Ultrastructure of ulvan: A polysaccharide from green seaweeds

Ultrastructural analysis of the gel forming green seaweed sulfated polysaccharide ulvan revealed a spherical‐based morphology (10–18 nm diameter) more or less aggregated in aqueous solution. At pH 13 in TBAOH (tetrabutyl ammonium hydroxyde) or NaOH, ulvan formed an open gel‐like structure or a continuous film by fusion or coalescence of bead‐like structures, while in acidic pH conditions, ulvan appeared as dispersed beads. Low concentrations of sodium chloride, copper or boric acid induced the formation of aggregates. These results highlight the hydrophobic and aggregative behavior of ulvan that are discussed in regard to the peculiar gel formation and the low intrinsic viscosity of the polysaccharide in aqueous solution. © 2009 Wiley Periodicals, Inc. Biopolymers 91: 652–664, 2009. This article was originally published online as an accepted preprint. The “Published Online” date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at biopolymers@wiley.com     

NMR spectroscopic characterisation of oligosaccharides from two Ulva rigida ulvan samples (Ulvales, Chlorophyta) degraded by a lyase

The chemical structure and the sequence of repeating units in ulvans of similar compositions from two different Ulva rigida samples collected in the Canary Islands and in Brittany were studied after ulvan-lyase degradation and NMR spectroscopic analysis of the reaction products. Both ulvans were composed of ulvanobiuronic acid 3-sulfate type A [-->4)-beta-D-GlcA-(1-->4)-alpha-L-Rha 3-sulfate-(1-->] (symbolised as A3s) and contained disaccharides composed of [-->4)-beta-D-Xyl-(1-->4)-alpha-L-Rha 3-sulfate-(1-->] and [-->4)-beta-D-Xyl 2-sulfate-(1-->4)-alpha-L-Rha 3-sulfate], respectively referred to as ulvanobiose 3-sulfate (U3s) and ulvanobiose 2',3-disulfate (U2's,3s). In the Canary Islands sample, these U3s and U2's,3s occurred dispersed among A3s sequences and as short blocks of two or three units. In contrast, in the Brittany samples, these units were dispersed among A3s structures and next to A3s units branched at O-2 of alpha-L-Rha 3-sulfate by a terminal beta-D-GlcA and symbolised as A2g,3s. However, more complex structures are likely to occur in the enzyme resistant fraction remaining from this ulvan. An average structure sequence of these two ulvans was proposed. The transposition of the 13C NMR data of the new identified structures to the parent polysaccharides was not possible, probably due to the different sequence distributions affecting the carbons chemical shifts.     

Comparative analysis of sulfated galactans from red algae by reductive hydrolysis and mild methanolysis coupled to two different HPLC techniques

The sugar determination of the sulfated galactans, agars and carrageenans of various red algae was performed using two different techniques of depolymerisation with subsequent HPLC analysis: 1) reductive hydrolysis/ HPAEC-PAD; 2) mild methanolysis/ RPLC-DR. Both techniques were optimized to release quantitatively the composite sugars (galactose, 6-O-methyl-galactose, the labile 3,6-anhydrogalactose and 2-O-methyl-3,6-anhydrogalactose residues) and precise relative response factors of authentic 3,6-anhydrogalactose were determined. The methanolysate neutralisation step, performed subsequently to methanolysis depolymerisation, was demonstrated as a key step for the quantitative recovery of the anhydrogalactose residues. The yield of the main sugars released by the two techniques were in good agreement for the commercial agarose and iota and kappa carrageenans studied. This revised version was published online in June 2006 with corrections to the Cover Date.     

Light quality affects morphology and polysaccharide yield and composition of Gelidium sesquipedale (Rhodophyceae)

Morphology and polysaccharide characterization of Gelidium sesquipedale (Clem.) Bornet et Thuret were studied in cultures grown under various light qualities. White light (WL), blue light (BL) and red light (RL) (all at photon fluence rate of 40 μmol m-2 s-1) were used for the study of morphological characteristics, and in addition yellow light (YL) for polysaccharide characterization. RL and BL induced a proliferating growth, which resulted in bushy plants under RL. Cortical cells of BL-grown plants were smaller and presented a higher density per unit area, whereas those of WL- and RL-grown alga were larger. Medullary cells followed the inverse pattern. Light quality also affected polysaccharide yield and composition, with the yield being higher under BL, RL or YL than WL. Most of the polysaccharide was extracted in distilled water at 100 °C, while a low amount was solubilized at 22 °C and 120 °C. Extracts from BL-grown alga presented the highest galactan content. The starch concentration was lower in extracts from RL-, BL- and YL-cultivated alga than in those from the initial plants. The degree of substitution with methoxyl groups and precursor was very low in all the agar fractions, but fractions extracted from BL- and WL-grown alga were more substituted by precursor. The highest sulfate content was reached under BL (about 9% w/w) and the highest 2-O-methyl-3,6-anhydro-L-galactose and 6-O-methyl-D-galactose content were found in extracts from alga grown under YL. This revised version was published online in June 2006 with corrections to the Cover Date.     

Population genetic structure of North Atlantic, Mediterranean Sea and Sea of Cortez fin whales, Balaenoptera physalus (Linnaeus 1758): analysis of mitochondrial and nuclear loci

Samples were collected from 407 fin whales, Balaenoptera physalus , at four North Atlantic and one Mediterranean Sea summer feeding area as well as the Sea of Cortez in the Pacific Ocean. For each sample, the sex, the sequence of the first 288 nucleotides of the mitochondrial (mt) control region and the genotype at six microsatellite loci were determined. A significant degree of divergence was detected at all nuclear and mt loci between North Atlantic/Mediterranean Sea and the Sea of Cortez. However, the divergence time estimated from the mt sequences was substantially lower than the time elapsed since the rise of the Panama Isthmus, suggesting occasional gene flow between the North Pacific and North Atlantic ocean after the separation of the two oceans. Within the North Atlantic and Mediterranean Sea, significant levels of heterogeneity were observed in the mtDNA between the Mediterranean Sea, the eastern (Spain) and the western (the Gulf of Maine and the Gulf of St Lawrence) North Atlantic. Samples collected off West Greenland and Iceland could not be unequivocally assigned to either of the two areas. The homogeneity tests performed using the nuclear data revealed significant levels of divergence only between the Mediterranean Sea and the Gulf of St Lawrence or West Greenland. In conclusion, our results suggest the existence of several recently diverged populations in the North Atlantic and Mediterranean Sea, possibly with some limited gene flow between adjacent populations, a population structure which is consistent with earlier population models proposed by Kellogg, Ingebrigtsen, and Sergeant.     

Gelling properties of water-soluble polysaccharides from proliferating marine green seaweeds (Ulva spp.)

Water-soluble polysaccharides (12·2% of the algal dry weight) were extracted from marine green seaweed (Ulva spp.) which proliferate along the Brittany shores of France. They were composed of 18·4% rhamnose, 4·4% glucose, 1·9% xylose, 0·9% mannose, 0·9% galactose, 15·2% uronic acid, 15·8% sulphate and 23·7% ash based on the extract dry weight. These polysaccharides, formed a weak gel (about 3 Pa) at a concentration of 1·6% (w/v) in deionized water. The elastic modulus increased to about 160 Pa when boric acid (15–33 m ) was added and reached 250 Pa when both boric acid (7 m ) and calcium chloride (7 m ) were present. Adjusting the pH to 7·5 or higher by sodium tetraborate, phosphate or Tris-HCl buffers was detrimental to the gel. These results demonstrate that the poorly exploited biomass of Ulva spp. is a source of gelling polysaccharides of potential economical value. Mechanisms for gel formation which unusually involve both boron and calcium ions are proposed and will be studied further.     

Fine Needle Aspiration Cytodiagnosis of Subacute (De Quervain's) Thyroiditis In an Endemic Goitre Area

Between 1977 and 1989 252 fine needle aspirates (FNAs) of the thyroid from patients with a clinical suspicion of subacute granulomatous (de Quervain's) thyroiditis were examined in the Department of Pathology of the University of Innsbruck, Austria. In the same period 31 cases with preoperative FNA were diagnosed histologically as subacute thyroiditis. Only in three of these cases were the cytological features of de Quervain's thyroiditis found in the preoperative FNA. However, in 13 of these 31 cases a cytological suspicion of malignancy was obtained. Subsequent histological examination revealed an acute phase inflammation of de Quervain's thyroiditis in most of these cases. We conclude that an accurate FNA diagnosis of de Quervain's thyroiditis, particularly in the acute stage, may cause difficulties due to a lack of typical features and the appearance of atypical thyroid follicular cells. For the cytopathologist, accurate clinical information relating to the possibility of de Quervain's thyroiditis is essential if unnecessary surgery is to be avoided.     

Purification and characterization of an extracellular β-glucosidase from the anaerobic fungus Piromyces sp. strain E2

An extracellular -glucosidase (EC 3.2.2.21) from the anaerobic fungus Piromyces sp. strain E2 was purified. The enzyme is a monomer with a molecular mass of 45 kDa and a pI of 4.15. The enzyme readily hydrolyzes p-nitrophenyl--d-glycoside, p-nitrophenyl--d-fucoside, cellobiose, cellotriose, cellotetraose and cellopentaose but is not active towards Avicel, carboxymethylcellulose, xylan, p-nitrophenyl--d-galactoside and p-nitrophenyl--d-xyloside. To cleave p-nitrophenyl--d-glucoside the maximum activity is reached at pH 6.0 and 55°C, and the enzyme is stable up to 72 h at 40°C. Activity is inhibited by d-glucurono--lactone, cellobiose, sodium dodecyl sulfate, Hg²⁺ and Cu²⁺ cations. With p-nitrophenyl--d-glycoside, p-nitrophenyl--d-fucoside, and. cellobiose as enzyme substrates, the K _m and V _max balues are 1.5 mM and 25.5 IU·mg^-1, 1.1. mM and 133 IU·mg^-1, and 0.05 mM and 55.6 IU·mg^-1, respectively.