Dehydration of nigeran crystals: crystal structure and morphological aspects.

The crystal structure of anhydrous nigeran, poly[(1 → 3)-α-d-maltose], obtained from Penicillium crustosum has been determined by a combined electron diffraction. X-ray diffraction and packing analysis. The electron diffraction pattern from solution-grown single crystals shows some (h k I) reflections in the baseplane pattern. The polymer crystallizes with two chains passing through the cell of dimensions:$\text{a = 17.76, b = 6.0}\text{and}\text{c = 14.62}\text{A}\text{?}$ (fiber repeat). The space group is P2₁2₁2₁. The glycosidic torsion angles of this poly(disaccharide) were determined using an iteration process. The results are analyzed on the basis of the effect of side-group orientations on backbone conformation, and are compared with those obtained from a survey of relevant linear and cyclic oligosaccharides.The crystallographic reliability index was R_e = 0.25 and R_x = 0.30 when the model was tested against electron and X-ray diffraction data, respectively. The poly(disaccharide) chain is a 2-fold helix stabilized by an intrachain hydrogen bond between contiguous α-(1 → 4) residues. The hydroxymethyl side-chains are in the gauche-gauche form. Two such chains pack with anti-parallel polarity and the 2-fold screw axis coincides with the macromolecular axis. A network of hydrogen bonds holds the chains together in the crystal.In the condensed state, the nigeran chains are more or less extended depending on the state of hydration. The two extremes correspond to the “dry” and “wet” crystal forms. The transition between the two conformations takes place reversibly in the crystalline state. This is observed on solution-grown crystals, as well as in vivo where nigeran is found to occur in crystalline domains. Such a transition is analyzed in terms of the conformational flexibility of the backbone and in terms of the affine deformation concept. Morphological and textural transformations occurring as a result of drying are suggested to have important consequences on the subsequent microbiology such as enzymic digestion.     

Transcriptional response to alcohol exposure in Drosophila melanogaster

Background  

Alcoholism presents widespread social and human health problems. Alcohol sensitivity, the development of tolerance to alcohol and susceptibility to addiction vary in the population. Genetic factors that predispose to alcoholism remain largely unknown due to extensive genetic and environmental variation in human populations. Drosophila, however, allows studies on genetically identical individuals in controlled environments. Although addiction to alcohol has not been demonstrated in Drosophila, flies show responses to alcohol exposure that resemble human intoxication, including hyperactivity, loss of postural control, sedation, and exposure-dependent development of tolerance.     

Application of self-cycling fermentation technique to the production of poly-beta-hydroxybutyrate

The production of poly-beta-hydroxybutyrate (PHB) by Alcaligenes eutrophus DSM 545 in a cyclone bioreactor was compared using various culture methods: batch, fed-batch, and self-cycling fermentation (SCF) with and without extended periods of nutrient deprivation. SCF is a semi-continuous method that results in a nutrient limitation for every successive generation of cells and, therefore, may have advantages for products whose formation follow secondary metabolite kinetics. Use of the SCF technique without extended nutrient deprivation produced a PHB concentration of 1.2 g L(-1) as 40% of the biomass dry weight. With nitrogen deprivation for 4 or 6 h, the concentration of PHB decreased when compared to the standard SCF technique. However, nitrogen deprivation periods of 8 h resulted in an increase in PHB concentration to 2.7 g L(-1) or 59% of the biomass dry weight. The nutrient cycling may act to repress PHB accumulation during periods of nitrogen deprivation, unless a time threshold has been reached, after which PHB accumulation occurs as in normal batch culture. (c) 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 55: 815-820, 1997.     

Enzymatic degradation of β(1 → 4) xylan single crystals

The enzymatic degradation of β(1 → 4) xylan single crystals with xylanases was investigated by electron microscopy and electron diffraction. The enzyme attack takes place at the edge of the crystals and progresses towards their centers. This is consistent with an endo-enzyme mechanism, where the enzyme interacts essentially with the accessible xylan chains located at the crystal periphery.     

Study of hydration of cross-linked high amylose starch by solid state 13C NMR spectroscopy

Starch is subjected to chemical treatments such as cross-linking or hydroxypropylation to meet the material requirements for food uses or controlled release in the pharmaceutical industries. In this work, two types of cross-linking formulations have been employed for the preparation of high amylose starch for use as an excipient for sustained drug release. The structural differences and chain dynamics of the modified starches in the dry and hydrated states have been compared by the use of variable contact time cross polarization-magic angle spinning solid state (13)C NMR spectroscopy.     

The genetic basis of alcoholism: multiple phenotypes,many genes,complex networks

Alcoholism is a significant public health problem. A picture of the genetic architecture underlying alcohol-related phenotypes is emerging from genome-wide association studies and work on genetically tractable model organisms.     

Gamma-ray crosslinking of poly(3-hydroxyoctanoate-co-undecenoate)

The gamma-ray crosslinking of films made of poly(3-hydroxyoctanoate) containing undecenoate moieties (up to 33 mole%) were studied. X-ray diffraction, thermal analysis, dynamic mechanical analysis (DMA), solid state nuclear magnetic resonance (NMR) spectroscopy and degree of crosslinking (swelling analysis) as a function of irradiation dose were evaluated for treatments in air or in N(2) atmosphere. After uncrosslinked material was isolated by CHCl(3) extraction, solid state NMR data suggested that only a small percentage of the double bonds took part in the formation of irradiation crosslinks. Crosslinking in N(2) was more efficient than in air and a 20 kGy dose was sufficient for optimal crosslinking. The X-ray diffraction patterns of the polymer films were unaffected by moderate irradiation. The use of sodium hypochlorite to isolate poly(3-hydroxyoctanoate-co-undecenoate) samples resulted in partial chlorination of the double bonds and considerable depolymerization.     

Bacterial swimming strategies and turbulence

Most bacteria in the ocean can be motile. Chemotaxis allows bacteria to detect nutrient gradients, and hence motility is believed to serve as a method of approaching sources of food. This picture is well established in a stagnant environment. In the ocean a shear microenvironment is associated with turbulence. This shear flow prevents clustering of bacteria around local nutrient sources if they swim in the commonly assumed "run-and-tumble" strategy. Recent observations, however, indicate a "back-and-forth" swimming behavior for marine bacteria. In a theoretical study we compare the two bacterial swimming strategies in a realistic ocean environment. The "back-and-forth" strategy is found to enable the bacteria to stay close to a nutrient source even under high shear. Furthermore, rotational diffusion driven by thermal noise can significantly enhance the efficiency of this strategy. The superiority of the "back-and-forth" strategy suggests that bacterial motility has a control function rather than an approach function under turbulent conditions.