose is a component of plant cell wall pectic polysaccharides, diverse secondary metabolites, and some glycoproteins. The biosynthesis of the activated nucleotide-sugar form(s) of rhamnose utilized by the various rhamnosyltransferases is still elusive, and no plant enzymes involved in their synthesis have been purified. In contrast, two genes (rmlC and rmlD) have been identified in bacteria and shown to encode a 3,5-epimerase and a 4-keto reductase that together convert dTDP-4-keto-6-deoxy-Glc to dTDP-β-l-rhamnose. We have identified an Arabidopsis cDNA that contains domains that share similarity to both reductase and epimerase. The Arabidopsis gene encodes a protein with a predicated molecular mass of approximately 33.5 kD that is transcribed in all tissue examined. The Arabidopsis protein expressed in, and purified from, Escherichia coli converts dTDP-4-keto-6-deoxy-Glc to dTDP-β-l-rhamnose in the presence of NADPH. These results suggest that a single plant enzyme has both the 3,5-epimerase and 4-keto reductase activities. The enzyme has maximum activity between pH 5.5 and 7.5 at 30°C. The apparent K(m) for NADPH is 90 μm and 16.9 μm for dTDP-4-keto-6-deoxy-Glc. The Arabidopsis enzyme can also form UDP-β-l-rhamnose. To our knowledge, this is the first example of a bifunctional plant enzyme involved in sugar nucleotide synthesis where a single polypeptide exhibits the same activities as two separate prokaryotic enzymes

Secondary cell wall polysaccharides from Bacillus cereus strains G9241, 03BB87 and 03BB102 causing fatal pneumonia share similar glycosyl structures with the polysaccharides from Bacillus anthracis

Secondary cell wall polysaccharides (SCWPs) are important structural components of the Bacillus cell wall and contribute to the array of antigens presented by these organisms in both spore and vegetative forms. We previously found that antisera raised to Bacillus anthracis spore preparations cross-reacted with SCWPs isolated from several strains of pathogenic B. cereus, but did not react with other phylogenetically related but nonpathogenic Bacilli, suggesting that the SCWP from B. anthracis and pathogenic B. cereus strains share specific structural features. In this study, SCWPs from three strains of B. cereus causing severe or fatal pneumonia (G9241, 03BB87 and 03BB102) were isolated and subjected to structural analysis and their structures were compared to SCWPs from B. anthracis. Complete structural analysis was performed for the B. cereus G9241 SCWP using NMR spectroscopy, mass spectrometry and derivatization methods. The analyses show that SCWPs from B. cereus G9241 has a glycosyl backbone identical to that of B. anthracis SCWP, consisting of multiple trisaccharide repeats of: →6)-α-d-GlcpNAc-(1 → 4)-β-d-ManpNAc-(1 → 4)-β-d-GlcpNAc-(1→. Both the B. anthracis and pathogenic B. cereus SCWPs are highly substituted at all GlcNAc residues with α- and β-Gal residues, however, only the SCWPs from B. cereus G9241 and 03BB87 carry an additional α-Gal substitution at O-3 of ManNAc residues, a feature lacking in the B. anthracis SCWPs. Both the B. anthracis and B. cereus SCWPs are pyruvylated, with an approximate molecular mass of ≈12,000 Da. The implications of these findings regarding pathogenicity and cell wall structure are discussed