Influence of glycosidic linkages and molecular weight on the fermentation of maltose-based oligosaccharides by human gut bacteria

A structure-function study was carried out to increase knowledge of how glycosidic linkages and molecular weights of carbohydrates contribute toward the selectivity of fermentation by gut bacteria. Oligosaccharides with maltose as the common carbohydrate source were used. Potentially prebiotic alternansucrase and dextransucrase maltose acceptor products were synthesized and separated into different molecular weights using a Bio-gel P2 column. These fractions were characterized by matrix-assisted laser desorption/ionization time-of-flight. Nonprebiotic maltooligosaccharides with degrees of polymerization (DP) from three to seven were commercially obtained for comparison. Growth selectivity of fecal bacteria on these oligosaccharides was studied using an anaerobic in vitro fermentation method. In general, carbohydrates of DP3 showed the highest selectivity towards bifidobacteria; however, oligosaccharides with a higher molecular weight (DP6-DP7) also resulted in a selective fermentation. Oligosaccharides with DPs above seven did not promote the growth of "beneficial" bacteria. The knowledge of how specific structures modify the gut microflora could help to find new prebiotic oligosaccharides.

In vitro fermentation and prebiotic potential of novel low molecular weight polysaccharides derived from agar and alginate seaweeds

Fermentation properties and prebiotic potential of novel low molecular weight polysaccharides (LMWPs) derived from agar and alginate bearing seaweeds was investigated. Ten LMWPs were supplemented to pH, temperature controlled anaerobic batch cultures inoculated with human feces from three donors, in triplicate. Microbiota changes were monitored using Fluorescent in-situ hybridization and short chain fatty acids, the fermentation end products were analysed using gas chromatography. Of the ten LMWPs tested, Gelidium seaweed CC2253 of molecular weight 64.64 KDa showed a significant increase in bifidobacterial populations from log(10) 8.06 at 0 h to log(10) 8.55 at 24 h (p = 0.018). For total bacterial populations, alginate powder CC2238 produced a significant increase from log(10) 9.01 at 0 h to log(10) 9.58 at 24 h (p = 0.032). No changes were observed in the other bacterial groups tested viz. Bacteroides, Lactobacilli/Enterococci, Eubacterium rectale/Clostridium coccoides and Clostridium histolyticum. The polysaccharides also showed significant increases in total SCFA production, particularly acetic and propionic acids, indicating that they were readily fermented. In conclusion, some LMWPs derived from agar and alginate bearing seaweeds were fermented by gut bacteria and exhibited potential to be used a novel source of prebiotics.

The effect of the molecular weight on the electro-optic properties of methacrylate-based side-chain liquid crystal polymers

A series of methacrylate-based side-chain liquid crystal polymers has been prepared with a range of molecular weights. For the high molecular weight polymers a smectic phase is observed with a very narrow nematic range; however, for low molecular weight polymers only the nematic phase is observed. A marked reduction in the glass transition temperature, TSN and TNI is observed with a reduction in the molecular weight. The orientational order parameters for these polymers in the liquid crystal phase have been determined using infra-red dichroism. It is found that the higher the molecular weight of the polymer, the greater is the threshold voltage of the electro-optic response and the lower the order parameter. The increase in the threshold voltage with increasing molecular weight may be related to the intrinsic curvature elasticity and hence to the coupling between the mesogenic units and the polymer backbone.

The role of root exuded low molecular weight organic anions in facilitating petroleum hydrocarbon degradation: current knowledge and future directions

Rhizoremediation is a bioremediation technique whereby enhanced microbial degradation of organic contaminants occurs within the plant root zone (rhizosphere). It is considered an effective and affordable ‘green technology’ for remediating soils contaminated with petroleum hydrocarbons (PHCs). This paper critically reviews the potential role of root exuded compounds in rhizoremediation, with emphasis on commonly exuded low molecular weight aliphatic organic acid anions (carboxylates). The extent to which remediation is achieved shows wide disparity among plant species. Therefore, plant selection is crucial for the advancement and widespread adoption of this technology. Root exudation is speculated to be one of the predominant factors leading to microbial changes in the rhizosphere and thus the potential driver behind enhanced petroleum biodegradation. Carboxylates can form a significant component of the root exudate mixture and are hypothesised to enhance petroleum biodegradation by: i) providing an easily degradable energy source; ii) increasing phosphorus supply; and/or iii) enhancing the contaminant bioavailability. These differing hypotheses, which are not mutually exclusive, require further investigation to progress our understanding of plant–microbe interactions with the aim to improve plant species selection and the efficacy of rhizoremediation.

Recovery and upgrading bovine rumen protein by extrusion: Effect of lipid content on protein disulphide cross-linking, solubility and molecular weight

Bovine rumen protein with two levels of residual lipids (1.9% or 3.8%) was subjected to thermoplastic extrusion under different temperatures and moisture contents. Protein Solubility in different buffers, disulphide cross-linking and molecular weight distribution were determined on the extrudates. After extrusion, samples with 1.9% residual lipids content had a higher concentration of protein insoluble by undetermined forces, irrespective of feed moisture and processing temperature used. Lipid content of 3.8% in the feed material resulted in more protein participating in the extrudate network through non-covalent interactions (hydrophobic and electrostatic) and disulphide bonds. A small dependency of the extrusion process on moisture and temperature and a marked dependency on lipid content, especially phospholipid, was observed, Electrophoresis under non-reducing conditions showed that protein extrusion with low feed moisture promoted high molecular breakdown inside the barrel, probably due to intense shear force, and further protein aggregation at the die end. (C) 2009 Elsevier Ltd. All rights reserved.

Phase behavior and crystallization in blends of a low molecular weight polyethylene-block-poly(ethylene oxide) diblock copolymer and poly(hydroxyether of bisphenol A)

The phase behavior, morphology and crystallization in blends of a low-molecular-weight (Mn = 1400) double-crystalline polyethylene-block-poly(ethylene oxide) (PE-PEO) diblock copolymer with poly(hydroxyether of bisphenol A) (PH) were investigated by differential scanning calorimetry, transmission electron microscopy and small-angle X-ray scattering. The symmetric PE-PEO diblock copolymer consists of a PH-miscible PEO block and a PH-immiscible PE block. However, PH only exhibits partial miscibility with the PEO block of the copolymer in the PH/PE-PEO blends; both macrophase and microphase separations took place. There existed two macrophases in the PH/PE-PEO blends, i.e., a PH-rich phase and a PE-PEO copolymer-rich phase. The PE block of the copolymer in the blends exhibited fractionated crystallization behavior by homogeneous nucleation. There appeared three crystallization exotherms related to the crystallization of the PE block within three different microenvironments in the PH/PE-PEO blends.

Immunostimulatory polysaccharides from Chlorella pyrenoidosa. A new galactofuranan. Measurement of molecular weight and molecular weight dispersion by DOSY NMR.

Fractionation of the hot water extract of Chlorella pyrenoidosa was performed using a combination of ethanol precipitation, size exclusion chromatography, and anion exchange chromatography. One fraction contained a new polysaccharide, and this compound was shown to be a 1→2-linked β-d-galactofuranan from its 1D and 2D 1H and 13C NMR spectra, with a molecular weight of 15 kDa from DOSY NMR measurements. A number of other fractions were shown to have the same repeating unit as the previously identified arabinogalactan. However, arabinogalactans from different fractions were shown by DOSY NMR to have different molecular weights, which ranged from 27 to 1020 kDa. Agreement with molecular weights measured for some of these fractions by SEC-MALS was very good, further confirming the relationship established by Viel et al. between molecular weights of neutral polysaccharides and self-diffusion coefficients. The smaller molecular weight polysaccharides, the galactofuranan and the 27 and 50 kDa arabinogalactans, were shown to be close to monodisperse by analysis of the distributions of the self-diffusion coefficients for the polymers. The larger arabinogalactans had considerable variation in their molecular weights (188 ± 109 kDa and 1020 ± 370 kDa). Only the two larger arabinogalactans showed immunostimulatory activity.

Modulating the interaction of CXCR4 and CXCL12 by low-molecular-weight heparin inhibits hepatic metastasis of colon cancer

Liver metastasis is the major obstacle for prolonging the survival of colon cancer patients. Low-molecular-weight heparin (LMWH), a common drug for venous thromboembolism, has displayed beneficial effects in improving the survival of cancer patients, though the mechanism remains unclear. This study aimed to investigate the effects of LMWH on hepatic metastasis of colon cancer and its underlying molecular mechanism by targeting the interaction of the chemokine receptor CXCR4 and its ligand CXCL12 (formerly known as stromal cell-derived factor 1α, SDF-1α), as the CXCR4-CXCL12 axis has been shown to regulate the interaction of cancer cells and stroma. Experimental results revealed that LMWH (Enoxaparin, 3500-5500 Da) inhibited the CXCL12-stimulated proliferation, adhesion and colony formation of human colon cancer HCT-116 cells that highly expressed CXCR4. Interestingly, LMWH or an anti-CXCR4 blocking antibody diminished the migrating and invading abilities of HCT116 cells stimulated by the recombinant CXCL12 protein or liver homogenates which contained endogenous CXCL12 protein. Although LMWH did not significantly inhibit the growth of subcutaneous colon tumors, it significantly suppressed the formation of hepatic metastasis established by intrasplenic injection of colon cancer cells in nude Balb/c mice and also downregulated the expression of CXCL12 in hepatic sinusoidal endothelial cells. The results suggest that LMWH inhibits the formation of hepatic metastasis of colon cancer by disrupting the interaction of CXCR4 and CXCL12, supporting that perioperative administration of LMWH may help to prevent the seeding and subsequent growth of hepatic metastases of colon cancer cells.

Coagulation and nano-filtration: a hybrid system for the removal of lower molecular weight organic compounds (LMWOC)

The removal of lower molecular weight organic compounds (LMWOC) from water is of increasing concern. While, nano-fi ltration (NF) is a good option, it removes only a fraction of the LMWOC. In this paper, NF experiments were conducted to remove oxalic acid and diuron in combination with coagulation using poly-aluminum chloride (PAC) as the coagulant. The results showed that this hybrid treatment system was effective in removing oxalic acid where almost a 100% removal effi ciency of oxalic acid was achieved. However, using PAC as coagulant to remove diuron from water was not effective. In order to improve the removal efficiency of diuron, 0.02 M NaCl was added to diuron and a 40% increase in the removal of diuron was achieved. Higher removal of diuron was achieved when the solution was treated with reverse osmosis (RO) when compared to the nano-filtration.