Exploring the Diversity of Red Microalgae for Exopolysaccharide Production

International audienceMicroalgae constitute a remarkable biological diversity but a limited number of them have been the object of study for their ability to produce exoplysaccharides (EPS). Among them, the red marine microalgae Porphyridium or Rhodella produce sulphated EPS, exhibiting some biological activities with potential interest in the pharmaceutical and cosmetic industries. EPS from Porphyridium and Rhodella being relatively similar in their composition, it has long been considered that all the red microalgae produced similar EPS and no attention was paid to other red microalgae. The objective of our work was then to explore the diversity of red microalgae for the production of EPS, focusing in this first step on the screening of the strains for their ability to produce EPS and preliminary structural characterization. The study was conducted with 11 microalgae strains belonging to the proteorhodophytina subphylum. All microalgae were able to produce EPS, released in the culture medium (strains belonging to Porphyridiophyceae and Rhodellophyceae classes) or remaining bound to the cells (strains from Stylonematophyceae class). The analysis of monosaccharides composition was found significantly different, with for instance high levels of glucuronic acids in the EPS from C. japonica and N. cyanea, but also strong differences in the sulphation degrees of polymers (between 1.2 and 28.7% eq. SO4)

Improvement of exopolysaccharide production by Porphyridium marinum

International audienc

An alternative method for the determination of polysaccharide cleavage enzymes activities

International audienceMost of usual methods used to detect and quantify polysaccharide cleavage enzymes (PCE) are not adapted to high throughput. In this work, enzymatic activities of three enzymes, namely an endocellulase (EC 3.2.1.4), an exocellulase (EC 3.2.1.91) and an alginate lyase (EC 4.2.2.3) were characterized by classical Michaelian model (Km, Vmax). Enzymatic activities were then determined by the use of the Enzyme Ring Test® (ERT®) method which allowed following the depolymerization of polysaccharides by PCE. Kinetic parameters were determined and compared to the ones obtained by classical methods. Besides, the ERT® technology clearly showed the possibility to discriminate endolytic and exolytic enzymatic mechanisms

The red microalga Flintiella sanguinaria as a new exopolysaccharide producer

International audienc

Antioxidant activities of a polyglucuronic acid sodium salt obtained from TEMPO-mediated oxidation of xanthan.

International audienceA xanthouronic acid sodium salt called xanthouronan was produced from xanthan by regioselective oxidation with NaOCl/NaBr using 2,2,6,6-tetramethylpiperidine-1-oxy radical (TEMPO) as catalyst. The efficiency of the one pot TEMPO-mediated oxidation was confirmed by HPAEC-PAD, 13C NMR, and FT-IR. The oxidation degree was close to 98% and the mass yield of this new polyglucuronic acid was higher than 90% (w/w). The macromolecular characterization of xanthouronan using SEC-MALLS showed a molecular size reduced by a third due to the oxidation treatment and the degree of polymerization (DP) of the xanthouronan form was about 665. The evaluation of the enzymatic degradation of this C-6 carboxylated xanthan by various polysaccharide hydrolases and one polysaccharide lyase showed its high resistant to biodegradation. The antioxidant activity of xanthouronan was also tested by using the 2,2′-diphenyl-1-picrylhydrazyle (DPPH) and hydroxyl radical procedures. At 1 g/L, xanthouronan presented 75% of the ascorbic acid antioxidant activity

Oligosaccharides biologiquement actifs obtenus par dégradation enzymatique d’un arabinogalactane extrait de cladodes de Cereus triangularis

International audienc

Biochemical Characterization of a Bifunctional Enzyme Constructed by the Fusion of a Glucuronan Lyase and a Chitinase from Trichoderma sp.

International audienceBifunctional enzymes created by the fusion of a glucuronan lyase (TrGL) and a chitinase (ThCHIT42) from Trichoderma sp. have been constructed with the aim to validate a proof of concept regarding the potential of the chimera lyase/hydrolase by analyzing the functionality and the efficiency of the chimeric constructions compared to parental enzymes. All the chimeric enzymes, including or nor linker (GGGGS), were shown functional with activities equivalent or higher to native enzymes. The velocity of glucuronan lyase was considerably increased for chimeras, and may involved structural modifications at the active site. The fusion has induced a slightly decrease of the thermostability of glucuronan lyase, without modifying its catalytic activity regarding pH variations ranging from 5 to 8. The biochemical properties of chitinase seemed to be more disparate between the different fusion constructions suggesting an impact of the linkers or structural interactions with the linked glucuronan lyase. The chimeric enzymes displayed a decreased stability to temperature and pH variations, compared to parental one. Overall, TrGL-ThCHIT42 offered the better compromise in terms of biochemical stability and enhanced activity, and could be a promising candidate for further experiments in the field of fungi Cell Wall-Degrading Enzymes (CWDEs

A new exopolysaccharide from Flintiella sanguinaria : production and structural characterization

International audienc

The Effect of Ultrasound Pretreatment on Pectin Extraction from Watermelon Rind Using Microwave-Assisted Extraction

Ultrasound pretreatment and microwave-assisted extraction (MAE) techniques were used to extract pectin from watermelon rind. This work investigated the effect of the power and time of pretreatment on the yield and characteristics of the extracted pectin. Imaging studies showed that ultrasonic pretreatment changed the morphology of the raw powder, leading to a greater porosity, and facilitated the extraction process. The highest extraction yield of pectin was 19.08% (w/w), for 5 min of extraction at 500 W ultrasonic pretreatment. Ultrasonic pretreatment affected the degree of esterification and the galacturonic acid content of pectin. The galacturonic acid content of all samples was higher than 69.0%. Extraction pretreatment reduced the surface tension value of the aqueous solution of pectin and affected the foam capacity of pectin and its monosaccharidic composition. The ultrasonic pretreatment caused significant changes in pectin characteristics, such as intrinsic viscosity, viscosity average, molecular weight, ratio of homogalacturonan to rhamnogalacturonan and the water holding capacity. In addition, kinetic studies showed that a kinetic empirical model adequately describes the effect of ultrasonic pretreatment on foam stability and its half-time

Un nouvel exopolysaccharide issu de la microalgae Flintiella sanguinaria: production et caractérisation

International audienc