Céline Laroche

New Developments and Prospective Applications for β (1,3) Glucans

Publications and patents relative to newly observed functions of beta-(1,3)-D-glucans have notably increased in the last few years with the exploitation of their biological activities. The term beta-(1,3)-D-glucans includes a very large number of polysaccharides from bacterial, fungal and vegetable sources. Their structures have a common backbone of beta-(1,3) linked glucopyranosyl residues but the polysaccharidic chain can be beta-(1,6) branched with glucose or integrate some beta-(1,4) linked glucopyranosyl residues in the main chain. Except for the curdlan, a bacterial linear beta-(1,3)-D-glucans, and for the scleroglucan produced by Sclerotium rolfsii, the main drawback limiting the development of these polysaccharides is the lack of efficient processes for their extraction and purification and their cost. However new applications in agronomy, foods, cosmetic and therapeutic could in a next future accentuate the effort of research for their development. So this review focuses on these beta-(1,3)-D-glucans with the objective to detail the strategies employed for their extraction and the relation structure-functions identified when they induce biological activities.

Separation and fractionation of exopolysaccharides from Porphyridium cruentum

In this work the extraction of EPSs from culture media of Porphyridium cruentum, by dialysis, solvent-precipitation with 3 polar alcohols (methanol, ethanol and isopropanol) and membrane separation techniques has been studied. Diafiltration (DF) using a membrane with a 300 kDa molecular weight cut off was the most efficient technique compared to solvent-extraction and dialysis methods. After extraction, EPS fraction was characterized in terms of rheological properties and biochemical content. The product exhibited shear thinning behavior and a critical overlap concentration equal to 0.6 g/L. The monosaccharide composition was investigated after acidic hydrolysis. Xylose, galactose, glucose and glucuronic acid were identified as the main constitutive monomers.

Involvement of Acyl Coenzyme A Oxidase Isozymes in Biotransformation of Methyl Ricinoleate into γ-Decalactone by Yarrowia lipolytica

ABSTRACT We reported previously on the function of acyl coenzyme A (acyl-CoA) oxidase isozymes in the yeast Yarrowia lipolytica by investigating strains disrupted in one or several acyl-CoA oxidase-encoding genes (POX1 throughPOX5) (H. Wang et al., J. Bacteriol. 181:5140–5148, 1999). Here, these mutants were studied for lactone production. Monodisrupted strains produced similar levels of lactone as the wild-type strain (50 mg/liter) except for Δpox3, which produced 220 mg of γ-decalactone per liter after 24 h. The Δpox2 Δpox3 double-disrupted strain, although slightly affected in growth, produced about 150 mg of lactone per liter, indicating that Aox2p was not essential for the biotransformation. The Δpox2 Δpox3 Δpox5 triple-disrupted strain produced and consumed lactone very slowly. On the contrary, the Δpox2 Δpox3 Δpox4 Δpox5 multidisrupted strain did not grow or biotransform methyl ricinoleate into γ-decalactone, demonstrating that Aox4p is essential for the biotransformation.

Production and characterization of new families of polyglucuronic acids from TEMPO-NaOCl oxidation of curdlan

Curdlan from Agrobacterium sp. was oxidized using 2,2,6,6,-tetramethylpiperidine-1-oxyl radical (TEMPO)-NaBr-NaClO systems at pH 11. The effects of oxidation conditions on degrees of oxidation and polymerization of the products obtained were studied using SEC-MALLS, NMR and IR analyses. Different families of water-soluble beta-(1,3)-polyglucuronic and beta-(1,3)-polyglucoglucuronic acid sodium salts were quantitatively generated with a yield of 80% and without significant loss of their molecular weights. Given that beta-(1,3)-polyglucuronic acids prepared from the regioselective oxidation of curdlan by the TEMPO-NaBr-NaClO systems regularly consist of the glucuronic acid repeating unit; they may open new biotechnological fields for the utilizations of water soluble forms of curdlan.

Achievement of rapid osmotic dehydration at specific temperatures could maintain high Saccharomyces cerevisiae viability

Various methods have been tried to prevent cell mortality during dehydration, but the reasons why microorganisms die when submitted to dehydration and rehydration are not well understood. The aim of this study was to further investigate the reasons for yeast mortality during dehydration. Osmotic dehydration and rehydration of Saccharomyces cerevisiae W303-1A were performed at different temperatures. Two different approaches were used: isothermic treatments (dehydration and rehydration at the same temperature), and cyclic treatments (dehydration at an experimental temperature and rehydration at 25°C), with significant differences in viability found between the different treatments. Dehydration at lower and higher temperatures gave higher viability results. These experiments allowed us to propose a hypothesis that relates mortality to a high water flow through an unstable membrane during phase transition.

Production, extraction and characterization of microalgal and cyanobacterial exopolysaccharides

The current interest of scientific but also industrial communities for the exploitation of microalgae is correlated with the development of specific culture and downstream processes. These processes are currently in progress, and the increasing of knowledges led to emergence of high value compounds such as pigments, proteins, polysaccharides, unsaturated fatty acids, enzymes and others. Exopolysaccharides from microalgae have been at this time poorly explored despite their original structural features associated with specific biological and physico-chemical properties. This situation could be changed in a next future with the lowering of costs for microalgae exploitation and the increasing of literature giving the structural data and specific properties of these biopolymers. The aim of this review is to do the state of the art of processes for exopolysaccharide production and extraction from microalgal biomass and the analytical strategies for their characterization.

Highly sulphated galactan from Halymenia durvillei (Halymeniales, Rhodophyta), a red seaweed of Madagascar marine coasts.

Halymenia durvillei is a red seaweed with a great potential as sulphated galactan producer collected in the coastal waters of small island of Madagascar (Nosy-be in Indian Ocean). To elucidate the structure of its polysaccharide, NMR (1H and 13C), FTIR, HPAEC and different colorimetric methods were carried out. It has been shown that this polysaccharide, consisted mainly of galactose, was branched by xylose and galactose in minor amounts. Arabinose and fucose were also detected. This galactan was found highly sulphated (42%, w/w) and pyruvylated (1.8%, w/w). Analysis of glycosidic linkages by CPG-MS and 13C NMR indicated that the polysaccharide has the defining linear backbone of alternating 3-beta-D-galactopyranosyl units and 4-linked alpha-L/D-galactopyranosyl residues. 3,6-Anhydrogalactose units have been also detected in minor quantity. This lambda-carrageenan like polysaccharide has shown original sulphatation patterns with 2-O (26%) or 2/6-O (58%) sulphated 3-linked beta-D-galactopyranosyl units and 6-O (19%) or 2/6-O (47%) 4-linked alpha-L/D-galactopyranosyl residues.

Unexpected Thermal Destruction of Dried, Glass Bead-Immobilized Microorganisms as a Function of Water Activity

ABSTRACT To help us understand the factors and mechanisms implicated in the death of microorganisms or their resistance to temperature in a low water activity environment, microorganisms were dried on the surface of glass beads before being subjected to high temperatures for a short period followed by rapid cooling. Two microorganisms were studied: the yeast Saccharomyces cerevisiae and the bacterium Lactobacillus plantarum. Experiments were carried out at 150, 200, and 250°C, with four durations of heat treatment and seven levels of initial water activity between 0.10 and 0.70. We observed an unexpected range of water activity, between 0.30 and 0.50, at which microorganisms were more resistant to the various treatments, with maximal viability at 0.35 for L. plantarum and 0.40 for S. cerevisiae.

New Method Showing the Influence of Matrix Components in Leuconostoc mesenteroides Biofilm Formation

Studying biofilm formation and influence of the matrix composition was heavy because only old and long methods were employed up to now: confocal microscopy, fluorescent chemical markers, and/or dying techniques. In this context, an innovative tool, the BioFilm Ring Test®, was here employed to explore the role of exopolysaccharides, proteins, and nucleic acids in the formation of biofilm by Leuconostoc mesenteroides. The principle is to add magnetic particles in the culture medium. When a biofilm is formed, particles are unable to migrate in the media to form a ring when a magnet is brought nearer to the well. Therefore, culture media supplemented with proteases, glycanases, and/or nucleases allowed us to identify the involvement of these substances in L. mesenteroides biofilm formation. The results permitted to demonstrate that dextran, proteins, and nucleic acids are implied in biofilm formation.

Optimisation of culture parameters for exopolysaccharides production by the microalga Rhodella violacea

A unicellular Rhodophyte was identified by sequencing of its 18S rRNA encoding gene as belonging to the Rhodella violacea specie. With the objective to optimise the production of biomass and exopolysaccharide by this strain, effects of irradiance, pH and temperature on its photosynthetic activity were investigated. In a second time a stoichiometric study of the well-known f/2 medium led to its supplementation in N and P to increase biomass and then exopolysaccharide yields when the strain was cultivated in photobioreactors. The use of optimal conditions of culture (irradiance of 420 μE/m(2)/s, pH of 8.3 and temperature of 24 °C) and f/2 supplemented medium led to significant increases of biomass and exopolysaccharide productions. The structural characterisation of the produced exopolysaccharide revealed that it was sulphated and mainly composed of xylose. The different culture conditions and culture media tested had no significant impact on the structure of produced exopolysaccharides.