Henri Morvan

Sulphated exopolysaccharides produced by two unicellular strains of cyanobacteria, Synechocystis PCC 6803 and 6714

The exopolysaccharides (EPS) of two unicellular strains of cyanobacteria Synechocystis PCC 6803 and 6714, formed labile, radial structures, uniformly distributed on the cell surface, and stainable by specific dyes for acidic polysaccharides. The two strains produced EPS at similar rates, which depended, along with the duration of the producing phase, on the incubation conditions. The exopolysaccharides from both strains were constituted of at least 11–12 mono-oses, probably forming several types of polymers. They contained about 15–20% (w/w) uronic derivatives and 10–15% (w/w) osamines. Proteins represented 20–40% of total weight. A most interesting feature was the presence of 7–8% (molar ratio) sulphate residues, a characteristic that is otherwise limited to exopolysaccharides produced by eukaryotic algae.

HEAVY METAL ADSORPTION BY CRUDE CONIFEROUS BARKS: A MODELLING STUDY

ABSTRACT Equilibria and mechanisms involved in the adsorption process of metal ions (Cr3+, Cu2+, Ni2+, Pb2+ and Zn2+) from aqueous solutions using coniferous barks as biosorbent substrate were investigated. Crude barks were used in this study since previous experiments showed a decreasing uptake for chemically treated barks in the considered granulometry. In our experimental conditions, the maximum binding capacity of barks followed the decreasing order Cr3+>Cu2+>Pb2+>Ni2+>Zn2+ whereas their general binding affinity decreased as: Pb2+>Cr3+> Ni2+>Zn2+>Cu2+. Adsorption isotherms at the optimal physico-chemical conditions were established and the adsorption phenomenon was described by the non-competitive Langmuir adsorption model which fitted well the experimental data. An evaluation of adsorption capability was carried out using model parameters which were graphically determined. Models for removal of cations have been discussed; they represent efficient tools for predicting the behaviour of the biosorbents in metal ion adsorption systems.

Removal of heavy metal ions from aqueous solution by modified barks

Abstract Bark, a common waste product in forestry, can be used to selectively remove cations, especially toxic heavy metals from mono or multi saline solutions. Picea, Pinus, Pseudotsuga, Larix, Tectona and Afzelia barks have been used in glass columns, after grinding and treatment with formaldehyde in acid media, to study their ability in binding toxic heavy metal ions such as Pb2+, Zn2+, Cr2+, Fe2+ and Cu2+. The metals are exchanged against protons on the bark substrates that presumably contain carboxyl groups in both pectin and tannin compounds. Removal of these ions depends upon the nature of the bark used, the grain size and the predominant heavy metal ions present in the solutions. The metal ions could be stripped by addition of 0.1 ? HCl, making the substrate regeneration and its reutilization possible.

Isolation and characterization of free glycans of the oligomannoside type from the extracellular medium of a plant cell suspension

The oligosaccharides Man5GlcNAc and Man3(Xyl)GlcNAc(Fuc)GlcNAc presumed to originate fromN-glycosyl proteins have been purified from an extracellular medium (concentration: 2–5 mg/l of 14 day cultures) of white campion (Silene alba) suspension culture. Their primary structures have been determined by1H-400-MHz NMR spectroscopy and FAB-MS spectrometry. They are probably the result of an autophagic process including protein catabolism due to sucrose starvation. Additional identification of digalactosylglycerol (galactolipid breakdown) argues for this hypothesis.

Agar fractions could protect apple shoots cultured in liquid media against hyperhydricity

Apple shoots were grown in a Murashige and Skoog liquid proliferation medium containing 4.4 10 -6 M BA, and supplemented with various fractions of agar. Hydrolysed agar from Difco was able to overcome hyperhydricity when its concentration was increased to 0.7%. Among the fractions isolated from this hydrolysed agar, only oligosaccharides were found to reduce the occurrence of this developmental abnormality. The most anti-hyperhydric fraction had a molecular weight slightly less than 1900 daltons and contained methylated and sulphated galactose derivatives.

Carbon Starvation Increases Endoglycosidase Activities and Production of "Unconjugated N-Glycans" in Silene alba Cell-Suspension Cultures

We previously reported the occurrence of oligomannosides and xylomannosides corresponding to unconjugated N-glycans (UNGs) in the medium of a white campion (Silene alba) cell suspension. Attention has been focused on these oligosaccharides since it was shown that they confer biological activities in plants. In an attempt to elucidate the origin of these oligosaccharides, we studied two endoglycosidase activities, putative enzymes involved in their formation. The previously described peptide-N4-(N-acetyl-glucosaminyl) asparagine amidase activity and the endo-N-acetyl-[beta]-D-glucosaminidase activity described in this paper were both quantified in white campion cells during the culture cycle with variable initial concentrations of sucrose. The lower the sucrose supply, the higher the two activities. Furthermore, endoglycosidase activities were greatly enhanced after the disappearance of sugar from the medium. The production of UNGs in the culture medium rose correlatively. These data strongly suggest that the production of UNGs in our white campion cell-suspension system is due to the increase of these endoglycosidase activities, which reach their highest levels of activity during conditions of carbon starvation.

Characterization of the peptide-N4-(N-acetylglucosaminyl) asparagine amidase (PNGase Se) from Silene alba cells.

The peptide-N4-(N-acetylglucosaminyl) asparagine amidase (PNGase Se) earlier described [Lhernould S., Karamanos Y., Bourgerie S., Strecker G., Julien R., Morvan H. (1992)Glycoconjugate J9:191–97] was partially purified from culturedSilene alba cells using affinity chromatography. The enzyme is active between pH 3.0 and 6.5, and is stable in the presence of moderate concentrations of several other protein unfolding chemicals, but is readily inactivated by SDS. Although the enzyme cleaves the carbohydrate from a variety of animal and plant glycopeptides, it does not hydrolyse the carbohydrate from most of the corresponding unfolded glycoproteins in otherwise comparable conditions. The substrate specificity of this plant PNGase supports the hypothesis that this enzyme could be at the origin of the production of ‘unconjugated N-glycans’ in a suspension medium of culturedSilene alba cells.

Peptide-N4-(N-acetylglucosaminyl)asparagine amidase (PNGase) activity could explain the occurrence of extracellular xylomannosides in a plant cell suspension

We have previously isolated mannoside and xylomannoside oligosaccharides with one or two terminal reducingN-acetylglucosamine residues from the extracellular medium of white campion (Silene alba) suspension culture. We have now demonstrated the presence of peptide-N4-(N-acetylglucosaminyl)asparagine amidase (PNGase) activity in cell extracts as well in the culture medium that could explain the production of those compounds. An additional xylomannoside, (GlcNAc)Man3(Xyl)GlcNAc(Fuc)GlcNAc, was characterized, and1H- and13C-NMR assignments for the oligosaccharide Man3(Xyl)GlcNAc(Fuc)GlcNAc were obtained using homonuclear and heteronuclear spectroscopy (COSY).

Metal accumulation by immobilized cyanobacterial mats from a thermal spring

Abstract The metal‐binding properties of lyophilized cyanobacterial mats occurring in a thermal spring were investigated. The general binding efficiency decreased in the order Cu > Ni > Pb > Cr. Most metal sorption occurred within 15 min, and it was strongly pH‐dependent. The sorption of Cu was depressed in the case of competition with other metals or cations. The metal‐binding properties are probably due to a high density of anionic charges, especially carboxyls, identified in the capsular polymer. The feasability to use columns packed with the biomass immobilized with silica gel for the removal of metals is demonstrated. The metals were successfully desorbed and these columns were effective during several adsorption‐desorption cycles.

IDENTIFICATION BY NMR SPECTROSCOPY OF OLIGOSACCHARIDES OBTAINED BY ACIDOLYSIS OF THE CAPSULAR POLYSACCHARIDES OF A THERMAL BIOMASS

This study deals with the chemical characterization of a capsular polysaccharide (CPS) produced by a thermal biomass largely comprising the cyanobacterium Mastigocladus laminosus. The sugar moiety of this polymer is composed of seven neutral monosaccharides (Rha, Fuc, Ara, Xyl, Man, Glc, Gal) and two uronic acids (GalA, GlcA). Proteins represent 18% of the dry weight of the CPS. Organic acid substituents (acetate, pyruvate, succinate) were also detected and estimated by high-performance liquid chromatography. The presence of sulfate groups (5% w/w) was observed, which represents a relatively rare feature for cyanobacteria. Acidic hydrolysis of the purified polysaccharide led to the isolation of four oligosaccharidic fractions. NMR spectroscopy studies of two of the four purified oligosaccharides allowed them to be identified as: alpha-GlcA-(1-->2)-alpha-GalA-(1-->2)-Man and alpha-GlcA-(1-->2)-alpha-GalA-(1-->2)-beta-Man-(1-->4)-beta-Gal-(1 -->2)-Rha.