Physico-chemical characterization and biological potential of exopolysaccharides derived from microalgae isolated from the Algerian Sahara

Abstract

The main objective of this work was the isolation of a microalga producing polysaccharides, the structural characterization of the exopolysaccharides and the evaluation of its biological potential. This study began by the measurement of the physico-chemical parameters of water from two Lakes in Ouargla region Algeria; Lake Hassi BenAbdellah and Lake Chott Aïn El-Beida. The water of the first Lake was categorized as ‘brackish’ water due to the moderate salinity 14.15 g L-1, the second Lake’s water was categorized as ‘hypersaline’ where the salinity reached 51,46 g L-1. An assessment of the microalgal flora in these two Lakes was performed using multitude of mediums. Overall, high biodiversity was observed in both Lakes. In Case of Chott Aïn El-Beida Lake, a total of 122 species was seen, the most frequent species belong to Chlorphyceae (37.70%). It is noticed also dominance of Bacillariophyceae with high percentage (33.60%). Cyanophyceae present the lower percentage (6.56%) with minor occurrence. In case of Lake Hassi BenAbdellah, an enormous diversity was also detected; 182 different morphologies were observed, as well, Chlorophyceae dominate with a percentage of (38.46%), followed by Bacillariophyceae 26.37% and Cyanophyceae 26.62% respectively. Five microlagal strains were isolated from Chott Aïn El-Beida Lake (S1, S2, S3, S4 and S5), Chlorella sp. (S3), strain was selected for cultivation, exopolysaccharide extraction and characterization. The extracts from Chlorella sp. (S3), were characterized with several analyses. Biochemical analysis of the exopolysaccharides reveal different fractions; total sugar 65.26±0.017 (%w/w), proteins: 13.04± 0.011 (%w/w), and polyphenols: 0,267±0,022 (mg GAE g-1). For the other strains the total sugar content was between 45.87 and 61.75 (%w/w). The FT-IR analysis performed on the exopolysaccharides of the five isolates reveal a characteristic infrared imprint of carbohydrates was observed with particular functional groups. The gas chromatography–mass spectrometry on Chlorella sp. (S3), extracts revealed a hetero-exopolysaccharide of galactose 35.75%, glucose 21.13%, xylose 16.81%, fructose 6.96%, arabinose 5.10%, and glucuronic acid 2.68%. The assessment of the anti-hyperglycemic activity has shown a significant α-D-glucosidase inhibition of 80.94 ± 0.01% at 10 mg mL−1 with IC50 equal to 4.31 ± 0.20 mg mL−1.